Research goals of special concern for Carcharhinus leucas (Carcharhiniformes: Carcharhinidae) in Latin America – biological, distributional, and conservation priorities

Peter Gausmann^1,2 , Philip Matich^3,4 and Nadia Sandoval Laurrabaquio-Alvarado^5,6

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Associate Editor: Jennifer Wyffels

Section Editor: Toby Daly-Engel

Editor-in-chief: Carla Pavanelli

Abstract​

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Introduction​

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As the human population and its footprint continue to grow, so too does our need to identify and pursue ever-changing conservation goals. Habitat degradation, wildlife declines, and the loss of biodiversity are among the top priorities (Turner et al., 2024). In the ocean, overfishing is also a significant concern, particularly for sharks and rays with over one-third of extant species threatened by extinction (Dulvy et al., 2021; Pacoureau et al., 2023; Torres-Romero, Pérez Jiménez, 2024). More than 100 million sharks are killed each year (Worm et al., 2024), and persistent overharvesting of many species of chondrichthyans has led to severe population declines and conservation crises. Globally, sharks and rays have faced declines of more than half of their populations since 1970 (Dulvy et al., 2024), which is of concern for conservation as well as food and economic security. Due to these serious population declines, chondrichthyans (sharks, skates, rays, and chimaeras) belong to the most threatened vertebrate lineages (Temple et al., 2025).

Among sharks, the speciose family Carcharhinidae Jordan & Evermann, 1896 (requiem sharks) is the most economically important family for fisheries in the tropics, because of its core distribution in lower latitudes (Compagno, 1984). Rosales-Melgar et al. (2024) reported that between 2014–2022, exports from Central America almost exclusively consisted of Carcharhinidae species (96.4%). Globally, requiem sharks were recently estimated to comprise one-third of the annual chondrichthyan catch and two-thirds of the fin trade of coastal sharks, and because they are inadequately managed in many regions, 71% of Carcharhinidae species are threatened worldwide (Sherman et al., 2023). Thus, there is an urgent need for conservation measures for these sharks. The recent addition of Carcharhinidae to CITES Appendix II (United Nations, 2024) was an important international step toward addressing this need. However, clarity on management and conservation priorities are still lacking in many regions, which will require stock assessments and more thorough monitoring of fisheries landings and bycatch.

Among the cosmopolitan species of requiem sharks that require additional conservation attention, Carcharhinus leucas (Valenciennes, 1839), the bull shark, has one of the highest encounter rates with humans, because of its proclivity to use coastal, estuarine, and connected freshwater habitats in the tropical, subtropical, and warm-temperate regions of the world (Compagno, 1984; Ebert et al., 2021). This euryhaline shark connects freshwater and marine food webs (Rosenblatt et al., 2013; Matich et al., 2020a,b, 2021), and is exposed to numerous threats across its distribution, including overfishing and habitat loss, with severe population declines reported for many regions (e.g., Asiedu et al., 2024). As such, C. leucas is assessed by the International Union for the Conservation of Nature (IUCN) as Vulnerable (VU) and globally decreasing (Rigby et al., 2021).

In addition to overfishing and habitat loss, C. leucas populations also suffer from mitigation measures targeting the reduction of shark bites such as culling, drumlines, and shark nets that are primarily used in countries with high numbers of tourist water users such as Brazil, South Africa, and Australia (Haig et al., 2018; OʼConnell et al., 2022). These measures represent lethal strategies and have the potential to significantly reduce local stocks (Roff et al., 2018; Mourier et al., 2021), particularly because C. leucas has a very low recovery potential attributed to its late-maturation and low reproductive output (Cailliet et al., 2005; Saldaña-Ruiz et al., 2022). The age of maturation has been estimated from 9-18 years for C. leucas (Branstetter, Stiles, 1987; Cruz-Martínez et al., 2005; Neer et al., 2005; Natanson et al., 2014), and the maximum reported litter size is 14 pups in the Indian Ocean (Nevill et al., 2013). Considering these conservative life history traits with its purported biennial reproductive cycle (Jara-Aguirre, 2021), C. leucas has a very limited intrinsic rebound potential of r = 0.027 (comparable to the near-related C. plumbeus (r = 0.028); Smith et al., 1998), hindering the speciesʼ capacity to withstand population depletion. Thus, this shark is highly susceptible to overexploitation, which makes it a conservation priority.

Research on C. leucas has provided important knowledge and insight into the behavior, biology, and ecology of this species (e.g., Curtis et al., 2011, 2013; Heupel, Simpfendorfer, 2011; Tillett et al., 2012; Daly et al., 2014; Lea et al., 2015; Matich, Heithaus, 2015; Constance et al., 2024; Gausmann, 2024). However, well-investigated areas are mainly in the developed world (e.g., Australia, South Africa, United States), with large parts of the bull sharkʼs range considered data-poor, including Latin America (a definition of this area is given in the Material and Methods section), which is a major provider of shark fins to the Asian shark fin market (Shea, Slee, 2024). In Latin America, many shark fisheries are unregulated, unenforced, and/or unreported/underreported (Zarate, Hearn, 2008; López-Garro, Zanella, 2021), and although C. leucas is reported to be rarely a target species, it is commonly caught in both commercial and recreational fisheries (Simpfendorfer, Burgess, 2005). Applegate et al. (1993) reported that C. leucas was probably the most important commercially fished shark species in the Caribbean waters of Mexico, which was recently confirmed by Diario Oficial de la Federación (2022). However, C. leucas has declined over the last three decades as a result of overfishing in Campeche (Fig. 1), Quintana Roo, Tamaulipas, Veracruz, and Yucatan (Bonfil, 1994, 1997; Marcos-Camacho et al., 2016; Álvarez et al., 2020; Martínez-Candelas et al., 2020). Similarly, landings of C. leucas have noticeably decreased in the Gulf of California since 1939 (Saldaña-Ruiz et al., 2017). Carcharhinus leucas is also an important target species in other parts of Latin America, including the mouth of the Amazon River (Marajoara Gulf) (Alencar et al., 2001; Barthem, 2015), the neighbouring Maranhão, Brazil (Piorski et al., 2021), and coastal Ecuador (Martínez-Ortíz et al., 2007; Souza-Araujo et al., 2021), highlighting the exploitation of C. leucas across this region.

FIGURE 1| A. Bull sharks such as this single specimen landed on the 23rd August 2023 at Seybaplaya, Campeche, Mexico, are targeted in great numbers by artisanal, small-scale, and industrial fisheries in the waters of the southern Gulf of Mexico (© Andrés Irigoyen-Solis). B. Small juvenile bull sharks displayed to be sold at the “Ver-o-Peso” fish market in Belém, Pará, Brazil, on the 10th October 2018. This species is of high local economic interest in Northeast Brazil, and this picture illustrates that potential nurseries overlap with fishing grounds in the Amazon region (© Rodrigo Barreto).

Carcharhinus leucas is found in nearshore, marine waters, but also penetrates low-salinity habitats (Thorson, 1982), particularly during early life history stages (Pillans, 2006; Heupel, Simpfendorfer, 2008; Curtis et al., 2011; Matich, Heithaus, 2012; Niella et al., 2022). This behavior promotes juvenile survival by reducing predation risk (Heupel, Simpfendorfer, 2011; Lofthus et al., 2024), but increases their susceptibility to human impacts (Simpfendorfer, Burgess, 2005; Kyne et al., 2012). In Latin America, C. leucas is known to occur in > 90 specific locations with fresh and brackish water conditions (Gausmann, 2021). However, the use of low-salinity habitats is not homogenous, with only 13 rivers, lakes, estuaries, and lagoons reported as C. leucas habitat in the Pacific compared to 78 in the Atlantic (Gausmann, 2021), reflecting geographic differences in topography, and the conservation value of freshwater habitats connected to the Pacific due to their paucity (e.g., De la Llata Quiroga et al., 2023).

Thomas B. Thorson was a pioneer in studying freshwater elasmobranchs in Central America and devoted his career to this research, with special emphasis on C. leucas (an extensive bibliography of Thorsonʼs lifetime work was compiled by Pollerspöck, Straube, 2024). Thorsonʼs work on sharks in Latin America ended in the 1980s, partly due to the increasing political crisis in many countries, which made research in this region challenging. Research on C. leucas in the freshwater systems of Latin America have since been limited (Oliveira et al., 2023), with many unresolved research questions. There is currently no data available on the distribution and habitat use of euryhaline sharks and sawfish for most freshwater and brackish systems of Latin America, which hinders an assessment of their conservation status and the implementation of successful conservation measures. Blaber, Barletta (2016) highlighted this data gap, and despite the increasing number of Latin American chondrichthyan studies over the past decade, there is still a need to redirect efforts toward specific research areas, regions, and species that currently show major information gaps like C. leucas in freshwater and brackish systems (Espinoza et al., 2018). Becerril-García et al. (2022) recently outlined important research priorities for the conservation of chondrichthyans in Latin America, emphasizing the need to assess freshwater ecosystems more comprehensively as elasmobranch habitats. In addition to overfishing, the identification of other anthropogenic threats as well as those posed by the environment is of special concern for freshwater chondrichthyan conservation in Latin America, because of extensive habitat alterations and deteriorations across the region (Reis et al., 2016). Population assessments of euryhaline and freshwater elasmobranchs are scarce (Jorgensen et al., 2022), thereby increasing the challenge of assessing the consequences of these threats.

