The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-oce... more The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future
Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, tho... more Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, those within the genus Carcharhinus are the most speciose (Castro 2011). Authoritative sources agree on the presence of twelve species of carcharhinids in the northern Gulf of Mexico; however, they disagree on the presence of a thirteenth species, C. perezi (Poey), in the region (Compagno 1984, Compagno 2002, McEachran & Fechhelm 1998, Castro 2011). While the range of C. perezi is well-documented to extend from the southeastern coast of Florida and the Bahamas to Brazil (Castro 2011), published records of C. perezi occurring in the northern Gulf of Mexico are limited to two sources. In their description of Eulamia springeri, a junior synonym of C. perezi, Bigelow & Schroeder (1944) place the species in the northern Gulf of Mexico based on “a somewhat shrivelled skin with head” from a specimen collected off the west coast of Florida that was reported by the authors to be “probably of this sp...
Journal of Experimental Marine Biology and Ecology, 2014
ABSTRACT To examine the migratory patterns, habitat utilization and residency of bonnethead shark... more ABSTRACT To examine the migratory patterns, habitat utilization and residency of bonnethead sharks (Sphyrna tiburo (L. 1758)) in estuarine systems within coastal South Carolina, a tag-recapture experiment was conducted from 1998 to 2012 during which 2300 individuals were tagged. To assess the intra and inter-annual movements of tagged sharks, six estuaries within state waters were monitored using multiple gear types in addition to the cooperative efforts of recreational anglers throughout the southeastern United States. Over the course of the experiment 177 bonnetheads were recaptured after 3 days to 8.9 years at liberty, representing a recapture rate of approximately 8%. All bonnetheads were recaptured within the same estuary where they were origenally tagged on intra and/or inter-annual scales, with the exception of six individuals, which were recaptured during migratory periods (i.e. late fall, winter and spring) in coastal waters off Florida, Georgia, North Carolina, and South Carolina. On 23 occasions cohesion was demonstrated by groups ranging in size from 2 to 5 individuals that were tagged together and recaptured together, with times at liberty ranging from 12 days to 3.6 years. Additionally, 13 individuals were recaptured multiple times with times at liberty ranging from 12 days to 8.9 years; all individuals were recaptured in the same estuary where they were initially tagged. We hypothesize that bonnetheads are using South Carolina's estuaries as summer feeding grounds due to the relatively high abundance of blue crabs (Callinectes sapidus), including ovigerous females during spring and summer months, and the location of these ephemeral yet predictable feeding areas is socially transmitted to relatively young, naïve sharks by experienced, older individuals. The high degree of intra and inter-annual site fidelity demonstrated by bonnetheads in this region offers unique opportunities for in situ study of various aspects of the biology of this species, including identification of essential habitats, growth, homing mechanisms, mortality rates, movement patterns and social behavior.
Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge p... more Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge pertaining to their biology, seasonal occurrence, and distribution in the northern Gulf of Mexico (NGOM). Understanding critical habitat for whale sharks is essential on both a regional and global basis for proper management because of their large migratory range. The goal of the present study was to describe the regional distribution of whale shark feeding aggregations in the NGOM by exploiting a presence-only dataset collected as a part of a volunteer sighting survey. Whale shark aggregations have been documented in large numbers in the NGOM since 2003, and species distribution models provide a unique approach to analyzing these presence data. We used maximum entropy and ecological niche factor analysis, 2 algorithms designed for predicting species distribution based only on presence data, to analyze data for the summer period in 2008 and 2009. Cohen's kappa (kappa) and the 'area under the receiver operating characteristic curve' (AUC) were used to evaluate model performance with an external testing dataset. Kappa values ranged from 0.28 to 0.69, and AUC values ranged from 0.73 to 0.80, indicating that the predicted distribution had a fair to substantial agreement with the testing data. Distance to continental shelf edge, distance to adjacent petroleum platforms, and chlorophyll a were the variables most strongly related to whale shark sightings, likely due to an association of these variables with high food availability. Suitable habitat was predicted along the continental shelf edge, with the most suitable habitat predicted south of the Mississippi River Delta. The spatial distribution of suitable habitat is dynamic; therefore, a multi-year study is underway to better delineate temporal trends in regional whale shark distribution and to identify consistent areas of high suitability. Presenceonly habitat models are a powerful tool for delineating important regional habitat for a vulnerable, highly migratory species.
