Meta‐analysis of post‐release fishing mortality in apex predatory pelagic sharks and white marlin

Abstract

Robust assessments of the effects of fishing require accounting for components of fishing mortality, including post‐release fishing mortality (Fr). Random‐effects meta‐analysis synthesized Fr in seven pelagic shark species captured, tagged and released with 401 pop‐up satellite archival tags compiled from 33 studies and three gears (longline, purse‐seine, rod & reel). The majority of Fr outcomes occurred within days of release, and the summary effect size for Fr was 0.27 [95% CI: 0.19–0.36], ranging from a low pooled effect size of 0.17 for blue shark (Prionace glauca, Carcharhinidae) to 0.38 (silky shark, Carcharhinus falciformis, Carcharhinidae). Fr rates in blue shark were consistent over dissimilar spatial and temporal scales, and results from earlier meta‐analysis were replicated, which is the most powerful way to authenticate results. Condition at tagging was a strong predictor, and dichotomized survival outcomes in silky shark and no sex‐, size‐, location‐ or gear‐specific Fr rates were demonstrated. Meta‐analyses and sensitivity analyses indicated exposure to risk factors and conditions whilst caught on the gear probably had the largest explanatory effect on Fr, rather than stressors incurred during handling and release. Records from 549 tagged istiophorid billfishes (six species, three gears, 43 studies) demonstrated they are more robust to stressors sustained during capture, handling and release than pelagic sharks. Findings from previous meta‐analysis on Fr rates in white marlin (Kajikia albida, Istiophoridae) were replicated. Synthesized Fr rates enable prioritizing approaches to mitigate by‐catch fishing mortality, to improve the quality of stock and ecological risk assessments and to expand our knowledge of factors influencing trophic structure.

The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies

“…Odontocete interactions on pelagic longlines occur quickly and can be dangerous for the crew, providing little opportunity for fishermen or observers to collect identifying information (e.g., dorsal fin photos for photo-identification) or deploy location satellite-linked tags. This reduces the opportunity to collect data on survival outcomes of released whales (NOAA Fisheries, 2014), as has been done for other taxa captured accidentally on longlines such as sea turtles (Swimmer et al, 2014), billfish (Musyl et al, 2015), and sharks (Musyl and Gilman, 2019). In the absence of such empirical information, the criteria NMFS uses to categorize serious vs. non-serious injury for these fleets (NOAA Fisheries, 2014) have been developed almost entirely from expert opinion generated in a technical workshop held in 2007 (Andersen et al, 2008).…”

Improved estimation of discard mortality rates with in situ experiments involving electronic and traditional tagging

“…Important improvements in precision with the addition of tag returns were observed for all groups except, in most instances, for the group with the lowest DM rate. Improvements resulting from the addition of traditional tag returns were greatest when the number of electronic tags was small, and the method is therefore particularly suited to studies with small samples as often occurs when pop-up archival tags are used (e.g., Musyl et al 2014;Musyl and Gilman, 2019). For example, for a study with 50 electronic tags, the CV of estimates for groups other than the one associated with the lowest rate could be reduced by up to 25% by including between around 40 to 180 tag returns, depending on the number of groups and the difference in DM rates between groups (Figs.…”

Effect of pelagic longline bait type on species selectivity: a global synthesis of evidence

“…The speciesspecific samples sizes were too small to consider potentially informative covariates. We therefore only used random-effects models rather than fixed-or mixed-effects or meta-regression models that have been used in other recent ecological meta-analyses (e.g., Gilman et al 2016b;Pfaller et al 2018;Musyl and Gilman 2019).…”

“…Conducting species-specific meta-analyses of the effect of pelagic longline bait type on at-vessel and post-release survival is an additional research priority (Gilman et al 2016b;Musyl and Gilman 2019). Supplemental Material Section S5 reviews the underlying mechanisms for the effect of bait type on the risk of mortality, including effects of bait type on anatomical hooking position and size-and sex-selectivity.…”