Our study identifies research areas of top priority for C. leucas in Latin America based on data gaps identified from a review of the literature, published media, and recommendations from researchers across the region. This survey focuses on seven sites of interest in Mexico, Guatemala, Nicaragua, Panama, Venezuela, and Brazil, because of their biogeographical importance and/or reproductive significance for C. leucas, with the goal of not only highlighting research questions of special concern, but broadly rekindling interest in ʽsharks in fresh waters of Latin Americaʼ among the scientific community, with a focus on updating the status of locations in Latin America that have been historically identified as crucial for C. leucas but are now understudied and largely unprotected.

Material and methods

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Study area. The study area includes all countries of continental Latin America as well as the biggest island states of the Greater Antilles that lie within the distribution of Carcharhinus leucas. Chile and mainland countries such as Bolivia and Paraguay where C. leucas does not occur were excluded. Latin America is broadly defined here to include not only Spanish and Portuguese-speaking countries, but countries with other official languages in the neotropics, including Guyana, Suriname, French Guyana, and Belize. As such, the study area spans the waters of the Tropical Eastern Pacific from Mexico to Peru and the western Atlantic Ocean from Mexico to northern Argentina (estuary of the Río de la Plata), consisting of the following 23 countries and overseas territories populated by ~665 Mio. people (Statista Inc., 2022): Argentina, Belize, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, French Guyana, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Nicaragua, Panama, Peru, Puerto Rico, Suriname, Uruguay, Venezuela (Fig. 2).

FIGURE 2| Distribution of research goals for Carcharhinus leucas in Latin America based on scientist interviews. Numbers in brackets after the country abbreviations = numbers of responding scientists in relation to requested scientists for each country; colored numbers represent sites of special scientific concern: 1 (red) = Gulf of California, 2 (orange) = Terminos Lagoon, 3 (yellow) = Lake Izabal-Dulce River system, 4 (green) = Lake Nicaragua-San Juan River system, 5 (blue-green) = Panama Canal and Lake Gatun, 6 (blue) = Lake Maracaibo, 7 (purple) = Amazon River system.

Expert surveys. To understand the perspective of local experts, shark scientists across Latin America (n = 110; Tab. S1) were solicited similar to Hays et al. (2016). Due to the paucity of experts in some Latin American countries, we did not set a threshold of publications on the topic of “sharks” in general and “Carcharhinus leucas” in particular for the scientists we asked. Therefore, all experts who had at least one publication on this topic were considered for the survey. Some of the experts involved derived from recommendations from other requested Latin American experts. Each scientist was asked to provide research goals that would improve knowledge on C. leucas in their study area:

1. In your opinion, what topic or aspect regarding Carcharhinus leucas should be investigated, and which research goal should be prioritized?

2. Based on your expertise, which location(s) are priorities for this research?

Responses were compiled and grouped based on respective research topics and similarities (see Results; Tab. 1). More than half of the Latin American countries were represented by at least one expert (see Results; Tab. S1), however, several countries, particularly those with small populations (e.g., Haiti, Dominican Republic, Puerto Rico, El Salvador, Belize), did not have any experts respond (Tab. S1).

TABLE 1 | Research goals for Carcharhinus leucas based on responses from Latin American scientists.

No	Research goal	Number of answers
1	Non-nursery habitat use and distribution (incl. migration)	25 (68%)
2	Life history and biology (e.g., age and growth, reproduction, population dynamics)	18 (49%)
3	Fisheries impacts	17 (46%)
4	Identification of nurseries and other conservation areas	16 (43%)
5	Non-fisheries human impacts (e.g., habitat degradation, pollution)	15 (41%)
6	Occurrence in artisanal fisheries	10 (27%)
7	Genetic population structure	4 (11%)
8	Ecological role	4 (11%)
9	Non-human impacts (e.g., climate change, extreme climate events, lack of prey)	3 (8%)
10	Shark bites	1 (3%)

Literature review, investigation of online media and museum records. To complement the recommendations from Latin American scientists, a literature review was conducted in Google Scholar, Scopus, and Web of Science using relevant key words in English, Spanish, and Portuguese pertaining to C. leucas in Latin America (e.g., “Carcharhinus leucas”; “Latin America”; “tiburon toro”; “tubarão-cabeça-chata”; “freshwater”; “agua dulce”; “água doce”). Results were compiled to derive locations that are currently or were historically important for C. leucas. We filtered these results based on our knowledge of critical habitats of this species, resulting in seven sites we considered most important for the life history of C. leucas and crucial for maintaining stable populations in Latin America. These seven sites compose the Gulf of California, Terminos Lagoon, Lake Izabal-Dulce River system, Lake Nicaragua-San Juan River system, Panama Canal and Lake Gatun, Lake Maracaibo, and the Amazon River system (Tab. 2; Fig. 2).

TABLE 2 | Localities of scientific concern for Carcharhinus leucas in Latin America based on the results of literature review conducted by the authors as well as their own experiences. Numbers with asterisk = locations that were also mentioned by the interviewed Latin American scientists.

No	Locality toponym	Country	Geographical coordinates / spatial extension	Regional climate conditions
1*	Gulf of California	Mexico	31.70°N, -114.80°W to 24.30°N, -107.50°W	Subtropical
2	Terminos Lagoon	Mexico	18.50°N, -91,85°W to 18.80°N, -91.29°W	Tropical
3	Lake Izabal-Dulce River system	Guatemala	15.36°N, -89.32°W to 15.81°N, -88.75°W	Tropical
4	Lake Nicaragua-San Juan River system	Nicaragua / Costa Rica	12.09°N, -85.87°W to 10.79°N, -83.58°W	Tropical
5*	Panama Canal and Lake Gatun	Panama	9.27°N, -79.91°W to 8.97°N, -79.58°W	Tropical
6*	Lake Maracaibo	Venezuela	10.99°N, -71.60°W to 9.03°N, -71.61°W	Tropical
7*	Amazon River system	Brazil / Colombia / Peru	0.70°N, -50.19°W to -8.37°S, -74.52°W	Tropical

Published data and historic records play a pivotal role in assessing species status, with inferences on occurrence or extirpation generally based on past observations in the absence of long-term monitoring data (Rivadeneira et al., 2009). Thus, an extensive review and synthesis of historic records, media reports (newspapers, social media, and networks; Tab. S2), and museum specimens (Tab. S3) were also included to supplement data from scientific literature. Online media references underwent a critical check on their reliability based on published literature and known information pertaining to C. leucas (e.g., morphology, behavior). For each location, ecosystem characteristics and a short chronological summary of research conducted on sharks were composed, including the present state of knowledge. The derivation of important research questions for C. leucas in Latin America, including those for the seven sites we identified to be of top priority, is summarized in the results and discussion section.

All size measurements and estimations of length of C. leucas specimens reported and recorded at these sites are provided in cm total length (TL). Museum and institutional abbreviations of voucher specimens housed in collections are described in the following format according to Sabaj (2020): CAS-SU: California Academy of Sciences, Ichthyological Collection, incl. specimens from the historical collection of Stanford University (SU), San Francisco; CMNFI: Canadian Museum of Nature, Fish Collection, Ottawa; MCZ: Museum of Comparative Zoology, Harvard University, Cambridge; MOVI: Museu Oceanográfico do Vale do Itajaí, Santa Catarina; NMW: Naturhistorisches Museum, Wien; TCWC: Texas Cooperative Wildlife Collection, Texas A&M University, College Station, Texas; TU: Royal D. Suttkus Fish Collection, Tulane University Biodiversity Research Institute (TUBRI), New Orleans; UCLA: University of California at Los Angeles, Los Angeles; UCR: Museo de Zoología, Escuela de Biología, Universidad de Costa Rica, San Pedro de Montes de Oca; USNM: Smithsonian Institution National Museum of Natural History, Washington, D.C.

