Long‐Term Trends in Juvenile Atlantic Sturgeon Abundance May Signal Recovery in the Hudson River, New York, USA

Abstract

Overfishing, bycatch, and habitat loss and alteration during the late 19th century to the end of the 20th century caused significant declines in Atlantic Sturgeon Acipenser oxyrinchus stock abundances along the Atlantic coast. To prevent further stock reductions, a coastwide harvest moratorium was implemented in 1998. With fishery‐dependent data unavailable to inform stock management, fishery‐independent surveys contribute vital information for monitoring population trends by providing data for evaluating the effectiveness of the moratorium and for informing recovery planning. In 2004, a standardized monitoring survey was developed to assess trends in the relative abundance of juvenile Atlantic Sturgeon in the Hudson River, New York. The multimesh anchored gill‐net survey randomly sampled locations in soft, deep depositional areas of Haverstraw Bay from late February through early May. Predicted length‐at‐age relationships were used to infer annual age structure and to examine the relationships between age and annual catch rates. Generalized additive regression modeling was used to describe the relationships between the environmental variables and catch rates and to standardize the abundance index to account for variability in environmental conditions over time. Atlantic Sturgeon catch rates generally increased with increasing water temperature and salinity, and the standardized abundance index (accounting for environmental variability) was highly correlated with the nominal abundance index. In the 16 years of annual monitoring, there has been a significant increase in the relative abundance of juvenile Atlantic Sturgeon. The average catch rate in recent years (2012–2019) is more than twice that observed during the first 8 years (2004–2011) of the survey, as the effects of the moratorium are expected to be delayed due to the long maturation period of Atlantic Sturgeon. These trends suggest that juvenile Atlantic Sturgeon in the Hudson River may be recovering in response to the moratorium and demonstrate the need for long‐term fisheries‐independent monitoring to document abundance trends in slow‐maturing, long‐lived species.

Evaluating population trends of juvenile Atlantic Sturgeon at low abundance in a dynamic estuarine environment (Hudson River, New York)

“…We found that catch rates were highest ~27 km downstream of the salt front in mesohaline waters, declined abruptly in higher salinity waters, and declined gradually into fresh water, with the highest catch rate location in some years closer to the predicted salt front, which supports previous research showing positive relationships between catch rates and salinity (Pendleton & Adams, 2021) and distributional observations across multiple systems (Fox & Peterson, 2019; Haley et al, 1996; Hatin et al, 2007; Moser & Ross, 1995; Secor et al, 2000). Availability is described as the ratio between the population range and the fraction affected by the survey (Arreguin‐Sanchez, 1996).…”

“…Most conditions of this protocol were completed annually during 2004–2015, although occasional samples were collected at temperatures below 4°C. We subset catch data to include only fish with total length ≤ 950 mm, which corresponds to the estimated upper length of an age‐5 Atlantic Sturgeon (Dunton et al, 2016; Pendleton & Adams, 2021). Restricting size of fish included in the index limited the potential effect of larger non‐natal sub‐adult fish migrating between estuaries.…”

“…Assuming the alternative index aligns more closely with true abundance (see Arreguin-Sanchez, 1996;Harley et al, 2001;Maunder & Punt, 2004;Wilberg et al, 2010), the Hudson River population may be growing at a higher rate (r = 0.15) than previously thought during 2004-2015 (Pendleton & Adams, 2021). Temperature and salt front location were important covariates associated with susceptibility and availability of sturgeon to the standardized survey (Sweka et al, 2006(Sweka et al, , 2007.…”

“…Following an experimental stocking in 1994 (Mohler, 2000; Mohler et al, 2012) and closure of harvest to the adult spawning stock in 1998 (Kahnle et al, 1998), the New York State Department of Environmental Conservation (NYS‐DEC), in cooperation with the U.S. Fish and Wildlife Service (USFWS), initiated a relative abundance monitoring program in 2004 to track population change (Pendleton & Adams, 2021; Sweka et al, 2006, 2007). Unfortunately, like many other existing fishery‐independent surveys (ASMFC, 2017), presumably low juvenile abundance and variable environmental conditions within the survey area (Geoghegan et al, 1992) initially produced a CPUE data set with high variability and excessive zero observations.…”

“…Following an experimental stocking in 1994 (Mohler, 2000;Mohler et al, 2012) and closure of harvest to the adult spawning stock in 1998 (Kahnle et al, 1998), the New York State Department of Environmental Conservation (NYS-DEC), in cooperation with the U.S. Fish and Wildlife Service (USFWS), initiated a relative abundance monitoring program in 2004 to track population change (Pendleton & Adams, 2021;Sweka et al, 2006Sweka et al, , 2007.…”