Carlos Alberto Nino Torres

Boat-based dolphin-watching tourism targeting common bottlenose dolphins (Tursiops truncatus) in the Mexican Caribbean is an increasing activity. Yet, tour boat compliance with local dolphin-watching guidelines has not been evaluated, and the impacts of these activities on local dolphin populations remain unknown. To address this gap, we used boat-based observations and aerial drone video recordings to evaluate tour boat compliance and described bottlenose dolphins' behavioral responses. We assessed tour boat adherence to key local guidelines, including observation time limits, maintaining minimum distances from dolphins, limiting the number of vessels, and controlling vessel speeds during approach and departure. To describe the behavioral responses of dolphins during tour boat activity, we quantified changes in directional movement, group cohesion, and swimming speed during boat interactions. Our findings revealed that 98% of the observed dolphin-watching events (n = 323) were non-compliant, with the most frequent violation being the proximity to dolphins. During boat interactions, 95% of dolphin directional changes were movements away from boat trajectories and 55% showed increased swimming speeds. These results underscore the need for monitoring and enforcing compliance with guidelines in dolphin-watching tourism, aiming to develop strategies to ensure the sustainability of this local tourism practice.

In the Yucatán Peninsula (Gulf of Mexico and Mexican Caribbean), the Whitespotted Eagle Ray (WSER) is traditionally fished and consumed by local communities as a primary source of fish protein. This study aims to evaluate the concentrations of heavy metals in muscle samples of WSER collected from artisanal fisheries in Campeche and Quintana Roo. The predominant metal distribution observed was As > Ni > Cr > Pb > Cd. Statistical analysis revealed significant differences in Pb, Ni, Cr, and Cd concentrations between the two locations, with Campeche exhibiting the highest levels. Our findings indicate that WSER can accumulate substantial amounts of heavy metals, particularly arsenic. The elevated concentrations of heavy metals not only pose serious health risks to individuals consuming WSER—known to adversely affect hormonal functions and the nervous system in marine species—but also raise significant conservation concerns. These health risks to human consumers highlight the urgent need for public awareness regarding the potential contamination of local seafood. Furthermore, the impact of heavy metal accumulation on WSER populations threatens their sustainability, underscoring the dual significance of our findings for both public health and conservation efforts. Addressing these issues is crucial for protecting marine biodiversity and safeguarding the health of local communities.
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•WSER can accumulate substantial amounts of heavy metals in their muscle particularly arsenic.•The predominant metal concentration pattern observed in WSER muscle was As>Ni > Cr > Pb > Cd.•WSER from Campeche exhibiting the highest concentrations in Pb, Ni, Cr, and Cd.•High concentrations of heavy metals in WSER's represent a new threat for this specie having conservation implications•Regular consumption of WSER meat could represent a health risk for consumers in the Yucatan Peninsula.

Romeo and Juliet: a forbidden love story? A review of hybridization in keystone, aquatic megafauna. Hybridization, understood here as the sexual reproduction between individuals of different species, is relatively common in riverine, estuarine, and marine environments. Investigating hybridization in wild populations of aquatic megafauna species provides important insight into their biology, evolution, and conservation. Here, we conducted an extensive and systematic review of published reports of hybrids in keystone, aquatic megafauna, aiming to provide a clear summary of state-of-the-art and hybridization trends in this group. We selected 129 journal articles reporting 80 hybrids in aquatic megafauna. We included mammals (40.3 %), turtles (33.3 %), crocodilians (17.8 %), and elasmobranchs (8.5 %) that are widely distributed in oceans and continental waters. Our results showed a clear increase in reports of hybrids involving aquatic megafauna in recent years, possibly reflecting the improvement in molecular techniques. However, this increase could also be a consequence of translocation of organisms and habitat modification by humans, and may have a critical impact on conservation, particularly regarding already depleted populations. Hybridization has directly or indirectly facilitated the extinction of many species, but it has also played a crucial role in the evolution and adaptation of many others. To determine whether hybridization is a natural effect or a collateral effect of anthropic pressures we need to understand its implications on the conservation of aquatic megafauna.

The herpetofauna of the insular systems of Mexico is composed of 226 species, of which 14 are anurans, two are salamanders, and 210 are reptiles, comprised of two crocodilians, 195 squamates, and 13 turtles. Although the surface of the Mexican islands is only 0.26% of the Mexican territorial extension, these 226 species constitute 16.1% of Mexico's documented herpetofauna of 1405 species. We classified the Mexican islands into five physiographic regions: the islands of Pacific Baja California; the islands of the Gulf of California; the islands of the Tropical Pacific; the islands of the Gulf of Mexico; and the islands of the Mexican Caribbean. The highest species richness among these regions is in the Gulf of California, with 108 species, and the lowest richness is 40 for the islands of the Pacific Baja California and 46 for those of the Gulf of Mexico. We identified introduced species, risk of wildfires, climate change, and urban/tourist development as the main environmental threats impinging on these species. In addition, we assessed the conservation status of the native species by comparing the SEMARNAT (NOM-059), IUCN Red List, and the Environmental Vulnerability Score (EVS) systems. The comparison of these systems showed that the NOM-059 and the IUCN systems seriously underestimate the degree of threat for insular endemics, being particularly concerning for those insular species that are known only from their respective type localities. The EVS system proved to be practical and indicated that 94 species have a high vulnerability status, 62 a medium status, and 56 a low status. The Relative Herpetofaunal Priority system, which contrasts the number of endemic and threatened species among different physiographic areas, indicates that the regions with the highest priority are the Islands of the Gulf of California, followed by the islands of the Tropical Pacific. Finally, we discussed the completeness of the Mexican Natural Protected Areas on the insular systems of the country; the result is outstanding since Mexico is already close to achieving the goal of having all their islands under some degree of federal protection.

