Abstract
Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) experienced severe declines due to habitat destruction and overfishing beginning in the late 19th century. 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. Although habitats may be improving, the availability of high quality spawning habitat, essential for the survival and development of eggs and larvae may still be a limiting factor in the recovery of Atlantic sturgeon. To estimate adult Atlantic sturgeon spatial distributions during riverine occupancy in the Delaware River, we utilized a maximum entropy (MaxEnt) approach along with passive biotelemetry during the likely spawning season. We found that substrate composition and distance from the salt front significantly influenced the locations of adult Atlantic sturgeon in the Delaware River. To broaden the scope of this study we projected our model onto four scenarios depicting varying locations of the salt front in the Delaware River: the contemporary location of the salt front during the likely spawning season, the location of the salt front during the historic fishery in the late 19th century, an estimated shift in the salt front by the year 2100 due to climate change, and an extreme drought scenario, similar to that which occurred in the 1960’s. 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 be taking place. Identifying where suitable spawning substrate and water chemistry intersect with the likely occurrence of adult Atlantic sturgeon in the Delaware River highlights essential spawning habitats, enhancing recovery prospects for this imperiled species.
Highlights
The Delaware River Estuary historically supported the largest spawning population of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) until over-fishing and habitat degradation caused sharp declines in their numbers [1]
The lack of population increase given improved conditions in the Delaware River and the absence of directed fishing pressure were listed as the main drivers for the recent listing of the Atlantic sturgeon NY Bight distinct population segment under the Endangered Species Act [5]
Sediment information, and location of the salt front to determine if these factors play a significant role in the occurrence of adult Atlantic sturgeon during the spawning season in the Delaware River
Summary
The Delaware River Estuary historically supported the largest spawning population of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) until over-fishing and habitat degradation caused sharp declines in their numbers [1]. In addition to over-fishing, navigation projects in the Delaware River Estuary resulted in the removal of over 1.5 x 108 m3 of sediments, causing major changes in substrates, tidal flows, and salinity [3], [4], which likely altered Atlantic sturgeon spawning habitats. Directed harvest of Atlantic sturgeon ended in 1998 [6], the results of historic overharvest coupled with habitat change and ongoing issues of bycatch mortality have resulted in a > 99% decline from historic abundance levels to < 300 spawning adults annually [7]. Like all sturgeons (family Acipenseridae), Atlantic sturgeon require flowing freshwater and adherence of eggs to appropriate substrate for successful spawning [8]. Unconsolidated fine grain materials will adhere to the developing embryo resulting in abnormal development or mortality [11]
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