Use of the Gulf of Mexico as an overwintering area by western North Atlantic white sharks (Carcharodon carcharias)

The white shark, Carcharodon carcharias, is an iconic apex predator, playing an important ecological role across its range. Persistent bycatch and overfishing led to white shark declines, but recent studies in the North Western Atlantic (NWA) revealed evidence for regional recovery, and highlighted the importance of Southeastern Florida and the Gulf of Mexico as overwintering grounds for maturing white sharks. However, despite its proximity to Florida and comparably productive habitats, records of white sharks in The Bahamas are extremely rare, with a comprehensive survey of sightings and captures describing only one white shark between 1800 - 2010. Here, we reveal acoustic tracking detections of ten white sharks from 2020 - 2024 along the western edge of the Tongue of the Ocean off Central Andros Island, The Bahamas. White sharks were originally tagged off the coast of the United States and Canada, and detected off Andros Island, The Bahamas from November-May. White sharks were detected along the drop-off zone of the reef at ca. 25 m, exclusively between dusk and dawn, with the number of detections suggesting transient behavior. These findings expand our knowledge of white shark distribution in the NWA, highlighting data gaps in The Bahamas and underlining the importance of collaborative protective measures for species recovery.

Understanding how mobile, marine predators use three-dimensional space over time is central to inform management and conservation actions. Combining tracking technologies can yield powerful datasets over multiple spatio-temporal scales to provide critical information for these purposes. For the white shark (Carcharodon carcharias), detailed movement and migration information over ontogeny, including inter- and intra-annual variation in timing of movement phases, is largely unknown in the western North Atlantic (WNA), a relatively understudied area for this species. To address this need, we tracked 48 large juvenile to adult white sharks between 2012 and 2020, using a combination of satellite-linked and acoustic telemetry. Overall, WNA white sharks showed repeatable and predictable patterns in horizontal movements, although there was variation in these movements related to sex and size. While most sharks undertook an annual migratory cycle with the majority of time spent over the continental shelf, some individuals, particularly adult females, made extensive forays into the open ocean as far east as beyond the Mid-Atlantic Ridge. Moreover, increased off-shelf use occurred with body size even though migration and residency phases were conserved. Summer residency areas included coastal Massachusetts and portions of Atlantic Canada, with individuals showing fidelity to specific regions over multiple years. An autumn/winter migration occurred with sharks moving rapidly south to overwintering residency areas in the southeastern United States Atlantic and Gulf of Mexico, where they remained until the following spring/summer. While broad residency and migration periods were consistent, migratory timing varied among years and among individuals within years. White sharks monitored with pop-up satellite-linked archival tags made extensive use of the water column (0–872 m) and experienced a broad range of temperatures (−0.9 – 30.5°C), with evidence for differential vertical use based on migration and residency phases. Overall, results show dynamic inter- and intra-annual three-dimensional patterns of movements conserved within discrete phases. These results demonstrate the value of using multiple tag types to track long-term movements of large mobile species. Our findings expand knowledge of the movements and migration of the WNA white shark population and comprise critically important information to inform sound management strategies for the species.

We investigated the genetic structure of blacktip shark (Carcharhinus limbatus) continental nurseries in the northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea using mitochondrial DNA control region sequences and eight nuclear microsatellite loci scored in neonate and young-of-the-year sharks. Significant structure was detected with both markers among nine nurseries (mitochondrial PhiST = 0.350, P < 0.001; nuclear PhiST = 0.007, P < 0.001) and sharks from the northwestern Atlantic, eastern Gulf of Mexico, western Gulf of Mexico, northern Yucatan, and Belize possessed significantly different mitochondrial DNA haplotype frequencies. Microsatellite differentiation was limited to comparisons involving northern Yucatan and Belize sharks with nuclear genetic homogeneity throughout the eastern Gulf of Mexico, western Gulf of Mexico, and northwestern Atlantic. Differences in the magnitude of maternal vs. biparental genetic differentiation support female philopatry to northwestern Atlantic, Gulf of Mexico, and Caribbean Sea natal nursery regions with higher levels of male-mediated gene flow. Philopatry has produced multiple reproductive stocks of this commercially important shark species throughout the range of this study.