Results​ and Discussion​

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Expert surveys. Thirty-seven scientists from twelve countries across Latin America provided research recommendations and goals for Carcharhinus leucas in the region (34% response rate; Tab. S1). Most of the responding researchers originated from Brazil (n = 12) and Mexico (n = 8), with fewer responding scientists from smaller Latin American countries (Tab. S1). Responses were organized into 10 main topics (Tab. 1). Most responding scientists provided multiple recommendations, highlighting that information is lacking for many aspects of C. leucas in Latin America. Scientists often cited a lack of resources (i.e., funding) for research, and therefore data limitations, as the primary contributor to research goals.

Summarized, the interactions fisheries have with C. leucas was the most frequently noted priority (Tab. 1, number 3 and 6; Fig. 2), including missing information on landings data, time series analysis of catch per unit effort (CPUE), and catch composition (e.g., sex ratio, sizes, maturity stages). Fisheries impact (46%) and occurrences of C. leucas in artisanal fisheries (27%) can be counted together and represent 73% of scientists who highlighted fisheries concerns. Data gaps create a barrier to assessing the sustainability of fishing, and fisheries monitoring and management efforts are very limited in some regions (e.g., northeast Brazil) based on responses, hindering efforts to address other priorities if C. leucas continues to be overfished. Scientists reported that a stock assessment is a key first step to addressing fisheries impacts, along with outreach efforts with local communities to assess artisanal fisheries via local ecological knowledge. Fishing activities, particularly near key nursery habitats and those that coincide with times of reproduction, were identified as serious threats, and despite C. leucas not being a target species in many countries, bycatch was a concern for 20 scientists (54%). Fisheries data plays a key role in elasmobranch research in the region, thus a stronger relationship between scientists, fisheries managers, and fishing communities is clearly needed.

The evaluation and elimination of other threats was a priority for 49% of scientists, including habitat degradation due to pollution, coastal development, and climate change. Carcharhinus leucas life history and biology (49%) and genetic population structure (11%) were reported as data gaps in Latin America, however, understanding habitat use and identifying key areas for conservation, including potential nurseries, was of greater interest for most of the responding scientists (non-nursery habitat use: 68%; identification of nurseries and other conservation areas: 43%; Tab. 1). Prioritizing studies that assess distribution and habitat value overlap with understanding fisheries and non-fisheries impacts, because if essential habitat can be identified, then fisheries and land use regulations could be enacted that help protect these areas. Surprisingly, only one scientist (3%) based in Pernambuco, Brazil, identified shark bites as a research goal attributed to several incidents along the beaches of Recife between 1992 and 2006 (e.g., Hazin et al., 2008).

The impact of fisheries and C. leucas distribution were nearly ubiquitous priorities, but other topics varied based on the residence of responding scientists (Fig. 2). Non-fisheries threats (41%) were only recognized by respondents from five countries. Life history and biology (49% of the responding scientists) was a priority for half of the representative countries, while C. leucas population genetics (n = 3 countries) and ecological role (n = 2 countries) were among the least prioritized. Countries with multiple responding scientists exhibited geographic differences in priorities (Tab. S4), as well as locations within their respective countries that should receive attention. In Mexico, there was a clear focus on the Gulf of California, particularly Southern Baja California, Cabo Pulmo, Sinaloa to Nayarit, and the Yucatan Peninsula. Costa Rican scientists highlighted the Gulf of Nicoya, Nicoya Peninsula, and the Coyote Estuary, because of potential C. leucas nurseries. The Panama Canal was identified by Panamanian scientists as an area of interest where sport fishers capture juvenile bull sharks in considerable numbers, and a future tagging program in cooperation with these fishers is planned. Lake Maracaibo and the adjacent Gulf of Venezuela were of special concern, because of pollution and habitat degradation caused by oil spills, wastewater, and harmful algal blooms, and the lack of recent data on C. leucas distribution and habitat use. Surinamese scientists indicated that C. leucas is rare in their country despite favourable habitats, including the Coppename, Maroni, and Suriname Rivers and their estuaries, which could be attributed to overfishing and/or the need to use less traditional monitoring methods such as measuring environmental DNA (eDNA) for successful occurrence verification. Brazilian scientists also highlighted the considerable lack of information on C. leucas in their country despite extensive areas of suitable habitat, particularly freshwater systems and tributaries of the Amazon, São Francisco, and Doce Rivers and their respective deltas that may be important nursery habitat. Sixteen (43%) scientists prioritized the identification of C. leucas nursery areas, but none suggested a re-assessment of historic, but overexploited nurseries in Lake Izabal and Lake Nicaragua.

Literature review

Gulf of California. Carcharhinus leucas was first described in the Gulf of California (= Sea of Cortez; Fig. 3) by Rosenblatt, Baldwin (1958), who reported its distribution in the East Pacific from southern California, USA to Guayaquil, Ecuador. This species has been part of Mexican commercial fisheries in the northern Gulf of California and Gulf of Tehuantepec (Bonfil, 1994), but its abundance has declined through time, which is a result of overfishing, habitat deterioration, and naturally low availability of potential nursery habitat in the region (Galván-Magaña et al., 1989, 1996; Bizzarro et al., 2009; Saldaña-Ruiz, 2017; Saldaña-Ruiz et al., 2017). Due to the low number of rivers that drain into the Gulf of California, there is limited freshwater inflow from the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and Yaqui Rivers. The Colorado River was the largest source of freshwater before its use for irrigation and water storage (Schmidt et al., 2023). Today, the Colorado River no longer reaches the sea most years (Schmidt et al., 2022), which has undoubtably altered its function as C. leucas habitat. Hastings, Findley (2006) and Bonfil (2014) mentioned the occurrence of C. leucas near the Colorado River Delta, and it is plausible that this location was a potential nursery ground for bull sharks in the past, but its status fulfilling this function is currently unknown (Gausmann, 2021).

FIGURE 3| The Gulf of California is considered an area of special scientific concern for Carcharhinus leucas in the Northeast Pacific Ocean. At the marine reserve of Cabo Pulmo National Park (Baja California Sur; site 15), subadults and adults are frequently encountered, but small juveniles do not occur at this site (© Leonardo Gonzalez). 1) Colorado River, 2) Colorado River Delta Biosphere Reserve, 3) Isla Angel de la Guarda, 4) Deep benthic midriff islands, 5) Bahia de los Angeles, 6) Isla Tiburon, 7) Rio Sonora, 8) Rio Yaqui, 9) Bahia los Algodones, 10) Mulege-Santa Rosalia, 11) Bahia Concepcion, 12) Bahia de Loretc National Park, 13) Bahia de la Paz, 14) Cerralvo Island, 15) Cabo Pulmcg National Park, 16) Cabo San Lucas, 17) Rio Mayo, 18) Rio Fuerte, 19) Rio Sinaloa, 20) Bahia de Santa Maria- La Reforma, 21) Altata-Ensensada (Lazoon Suster, 22) Culiacan River, 23) Bahia la Guadalupana, 24) Urias Lagoon, 25) Presidio River, 26) Teacapan-Agua Brava Lagoon-Estuarine System. 27) Zona Marina de la Isla Isabel, 28) Bahia Magdalena.

Beyond the Colorado River Delta, the Gulf of California contains other important conservation areas, including Cabo Pulmo National Park and Bahía de Loreto National Park (SEMARNAT, 2018). Carcharhinus leucas inhabits both national parks (Reyes-Bonilla et al., 2016; Lara-Lizardi et al., 2022, 2024), as well as the Presidio River (Castro-Aguirre, 1978; Castro-Aguirre et al., 1999; Espinosa-Pérez et al., 2004; Miller et al., 2006, 2009), Bahía Concepción and the Bahía Magdalena-Almejas lagoon system (Gonzáles-Acosta et al., 2015, Rábago-Quiroz et al., 2024), the Altata-Ensenada Lagoon system, and Urias Lagoon (Gausmann, 2021). Regionally, 14 Important Shark and Ray Areas (ISRAs) for elasmobranch conservation have been designated in the Gulf (Jabado et al., 2023), with C. leucas and other sharks suspected to give birth in some of these ISRAs (Salomón-Aguilar et al., 2009).

Carcharhinus leucas expectantly exhibits variability in its distribution in the Gulf of California based on size, with the Presidio River, Altata-Ensenada Lagoon system, Urias Lagoon, and Teacapán-Agua Brava system serving as juvenile habitats (Applegate et al., 1993; Ruelas-Inzunza, Páez-Osuna, 2005, 2007; Bizzarro et al., 2009; Ruelas-Inzunza et al., 2014; Salomón-Aguilar et al., 2009; Gausmann, 2021). Data on size classes and habitat use of C. leucas in these systems are, however, largely lacking, preventing formal nursery assessments according to Heupel et al. (2007). Additionally, Ramirez-Amaro et al. (2013) reported on a juvenile C. leucas south of Bahia Magdalena, indicating that potential nursery(ies) could also be located northwest of Cabo Pulmo, but only subadult and adult C. leucas are found at Cabo Pulmo National Park (Lara-Lizardi et al., 2022, 2024). Lara-Lizardi et al. (2022, 2024) observed sex-based differences in C. leucas distribution at Cabo Pulmo, with females showing higher residency than males in most seasons, but departing in summer-fall presumably migrating for parturition because there is no source of freshwater inflow nearby suitable for juvenile habitat.

