Adult Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) Habitat Use and Run-Size in the Hudson River Hyde Park Reach, NY

摘要

Sturgeons (Acipenseridae) including the Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) are among the most threatened family of vertebrates. In the United States, Atlantic Sturgeon were listed under the Endangered Species Act in 2012. The listing delineated five Distinct Population Segments (DPS), four of which were classified as endangered (New York Bight (NYB), Chesapeake Bay, Carolina, and South Atlantic), while the Gulf of Maine was listed as threatened. Overall, Atlantic Sturgeon populations are significantly reduced from historic levels as a result of overfishing, habitat loss, and pollution. In the Hudson River, Atlantic Sturgeons population size has been affected heavily due to overfishing in the late 1800's. For recovery of the species, it's important to understand their habitat requirements. The first objective of my thesis was to assess adult Atlantic Sturgeon habitat use during their annual spawning migration while on purported spawning grounds. During 2013 and 2014, I surveyed the Hyde Park Reach of the Hudson River, NY using side-scan sonar which is a non-invasive sampling option. In this region, Atlantic Sturgeon selected for sand and muddy sands with sands substrates. Within the study site, hotspots of Atlantic Sturgeon were delineated in the middle of the reach just south of Esopus Island, and in the southeastern portion of the reach near Rogers Point. These likely spawners used multiple sediment types while in the riverine environment. The results of this study suggest Atlantic Sturgeon use the Hyde Park Reach as a possible spawning and staging site. These results also suggest that sediment type is not the only variable that is driving Atlantic Sturgeon presence. My second objective was to estimate the 2014 likely spawners run size of Atlantic Sturgeon using Swept-Area and N-mixture modeling. Estimated run-size abundances in the Hyde Park Reach using swept-area were 113 -- 188 Atlantic Sturgeon (95% CI's 74-275) for four-three consecutive surveys between 06/11/14 -- 07/02/14 while N-mixture estimates were 171 -- 306 Atlantic sturgeon (95% CI's 75 -- 560). It is important to note that these estimates do not account for individuals occurring in the other spawning sites in the Hudson River. Comparing the two models, the N-mixture model produced estimates at approximately 1 -- 2.3 times larger than swept-area estimates per time-period, likely due to the large variation in daily count data. In the case of a highly mobile species such as the Atlantic Sturgeon, it may be prudent to increase site sizes to include average movement of sturgeon, which would help to meet the assumptions of N-mixture modeling, and reduce variation in model estimates. Through my research efforts, I have been able to successfully sample Atlantic Sturgeon while on proposed spawning grounds with a non-invasive technology, which allowed for fine-scale habitat and behavior information during an important life stage that is currently not well understood. Gaining insights into the Hyde Park Reach as a possible spawning and staging location, will help to serve as important with future management efforts. Furthermore, understanding that sediment type may not be the only important factor while adult Atlantic Sturgeon are in the riverine environment and that habitat features near spawning grounds may want to be considered when developing management actions and the critical habitat designations in the riverine environment. Data from this thesis further underscores the need to identify and protect critical habitats thereby fostering conservation and recovery of this imperiled species. Finally, through this research I was also able to integrate side-scan sonar and acoustic telemetry as an effective approach for estimating run-size abundance of in the Hyde Park Reach of the Hudson River. The approach presented here appears to be a viable option and can be fitted for Atlantic Sturgeon or other large species in other river systems, which could aid in the restoration of this endangered species.