Tissue metal concentrations and antioxidant enzyme activity in western north Atlantic white sharks (Carcharodon carcharias)

Greatly increased concentrations of particulate iron were found within 1000 m of the bottom in the northwest Atlantic and eastern Gulf of Mexico (6 times and 3 to 4 times the average of shallower water, respectively) while only slightly increased concentrations were found within 1000 m of the bottom in the Caribbean and western Gulf of Mexico (2 times the average concentration in shallower water). These distributions agree with published light-scattering studies of deep ocean water, and are hemical evidence of a near-bottom nepheloid layer. It is concluded that the increase in the near-bottom concentrations of particulate iron is not a water mass effect, but arises from interaction of water with the bottom.

Habitat shifts that occur during the life cycles of marine fishes influence population connectivity and structure. A generalized additive modeling approach was used to characterize relationships between environmental variables and the relative abundance of red snapper Lutjanus campechanus over unconsolidated substrate on the continental shelf (<150 m) of the U.S. Gulf of Mexico (GoM) at three different life stages: juvenile (age-0, <125 mm FL), sub-adult (age-1-2, 125–300 mm FL), and adult (age-2+, >300 mm FL). Fisheries independent data (2008–2014) were used to develop separate models for both the eastern and western GoM, and final models were used to predict the relative availability of suitable habitat for each life stage across the two regions. Predictor variables included in final models varied by age class and region, with depth, dissolved oxygen, longitude, and distance to artificial structure common to most models. Depth was among the most influential variables in all models, and preferred depth increased with increasing size/age. Regional differences in fish-habitat relationships were also observed, as relative abundance of larger red snapper over unconsolidated substrates was more closely linked to artificial structure in the eastern GoM. The location of predicted high quality habitat for juvenile red snapper was greatest on the inner Texas shelf and a smaller area east of the Mississippi River Delta, suggesting these two areas may represent important nursery grounds for the respective regions. Clear ontogenetic shifts in the spatial distribution of predicted high quality habitat were evident in both the eastern (expansion from west to east with age) and western (shift from inshore to offshore) GoM. Given the unique population dynamics between the eastern and western GoM, improving our understanding of spatial and temporal variability in habitat quality may be important to maintaining connectivity between juvenile and adult habitats, and may enhance recovery and management of red snapper stocks in the GoM.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 580:1-16 (2017) - DOI: https://doi.org/10.3354/meps12306 FEATURE ARTICLE Movements of the white shark Carcharodon carcharias in the North Atlantic Ocean G. B. Skomal1,*, C. D. Braun2,3, J. H. Chisholm1, S. R. Thorrold4 1Massachusetts Division of Marine Fisheries, 836 South Rodney French Blvd., New Bedford, MA 02744, USA 2MIT-WHOI Joint Program in Oceanography, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 3MIT-WHOI Joint Program in Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 4Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA *Corresponding author: gregory.skomal@state.ma.us ABSTRACT: In the western North Atlantic, much of what is known about the movement ecology of the white shark Carcharodon carcharias is based on historical fisheries-dependent catch records, which portray a shelf-oriented species that moves north and south seasonally. In this study, we tagged 32 white sharks (16 females, 7 males, 9 unknown), ranging from 2.4 to 5.2 m total length, with satellite-based tags to investigate broad-scale movements in the North Atlantic. Based on 10427 days of tracking data, we found that white sharks are more broadly distributed, both horizontally and vertically, throughout the North Atlantic than previously understood, exhibiting an ontogenetic shift from near-coastal, shelf-oriented habitat to pelagic habitat with frequent excursions to mesopelagic depths. During the coastal phase, white sharks migrated seasonally from the northeast shelf in the summer to overwintering habitat off the southeastern US and the Gulf of Mexico, spending 95% of their time at <50 m depth. During the pelagic phase, subadult and adult white sharks exhibited wide-ranging movements during the fall, winter, and spring into the broader Atlantic over a 30° latitudinal range and as far east as the Azores. These sharks moved daily to depths of up to 1128 m, spending significant time at specific mesopelagic depth zones through a temperature range of 1.6 to 30.4°C. We believe these movements are associated with offshore foraging facilitated by the thermal physiology of the species. Our findings extend the known essential habitat for the white shark in the North Atlantic beyond existing protection, with implications for future conservation. KEY WORDS: White shark · Habitat utilization · Behavior · Migration · Carcharodon carcharias · Life history Full text in pdf format Information about this Feature Article NextCite this article as: Skomal GB, Braun CD, Chisholm JH, Thorrold SR (2017) Movements of the white shark Carcharodon carcharias in the North Atlantic Ocean. Mar Ecol Prog Ser 580:1-16. https://doi.org/10.3354/meps12306 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 580. Online publication date: September 29, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