Terminos Lagoon. Terminos Lagoon, located in the Mexican state of Campeche, is one of the most important hydrological networks of the country (Diario Oficial de la Federación, 1997; Soto-Galera et al., 2010) and the largest coastal lagoon in the southern Gulf of Mexico (Yáñez-Arancibia et al., 1980; Medina-Gómez et al., 2015). This lagoon is a complex eco-social system, where a high biodiversity (aquatic and terrestrial) coexists with important economic and social sectors, such as tourism, hydrocarbon industry, and fisheries (Medina-Gómez et al., 2015; Campos Flores, Crespo Guerrero, 2018). Despite its designation as a Mexican Protected Area since 1994 (Diario Oficial de la Federación, 1994), pollution deriving from oil spills and contamination with heavy metals poses a potential threat to the local ecosystems (Montalvo et al., 2014; Olivares-Rubio et al., 2024). Several environmental changes and species turnovers have been reported through the years at this site (Ramos-Miranda et al., 2005; Soto-Galera et al., 2010; Medina-Gómez et al., 2015; Paz-Ríos et al., 2021).

The presence of Carcharhinus leucas in the lagoon was first reported by Castro-Aguirre (1978) (Tab. 3). In Uribeʼs (1993) thesis, he found that C. leucas and Sphyrna tiburo (Linnaeus, 1758) (bonnethead shark) were the most abundant shark species in this estuary system (41.2% and 35.3% of catches, respectively). Uribe reported neonates and juveniles for both species (immature C. leucas ranging between 71–102 cm TL). A study on sharks outlined Campeche as the principal state for captures of C. leucas, including the main fishing ports such as Caleta (Ciudad del Carmen; Fig. 4), Isla Aguada, and Sabancuy located within Terminos Lagoon or in its near vicinity (Castillo-Géniz et al., 1998), indicating that potential nursery areas of C. leucas overlapped with areas of intensive fishing activities

TABLE 3 | Summary of locations of special interest regarding scientific research on Carcharhinus leucas in the Latin American region as identified by the authors with research goals and suggested investigation methods. Numbers with asterisk = locations that were also mentioned by the interviewed Latin American scientists.

No	Toponym	Year of the first record of Carcharhinus leucas	Research topic	Research goals	Research and investigation methods
1*	Gulf of California	1958	Reproduction	Identification of coastal nursery areas	Acoustic or satellite tracking, tagging
2	Terminos Lagoon	1978	Reproduction	Verification of the use of a nursery / estimation of population size / impacts of water pollution / development of appropriate educational tools targeting shark conservation	Catch per unit effort (CPUE), acoustic or satellite tracking, tagging, DNA sampling, local ecologically knowledge (interviews with local fishermen), tissue sampling
3	Lake Izabal-Dulce River system	1948	Reproduction	Verification of the use of a nursery / estimation of population size	Catch per unit effort (CPUE), acoustic or satellite tracking, tagging, DNA sampling, local ecologically knowledge (interviews with local fishermen)
4	Lake Nicaragua-San Juan River system	1877	Reproduction	Verification of the use of a nursery of regional significance / estimation of population size	Catch per unit effort (CPUE), acoustic or satellite tracking, tagging, local ecologically knowledge (interviews with local fishermen)
5*	Panama Canal and Lake Gatun	1948	Biogeography, genetics, distribution	Verification of possible canal passage and possible transfer of specimens; genetic sampling from specimens of Atlantic and Pacific origin	Environmental DNA (eDNA), fishing (gill net, hook and line) in both the canal and the lakes, tagging of marine Atlantic and Pacific specimens in the vicinity of the canal, ongoing DNA clustering of marine Atlantic and Pacific populations for confirmation of gene admixture
6*	Lake Maracaibo	1964	Reproduction	Verification of the use of a nursery / estimation of population size	Acoustic or satellite tracking, tagging, DNA sampling, local ecologically knowledge (interviews with local fishermen)
7*	Amazon River system	1913	Reproduction	Estimation of habitat use / confirmation of a nursery / impact of river impediments	Acoustic or satellite tracking, tagging, local ecologically knowledge (interviews with local fishermen)

FIGURE 4| Terminos Lagoon is an important nursery site for Carcharhinus leucas in the southern Gulf of Mexico. However, at this site, the local population is at risk from fisheries, environmental pollution, and habitat change. These small juvenile C. leucas were landed at the port of Ciudad del Carmen (© Nadia Sandoval Laurrabaquio-Alvarado). 1) Usumacinta River, 2) Palizada River, 3) Boca del Carmen, 4) Ciudad del Carmen, 5) Isla del Carmen, 6) Boca de Puerto Real, 7) Candaleria River, 8) Champoton.

Carcharhinus leucas has been one of the principal species captured in the southern Gulf of Mexico artisanal fisheries for decades (Castillo-Géniz et al., 1998; Pérez-Jimenez et al., 2012, 2016; Pérez-Jimenez, Mendez-Loaeza, 2015; Figs. 1, 4). It is both targeted and caught as bycatch year-round (Pérez-Jimenez, Mendez-Loaeza, 2015), with all life stages at risk: newborns, juveniles, adults, and pregnant females (Pérez-Jiménez et al., 2020). A recent study by Pérez-Jiménez, Mendoza-Carranza (2023) documented high proportions (> 90%) of immature sharks across approximately 12 species in the artisanal fisheries of Tabasco and Campeche. These findings highlight the coastal waters of both states, including Terminos Lagoon, as potential nursery habitats for juvenile sharks such as C. leucas.

Further targeted research is necessary to assess the current role of this lagoon as a nursery for C. leucas. Documented bull shark declines in the Gulf of Mexico (Pérez-Jiménez et al., 2012) and the nearby Mexican Caribbean (Rubio-Cisneros et al., 2023) appear to be driven by a combination of fishing pressure, pollution from the oil industry particularly in Terminos Lagoon (Campos Flores, Crespo Guerrero, 2018; Peña-Puch et al., 2021), and changes in water quality parameters such as temperature, salinity, and dissolved oxygen. It is known that C. leucas also uses smaller lagoons in the western part of the Terminos Lagoon system, including Pom Lagoon and Atasta Lagoon (D. Lon, 2021, pers. comm.).

Recently, an anomalous embryo (46.5 cm TL) showing synophthalmia (a rare congenital malformation in which the eyelids and eyes partially or completely fuse together to form a single orbital insert in the center of the face) and leucism was registered in a pregnant C. leucas that was captured in marine waters between the mouth of the Grijalva River and Terminos Lagoon (Wakida-Kusunoki et al., 2022). According to these authors, this anomaly, among other factors, can be related to the environmental pollution in this area. However, the possibility of genetic damage due to inbreeding resulting from a very low population size as a consequence of overfishing cannot be excluded.

Lake Izabal-Dulce River system. The first scientific record of Carcharhinus leucas from the Lake Izabal-Dulce River system (and from Guatemala) was described by Bigelow, Schroeder (1948), who reported two specimens (69.2 cm TL, ♀; 91.5 cm TL, ♀, USNM 134326; Fig. 5; Tab. S3) similar in size to those reported by Thorson et al. (1966; 69.4, 70.1, 108.8, and 120 cm TL, sex undetermined, uncataloged), and Garrick (1982; 127 cm TL, ♀, USNM 146542). Lake Izabal is the third largest lake in Central America (717 km²), which drains into the Caribbean Sea via the 40 km Dulce River (Thorson et al., 1966). For part of its length, the Dulce River expands into a small lake (El Golfete), which functions as an estuary based on saltwater incursion, making it appropriate habitat for euryhaline fish like juvenile C. leucas (Saunders et al., 1950). The sizes of all reported and collected C. leucas specimens were juveniles (Fig. 5; Tab. S3), indicating the Lake Izabal-Dulce River system functioned at least historically as a nursery before overfishing began in the 1960s.

FIGURE 5| The Lake Izabal-Dulce River system is an area of special scientific concern for Carcharhinus leucas in Central America. At this site, C. leucas was already fished out in the 1970s. The recorded juvenile specimens from this site indicate that Lake Izabal was a nursery for C. leucas, which is supported by collected material such as this specimen (USNM 134326: ♀, 91.5 cm TL) from 1946 collected at the northeast drainage by R. R. Miller (© Smithsonian Institution).