Dorsal fins, one of the most notable dolphin's physical features, play important kinematic and hydrodynamic roles and are related to physiological and environmental adaptation processes. Differences in dorsal fin shape have been recently associated with geographic variation, habitat specialization between ecotypes, and ontogenetic factors. We studied dorsal fin variation across several common bottlenose dolphin populations in the Caribbean. A total of 252 dorsal fin photographs from eight coastal regions in the Caribbean were selected for analysis. Dolphin dorsal fin proportions were compared among regions and compared with data previously collected from Holbox, Mexico. Dorsal fin models were constructed for each region. We found that across the Caribbean, coastal bottlenose dolphins exhibit low variation in dorsal fin shape, with the most common dorsal fin pattern having low and triangular shapes, two traits that greatly contrast with the oceanic ecotype. Also, significant differences in overall dorsal fin proportions found among some adjacent groups support the hypothesis that subgroups could be present even within extremely short geographical distances - as has been previously documented. The results of this study can be implemented in population monitoring efforts worldwide, as it uses free software and provides a step-by-step guideline to analyze the data.

Understanding predator-prey relationships is critical in ecology, but relatively challenging when investigating elusive marine megafauna. In this study, we document the presence of shark-inflicted injuries on coastal bottlenose dolphins (Tursiops truncatus) in the Mesoamerican Reef System using photo-identification methods. We analyzed data from a total of 533 photo-identified bottlenose dolphins in Mexico (Ascención Bay, Espíritu Santo Bay, and Chetumal Bay), Belize (Turneffe Atoll, Drowned Cayes, Barrier Reef, and Placencia), and Honduras (Utila). We identified 16 individuals with shark-inflicted injury scars consistent with attacks by large sharks of the Family Carcharhinidae. Additionally, two bottlenose dolphins were encountered with round-shaped crater wounds, likely inflicted by a cookiecutter shark (Isistius spp.). The prevalence of shark-inflicted wounds in bottlenose dolphins varied markedly between sites, with the highest prevalence in Placencia and Ascención Bay (Mexico), and lowest in Turneffe Atoll and Drowned Cayes (Belize). Further research is required to evaluate how predation risk shapes the ecology of bottlenose dolphins in the Mesoamerican Reef region.

Nursery areas are essential habitats for sharks, offering protection and increasing the survival of newborns. We conducted interviews with local fishers and collected data from artisanal fishery landings between January 2013 and December 2019 to investigate Chetumal Bay as a nursery area for the bull shark (
Carcharhinus leucas
) in the Mesoamerican Reef region. The bull shark is a coastal euryhaline shark that inhabits temperate and tropical waters worldwide. In the Mexican Caribbean, bull sharks are caught mainly as bycatch in a multi-specific artisanal fishery using nylon bottomset gillnets, longlines, and hand lines. We record 63 bull sharks in the catches ranging from 67 to 125 cm TL corresponding to immature individuals, 23 neonates with either open or healing umbilical scars (67 and 78 cm TL), and 40 YOY with present but healed umbilical scars (79 to 125 cm TL), with a notable absence of large size juveniles and adults in the catches. Bull sharks were present in landings between May and November; the highest abundance was during July. Our data provide evidence to recognize Chetumal Bay as a nursery area for bull sharks, meeting all the criteria proposed to identify nursery areas. These findings constitute the first documented evidence of a bull shark nursery area in an estuary within the Mexican Caribbean as well as within the entire region of the Mesoamerican Reef System. Moreover, we discuss the importance of this nursery in light of a newly described distinct lineage of bull sharks in Chetumal Bay.

The Mexican Caribbean is in one of the regions with the greatest diversity of elasmobranchs in the world. However, the population status of most of the shark and ray species in this region is unknown. We used a citizen science program based on divers to collect data about the diversity, abundance, and distribution of elasmobranchs in this region. We visited dive centers in six locations and performed structured interviews with divemasters, instructors, and owners of the diving centers. In total, 79 divers were interviewed, of which 69% had more than five years' experience diving in the Mexican Caribbean. Divers could identify 24 elasmobranch species for this region. Most of the divers (82%) reported a decrease in sightings of sharks and rays. Rays were the most frequently sighted species by divers (89%), and the spotted eagle ray (A. narinari) was the most common elasmobranch species reported in the region. Citizen science was a useful approach gathering for baseline information about sharks and rays in the Mexican Caribbean, increasing our knowledge of the abundance and distribution of some species in this region. Citizen science affords the opportunity to obtain long-term data that can be useful for management and conservation.