&lt;em&gt;Abstract.&lt;/em&gt;—Red snapper &lt;em&gt;Lutjanus campechanus &lt;/em&gt;larval occurrence and abundance during Southeast Area Monitoring and Assessment Program (SEAMAP) Summer Shrimp/Bottomfish (1982–2003) and Fall Plankton (1986–2003) surveys were examined to identify the time series of ichthyoplankton data that might best reflect trends in the red snapper spawning population in the U.S. Gulf of Mexico (GOM). Since bongo nets were more effective than neuston nets at capturing red snapper larvae only catches from bongo nets were used to estimate annual occurrence and abundance, i.e. the SEAMAP larval red snapper index. The summer survey was conducted during the peak of red snapper spawning in June and July, but limited and inconsistent coverage during this survey did not permit development of a reliable Gulfwide (U.S. continental shelf) index of larval abundance. In contrast, the fall survey conducted near the end of the spawning season in September yielded a 16 year time series over which to examine trends in red snapper abundance throughout the GOM. Although occurrence and abundance of red snapper larvae were lower during September than in June and July, estimates from both summer and fall surveys showed the same inter-annual patterns and were highly correlated. Larvae were eight times more abundant and occurred in five times as many samples in the western than in the eastern GOM. Separate standardized indices of relative abundance were generated for the western and eastern GOM. The standardization procedure accounted for the effects of year, time of day, depth and subregion in the western GOM, but only for subregion in the eastern GOM. Larval indices of red snapper abundance suggest an increased spawning stock in both the western and eastern GOM after 1995.

Highly mobile apex predators such as the shortfin mako shark (mako shark;Isurus oxyrinchus) serve an important role in the marine ecosystem, and despite their declining populations and vulnerability to overexploitation, this species is frequently harvested in high abundance in both commercial and recreational fisheries. In 2017, the North Atlantic stock was deemed overfished and to be undergoing overfishing and was recently listed in CITES Appendix II. Effective management of this species can benefit from detailed information on their movements and habitat use, which is lacking, especially in the Gulf of Mexico, a potential mating and parturition ground. In this study, we used satellite telemetry to track the movements of mako sharks in the western Gulf of Mexico between 2016 and 2020. In contrast to previous studies that have primarily tagged juvenile mako sharks (&amp;gt;80% juveniles), ∼80% of sharks tagged in this study (7 of 9) were presumed to be mature based on published size-at-maturity data. Sharks were tracked for durations ranging from 10 to 887 days (mean = 359 days; median = 239 days) with three mature individuals tracked for &amp;gt;2 years. Mako sharks tagged in this study used more of the northwestern Gulf of Mexico than reported in previous movement studies on juveniles, suggesting potential evidence of size segregation. While one mature female remained in the Gulf of Mexico over a &amp;gt;2-year period, predominantly on the continental shelf, two mature males demonstrated seasonal migrations ∼2,500 km from the tagging location off the Texas coast to the Caribbean Sea and northeastern United States Atlantic coast, respectively. During these migrations, mako sharks traversed at least 12 jurisdictional boundaries, which also exposed individuals to varying levels of fishing pressure and harvest regulations. Movement ecology of this species, especially for mature individuals in the western North Atlantic, has been largely unknown until recently. These data included here supplement existing information on mako shark movement ecology and potential stock structure that could help improve management of the species.