Thorson et al. (1966) reported claims from residents that sharks occurred abundantly throughout the Dulce River and Lake Izabal, and up the Polochic River. Michot et al. (2002) and Alvarado et al. (2005) highlighted that C. leucas was historically distributed from El Estor to San Felipe, and thereby used the entire system. However, Brinson (1973) described severe declines and a noticeable reduction in the abundance of C. leucas, with no reports of sharks shortly after (Brinson, Nordlie, 1975). Guatemalaʼs Fundación Defensores de la Naturaleza (2002) more recently reported the extirpation of C. leucas in both Polochic River and Lake Izabal, and Hacohen-Domené et al. (2020) did not record C. leucas in the artisanal elasmobranch fisheries at Livingston, Guatemala’s Caribbean coast. It is currently unknown if and how C. leucas use the Lake Izabal-Dulce River system, but one juvenile C. leucas was recently seen swimming at the surface of Lake Izabal (Tab. S2).

Lake Nicaragua-San Juan River system. The history of Lake Nicaragua and the culture of its people are indivisible linked to Carcharhinus leucas (Peréz, Mondragón, 2011). Early Spanish historiographers made observations of sharks in the 16th Century (Burke, 1979), and the first scientific report of sharks in Lake Nicaragua was made by Gill, Bransford (1877), which were very abundant (Smith, 1893), and likely the largest freshwater population of C. leucas in the world (Thorson, 1982). Lake Nicaragua is the third-largest lake in Latin America (7,897 km²), and it drains into the Caribbean Sea via the San Juan River, both of which were C. leucas habitat (Thorson, 1982; Fig. 6).

FIGURE 6| The Lake Nicaragua-San Juan River system was historically the most important nursery for Carcharhinus leucas in the entire Caribbean region (© Simon Dannhauer). 1) Granada, 2) Zapatera Island, 3) Ometepe Island, 4) San Juan del Norte, 5) San Juan River, 6) Colorado River.

The Lake Nicaragua-San Juan River system historically harbored a diversity of marine ichthyofauna, including C. leucas, Pristis pristis (Linnaeus, 1758) (common sawfish), and Megalops atlanticus (Lacepède, 1803) (Atlantic tarpon). From the 1960s–1980s, Thomas B. Thorson studied C. leucas in this extensive nursery (Astorqui, 1967), where sharks once migrated between freshwater habitats of Lake Nicaragua to the marine environments of the Caribbean Sea (Hagberg, 1968; Thorson, 1970a,b, 1971, 1972a, 1976, 1982; Tuma, 1976; Watson, Thorson, 1976). However, unsustainable fishing practices changed this. Nicaragua was the first country where commercial exploitation of sharks took place in Central America, including Lake Nicaragua and the San Juan River, beginning in the 1940s (Rojas et al., 2000). In the 1960s–1970s, Japan established a shark fin processing plant on the shores of the San Juan River and Lake Nicaragua at Granada, which exported C. leucas and P. pristis fins to China, Taiwan, Hong Kong, and Singapore (Davies, Pierce, 1972; Peréz, Mondragón, 2011; Contreras-MacBeath et al., 2024). Despite unsustainable fishing, Hagberg (1968) found C. leucas and P. pristis in considerable numbers in the late 1960s, but both species declined at alarming rates in the 1970s, leading to their near extirpation in the early 1980s (Astorqui, 1974; Thorson, 1982; Rojas et al., 2000; Martínez-Sánchez et al., 2001; Bustamante, Lamilla, 2006; Zarate, Hearn, 2008). Research expeditions to Lake Nicaragua during the 1990s-2000s consequently failed to find C. leucas or they were observed in very low numbers (Taniuchi, 1992, 2002; Tanaka, 1994; McDavitt, 2002; Zarate, Hearn, 2008).

The Nicaraguan government instituted a temporary moratorium on targeted fishing for sawfish and sharks (Thorson, 1982), and later declared them as prohibited species by national law (McDavitt, 2002), but this measure likely came too late (Zarate, Hearn, 2008). Carcharhinus leucas have been observed in Lake Nicaragua since 2000 (Martínez-Serrano et al., 2014; Información Puntual, 2020; Tab. S2), which may indicate site fidelity to this system. However, C. leucas of Lake Nicaragua have not recovered. Sharks no longer play a role in Lake Nicaragua fisheries, and individual sharks are only occassionally caught as bycatch in gillnets targeting other species. Nicaragua Investiga (2022) reported that bull sharks have only been sighted in the Lake Nicaragua-San Juan River system sporadically for decades, including two recent observations in 2020 from Zapatera Island.

Beyond the era of Thorsonʼs research, data and information about the occurrence and abundance of C. leucas from this locality is scarce (e.g., Astorga, 2023; Angulo et al., 2023). Most sharks studied from this system were immature, indicating its function as a nursery (Tab. S3). Extreme abundances of juveniles in the Lake Nicaragua-San Juan River system, coupled with a recently described distinct lineage of C. leucas in the Caribbean Sea (Laurrabaquio-Alvarado et al., 2021), indicate that this system could have been one of the most important nurseries for C. leucas in the region. In Nicaragua, scientific research on elasmobranchs currently focuses on the Pacific Ocean, with no attention given to the freshwater elasmobranchs of Lake Nicaragua due to limited funding (e.g., Hernández-Fernández et al., 2021; G. M. Hernández-Fernández, 2023, pers. comm.).

Panama Canal and Lake Gatun. The 82 km Panama Canal connects the Caribbean Sea and the Tropical East Pacific (Fig. 7), which had been disparate and impassable for marine biota since the emergence of the Isthmus of Panama ~3,5 myr ago, until 1914 when the canal was completed (Coates, Stallard, 2013). As a euryhaline shark, the low-salinity waters of the Panama Canal should provide no physiological barrier to C. leucas (Misra, Menon, 1955). However, there is only one verifiably record from the canal derived by literature – Bigelow, Schroeder (1948) reported a single juvenile (~110 cm TL, ♀, USNM 127134; Tab. S3) collected in 1937 at Miraflores Locks (Fig. 7). The canal includes several locks that account for sea level differences between Pacific and Caribbean waters (Fig. 7), and lift ships to Lake Gatun 26 m above sea level. Although increased observations of marine fish have been reported from Lake Gatun that successfully migrated through the locks (Colamarco et al., 2004; Smith et al., 2004; Sharpe et al., 2017; Schreiber et al., 2023), they do not include C. leucas. Neither historical reports on the fish of Lake Gatun (e.g., Herre, 1936; Hildebrand, 1939; Gunter, 1979) nor reports on the transfer of fish between ocean basins via the Panama Canal (McCosker, Dawson, 1975) mention C. leucas, suggesting its use is limited or absent, and C. leucas is an Isthmian relict in the eastern Pacific (Robertson et al., 2004).

FIGURE 7| The Panama Canal (dashed line) and Lake Gatun are of special scientific concern for Carcharhinus leucas in Central America. The only known record of this species from the canal zone derives from Miraflores Locks illustrated above (© Leonid Andronov).

The Panama Canal is, however, of interest concerning C. leucas conservation. The waterway presumably plays no role as a nursery in contrast to other low-salinity waterways discussed herein, because of its recent establishment and the apparent lack of sharks, but may affect C. leucas population structure in the western Atlantic and eastern Pacific. Populations are adapted to local-regional environmental conditions (Williams, 1966), which vary greatly between the eastern Pacific and Caribbean Sea. Testerman (2014) determined that the West Atlantic and Indo-Pacific populations of C. leucas are genetically distinct, but share some loci, which could be remnants of the gene pool prior to the emergence of the Isthmus of Panama, and/or admixture resultant from migration through the canal. These findings were supported by Postaire et al. (2024), with East Pacific C. leucas sampled in Panama (n = 15) genetically distinct from C. leucas in the Gulf of Mexico (n = 27), U.S. Atlantic coast (n = 7), and Brazil (n = 40). Considering these ocean basins have been largely biologically separated for millions of years, it is expected that C. leucas in the eastern Pacific are suited for different environmental conditions than those in the western Caribbean. The movement of sharks through the canal could thus have consequences if C. leucas are not suited to handle differences in temperature, salinity, and other factors, which could be transmitted to offspring. However, mingling between C. leucas populations originated in the Atlantic and Indo-Pacific by migrating specimens occasionally passing natural biogeographic barriers cannot be ruled out with certainty either (Daly et al., 2025).