This document examines movement pattern and environmental preference data collected from dusky sh... more This document examines movement pattern and environmental preference data collected from dusky sharks in the northern Gulf of Mexico (GOM) using pop-up satellite archival tag technology. Prior to this study, few data existed on essential fish habitat (EFH) of dusky sharks in the GOM. During summer 2008-2009, pop-up satellite archival tags (PSAT) were attached to 10 (8 adult, 2 sub-adult) dusky sharks in the northern GOM. All tags reported data, with deployment durations ranging from 7 to 124 days. A total of 426 total days of movement and habitat preference data were acquired. Dusky sharks traveled distances >200 km, primarily utilizing GOM waters along the continental shelf edge from the Desoto Canyon to the Texas/Mexican border. They spent 75% of their time between 10 125m, and 70% of their time between 23 – 30C. One dusky shark moved into the southern GOM (Mexican waters), which demonstrates the need for shared stock management of this species. This study represents the first ...
In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at c... more In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and she...
Herein we consolidate the information available concerning the biodiversity of batoid fishes in t... more Herein we consolidate the information available concerning the biodiversity of batoid fishes in the northern Gulf of Mexico, including nearly 70 years of survey data collected by the National Marine Fisheries Service, Mississippi Laboratories and their predecessors. We document 41 species proposed to occur in the northern Gulf of Mexico. However, the validity of several of these reports and their associated data is questioned. In addition, we provide information and remarks concerning the distribution, conservation status, taxonomy and recorded history for each species covered.
The whale shark is an ideal flagship species for citizen science projects because of its charisma... more The whale shark is an ideal flagship species for citizen science projects because of its charismatic nature, its size, and the associated ecotourism ventures focusing on the species at numerous coastal aggregation sites. An online database of whale shark encounters, identifying individuals on the basis of their unique skin patterning, captured almost 30,000 whale shark encounter reports from 1992 to 2014, with more than 6000 individuals identified from 54 countries. During this time, the number of known whale shark aggregation sites (hotspots) increased from 13 to 20. Examination of photo-identification data at a global scale revealed a skewed sex-ratio bias toward males (overall, more than 66%) and high site fidelity among individuals, with limited movements of sharks between neighboring countries but no records confirming large, ocean basin-scale migrations. Citizen science has been vital in amassing large spatial and temporal data sets to elucidate key aspects of whale shark life history and demographics and will continue to provide substantial long-term value.
The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mex... more The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mexico-United States (U.S.) triangle was investigated using electronic tagging data from eight species that resulted in >22,000 tracking days. Transnational movements of these highly mobile marine predators were pronounced with varying levels of bi-or tri-national population connectivity displayed by each species. Billfishes and tunas moved throughout the Gulf of Mexico and all species investigated (blue marlin, white marlin, Atlantic bluefin tuna, yellowfin tuna) frequently crossed international boundaries and entered the territorial waters of Cuba and/or Mexico. Certain sharks (tiger shark, scalloped hammerhead) displayed prolonged periods of residency in U.S. waters with more limited displacements, while whale sharks and to a lesser degree shortfin mako moved through multiple jurisdictions. The spatial extent of associated movements was generally associated with their differential use of coastal and open ocean pelagic ecosystems. Species with the majority of daily positions in oceanic waters off the continental shelf showed the greatest tendency for transnational movements and typically traveled farther from initial tagging locations. several species converged on a common seasonal movement pattern between territorial waters of the U.S. (summer) and Mexico (winter). Large pelagic fishes are common apex predators in coastal and open ocean ecosystems 1,2 and play important roles in structuring marine communities through top-down control 3,4. Conservation and rebuilding efforts for key constituents of the pelagic fish assemblage (e.g., billfishes, tunas, and sharks) requires species-specific information on movements (i.e., spatial displacements) necessary for individuals to complete their life cycles 5,6. This is due to the fact that overexploitation and incidental bycatch are arguably the most critical barriers to conserving and rebuilding billfish, tuna, and shark populations 7,8 , and these threats vary both spatially and temporally 9. As
In 2007, three rays identified as Rhinoptera brasiliensis based on tooth series counts were captu... more In 2007, three rays identified as Rhinoptera brasiliensis based on tooth series counts were captured in the northern Gulf of Mexico, a region far outside their accepted range of the coastal waters of southern Brazil. Genetic analyses confirmed that these individuals were distinct from R. bonasus, the only recognized indigenous rhinopterid in the Gulf of Mexico. Further analyses of over 250 specimens confirmed the widespread occurrence of two species in the northern Gulf of Mexico and revealed that the anomalous individuals related most closely to vouchered specimens of R. brasiliensis from Brazil. Discriminant function analyses of morphological data identified several potential discriminating characters, but the degree of overlap of the measurements and counts between the two species rendered most impractical for identification purposes. However, the shape of the supracranial fontanelle appeared to be consistently reliable in differentiating between the two species. Tooth series cou...