The ctenophore Mnemiopsis leidyi is one of the most successful marine bioinvaders on record. Native to the Atlantic coast of the Americas, M. leidyi invaded the Black Sea, Caspian and Mediterranean Seas beginning the in late 1980s, followed by the North and Baltic Seas starting in 2006, with major concomitant alterations in pelagic ecology, including fishery collapses in some cases. Using extensive native range sampling (21 sites), along with 11 invasive sites in the Black, Caspian, Mediterranean, North and Baltic Seas, we examined M. leidyi worldwide phylogeographic patterns using data from mitochondrial cytochrome b (cytb) and six nuclear microsatellite loci. Cytb and microsatellite data sets showed different levels of genetic differentiation in the native range. Analyses of cytb data revealed considerable genetic differentiation, recovering three major clusters (northwestern Atlantic, Caribbean, and South America) and further divided northwestern Atlantic sampling sites into three groups, separated approximately at Cape Hatteras on the US Atlantic coast and at the Floridian peninsula, separating the Gulf of Mexico and Atlantic coasts. In contrast, microsatellite data only distinguished samples north and south of Cape Hatteras, and suggested considerable gene flow among native samples with clear evidence of isolation by distance. Both cytb and microsatellite data sets indicated that the northern invaders (North/Baltic Seas) originated from north of Cape Hatteras, with cytb data pointing to Delaware and north. Microsatellite data indicated a source for the southern invaders (Black, Caspian and Mediterranean Seas) to be south of Cape Hatteras, while cytb data narrowed the source location to the Gulf of Mexico region. Both cytb and microsatellite data sets suggested that the southern invasion was associated with genetic bottlenecks while evidence was equivocal for the northern invasion. By increasing the native range spatial sampling, our dataset was able to sufficiently characterize patterns and levels of genetic differentiation in the native range of M. leidyi and identify likely biogeographic boundaries, allowing for the most complete characterization of M. leidyi’s invasion histories and most realistic estimates of its source region(s) to date.

We investigated phylogeographic relationships among American Mercenaria taxa by assessing variation in a 444 nucleotide fragment of the mitochondrial 16S ribosomal gene in clams sampled from four representative sites in January to November 1994. Three of these sites were in the Gulf of Mexico, one was on the Atlantic coast in South Carolina. Direct sequencing of this amplified gene fragment in 85 individuals revealed 21 haplotypes. Phylogenetic analyses consistently resolved this variation into three well supported clades, and within-clade genetic divergence levels were markedly lower than among-clade values. One of the clades, A, was taxon-specific, in that it solely and exclusively contained specimens of M. mercenaria (Linnaeus, 1758) sampled in South Carolina. The other two clades, B and C, were the most divergent and both encompassed specimens of M. campechiensis (Gmelin, 1791) and of M. campechiensis texana (Dall, 1902), sampled from the three Gulf of Mexico sites. Clade B was found at high frequencies at all three Gulf sites, whereas Clade C occurred at low frequencies at two western Gulf sites. We interpret this pattern as resulting from the secondary contact and introgression of two allopatrically differentiated Mercenaria taxa in the western Gulf of Mexico. Clade C haplotypes may represent relict mitochondrial lineages from original Gulf Mercenaria spp. populations that predate massive mitochondrial introgression by M. campechiensis. We further propose that the M. campechiensis texana nuclear genome is a mosaic, heavily weighted toward M. campechiensis, but containing some relict alleles inherited from the precontact population, especially those governing shell characteristics, which may be adaptive in cohesive sediments of bays and estuaries in the northwestern Gulf of Mexico.

