Performance of a low-cost, solar-powered pop-up satellite archival tag for assessing post-release mortality of Atlantic bluefin tuna (Thunnus thynnus) caught in the US east coast light-tackle recreational fishery

Abstract

BackgroundPop-up satellite archival tags (PSATs) are a valuable tool for estimating mortality of pelagic fishes released from commercial and recreational fishing gears. However, the high cost of PSATs limits sample sizes, resulting in low-precision post-release mortality estimates with little management applicability. We evaluate the performance of a lower-cost PSAT designed to enable large-scale post-release mortality studies. The tag uses solar rather than battery power, does not include a depth sensor, and transmits daily summaries of light and temperature data rather than high-resolution habitat profiles, contributing to a substantially lower per-unit price. We assessed the tag’s ability to detect mortality while also estimating the post-release mortality of juvenile (119–< 185 cm) Atlantic bluefin tuna (Thunnus thynnus) caught using light-tackle angling methods along the US east coast.ResultsUsing high-resolution data from previously deployed PSATs and environmental information from the general tagging location, we established parameters to infer mortality for Atlantic bluefin tuna using only daily summary data. We then deployed 22 PSATs, programmed to pop off after 31 days (thus providing 30 full daily summaries), on Atlantic bluefin tuna caught using light tackle off the coasts of Massachusetts and North Carolina, USA, in 2015 and 2016. Data were recovered for 15 tags with deployments ranging from 7 days (premature shedding) to 95 days (failed pop-off) and indicated that tagged fish spent sufficient time near the surface to keep the solar-powered tags fully charged. Fourteen fish demonstrated strong temporal changes in temperature indicating vertical movement in the water column, consistent with survival. One fish was predated upon after 17 days, likely by a shortfin mako, and was considered a natural mortality, resulting in a post-release mortality estimate of 0%.ConclusionsWhile low reporting rates complicated inferences about post-release mortality, the concept of using species-specific mortality parameters coupled with a reduced dataset shows promise as a cost-effective tool for detecting post-release mortality using PSATs. In addition, findings suggest that catch-and-release angling is a viable conservation strategy for juvenile Atlantic bluefin tuna caught in the US east coast light-tackle fishery.