Lake Maracaibo. Lake Maracaibo (Fig. 8) is the largest lake in South America, and has historically provided habiat to sharks as far south as the freshwaters of the Santa Ana River mouth (Schultz, 1949; Boeseman, 1964; Thorson, 1970b). The lake is connected to the Gulf of Venezuela and Caribbean Sea through the Maracaibo Strait, forming the largest estuary of northern South America (Cervigón et al., 1993; Plotnikov, Aladin, 2011). The lake and estuary are an important C. leucas nursery and parturition site based on the abundance of neonates and juveniles (92.8% of catch), and the presence of mature females (Tab. S2; Sánchez, Tavares, 2010; Tavares, Sánchez, 2012; Ehemann et al., 2019). However, Venezuela is a data-poor region, and little information exists on the occurrence, distribution, and habitat use of Carcharhinus leucas in its waters. Carcharhinus leucas is targetted by the Venezuelan fishing fleet, although fisheries data for this species is lacking (Yegres et al., 1996). Anonymous (2013) reported sporadic captures of C. leucas by fishers from Lake Maracaibo and the mouth of the Catatumbo River, though there is no freshwater fishery for this species.

FIGURE 8| Lake Maracaibo in South America provides habitat to small juvenile Carcharhinus leucas. Sharks with visible umbilical scars indicate that Lake Maracaibo is a nursery for bull sharks in the southern Caribbean Sea (© Rafael Tavares).

Based on the largely outdated information and the paucity of reliable data for C. leucas, Lake Maracaibo did not manage to be designated as an Important Shark and Ray Area (ISRA). It is, however, an Area of Interest (AoI) but at least an Area of Interest (AoI) for South America by the ISRA project (Gausmann et al., 2025), indicating it had insufficient information to satisfy the ISRA criteria but may be designated as an ISRA in the future after a reassessment based on reliable data. This stresses the need for in-depth studies on C. leucas focusing on its distribution, abundance, and habitat use at this site.

Amazon River system. The Amazon River (Fig. 9) is the largest river system in the world, extending ~6,400 km through nine South American countries (Moura et al., 2016). Despite its geographic extent, records of Carcharhinus leucas from the Amazon are scarce (n = 35 over 110 years), and are mainly derived from incidental captures by artisanal fisheries. Starks (1913) first reported on a juvenile C. leucas (73.66 cm TL) from Belém, ~120 km from the sea, which has been followed by many authors since from Autazes, Iranduba, Lagoa dos Patos, Manaus, Santarém, and the Limoeiro, Mearim, Madeira, Tapajós, and Xingú, and Tocantins Rivers (Myers, 1952; Thorson, 1972b; Vizotto, Taddei, 1978; Werder, Alhanati, 1981; Soto, Nisa-Castro-Neto, 1998; Soto, Mincarone, 2004; Feitosa, Nunes, 2020; Gausmann, 2021; Tab. S2; Fig. 9). Myers (1952) reported on C. leucas in Iquitos, Peru ~4,000 km upstream, and Thorson (1972b) reported several C. leucas from the Ucayali River, Peru 4,200 km from the river mouth. This indicates that C. leucas, at least historically, made use of the entire Amazon main channel and beyond, spending years in this large river system (Dagosta, de Pinna, 2019).

FIGURE 9| The Amazon River system crosses multiple countries in South America, including Brazil where this fisherman poses with an immature male Carcharhinus leucas (~150 cm TL) incidentally captured in fishing nets on the 29th November 2016 along the river at Pinduri (Santarém, Pará State, Brazil) (© Jeso Carneiro). 1) Iquitos, 2) Ucayali River, 3) Pucallpa, 4) Negro/Salimoes River, 5) Madeira River, 6) Iranduba, 7) Autazes, 8) Tapajos River, 9) Pinduri, Santarem, 10) Limoeiro River, 11) Mearim River, 12) Tocantins River, 13) Xingu River.

The state of the Amazon, however, is at risk. Several hydropower plants and dams have been proposed, which pose a serious threat to this biodiversity hotspot that includes 2.406 native freshwater fish species, many of which are endemic (Jézéquel et al., 2020; Pelicice et al., 2021). The exploitation of fish in the Amazonian region has also increased at alarming levels (Wosnick et al., 2019). Because it is only sporadically caught, C. leucas is not of commercial interest in the Amazon, but Ferreira et al. (1996) reported they are occasionally found in fish markets of Santarém ~700 km from the sea where they are not utilized as food, rather displayed as tourist attractions (Fig. 9). The mouth and the estuary of the Amazon have been outlined as an important global elasmobranch conservation hotspot (Lutz et al., 2024), thus strong fishing pressure along the Amazon mouth expectantly affects the reproductive output of C. leucas considering the importance of this region for neonate, juvenile, and pregnant C. leucas (Wosnick et al., 2024).

Recommendations. Survey results from scientists and the literature review revealed commonalities in research and conservation priorities for Carcharhinus leucas in Latin America:

1. Assess and mitigate fisheries impacts (targeted and bycatch).

2. Engage communities and governments to ensure sustainable, non-destructive fisheries, and eliminate other threats (e.g., habitat degradation, pollution).

3. Conduct stock assessments that describe shark densities, age structure, distribution, essential habitat (e.g., nurseries), and genetic structure.

4. Identify and investigate previously unknown nurseries / re-assess historic nurseries.

5. Understand regional/local biological characteristics of C. leucas.

6. Secure/allocate resources for research efforts.

Data gaps create barriers to conservation efforts, and the paucity of recent information on C. leucas in Latin America makes this a priority worth addressing because of the species’ ecological role in freshwater, brackish, and marine ecosystems and its cultural importance in some countries (Astorqui, 1967; Thorson, 1982; Peréz, Mondragón, 2011). There are historic records of C. leucas in > 90 low-salinity habitats across Latin America (Gausmann, 2021), and recent media reports confirm its presence in some of these locations (Tab. S2). However, the infrequency of these reports highlights conservation concerns. Like many other sharks, C. leucas was significantly overfished in Latin America in the 20th century (e.g., Thorson, 1982; Saldaña-Ruiz et al., 2017), and overfishing is still the most persistent threat sharks face today (Dulvy et al., 2021; Fogliarini et al., 2024). Despite management efforts, recent densities estimates of C. leucas in Latin America indicate that i) fishery management policies were implemented too late and/or ignored, and ii) recovery may occur on timescales beyond human generation times due to the low reproductive rate of this species (Smith et al., 1998; Saldaña-Ruiz et al., 2022), particularly if overfishing is permitted to occur unchecked for extended periods as they were in the 20th century. While surveys and literature were not reviewed across the entire geographic range of C. leucas in Latin America, the locations discussed are representative of many other parts of this region where C. leucas is understudied (e.g., Usumacinta River, Mexico; Patuca River, Honduras; Chepo River, Panama; Magdalena River, Colombia; Orinoco River; Venezuela). Research, management, and conservation approaches, along with historic and current knowledge of C. leucas and the threats to this species, are not homogenous. However, there are some nearly ubiquitous concerns and solutions to address the understudied nature of C. leucas in Latin America, which we summarize below. As it was in the 20th century, research on C. leucas must become a priority again if this species is to recover and be preserved in Latin America.

Fisheries and other human uses. Unsustainable fishing has been and is the main threat to C. leucas in Latin America (Bonfil, 1997, 2014; Saldaña-Ruiz et al., 2017, 2022; Martínez-Candelas et al., 2020). In many parts of the world, including Latin America, fishing activities overlap with essential C. leucas habitats, which affects population stability and recovery (Osuka et al., 2025). In response to fisheries management, but more likely a lack of sharks, C. leucas are no longer reported as target species in freshwater systems of Latin America (Rojas et al., 2000; Bustamante, Lamilla, 2006). However, they are still taken as bycatch (Pérez-Jimenez, Mendez-Loaeza, 2015), and harvest rates are largely undocumented, because of the geographic separation between fishers and managers, and the limited resources allocated to fisheries management. If essential C. leucas habitats can be identified (see Distributions and Movements below), managing these waters more strictly could be a solution, but stakeholder engagement will be needed (e.g., Sabbagh, Hickey, 2019; Williams et al., 2023).

It is unlikely resources allocated to fisheries enforcement will be adequate due to economic conditions in many Latin American countries. Thus, compliance and self-enforcement are essential for C. leucas recovery. Working with fishers collaboratively to develop management plans will be necessary to achieve this goal, since stakeholders are more compliant when they are included in management decisions (Shiffman et al., 2021). Workshops with fishers in communities that overlap with essential C. leucas habitat offer an opportunity to give stakeholders a voice in decision-making, and in turn ownership in complying with fisheries regulations and supporting conservation goals (e.g., Sabbagh, Hickey, 2019; Dinkel, Sánchez-Lizaso, 2020). A co-management approach will aid in compliance and fisheries-dependent monitoring (Morgan, Burgess, 2005), which will be more effective for monitoring C. leucas than relying on fisheries-independent sampling alone (see Stock Assessments and Biological Characteristics below), and help develop ventures for alternative sources of income generated from sharks tied to their conservation rather than their harvesting.