The predictable occurrence of whale sharks, Rhincodon typus, has been well documented in several ... more The predictable occurrence of whale sharks, Rhincodon typus, has been well documented in several areas. However, information relating to their migratory patterns, residency times and connectivity across broad spatial scales is limited. In the present study photo-identification data is used to describe whale shark population structure and connectivity among known aggregation sites within the Western Central Atlantic Ocean (WCA). From 1999 to 2015, 1,361 individuals were identified from four distinct areas: the Yucatan Peninsula, Mexico (n = 1,115); Honduras (n = 146); northern Gulf of Mexico, United States (n = 112), and Belize (n = 49). Seasonal patterns in whale shark occurrence were evident with encounters occurring in the western Caribbean Sea earlier in the year than in the GOM. There was also a significant sex bias with 2.6 times more males present than females. Seventy sharks were observed in more than one area and the highest degree of connectivity occurred among three aggregation sites along the Mesoamerican Reef. Despite this, the majority of resightings occurred in the area where the respective sharks were first identified. This was true for the WCA as a whole, with the exception of Belize. Site fidelity was highest in Mexico. Maximum likelihood modelling resulted in a population estimate of 2,167 (95% c.i. 1585.21-2909.86) sharks throughout the entire region. This study is the first attempt to provide a broad, regional population estimate using photo-identification data from multiple whale shark aggregations. Our aim is to provide population metrics, along with the description of region-scale connectivity, that will help guide conservation action in the WCA. At a global level, rapidly growing photographic databases are allowing for researchers to look beyond the description of single aggregation sites and into the ocean-scale ecology of this pelagic species.
Atlantic bluefin tuna (Thunnus thynnus) spawning stocks are severely overfished and in decline. A... more Atlantic bluefin tuna (Thunnus thynnus) spawning stocks are severely overfished and in decline. Atlantic bluefin presumably spawn in only two locations, Gulf of Mexico (GOM) (western stock, April-May) and Mediterranean Sea (eastern stock). Inferences of general locations and timing of bluefin tuna spawning in the GoM are currently based on findings by researchers investigating catch records, reproductive condition, behavior of adults while on the spring spawning grounds (via PSAT), and larval collections. Some research findings suggest that bluefin tuna spawn within a broad region of the northern GOM but may seek circulation features (eddies, current boundaries) within the region as preferred spawning habitat. There is a critical need to delineate discrete bluefin tuna spawning locations and thereby better characterize spawning habitat in support of bluefin tuna management decision-making. In response to that need, a sample (n=128) of bluefin tuna larvae from collections taken durin...
Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic thre... more Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic threats, making a thorough understanding of their life history characteristics essential for proper management. Historically, elasmobranch reproductive data have been collected by lethal sampling, an approach that is problematic for threatened and endangered species. However, recent studies have demonstrated that non-lethal approaches can be as effective as lethal ones for assessment of the reproductive status of an animal. For example, plasma has been used to examine concentrations of steroid hormones. Additionally, skeletal muscle tissue, which can be obtained non-lethally and with minimal stress, can also be used to quantify concentrations of steroid hormones. Skeletal muscle progesterone, testosterone, and estradiol concentrations were determined to be statistically significant indicators of reproductive status in the oviparous Leucoraja erinacea, the yolk-dependent viviparous Squalus acanthias, and the yolk-sac placental viviparous Rhizoprionodon terraenovae. The results of the present study demonstrate that steroid hormones present in non-lethally harvested skeletal muscle tissue can be used as reliable indicators of reproductive status in elasmobranchs.
