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

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Estimating geo-referenced fishing effort is vital to develop advice for effective fisheries management. Many studies in recent decades have attempted to obtain complete, high-resolution effort data from vessel monitoring systems (VMSs). The main challenge in this regard is to develop a classification method for differentiating fishing activities (e.g., fishing days) from nonfishing activities in VMS data. This study developed a simple, novel classification criterion for a large-scale tuna longline (LTLL) fishery that has not been studied before. LTLL operations were first explored using observer data. Three approaches were designed for developing fishing-day classification criteria, using maximizing sum of sensitivity and specificity (SS) as the major performance measure and minimizing difference of SS as a reference. At least one VMS report with speed in the range of 2–5 kn (1 kn = 1.852 km·h–1) detected during the time-of-day period of 14:00–23:00 h was recommended as the criterion for defining a fishing day. Possible explanations for the differences between the estimated fishing days from VMS data and those reported on logbooks are discussed; most causes were related to specific features of the fishery.

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The Pacific bluefin tuna (Thunnus orientalis, PBF), an iconic fisheries species, is heavily exploited and its biomass is at a historically low level. To enhance effectiveness of management and conservation, a study was initiated to examine the demographic changes of the PBF between 2002 and 2015. Annual tuna age compositions were estimated by applying an empirical age-length key, based on the ages and lengths of 892 fish, to the length frequencies observed among annual catches in the northwestern Pacific spawning grounds located near Taiwan. Ages of the spawners concentrated in 7–20-years old (range = 4–28 years), corresponding to fork lengths between 200 and 240 cm. The size and age compositions were influenced by the strong 1994 and 1996 year-cohorts, which showed a relatively high abundance in most years except 2007–2009. Between 2013 and 2015, recruits of 2005–2009 year-cohorts (age 6–10) increased in relative abundance while the strong 1994 and 1996 year-cohorts decreased as they neared the end of their lifespan. PBF smaller than 200 cm were rarely found in the tropical areas and the mean sizes of the PBF caught south of 24°N were significantly larger than those caught north of 24°N. These results suggested that the choice of spawning latitudes of the PBF was influenced by the size of spawning adults. The sex ratio of smaller (<200 cm) and intermediate size classes (200–230 cm) was female biased (50–75%) while that of larger fish (>240 cm) were male biased (62–100%). The size and age composition of the PBF was mainly influenced by the recruitment of young spawners and was less sensitive to the catch of longline fisheries. However the impact of longline fisheries on the reproductive potential of this species warrants further investigation.

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