The first standardized, global assessment of these fishes, using Red List criteria, reveals threatened species needing protection.

Meta-analysis (inverse-variance, random-effects model) involving 46 studies was used to estimate the effect size of postrelease mortality (Fr) in six istiophorid billfish species (black marlin (Istiompax indica), blue marlin (Makaira nigricans), longbill spearfish (Tetrapturus pfluegeri), sailfish (Istiophorus platypterus), striped marlin (Kajikia audax), and white marlin (Kajikia albida)) following release from recreational, longline, and harpoon fishing gears. The studies involved 400 reporting pop-up satellite archival tags and 64 reporting acoustic (ultrasonic) tags. Despite fish being captured, tagged, and released under widely disparate conditions, locations, and gear types, Fr was homogeneous among species. Variability in Fr was principally due to random sampling error within studies with no evident patterns. Fifteen studies (33% of tags) indicated no mortality, and the overall summary effect size for Fr was 13.5% (95% CI: 10.3%–17.6%). Since the random-effects model decomposed to a fixed-effect model when the between-studies variance T2 = 0.00, results were confirmed using exact nonparametric inferential tests and sensitivity analyses. Our results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.

No abstract

No abstract

Pacific bluefin tuna Thunnus orientalis (PBFT) play important economic and ecological roles in the western Pacific Ocean. We currently lack basic information on PBFT foraging that would facilitate ecologically informed recovery strategies for this species. We used stable isotope analysis to investigate recent (previous ~1.5 yr based on isotopic turnover rate) trophic ecology of 261 giant (>180 cm), sexually mature PBFT entering their major spawning grounds off Taiwan. We performed amino acid-compound specific isotope analysis (AA-CSIA) on a subset of PBFT and select prey to assess the trophic position of PBFT in the western Pacific and to validate putative recent trans-Pacific migration from the eastern Pacific Ocean. Bayesian isotopic mixing model results suggested recent PBFT foraging off eastern Japan and in the Kuroshio-Oyashio transition region, with minimal inputs from the Sea of Japan and Taiwan waters. PBFT did not appear to feed primarily on zooplanktivorous forage fish (e.g. sardine, anchovy) but on higher trophic-level prey including mackerels, squids, and pomfrets. AA-CSIA confirmed a high trophic position (> 5) of PBFT in this region and identified putative recent trans-Pacific migration of 2 individuals. This study identifies the prey base that sustains giant PBFT before migrating to spawning grounds off Taiwan and sets the stage for future studies comparing the movements and ecology of PBFT in the western Pacific Ocean.