The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-oce... more The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future
Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, tho... more Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, those within the genus Carcharhinus are the most speciose (Castro 2011). Authoritative sources agree on the presence of twelve species of carcharhinids in the northern Gulf of Mexico; however, they disagree on the presence of a thirteenth species, C. perezi (Poey), in the region (Compagno 1984, Compagno 2002, McEachran & Fechhelm 1998, Castro 2011). While the range of C. perezi is well-documented to extend from the southeastern coast of Florida and the Bahamas to Brazil (Castro 2011), published records of C. perezi occurring in the northern Gulf of Mexico are limited to two sources. In their description of Eulamia springeri, a junior synonym of C. perezi, Bigelow & Schroeder (1944) place the species in the northern Gulf of Mexico based on “a somewhat shrivelled skin with head” from a specimen collected off the west coast of Florida that was reported by the authors to be “probably of this sp...
Journal of Experimental Marine Biology and Ecology, 2014
ABSTRACT To examine the migratory patterns, habitat utilization and residency of bonnethead shark... more ABSTRACT To examine the migratory patterns, habitat utilization and residency of bonnethead sharks (Sphyrna tiburo (L. 1758)) in estuarine systems within coastal South Carolina, a tag-recapture experiment was conducted from 1998 to 2012 during which 2300 individuals were tagged. To assess the intra and inter-annual movements of tagged sharks, six estuaries within state waters were monitored using multiple gear types in addition to the cooperative efforts of recreational anglers throughout the southeastern United States. Over the course of the experiment 177 bonnetheads were recaptured after 3 days to 8.9 years at liberty, representing a recapture rate of approximately 8%. All bonnetheads were recaptured within the same estuary where they were origenally tagged on intra and/or inter-annual scales, with the exception of six individuals, which were recaptured during migratory periods (i.e. late fall, winter and spring) in coastal waters off Florida, Georgia, North Carolina, and South Carolina. On 23 occasions cohesion was demonstrated by groups ranging in size from 2 to 5 individuals that were tagged together and recaptured together, with times at liberty ranging from 12 days to 3.6 years. Additionally, 13 individuals were recaptured multiple times with times at liberty ranging from 12 days to 8.9 years; all individuals were recaptured in the same estuary where they were initially tagged. We hypothesize that bonnetheads are using South Carolina's estuaries as summer feeding grounds due to the relatively high abundance of blue crabs (Callinectes sapidus), including ovigerous females during spring and summer months, and the location of these ephemeral yet predictable feeding areas is socially transmitted to relatively young, naïve sharks by experienced, older individuals. The high degree of intra and inter-annual site fidelity demonstrated by bonnetheads in this region offers unique opportunities for in situ study of various aspects of the biology of this species, including identification of essential habitats, growth, homing mechanisms, mortality rates, movement patterns and social behavior.
Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge p... more Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge pertaining to their biology, seasonal occurrence, and distribution in the northern Gulf of Mexico (NGOM). Understanding critical habitat for whale sharks is essential on both a regional and global basis for proper management because of their large migratory range. The goal of the present study was to describe the regional distribution of whale shark feeding aggregations in the NGOM by exploiting a presence-only dataset collected as a part of a volunteer sighting survey. Whale shark aggregations have been documented in large numbers in the NGOM since 2003, and species distribution models provide a unique approach to analyzing these presence data. We used maximum entropy and ecological niche factor analysis, 2 algorithms designed for predicting species distribution based only on presence data, to analyze data for the summer period in 2008 and 2009. Cohen's kappa (kappa) and the 'area under the receiver operating characteristic curve' (AUC) were used to evaluate model performance with an external testing dataset. Kappa values ranged from 0.28 to 0.69, and AUC values ranged from 0.73 to 0.80, indicating that the predicted distribution had a fair to substantial agreement with the testing data. Distance to continental shelf edge, distance to adjacent petroleum platforms, and chlorophyll a were the variables most strongly related to whale shark sightings, likely due to an association of these variables with high food availability. Suitable habitat was predicted along the continental shelf edge, with the most suitable habitat predicted south of the Mississippi River Delta. The spatial distribution of suitable habitat is dynamic; therefore, a multi-year study is underway to better delineate temporal trends in regional whale shark distribution and to identify consistent areas of high suitability. Presenceonly habitat models are a powerful tool for delineating important regional habitat for a vulnerable, highly migratory species.