Sharks are extensively harvested for their fins and meat around the world, but the perspective that sharks are more valuable alive than dead has taken hold in some countries (Cisneros-Montemayor et al., 2020). For example, The Bahamas declared its waters a shark sanctuary in 2011, and sharks cannot be targeted or landed in order to support tourism (Sherman et al., 2018). Shark diving generates more than $140 million US annually in The Bahamas, and ecotourism offers a viable alternative to fisheries for C. leucas in some parts of Latin America. Sánchez Crispín et al. (2008) described the sharks of Lake Nicaragua as a tourist attraction when they were abundant. Suárez (2016) also reported the value of Lake Nicaraguaʼs aquatic resources, and outlined the potential economic benefits of C. leucas in generating income through tourism. Fishers in many developing countries have turned to ecotourism, because it offers a more profitable and reliable livelihood than fishing, thus economic benefits resultant from keeping C. leucas alive is expected in many Latin American countries. Logistics (e.g., marketing, scheduling) and initial financial support will, however, be needed for this transition to be successful, and ecotourism is not only tied to protecting sharks, but their habitat.

Waterway alterations. Considering the lack of recent information on C. leucas in much of Latin America, conservative decision making via the precautionary approach is warranted for fisheries regulations, and more holisticly, regulating human degradation of ecosystems. Recent adoptions of ecosystem-based management, i.e., an approach that recognizes the full array of interactions within an ecosystem, are likely too multidimensional for most Latin American countries due to resource limitations (e.g., Dulvy et al., 2017; Mouton et al., 2025). Yet, habitat protection is within the capacity of most countries, with special consideration given to the alteration of waterways, which is among the most destructive forms of habitat degradation that pose a threat to C. leucas and many other species in Latin America (Rigby et al., 2021).

Hydropower plants along rivers prevent the dispersal of fish, and have led to widespread declines in abundance and biodiversity (Rolls et al., 2014; Parreira, Nabout, 2023). For example, dams now extensively limit the migrations of C. leucas in the Zambezi River from 1,120 km historically to ~640 km (Bass et al., 1973; Bell-Cross, Minshull, 1988; Gausmann, 2021). In North Americaʼs Mississippi River, dams now prevent C. leucas from migrating to the upper reaches of the river where it was historically reported (Thomerson et al., 1977), with similar consequences in other American rivers (e.g., Matich et al., 2020a). In Iraq, C. leucas once traveled up the Tigris River to Baghdad ~850 km from the sea, but today dams prevent their movements upstream (Moore, 2018; Gausmann, 2021). In Latin America, the Bayano River in Panama was presumably a historic nursery for the east Pacific population of C. leucas, however, it is no longer accessible for parturition because of the damming of the river (Montoya, Thorson, 1982). Hydropower dams in the Tocantins-Araguaia River basin and other parts of Amazonia similarly threaten C. leucas (Feitosa, Nunes, 2020). The consequences of hydroelectric dams on C. leucas in Latin America are understudied, but it is suspected that current distributions are more restricted because of impassable structures in many waterways, and continued river fragmentation will affect both the quality and quantity of potential nursery habitats, and therefore conservation efforts. As such, the prevention of future dam construction is an important conservation measure across Latin America, and understanding the distribution and movement patterns of C. leucas is an important research priority to assess and mitigate these impacts.

Distributions and movements. Carcharhinus leucas exhibit notable ontogenetic habitat shifts, spending years in low-salinity environments as juveniles, then transitioning to marine waters (Werry et al., 2011). Females seek out these low-salinity habitats for parturition, and regional philopatry can lead to long distance migrations to and from nurseries by adult females (Daly et al., 2014; Heupel et al., 2015; Lea et al., 2015; Niella et al., 2017; Smoothey et al., 2019; Lédée et al., 2021; Lubitz et al., 2022). Evolutionarily, this behavior is hypothesized to optimize fitness by increasing offspring survival, because the habitation of low-salinity nursery habitats limits interactions with marine predators, thereby reducing risk (Heupel, Simpfendorfer, 2011; Matich, Heithaus, 2015; Lofthus et al., 2024). Historically, many Latin American estuaries and river systems functioned as nurseries, but today, the locations of C. leucas nurseries are unclear across much of the region. For example, Hoyos-Padilla et al. (2023) recently reported on pregnant female bull sharks at Playa del Carmen, Quintana Roo, Mexico, but it is unclear where their parturition grounds are located. The nearest known nursery is in Chetumal Bay ~360 km south of Playa del Carmen (Blanco-Parra et al., 2022), but there may be more proximate potential nurseries that have not yet been identified. Lake Nicaragua and Lake Izabal were historically nurseries (Thorson et al., 1966; Jensen, 1976), but the abundance and distribution of C. leucas in these systems has not been studied for decades, thus their function is unclear (Heupel et al., 2007). Therefore, the ability to protect and regulate fisheries in essential nursery grounds is hindered (e.g., bans on destructive methods like gillnets; Froeschke et al., 2013). Understanding the connection between adult females and low-salinity habitats as parturition sites is a necessary step to address this knowledge gap, and many surveyed experts highlighted the need for investigating C. leucas distributions and movements, along with nursery locations. The use of telemetry (satellite, acoustic) offers the opportunity to collect meaningful data to accomplish this goal, particularly pop-up satellite archival tags (PSATs) that only require a single tagging event. Yet, considering the limited resources currently available for shark research in Latin America and the cost of employing these methods, other approaches may be more advantageous, with telemetry providing complementary data when affordable. Catch records and sample collection from fisheries landings offers a more widely applicable starting point for data collection (Saldaña-Ruiz et al., 2017; Gibson et al., 2019) that can subsequently be used for more targeted scientific inquiry. Our survey results revealed that many Latin American shark scientists depend on fisheries data because of the paucity of financial support for research. Considering fisheries data is familiar to scientists in the region, governments should strive to make this data more widely accessible, and increase the ability of fishers to report their landings.

Stock assessment and biological characteristics. Adult C. leucas are found throughout the coastal waters of Latin America, and select locations (e.g., Terminos Lagoon) are viable nurseries based on the abundance and residency of juvenile C. leucas (Uribe, 1993; Bonfil, 1997). Yet, stock assessments and evaluations of regional biological characteristics (e.g., age-growth) of C. leucas in marine and freshwater ecosystems of Latin America are needed. Considering the limited financial resources available for such endeavors, and limited reporting infrastructure for many Latin American fisheries (although see suggestion above), the use of media reports is a viable starting point (e.g., Burgess et al., 2010). The examination of media reports for records of C. leucas has a long history (e.g., Kennedy, 1937; Thomerson et al., 1977; Coad, Al-Hassan, 1989; Matich et al., 2020a; Shell, Gardner, 2021), and while reports of C. leucas sightings and incidental catches by fishers (Tab. S2) are of limited scientific value on their own, they offer researchers locations where sharks may be sampled with success, and can be a starting point for designing and implementing more formal assessments. The use of fishersʼ local ecological knowledge has recently increased not only in shark sciences, including studies of C. leucas (e.g., Nascimento et al., 2023), but teleost fish in Latin America (e.g., Silvano et al., 2023), and sawfish from the San Juan River in Costa Rica and Nicaragua (Astorga, 2023). Working with communities that encounter C. leucas is thus an important priority to not only reduce their impacts (see Fisheries and other Human Uses above), but provide accounts that will increase the efficacy of scientific inquiry (Gibson et al., 2019; Sun et al., 2021).

Working with local communities will require several key components. First, residents must be encouraged, if not incentivized, to report all shark sightings and captures with photographic evidence when possible, including sharks that are harvested for consumption and sale. While the reduction/elimination of fishing for C. leucas in Latin America is a priority, developing trust with local stakeholders is currently a more pressing conservation goal. Communities must then be empowered to share reports of C. leucas encounters, either i) online with searchable keywords (e.g., bull shark, river shark, freshwater shark) and pertinent information (location, date of sighting/capture, approximate size), or ii) with a trusted conservationist or research scientist. Iqbal et al. (2019a,b) and Gausmann, Hasan (2022) investigated the distribution of C. leucas in fresh waters of Indonesia by captures from fishers. Feitosa et al. (2016) and Feitosa, Nunes (2020) similarly worked with local fishers in Brazil, and data on the occurrence of C. leucas reported by fishers in the Patuca River, Honduras, was published by Esselman, Opperman (2010). The acquisition of local ecological knowledge will require relationships between scientists and community liaisons who can bridge language and cultural gaps, and incentives may be necessary, which could take on many forms, including economic benefits. Data will need to be centralized in a location accessible to conservation organizations, management agencies, researchers, and the public comparable to the International Shark Attack File – ISAF (https://www.floridamuseum.ufl.edu/shark-attacks/). Future advancements in artificial intelligence (AI) also offer the opportunity to broadly search online records and report findings to the centralized database. More formal stock assessments and studies on C. leucas biology can then be designed and implemented strategically to optimize data collected in lieu of resource limitations.

