Search

Comparing co-occurring species may provide insights into how aspects of ecology may play a role in influencing their microbial communities. During the 2019 commercial shrimp trawl season off coastal Georgia, swabs of skin, gills, cloaca, and gut were taken for three species of batoids (Butterfly Ray, Bluntnose Stingray, and Atlantic Stingray) and one shark species (Atlantic Sharpnose) for high-throughput sequencing of the V4 region of the bacterial 16S rRNA gene. White muscle was analyzed for stable isotopes (δ13C and δ15N) to evaluate potential niche overlap in these four sympatric mesopredators. Significant differences were found in both δ13C and δ15N signatures across species, suggesting a degree of resource partitioning. When examined within tissue type, the host species had a weak effect on β-diversity for cloaca and skin, with no differences found for gill and gut samples. However, network analysis metrics demonstrated a stronger species-specific effect and distinct microbial community relationships were apparent between the shark and batoids, with the former having tighter networks for both internally- and externally-influenced tissues (gut/cloaca and skin/gills, respectively). Despite overlapping habitat use, species' microbiomes differed in their organizational structuring that paralleled differences in stable isotope results, suggesting a mediating role of species-specific ecology on bacterial microbiomes. [ABSTRACT FROM AUTHOR]

The white shark (Carcharodon carcharias) is a wide-ranging apex predator in the northeastern Pacific (NEP). Electronic tagging has demonstrated that white sharks exhibit a regular migratory pattern, occurring at coastal sites during the late summer, autumn and early winter and moving offshore to oceanic habitats during the remainder of the year, although the purpose of these migrations remains unclear. The purpose of this study was to use stable isotope analysis (SIA) to provide insight into the trophic ecology and migratory behaviors of white sharks in the NEP. Between 2006 and 2009, 53 white sharks were biopsied in central California to obtain dermal and muscle tissues, which were analyzed for stable isotope values of carbon (δ(13)C) and nitrogen (δ(15)N). We developed a mixing model that directly incorporates movement data and tissue incorporation (turnover) rates to better estimate the relative importance of different focal areas to white shark diet and elucidate their migratory behavior. Mixing model results for muscle showed a relatively equal dietary contribution from coastal and offshore regions, indicating that white sharks forage in both areas. However, model results indicated that sharks foraged at a higher relative rate in coastal habitats. There was a negative relationship between shark length and muscle δ(13)C and δ(15)N values, which may indicate ontogenetic changes in habitat use related to onset of maturity. The isotopic composition of dermal tissue was consistent with a more rapid incorporation rate than muscle and may represent more recent foraging. Low offshore consumption rates suggest that it is unlikely that foraging is the primary purpose of the offshore migrations. These results demonstrate how SIA can provide insight into the trophic ecology and migratory behavior of marine predators, especially when coupled with electronic tagging data.

From May 2003 to February 2005,20 female leopard sharks (78 -140 cm TL) were tagged with acoustic transmitters in Elkhorn Slough, California, and their movements and habitat use were examined using acoustic tracking techniques. Nine sharks were manually tracked for 20-71.5 h, and 11 sharks were monitored for 4-443 d using an array of acoustic receivers. Use of different regions in Elkhorn Slough by tagged sharks changed seasonally and was associated with changes in temperature, salinity, and dissolved oxygen. Sharks used Elkhorn Slough National Estuarine Research Reserve (ESNERR) extensively throughout the year, but especially during the spring and summer. ESNERR appeared to be important as both a foraging and nursery area, likely due to the abundance of intertidal mudflats. Movements and habitat use were tidally influenced, and likely were related to the distribution of important prey items in Elkhorn Slough.