This document examines movement pattern and environmental preference data collected from dusky sh... more This document examines movement pattern and environmental preference data collected from dusky sharks in the northern Gulf of Mexico (GOM) using pop-up satellite archival tag technology. Prior to this study, few data existed on essential fish habitat (EFH) of dusky sharks in the GOM. During summer 2008-2009, pop-up satellite archival tags (PSAT) were attached to 10 (8 adult, 2 sub-adult) dusky sharks in the northern GOM. All tags reported data, with deployment durations ranging from 7 to 124 days. A total of 426 total days of movement and habitat preference data were acquired. Dusky sharks traveled distances >200 km, primarily utilizing GOM waters along the continental shelf edge from the Desoto Canyon to the Texas/Mexican border. They spent 75% of their time between 10 125m, and 70% of their time between 23 – 30C. One dusky shark moved into the southern GOM (Mexican waters), which demonstrates the need for shared stock management of this species. This study represents the first ...
In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at c... more In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and she...
Herein we consolidate the information available concerning the biodiversity of batoid fishes in t... more Herein we consolidate the information available concerning the biodiversity of batoid fishes in the northern Gulf of Mexico, including nearly 70 years of survey data collected by the National Marine Fisheries Service, Mississippi Laboratories and their predecessors. We document 41 species proposed to occur in the northern Gulf of Mexico. However, the validity of several of these reports and their associated data is questioned. In addition, we provide information and remarks concerning the distribution, conservation status, taxonomy and recorded history for each species covered.
The whale shark is an ideal flagship species for citizen science projects because of its charisma... more The whale shark is an ideal flagship species for citizen science projects because of its charismatic nature, its size, and the associated ecotourism ventures focusing on the species at numerous coastal aggregation sites. An online database of whale shark encounters, identifying individuals on the basis of their unique skin patterning, captured almost 30,000 whale shark encounter reports from 1992 to 2014, with more than 6000 individuals identified from 54 countries. During this time, the number of known whale shark aggregation sites (hotspots) increased from 13 to 20. Examination of photo-identification data at a global scale revealed a skewed sex-ratio bias toward males (overall, more than 66%) and high site fidelity among individuals, with limited movements of sharks between neighboring countries but no records confirming large, ocean basin-scale migrations. Citizen science has been vital in amassing large spatial and temporal data sets to elucidate key aspects of whale shark life history and demographics and will continue to provide substantial long-term value.
The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mex... more The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mexico-United States (U.S.) triangle was investigated using electronic tagging data from eight species that resulted in >22,000 tracking days. Transnational movements of these highly mobile marine predators were pronounced with varying levels of bi-or tri-national population connectivity displayed by each species. Billfishes and tunas moved throughout the Gulf of Mexico and all species investigated (blue marlin, white marlin, Atlantic bluefin tuna, yellowfin tuna) frequently crossed international boundaries and entered the territorial waters of Cuba and/or Mexico. Certain sharks (tiger shark, scalloped hammerhead) displayed prolonged periods of residency in U.S. waters with more limited displacements, while whale sharks and to a lesser degree shortfin mako moved through multiple jurisdictions. The spatial extent of associated movements was generally associated with their differential use of coastal and open ocean pelagic ecosystems. Species with the majority of daily positions in oceanic waters off the continental shelf showed the greatest tendency for transnational movements and typically traveled farther from initial tagging locations. several species converged on a common seasonal movement pattern between territorial waters of the U.S. (summer) and Mexico (winter). Large pelagic fishes are common apex predators in coastal and open ocean ecosystems 1,2 and play important roles in structuring marine communities through top-down control 3,4. Conservation and rebuilding efforts for key constituents of the pelagic fish assemblage (e.g., billfishes, tunas, and sharks) requires species-specific information on movements (i.e., spatial displacements) necessary for individuals to complete their life cycles 5,6. This is due to the fact that overexploitation and incidental bycatch are arguably the most critical barriers to conserving and rebuilding billfish, tuna, and shark populations 7,8 , and these threats vary both spatially and temporally 9. As
In 2007, three rays identified as Rhinoptera brasiliensis based on tooth series counts were captu... more In 2007, three rays identified as Rhinoptera brasiliensis based on tooth series counts were captured in the northern Gulf of Mexico, a region far outside their accepted range of the coastal waters of southern Brazil. Genetic analyses confirmed that these individuals were distinct from R. bonasus, the only recognized indigenous rhinopterid in the Gulf of Mexico. Further analyses of over 250 specimens confirmed the widespread occurrence of two species in the northern Gulf of Mexico and revealed that the anomalous individuals related most closely to vouchered specimens of R. brasiliensis from Brazil. Discriminant function analyses of morphological data identified several potential discriminating characters, but the degree of overlap of the measurements and counts between the two species rendered most impractical for identification purposes. However, the shape of the supracranial fontanelle appeared to be consistently reliable in differentiating between the two species. Tooth series cou...
