Modeling the health and distribution of essential fish habitat for highly migratory sport fishes to preserve future stocks in the southeastern US

Highly migratory (HM) sport fishes such as sharks, tuna, and marlin are a challenge for conservation because they have large ranges that cross many jurisdictional boundaries. Sharks are especially at risk: their numbers have dropped more than 70% in the past 35 years, and one-third of species are now vulnerable to extinction. Their slow growth and reliance on shallow coastal nurseries for harboring young in the first few years of life—classified as Essential Fish Habitat (EFH)—make sharks vulnerable to overfishing, pollution, and development. But seascape- level conservation of large fishes is hampered by a general lack of knowledge on the specific environmental factors that can negatively affect EFH, or if the animals that use them will be ecologically and genetically suited to survive under future conditions. Understanding these dynamics is important for protecting sport fish stocks, but while migration can be measured with tagging and telemetry, evidence of reproductive connections can only be found with DNA. Even when genetic have been done on relevant species, though, their results are almost never applied to management because of the lack of tools to integrate these findings with spatial analyses used in stock assessments, like Species Distribution Modeling (SDMs). Yet models like SDMs are exponentially more accurate when they include genetic data on ecotypes, which are distinct subpopulations that have adapted to different conditions, and have different habitat requirements. With prior MSCGP support, we addressed this lack by developing a prototype Genetic SDM (GSDM), which we found to have exponentially more predictive power than regular SDMs. With the current proposal, we aim to further develop this technical framework by testing it on nurse sharks (Ginglymostoma cirratum) in the northwest Atlantic, a charismatic but poorly-studied species that has experienced impacts from marine heatwaves and is considered globally vulnerable to extinction. By leveraging our library of hundreds of pre-existing nurse shark tissues collected over 35 years, we will (1) identify nurse shark ecotypes and use them to model future EFH, (2) measure patterns of connectivity between EFH at both the population and individual level, and (3) examine how measures of genetic viability change over time, particularly before and after marine heatwaves. This work will deliver the first seascape-level conservation plan for a migratory sport fish, while meeting the need for approachable new ways for managers to obtain, integrate, and apply research findings to better direct the conservation of sport fishes. The project area spans the majority of the Atlantic and northern Gulf states and into the Caribbean by leveraging the PI’s membership in the FACT Network, a group of scientists and institutions who manage an array of receivers for tracking large migratory fishes and share data across state boundaries throughout the northwest Atlantic. By partnering with NOAA Fisheries and state agencies like the Florida Fish and Wildlife Conservation Commission, we will ensure results will be directly relevant, inexpensive, and accessible to non-specialists. This proposal aligns with FY-26 Strategic Priorities in Conservation & Science by specifically addressing aspects of habitat connectivity, fish and wildlife health, and emerging technologies. These results will help managers anticipate and plan for future habitat shifts, strengthening fisheries resilience by advancing the successful long-term conservation of HM sport fishes.