Speaker I: Dr. Alanna Mnich Finn
Title: Fisheries Science Through the Lens of Chemical Oceanography
Abstract: The Atlantic bluefin tuna (ABFT) is an ecologically and commercially important species, acting as an apex predator and supporting a valuable fishery. Current management defines ABFT as two separate stocks, constituted by an eastern stock that spawns in the Mediterranean Sea and a western stock that spawns in the Gulf of Mexico, that differ in their respective biomasses. A recent discovery of ABFT larvae in the Slope Sea off the northeastern coast of the United States has led to questions about spawning in this region and implications for management based on the current two-stock hypothesis. Using known trends in isotope fractionation, predicted isoscapes of the Atlantic Ocean, and modern developments in analytical tools, fundamentals in chemical oceanography can be employed to test hypotheses surrounding ABFT stock identification. For this work, a secondary ion mass spectrometer (SIMS) ion microprobe approach was used to measure δ18O signatures in the otoliths of ABFT larvae from the Slope Sea and Gulf of Mexico to establish western stock spawning site signatures. Regional baseline signatures were used in a case study of identification of adult ABFT to natal origin, made possible by fishing industry collaboration. Adult ABFT otoliths were analyzed by SIMS to generate δ18O signature transects from core to edge, providing a temperature and salinity-based map of their migratory history from spawning to capture. The results of this work provide evidence of ABFT spawning in the Slope Sea and the novel methods outlined can be a useful tool for the same applications in other fisheries.
Speaker II: Dr. Grace Casselberry
Title: Nine years of tiger shark (Galeocerdo cuvier) spatial ecology in the U.S. Virgin Islands: Fine-scale residency and long-distance migration
Abstract: Fisheries management of highly migratory species in the Caribbean presents numerous challenges related to the geography of the region and resources available for regulatory enforcement. Consequently, shark populations in the Caribbean have undergone significant declines due to overharvest and habitat loss, with the U.S. Virgin Islands (USVI) identified as one of the last strongholds for these populations. To provide a more complete understanding of tiger shark (Galeocerdo cuvier) movements in the USVI and the greater Caribbean, 26 sharks were tagged with coded acoustic telemetry transmitters and 17 received additional fin mounted, real-time transmitting satellite tags in Buck Island Reef National Monument (BIRNM), a marine protected area (MPA) in St. Croix, USVI. This ultimately amassed a dataset of over 40,000 acoustic detections and over 4,000 satellite tag positions generated between May 2015 and June 2024. Random forest algorithms applied to hourly presence within the BIRNM acoustic array revealed that month of the year, sea surface temperature, moon phase, and time of day most influenced use of BIRNM, with the interaction between night hours and the full moon having the strongest influence on residency. Integrated acoustic and satellite telemetry tracks revealed that sharks spent time in the jurisdictional waters of all islands in the U.S. Caribbean but also crossed boundaries into nine other Caribbean nations and spent extensive time in international waters in the Caribbean Sea and Northwestern Atlantic. Network analysis revealed the strongest connectivity between the U.S. Caribbean and coastal Venezuela, where one shark was harvested in a gillnet fishery 57 days after tagging. These results highlight the complexity of spatial management approaches for highly mobile, wide-ranging species.
Speaker III: Dr. James Heiss
Title: Marine influences on coastal surface and subsurface hydrology
Abstract: Coastal hydrological systems are essential resources for communities worldwide and regulate nutrient fluxes to the nearshore marine ecosystems. Changes in ocean water levels strongly influence coastal hydrological systems via surface water and groundwater flow pathways that span the land-sea transition zone. This presentation will explore how ocean water level change controls surface and groundwater processes from episodic to decadal time scales. Emphasis will be placed on sea level rise, tidal flooding, and storm surge as drivers of hydrological change in coastal watersheds, barrier islands, and beach aquifers. The loss of coastal watersheds due to inundation from rising seas is partly offset by inland watershed migration and new watershed formation. Future tidal flooding and storm surge can substantially alter groundwater salinity distributions in coastal aquifers. Understanding marine influences, particularly ocean water level change, on surface water and aquifer systems will be critical for managing water resources and protecting nearshore ecosystems due to coastal population growth, sea level rise, and climate change.