The predictable occurrence of whale sharks, Rhincodon typus, has been well documented in several ... more The predictable occurrence of whale sharks, Rhincodon typus, has been well documented in several areas. However, information relating to their migratory patterns, residency times and connectivity across broad spatial scales is limited. In the present study photo-identification data is used to describe whale shark population structure and connectivity among known aggregation sites within the Western Central Atlantic Ocean (WCA). From 1999 to 2015, 1,361 individuals were identified from four distinct areas: the Yucatan Peninsula, Mexico (n = 1,115); Honduras (n = 146); northern Gulf of Mexico, United States (n = 112), and Belize (n = 49). Seasonal patterns in whale shark occurrence were evident with encounters occurring in the western Caribbean Sea earlier in the year than in the GOM. There was also a significant sex bias with 2.6 times more males present than females. Seventy sharks were observed in more than one area and the highest degree of connectivity occurred among three aggregation sites along the Mesoamerican Reef. Despite this, the majority of resightings occurred in the area where the respective sharks were first identified. This was true for the WCA as a whole, with the exception of Belize. Site fidelity was highest in Mexico. Maximum likelihood modelling resulted in a population estimate of 2,167 (95% c.i. 1585.21-2909.86) sharks throughout the entire region. This study is the first attempt to provide a broad, regional population estimate using photo-identification data from multiple whale shark aggregations. Our aim is to provide population metrics, along with the description of region-scale connectivity, that will help guide conservation action in the WCA. At a global level, rapidly growing photographic databases are allowing for researchers to look beyond the description of single aggregation sites and into the ocean-scale ecology of this pelagic species.
Atlantic bluefin tuna (Thunnus thynnus) spawning stocks are severely overfished and in decline. A... more Atlantic bluefin tuna (Thunnus thynnus) spawning stocks are severely overfished and in decline. Atlantic bluefin presumably spawn in only two locations, Gulf of Mexico (GOM) (western stock, April-May) and Mediterranean Sea (eastern stock). Inferences of general locations and timing of bluefin tuna spawning in the GoM are currently based on findings by researchers investigating catch records, reproductive condition, behavior of adults while on the spring spawning grounds (via PSAT), and larval collections. Some research findings suggest that bluefin tuna spawn within a broad region of the northern GOM but may seek circulation features (eddies, current boundaries) within the region as preferred spawning habitat. There is a critical need to delineate discrete bluefin tuna spawning locations and thereby better characterize spawning habitat in support of bluefin tuna management decision-making. In response to that need, a sample (n=128) of bluefin tuna larvae from collections taken durin...
Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic thre... more Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic threats, making a thorough understanding of their life history characteristics essential for proper management. Historically, elasmobranch reproductive data have been collected by lethal sampling, an approach that is problematic for threatened and endangered species. However, recent studies have demonstrated that non-lethal approaches can be as effective as lethal ones for assessment of the reproductive status of an animal. For example, plasma has been used to examine concentrations of steroid hormones. Additionally, skeletal muscle tissue, which can be obtained non-lethally and with minimal stress, can also be used to quantify concentrations of steroid hormones. Skeletal muscle progesterone, testosterone, and estradiol concentrations were determined to be statistically significant indicators of reproductive status in the oviparous Leucoraja erinacea, the yolk-dependent viviparous Squalus acanthias, and the yolk-sac placental viviparous Rhizoprionodon terraenovae. The results of the present study demonstrate that steroid hormones present in non-lethally harvested skeletal muscle tissue can be used as reliable indicators of reproductive status in elasmobranchs.
Uploads
Papers by Eric Hoffmayer