Bycatch represents a conservation problem when endangered species are affected. Sea turtles are highly vulnerable to this threat as their critical habitats overlap with fishing zones in all regions of the world. We used sequences of the mitochondrial DNA control region obtained from loggerhead (Caretta caretta) and green (Chelonia mydas) turtles to determine the migratory routes between nesting habitats in the Yucatán Peninsula and their critical marine habitats in the Northwest Atlantic. Mixed Stock Analysis revealed that loggerheads from Quintana Roo migrated to foraging areas in the northwestern Atlantic. Migratory routes used by green turtles are determined by their natal nesting colony: (1) green turtles from the Gulf of Mexico migrate to foraging aggregations in Texas and the northern Gulf of Mexico, (2) Mexican Caribbean turtles travel to foraging grounds in Florida, and (3) a smaller proportion of individuals born in the Yucatán Peninsula display a local connectivity pattern. Our results suggest that the migratory corridors used by Mexican loggerheads overlap with longline fisheries in the mid-Atlantic where sea turtle bycatch is comprised predominantly of immature individuals. Green turtles from the Yucatán Peninsula migrate to critical habitats that overlap with shrimp trawl fisheries within the Gulf of Mexico. Bycatch data and the identification of migratory corridors used by loggerheads and green turtles suggests that shrimp trawl fisheries on the east coast of the U.S. and the Gulf of Mexico pose a serious threat to the conservation and recovery of Mexican sea turtle populations.

Summary This paper reviews industry knowledge of the Gulf of Mexico circulation feature known as the Loop Current. Data obtained in Green Canyon in 1989indicate how the Loop Current influences drilling operations. The paper alsodiscusses the analytic and operational considerations for drilling-riser andstation-keeping system management when these currents are of concern. Introduction The Loop Current, the principal deepwater current in the Gulf of Mexico, ispart of the north Atlantic Ocean's western-boundary current. It is formed from water that flows into the Caribbean Sea from the western north Atlantic, thesouth Atlantic, and the Mediterranean Sea. The Caribbean Sea water flows intothe gulf through the Yucatan Strait, loops around Cuba, and exits via the Florida Straits, where it becomes source water for the Gulf Stream. Althoughthe north Atlantic's circulation has been studied for more than 50 years, eventhe more recent studies barely touch on circulation within the Gulf of Mexico. Significant questions remain from studies conducted as recently as the early1960, s. Since then, however, researchers from academe and industry have expanded understanding of the Loop Current's characteristics. Loop Current Characteristics Although much remains to be learned, an understanding of several basic aspects of the Loop Current is emerging. First, analysis of satellite data thathave been available since the early 1970's indicates that the mean position ofthe Loop Current lies in the position of the Loop Current lies in the deepwaterregion of the east-central Gulf of Mexico. Vukovich et al. and Auer, whosummarized the periods of 1973–77 and 1980–85, respectively, suggest that theme an position of the Loop Current's western position of the Loop Current'swestern boundary lies between 88 and 89 degrees W, with the north boundary atabout 27 degrees N. This estimate places the mean location just within the southeastern corner of the Atwater Valley leasing area. Vukovich et al. and Auer indicate that a large amount of annual variability has been observed withrespect to this mean position. Second, the Loop Current has a cycle of northwesterly movement within the Gulf of Mexico. Although the forcing mechanisms behind this movement are notwell understood, most research suggests that the cycle is approximately annualin period. Recent analysis of nearly 14 years of Loop Current position data suggests that the movement is bimodal, with dominant periods of both 1 and 21/2 years; however, the data are insufficient to determine the significance ofthe longer period. Although early research suggested that the maximum northward movement occurred during the summer, it is now generally recognized thatnorthward movement can occur at any time during the year. Third, the northward movement is frequently associated with the formation ofeddies that detach from the Loop Current and translate west-southwest acrossthe gulf. Although the northward movement can affect deepwater lease areas, detached eddies pose an even more significant problem because of their tendencyto translate west across drilling regions. Some evidence* suggests that threedetached eddies moved into the Green Canyon lease area between 1979 and1988. Fourth, measurements of near-surface current as high as 4 knots [2 m/s] havebeen recorded in eddies recently detached from the Loop Current. Available datado not indicate that the maximum possible speed in the Loop Current is any lessthan that figure. Current profiles associated with both the Loop Current andits eddies are highly sheared. These high surface speeds drop to about 1 knot[0.5 m/s] at 650 ft [200 m] and 1/2 knot [0.25 m/s] at 130 ft [400 m] depth. Features with lower surface speeds also have lower speeds at depth. Fifth, advances in modeling techniques and high-speed computing have led tothe development of basin-wide models that aid understanding of Gulf of Mexicodeepwater circulation. For example, Refs. 11 and 13 suggest that wind forcingplays a larger role than previously thought, and Ref. 12 suggests that acorrelation may exist between sea level near Florida and the location of the Loop Current. Nevertheless, much research remains to be done to understandfully the mechanisms that drive the movement of the Loop Current and lead toeddy formation. JPT P. 1046