Visiting fish markets and interacting with fishmongers offers another avenue from which to gather information and collect specimens (Moore, 2018), which can aid stock assessments that rely on the evaluation of genetic relatedness among individuals within and across management areas. The Gulf of Mexico and Caribbean Sea includes dozens of Exclusive Economic Zones (EEZs), and the Tropical Eastern Pacific is comprised of 10 countries alone. Defining bull shark stocks in Latin America is thus of great consequence, because the management strategies implemented by one country may impact shark conservation in others (e.g., Godin, Worm, 2010), and it may help identify potential nurseries that disproportionately contribute to the population(s). Therefore, understanding the genetic structure of Latin American bull sharks is a priority. Laurrabaquio-Alvarado et al. (2021) recently reported on a divergent lineage of C. leucas in the Caribbean Sea, reflecting a phylogeographic break from adjacent populations in the Gulf of Mexico and South America. The Caribbean Sea was presumably supported historically by C. leucas from the Lake Nicaragua-San Juan River and Lake Izabal-Dulce River nurseries, but this is expected to have changed in recent decades because of their near extirpation. Blanco-Parra et al. (2022) recently identified Mexicoʼs Chetumal Bay as another important nursery area for the Caribbean lineage of C. leucas. However, the genetic structure of C. leucas in Latin America is still largely unresolved, hindering our ability to understand how effective conservation or overfishing in one nursery could impact C. leucas in others.

Bull sharks are highly mobile, with large geographic ranges. We therefore do not expect sharks in disparate Caribbean and Gulf of Mexico nurseries to be unique populations/stocks, but there may be genetic structuring based on the proximity of nurseries (TinHan et al., 2020). Carcharhinus leucas exhibits regional philopatry, with females exhibiting site fidelity for reproductive purposes (Tillett et al., 2012; Laurrabaquio-Alvarado et al., 2019). This behavior can limit genetic exchange between populations with site-attachments (Pirog et al., 2019; Glaus et al., 2020; Devloo-Delva et al., 2023), and increases susceptibility to overexploitation, because overfishing a freshwater nursery could significantly impact population stability. Management differences across Latin American countries, including the prevention vs. allowance of overfishing, may consequently lead to some freshwater systems serving as C. leucas sources and others as sinks. Environmental and ecological conditions shape population dynamics, but recent human actions have likely altered source-sink dynamics, and potentially affected the contributions bull sharks from each nursery make toward the gene pool. As such, assessments of genetic relatedness in freshwater systems, and across Latin America more broadly, is paramount to C. leucas conservation efforts in the region. Collecting shark samples from fish markets has been a widely implemented practice (e.g., Peiris et al., 2021), and should be used to complement more traditional approaches to increase sample sizes. Such an endeavor can be resource intensive, therefore establishing relationships with communities who regularly encounter sharks offers a valuable pathway to achieving this goal (see above).

Climate change and future perspectives. Finally, while overfishing and habitat degradation are the most pressing issues facing elasmobranchs today (Dulvy et al., 2021), climate change poses an additional threat. As water temperatures rise, aquatic animals in tropical latitudes face the challenge of persisting in warmer, less oxygenated waters, or shifting their distributional ranges to higher latitudes (Perry et al., 2005; Dahms, Killen, 2023). While behavioral adjustments have been observed among some shark species (e.g., Hammerschlag et al., 2022; Bowers, Kajiura, 2023), the effects of climate change on this taxonomic group is vastly understudied. Among C. leucas, coastal ecosystems in temperate and subtropical latitudes may become more suitable for juveniles, as has been observed in the northwestern Atlantic Ocean (Bangley et al., 2018; Matich et al., 2024; Mullins et al., 2024). However, the impacts in more equatorial nursery habitats, including those in Latin America, have not been evaluated (e.g., Cerutti-Pereyra et al., 2024). Coupled with challenges pertaining to historic overfishing and nursery degradation, there is a need to address data gaps concerning C. leucas biology and ecology across the region to determine how C. leucas will respond to climate change (Matich et al., 2024).

Domestic funding is currently very limited for elasmobranch research in much of Latin America. Comparatively, financial support is much greater in developed countries because of the beneficial subsidies (e.g., fisheries management) that governments and management organizations invest in to preserve their natural resources. Collaborations between shark scientists in developed countries that have greater access to financial resources, with those in developing countries that have access to species of conservation interest (i.e., C. leucas) is a desirable mechanism to accomplish the research and conservation objectives we propose. If the protection and recovery of historically overfished species like C. leucas is a priority in the region, local governments and NGOs must offer more support to Latin American scientists, and collaboration and support from international partners is necessary. As such, we encourage scientists to intensify investigations on C. leucas distribution, habitat use, and population status to mitigate current data gaps necessary for conservation decisions, with a focus on updating the status of locations in Latin America that have been historically identified as crucial for C. leucas but are now understudied and largely unprotected. This has the potential to contribute to the long-term survival of this iconic predator, which is indispensable for the stability of freshwater, brackish, and marine ecosystems in the region.

Acknowledgments​

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We are very grateful to all the scientists across Latin America who responded to our survey request and contributed to this research. We thank Grettel Marisol Hernández-Fernández (UNAN) for providing information on elasmobranchs in Nicaragua, and Lennart Schreiber (UB, ZMT) for sharing information on investigation methods used in the Panama Canal. We also give thanks to Diana Lon (ECOSUR) for information on the distribution of C. leucas in Terminos Lagoon. We acknowledge the collection manager Diane Pitassy (SI) for the production and transmission of photographic material of a voucher specimen housed in the ichthyological collection of the Smithsonian Institution. We are grateful to Andrés Irigoyen-Solis (Ciencia de Tiburones, Mexico.) for a picture of C. leucas from Campeche, Rodrigo Barreto (ICMBio) for a picture from a fish market in Northeast Brazil, Jeso Carneiro (Santarém, Amazônia) for his permission to publish a photo of C. leucas from the Amazon River, and Rafael Tavares (CIT, IVIC) for a photo of C. leucas from Lake Maracaibo. We are grateful to the following persons for providing hard-to-access literature: Eloisa Pinheiro Giareta (UFPR), Mariana Haueisen Pinheiro (PUCRS), Nicolás R. Ehemann (Universität Konstanz), Adrián Felipe González‐Acosta (IPN), Felipe Galván-Magaña (IPN), Alexandre Pires Marceniuk (UFPB), and Edgar Mauricio Hoyos-Padilla (Pelagios Kakunjá). We also acknowledge the editors and anonymous reviewers of Neotropical Ichthyology.

References​

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Authors

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Peter Gausmann^1,2 , Philip Matich^3,4 and Nadia Sandoval Laurrabaquio-Alvarado^5,6

^[1]    Geographisches Institut, Fakultät für Geowissenschaften, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, North Rhine-Westphalia, Germany. mailto:peter.gausmann@rub.de (corresponding author).

^[2]    Deutsche Elasmobranchier-Gesellschaft e.V., Centrum für Naturkunde, Universität Hamburg, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany.

^[3]    Saving the Blue, Cooper City, Florida 33328, USA. matich.philip@gmail.com.

^[4]    Marine Biology Department, College of Marine Sciences & Maritime Studies, Texas A & M University at Galveston, Galveston, Texas 77554, USA.

^[5]    El Colegio de la Frontera Sur, Av. Rancho Polígono 2-A, Ciudad Industrial, CP 24500 Lerma, Campeche, Mexico. nadia.sandoval@guest.ecosur.mx.

^[6]    Takata Research Center A. C. Mahahual s/n, CP 77976, Municipio Othón P. Blanco, Quintana Roo, Mexico

Authors’ Contribution

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Peter Gausmann: Conceptualization, Data curation, Investigation, Methodology, Supervision, Writing-original draft, Writing-review and editing.

Philip Matich: Methodology,Validation, Visualization, Writing-original draft, Writing-review and editing.

Nadia Sandoval Laurrabaquio-Alvarado: Investigation, Writing-original draft, Writing-review and editing.

Ethical Statement​

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Not applicable.

Competing Interests

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The author declares no competing interests.

Data availability statement

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The data supporting the findings of this study are included in the supplementary material of this article.

Funding

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The authors received no financial support for the research, authorship, and publication of this article.

How to cite this article

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Gausmann P, Matich P, Laurrabaquio-Alvarado NS. Research goals of special concern for Carcharhinus leucas (Carcharhiniformes: Carcharhinidae) in Latin America – biological, distributional, and conservation priorities. Neotrop Ichthyol. 2025; 23(3):e250034. https://doi.org/10.1590/1982-0224-2025-0034

Copyright​

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Distributed under

Creative Commons CC-BY 4.0

© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted May 27, 2025

Submitted July 26, 2024

Epub November 7, 2025