Understanding regional migration, residency dynamics, and associated trophic ecology can inform recovery strategies for pelagic species such as Pacific bluefin tuna (Thunnus orientalis) (PBFT). PBFT residency duration in the eastern Pacific is uncertain, particularly for larger individuals (here, >100 cm or ~3+ years of age). We applied a previously tested 'chemical tracer toolbox' (Fukushima-derived radiocesium and [sup.13]C and [sup.15]N stable isotope signatures) to examine migratory and residency patterns and dietary inputs of 428 age 1-6+ PBFT collected from 2012 to 2015 in the eastern Pacific Ocean. Age 1-3 individuals were a mix of residents and recent ([less than or equal to] 500 day) migrants, while 98% of age 3-4 and 100% of age 4-6.3 year old PBFT were resident for >500 days in the eastern Pacific. Zooplanktivorous forage (e.g., sardine, anchovy, pelagic red crab, and trophically similar species) of the California Current Ecosystem constituted 57%-82% of diet across PBFT sizes. Migration timing estimates show that PBFT may spend 2-5 years in the eastern Pacific Ocean before returning to the western Pacific. La comprehension des migrations regionales, de la dynamique de residence et de l'ecologie trophique associee peut eclairer l'elaboration de strategies de retablissement pour des especes pelagiques comme le thon rouge du Pacifique (Thunnus orientalis) (TRP). La duree de residence des TRP dans l'ocean Pacifique oriental n'est pas bien etablie, particulierement pour les grands individus (>100 cm ou ages de ~3 ans et plus). Nous avons utilise une boite a outils de traceurs chimiques eprouvee (signatures de radiocesium derive de Fukushima et des isotopes stables [sup.13]C et [sup.15]N) pour examiner les motifs de migration et de residence et les apports alimentaires de 428 TRP ages de 1 an a plus de 6 ans, preleves de 2012 a 2015 dans le Pacifique oriental. Les individus de 1 a 3 ans constituaient un melange de residents et de migrants recents ([less than or equal to] 500 jours), alors que 98 % des TRP de 3-4 ans et 100 % des TRP de 4-6,3 ans avaient reside pendant >500 jours dans le Pacifique oriental. Des especes-four-rage zooplanctonivores (p. ex. sardine, anchois, crabe rouge pelagique et especes apparentees sur le plan trophique) de l'ecosysteme du courant de Californie constituaient de 57 % a 82 % du regime alimentaire des TRP, toutes tailles confondues. Des estimations du moment des migrations montrent que les TRP pourraient passer de 2 a 5 ans dans le Pacifique oriental avant de retourner dans le Pacifique occidental. [Traduit par la Redaction], Introduction Tuna species support global fisheries and are subjected to variable fishing pressures. Some species have been resilient to fisheries exploitation, while others have experienced marked population declines (Collette et [...]

The salmon shark, Lamna ditropis, is an endothermic, apex predator in the productive waters of the Gulf of Alaska (GOA). To understand their role in these productive habitats and to identify and better understand their interactions with commercially important species and fisheries, detailed information regarding the distribution of the salmon shark is required. Archival data records from eight recovered pop-up archival transmitting (PAT) tags were analyzed to examine the geographic and vertical distribution of female salmon sharks and elucidate how their distribution changes in relation to the biotic and abiotic environment. Tagged sharks used the neritic habitats of the GOA for the duration of the PAT deployments. Sharks exhibited a diel periodicity in their dive behavior. Salmon sharks exhibited three different patterns of depth distribution (behavioral modes) that occurred during distinct oceanographic seasons, likely reflecting changes in their foraging ecology in response to seasonal changes in the distribution and availability of important prey. The distribution of salmon sharks in the GOA appears to follow consistent patterns and has a high degree of geographical and vertical overlap with commercially important prey species. This information increases our understanding of interactions between salmon sharks and commercial fisheries and may assist in fostering responsible management for this species. Les taupes du Pacifique, Lamna ditropis, sont des requins endothermes, predateurs de niveau trophique superieur, dans les eaux productives du golfe de l'Alaska (GOA). Il est necessaire d'obtenir des informations precises sur la repartition des taupes du Pacifique afin de comprendre leur role dans ces habitats productifs et d'identifier et de mieux evaluer leurs interactions avec les especes et les peches d'importance commerciale. Nous avons analyse les donnees archivees dans huit etiquettes emettrices detachables (PAT) recuperees pour etudier les repartitions geographique et verticale de taupes du Pacifique femelles et elucider comment leur repartition change en relation avec l' environnement biotique et abiotique. Les requins marques ont utilise les habitats neritiques du GOA pendant la duree de fonctionnement des PAT. Les requins possedent une periodicite journaliere dans leur comportement de plongee. Les taupes du Pacifique montrent trois patrons differents de repartition en profondeur (modes comportementaux) qui se manifestent durant des saisons oceanographiques differentes, ce qui reflete vraisemblablement leur ecologie de recherche de nourriture en reaction aux changements saisonniers dans la repartition et la disponibilite des proies importantes. La repartition des taupes du Pacifique dans le GOA semble suivre des patrons caracterises et montre un fort degre de chevauchement geographique et vertical avec les especes de proies d' importance commerciale. Ces informations augmentent notre comprehension des interactions entre les taupes du Pacifique et les peches commerciales et peuvent aider a mettre en oeuvre une gestion responsable de cette espece. [Traduit par la Redaction], Introduction The spatiotemporal patterns of distribution of a species are fundamental to its ecology and population dynamics (Dingle and Holyoak 2001; Morales and Ellner 2002). The salmon shark (Lamna ditropis) [...]