While significant progress has been made to characterize life history patterns, movement ecology, and regional estimates of abundance of white sharks (Carcharodon carcharias) in the Western North Atlantic (WNA), patterns of spatial distribution remain relatively unknown in the northern Gulf of Maine. In this study, we utilize data collected from multiple acoustic telemetry projects from 2012-2023 to assess the spatiotemporal distribution of white sharks along sections of the Maine coastline and regional offshore waters. Acoustic receivers were deployed each year from 2012-2019 (mean number of receivers ± SD: 11 ± 4), and effort increased following the first-ever white shark related fatality in Maine in 2020 (2020-2023: 40 ± 15). In total, 107 white sharks tagged by researchers in the WNA were detected, with the majority (n = 90) detected in shallow (&amp;lt;50 m depth) waters post-2019. Reflective of the tagged population at-large, total length of individuals ranged from 2.1 to 4.9 m, with most individuals estimated to be in the juvenile or subadult life stages. White sharks were detected between the months of May-December, with peaks between July and September, and were observed in close proximity to several of Maine’s western beaches and islands/outcroppings, with higher numbers observed at several sites in eastern Casco Bay. Although the overall quantity of detections was relatively low when compared to white shark aggregation sites in other regions, this study provides baseline information on the presence of this species in the northern Gulf of Maine. While future research should include expanded receiver coverage in eastern Maine and the use of additional tagging technologies, this study contributes early insights for informing marine spatial planning, fisheries management, and conservation strategies for white sharks in the region.

Context Over the past decade, the coastal waters off Cape Cod, Massachusetts, have emerged as the only known aggregation site for the white shark (Carcharodon carcharias) in the western North Atlantic. During periods of seasonal residency, white sharks patrol the shoreline in search of pinniped prey, bringing them in close proximity to popular beaches where people recreate. Aim To examine whether white sharks off Cape Cod are more likely to occupy shallow depths (and consequently more likely to overlap with recreational water users) under certain conditions. Methods We deployed short-term, pop-up satellite archival transmitting (PSAT) tags and acoustic transmitters on 14 subadult and adult white sharks off the coast of Cape Cod during the summer and fall of 2017. PSAT tags provided fine-scale depth and temperature data, which were combined with high-resolution location data obtained from an acoustic telemetry array, to identify the depth and temperature preferences of white sharks when resident in the area. Key results Sharks spent the majority (95%) of tracked time at depths of 0–31 m and at temperatures from 8.9°C to 20.7°C. During resident periods along Cape Cod, individuals spent almost half (47%) of their time at depths of less than 4.5 m, but made frequent excursions to mid-shelf depths, alternating between the surf zone and deeper offshore waters. Sharks were slightly more likely to occupy shallow depths at night during the new moon. The relationship between shark depth and lunar phase varied over the course of the day, suggesting the mechanism underlying lunar effects differs among diel periods. Conclusions Although the overall risk posed to humans by white sharks is low, there is a high potential for overlap between white sharks and recreational water users off Cape Cod. The risk of interaction may be slightly higher during periods when local environmental conditions favour the species’ predatory stealth by influencing prey behaviour or detectability. Implications This study provides the first glimpse into the fine-scale vertical habitat use of white sharks off Cape Cod, which can be used to better understand the risk to recreational water users and to inform public safety practices.