Using Acoustic Telemetry to Estimate Weakfish Survival Rates along the U.S. East Coast

Abstract

The Weakfish Cynoscion regalis, an economically important species, has declined over the last 30 years, corresponding with an increase in total mortality according to the most recent stock assessment. We estimated estuarinespecific and coastwide apparent survival of Weakfish by using a Cormack-Jolly-Seber model to provide insights into the spatiotemporal component of mortality. Telemetered Weakfish (n = 342) were released across five estuaries ranging from North Carolina to New Jersey between 2006 and 2016. In estuaries from Delaware Bay and northward, egress peaked around the third week of September; in North Carolina, egress peaked by the first week of November. For three estuaries with adequate sample sizes, apparent survival estimates were similar and a joint model including all telemetered Weakfish estimated an extremely low annual apparent survival rate of 0.001 (95% credible interval [CrI] = 0.002-0.0003) or annual apparent instantaneous total mortality of 7.25 (95% CrI = 6.28-8.05). At a minimum, 61% of telemetered Weakfish emigrated in the fall, but only 2 of 149 fish with long-lived transmitters were detected as returning to estuaries the following year. This is a small proportion for a fish that exhibits spawning site fidelity. We conclude that the disappearance of telemetered Weakfish represents mortality that occurs between emigration and the spring spawning period, potentially during overwinter periods on the continental shelf. Our study provides insights into the magnitude, timing, and location of Weakfish loss and facilitates an improved understanding of Weakfish population dynamics for use in stock rebuilding.

The Extent of Seasonally Suitable Habitats May Limit Forage Fish Production in a Temperate Estuary

“…Additionally, the lack of a significant relationship between annual relative abundance of juvenile weakfish and suitable habitat extent may have resulted from changes in predation mortality of juvenile weakfish. This hypothesis is consistent with the observed increase in natural mortality rates for this species in the 2000s (Atlantic States Marine Fisheries Commission [ASMFC], 2019; Krause et al, 2020); although the sources of increased natural mortality in weakfish remain unclear, increased predation is believed to have played a role (Atlantic States Marine Fisheries Commission [ASMFC], 2019). Abundances of other forage fishes may be limited by similar trophic interactions with their predators or prey, or by unsuitable egg and larval habitats in Chesapeake Bay.…”

Networked Animal Telemetry in the Northwest Atlantic and Caribbean Waters

“…Often, factors affecting population dynamics, such as fishing pressure and predation mortality, differ between spatially discrete stocks, and telemetry is a great tool with which to conduct place-based studies on these factors focused in particular core areas. For example, Krause et al (2020) assessed the relative importance of predation and fishery mortality on the Weakfish stock that reproduces in Bogue Sound, North Carolina, an area where the numbers of adult-sized Weakfish have been in serious decline.…”

“…Coastal‐scale tracking using receiver networks also allowed Bangley et al (2020, this themed issue) to identify potential associations between juvenile Dusky Sharks Carcharhinus obscurus and areas where oceanographic features created seasonal temperature stratification. By utilizing receiver networks covering areas both within and outside of estuaries, Myers et al (2020, this themed issue) and Krause et al (2020, this themed issue) were able to identify areas of transition between estuarine and oceanic habitats for Striped Mullet Mugil cephalus and Weakfish Cynoscion regalis , respectively.…”

“…Dusky Sharks tagged by Bangley et al (2020) were detected from the New York Bight to Cape Lookout, North Carolina. Networked telemetry can also reveal connections among freshwater, estuarine, and oceanic environments for anadromous (Gahagan and Bailey 2020) and estuarine‐spawning species (Krause et al 2020; Myers et al 2020). Networks covering areas within and outside of MPA boundaries can provide information on connectivity between animals protected by the MPA for at least part of their life cycle or annual migration and other, possibly unprotected habitats (Novak et al 2020).…”

“…For example, Braun et al (2019) combined telemetry data with oceanographic and fisheries catch data to fill in management‐relevant knowledge gaps for Swordfish Xiphias gladius in the Atlantic Ocean. Krause et al (2020) used a similar approach, bringing together a variety of methods, including acoustic telemetry, traditional mark–recapture, landings, and feeding habits data, to identify the sources of mortality in Weakfish. Combining all of these methods allowed Krause et al (2020) to determine that natural mortality likely had a stronger influence than fishing mortality on North Carolina Weakfish stocks and also allowed for possible identification of their major predators.…”