Quantifying vertical distributions of pelagic predators elucidates pelagic ecosystem structure and informs fisheries management. In the tropical South Atlantic Ocean, the recently designated large-scale marine protected area around Ascension Island hosts diverse pelagic predators for which basin-specific vertical habitat information is minimal or absent. We used pop-up satellite archival tags to analyse vertical habitat use in 12 species (bigeye tuna Thunnus obesus , blue marlin Makaira nigricans , blue shark Prionace glauca , dolphinfish Coryphaena hippurus , Galapagos shark Carcharhinus galapagensis , oceanic whitetip Carcharhinus longimanus , sailfish Istiophorus albicans , silky shark Carcharhinus falciformis , swordfish Xiphias gladius , tiger shark Galeocerdo cuvier , wahoo Acanthocybium solandri , and yellowfin tuna Thunnus albacares) and quantify parameters (temperature, dissolved oxygen, diel cycles, lunar phase) known to constrain vertical movements. Predator depth distributions varied widely, and classification trees grouped predators into four clades: (i) primarily epipelagic; (ii) partial thermocline use; (iii) oscillatory diving with thermocline/sub-thermocline use; and (iv) extensive use of sub-thermocline waters. Vertical habitat differences were linked to thermal physiology and foraging ecology, and species-specific physical constraints from other ocean basins were largely conserved in the South Atlantic. Water column features defined species-specific depth distributions, which can inform fisheries practices and bycatch risk assessments and population estimates. [ABSTRACT FROM AUTHOR]

Although there is a general perception of sharks as large pelagic, apex predators, most sharks are smaller, meso- and upper-trophic level predators that are associated with the seafloor. Among 73 shark species documented in the eastern North Pacific (ENP), less than half reach maximum lengths > 200 cm, and 78% occur in demersal or benthic regions of the continental shelf or slope. Most small (= 200 cm) species (e.g., houndsharks) and demersal, nearshore juveniles of larger species (e.g., requiem sharks) consume small teleosts and decapod crustaceans, whereas large species in pelagic coastal and oceanic environments feed on large teleosts and squids. Several large, pelagic apex predator species occur in the ENP, but the largest species (i.e., Basking Shark, Whale Shark) consume zooplankton or small nekton. Size-based dietary variability is substantial for many species, and segregation of juvenile and adult foraging habitats also is common (e.g., Horn Shark, Shortfin Mako). Temporal dietary differences are most pronounced for temperate, nearshore species with wide size ranges, and least pronounced for smaller species in extreme latitudes and deep-water regions. Sympatric sharks often occupy various trophic positions, with resource overlap differing by space and time and some sharks serving as prey to other species. Most coastal species remain in the same general region over time and feed opportunistically on variable prey inputs (e.g., season migrations, spawning, or recruitment events), whereas pelagic, oceanic species actively seek hot spots of prey abundance that are spatiotemporally variable. The influence of sharks on ecosystem structure and regulation has been downplayed compared to that of large teleosts species with higher per capita consumption rates (e.g., tunas, billfishes). However, sharks also exert indirect influences on prey populations by causing behavioural changes that may result in restricted ranges and reduced fitness. Except for food web modelling efforts in Alaskan waters, the trophic impacts of sharks are poorly incorporated into current ecosystem approaches to fisheries management in the NEP. [ABSTRACT FROM AUTHOR]

The blue marlin ( Makaira nigricans) is a highly migratory pelagic predator of tropical and subtropical seas. Information on the habitat use of marine species is fundamental to understanding their ecology and population dynamics and is needed to inform responsible management strategies. Using a long-term satellite tagging data set from The International Game Fish Association Great Marlin Race, we examined habitat use and how oxygen and temperature influence the horizontal and vertical distributions of blue marlin in the Central Pacific. Blue marlin primarily occurred in warm waters (26-30°C) and exhibited a diel bimodal depth distribution across the 5-year data record (2009-2013), with fish spending the majority of their time near the surface at night and at deeper depths during the day (25-100 m). The depth distribution of blue marlin was limited in areas where low oxygen and/or temperature conditions occur closer to the surface, with the extent of habitat compression being greatest when both oxygen and temperature were limiting. The migrations of blue marlin appeared restricted during the 2010 La Niña, when increased equatorial upwelling resulted in an extension of the cold, low oxygen waters of the cold tongue into the Central Pacific, creating a barrier to the trans-equatorial migrations that occurred during all other tagging years. If the frequency and intensity of La Niña events increases and the oxygen minimum layer continues to expand as has been predicted under certain climate change scenarios, the migratory behavior and habitat availability of blue marlin may be impacted. [ABSTRACT FROM AUTHOR]