Abstract
A rising trend in catches of non-targeted species have recently been observed in major fisheries including tuna longline fisheries, yet most of these species are unmanaged. Given their importance to local economies and sustainable livelihoods in many coastal countries, there is a need to provide plans for their management. However, most non-targeted species are data-limited which hampers the use of conventional assessment methods. This study applied a novel length-based Bayesian biomass estimator (LBB) method to five species from the Atlantic and Pacific Oceans. Estimates of growth, length at first capture and present relative biomass (B/B0, B/BMSY) of these species were gotten from length-frequency (LF) data. Of the ten populations (5 species from 2 regions) assessed, one has collapsed, one grossly overfished, and three overfished. Six populations had the ratio of mean lengths at first capture (Lc) on the mean length at first capture, which maximizes the catch and biomass (Lc_opt) greater than unity, indicating the presence of large-sized specimens in the populations. Two species faced intense fishing pressure in the Atlantic while one stock collapsed in the Pacific Ocean. Our results indicate that even non-targeted pelagic can be prone to over-exploitation. Therefore, there is an urgent need for stakeholders and fisheries managers to focus on improving fishery statistics and to conduct periodic monitoring of stock status indicators for non-target species.
Highlights
Most commercial fisheries target species of high economic values such as tunas and swordfish
Results obtained from the length-based Bayesian biomass estimator (LBB) analyses show that this model fits well to all 10 populations from the Atlantic and Pacific Oceans (Figures 1, 2 and Table 2)
The stock of this species was in a good state in the tropical eastern Atlantic ocean (F/M = 0.3, B/B0 = 0.67, and B/BMSY = 1.8), in the central Pacific Ocean, its stock was witnessing slight overfishing (F/M = 1, B/B0 = 0.35 and B/BMSY = 0.96)
Summary
Most commercial fisheries target species of high economic values such as tunas and swordfish. The fishing gears (longlines, purse seines) used to capture fish specimens do capture targeted species and harvest non-targeted (bycatch) species including sharks, small pelagic species (scombrids) and many others Some of these bycatches are at times discarded or Assessment 5 Species Using LBB retained without recording their catch or biological information. As indicated in the last FAO (2019) report, only around 12% of the world’s fisheries are properly managed or have sophisticated stock assessments for management purpose These non-targeted small pelagic are most often considered to be highly abundant and assumed not suffering from population decline given that they reproduce and grow at a faster rate. Given the lack of data reported for these fisheries, conventional stock assessment approaches cannot be used to assess their stocks
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