Habitat utilization of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus in the Delaware River, Bay and coastal Atlantic Ocean
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Animals utilize various environments throughout their life cycle to optimize growth, fitness, and survival. These environments are their habitats. As the lifecycle of an organism progresses, the resources needed, and thus the habitats preferred will change to fulfill the new requirements of the given life history stage. Resource needs for many organisms will also vary seasonally in both composition and specificity requiring organisms to shift their habitats to fulfill changing needs throughout the year. Incorporating species occurrence observations and environmental properties enables species distribution models to reliably estimate habitat locations. Destruction of habitat and overfishing beginning in the late 19th century severely depleted Atlantic Sturgeon populations. Subsequent to the boom and bust period of exploitation, there has been minimal fishing pressure and improving habitats. However, lack of recovery led to the 2012 listing of Atlantic Sturgeon under the Endangered Species Act. In this dissertation I utilize various sources of environmental data, species distribution modeling, and acoustic biotelemetry to gain insight into the occurrence and habitat use of adult Atlantic Sturgeon to further their protection and promote efficient resource management. ☐ To estimate adult Atlantic sturgeon spatial distributions during riverine occupancy in the Delaware River, I utilized a maximum entropy approach along with passive biotelemetry during the likely spawning season. I found that substrate composition and distance from the salt front significantly influenced the locations of adult Atlantic Sturgeon in the Delaware River. The movement of the salt front upstream as a result of dredging and climate change likely eliminated historic spawning habitats and currently threatens areas where Atlantic Sturgeon spawning may still be taking place. ☐ In the Delaware Bay I found that movement and residency patterns were driven primarily by depth, bottom temperature, and location. These findings revealed that as temperatures warm in the summer Atlantic Sturgeon maintain residency in deep areas near the mouth of the Delaware Bay where upwelling offshore waters keep bottom temperatures cooler than surrounding area. As water temperatures begin to cool in the fall this pattern of residency turns back into movement. ☐ By placing Atlantic Sturgeon in the context of dynamic, objective, and globally conservative seascapes, in a manner similar to landscape partitioning in the terrestrial environment, I was able to link Atlantic Sturgeon occurrence to one particular seascape associated with terrigenous input during their spring migration. To verify the seascape findings from the passive acoustic array I deployed an autonomous underwater vehicle to dynamically sample the seascape distribution in the coastal ocean to confirm the original hypothesis of selection for a given seascape. ☐ To expand the prediction of Atlantic Sturgeon occurrence for the entire seasonal cycle I matched fisheries independent biotelemetry observations of Atlantic Sturgeon with daily satellite observations to construct a time resolved spatial distribution model of Atlantic Sturgeon. I determined that depth, day-of-year, sea surface temperature, and light absorption by seawater are the most important predictors of Atlantic sturgeon occurrence. I found strong spatial differences in spring and fall migration patterns, when anthropogenic interactions peak. Cross-validated models correctly identified > 88% of biotelemetry observations in this study region and my models also correctly identified ~67% of fisheries dependent observations throughout the year. However, during their migrations, when harmful interactions were highest, models correctly identified ~91% of fisheries dependent observations. ☐ The Delaware Bay and River once supported the largest population of sturgeon in North America but due to anthropogenic impacts this population segment is severely depleted. Recent measures have aided to stabilize Atlantic Sturgeon populations but without further protection for habitats, such as those highlighted by this dissertation, recovery may never be realized. I strongly suggest that the dynamic models created in this body of work be used for guidance to managers and stakeholders to reduce interactions with this highly imperiled species thereby enhancing conservation and recovery efforts.
Description
Keywords
Biological sciences, Health and environmental sciences, AUV, Endangered species, Oceanography, Satellite remote sensing, Species distribution modeling, Telemetry