A rising trend in catches of non-targeted species has 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 data-limited length-based Bayesian biomass estimator (LBB) method to assess the stocks of five species from the Atlantic and Pacific Oceans. Estimates of growth, length at first capture and present relative biomass (B/B₀, B/B_MSY) of these species were gotten from length-frequency (LF) data. Of the ten populations (5 species from two 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 population 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.

The silky shark, Carcharhinus falciformis is one of the most heavily exploited sharks, being the main by-catch species in both tuna longline and purse-seine fisheries in tropical waters worldwide. Despite this severe exploitation, little is known about the species’ life history and population status. Silky sharks, like many other sharks, exhibit slow growth and low fecundity, indicating the urgency of developing assessment studies to aid in the implementation of conservation plans for their stocks. Because information on the catch and effort of this species is scarce, some length-based data-limited methods were applied in the present study to provide estimates of the status of the tropical Pacific silky shark population. As evident from the LBSPR analysis, the current spawning potential ratio (SPR) was found to be below the target reference point of SPR 40% and slightly above the limit reference point of SPR 20%. In addition, the LBB model also confirmed that this stock’s status is overfished with relatively low biomass levels. Furthermore, both models showed estimates of size selectivity at 50% and 95% that were lower than the estimated size at sexual maturity. In conclusion, the data-limited models developed in this study indicated that the silky shark stock in the tropical Pacific Ocean may be at risk of further decline. Additionally, the results show that growth and recruitment overfishing may be occurring in the silky shark’s population calling for immediate intensification of monitoring programs for these sharks as a pre-requisite to develop efficient management and conservation plans in the Pacific Ocean.

Chub mackerel (Scomber japonicus) is a major targeted species in the Northwest Pacific Ocean, fished by China, Japan, and Russia, and predominantly captured with purse seine fishing gear. A formal stock assessment of Chub mackerel in the region has yet to be implemented by the managing authority, that is, the North Pacific Fisheries Commission (NPFC). This study aims to provide a wider choice of potential models for the stock assessment of Chub mackerel in the Northwest Pacific using available data provided by members of the NPFC. The five models tested in the present study are CMSY, BSM, SPiCT, JABBA, and JABBA-Select. Furthermore, the influence of different data types and input parameters on the performance of the different models used was evaluated. These effects for each model are catch time series for CMSY, catch time series and prior of the relative biomass for BSM, prior information for SPiCT, and selectivity coefficients for JABBA-Select. Catch and CPUE (catch per unit effort) data used are derived from NPFC, while some life history information is referred from other references. The results indicate that Chub mackerel stock might be slightly overfished, as indicated by CMSY (B₂₀₂₀/B_MSY = 0.98, F₂₀₂₀/F_MSY = 1.12), BSM (B₂₀₂₀/B_MSY = 0.97, F₂₀₂₀/F_MSY = 1.21), and the base case run for the JABBA-Select (SB₂₀₂₀/SB_MSY = 0.99, H₂₀₂₀/H_MSY = 0.99) models. The results of the models SPiCT (B₂₀₂₀/B_MSY = 2.30, F₂₀₂₀/F_MSY = 0.31) and JABBA (B₂₀₂₀/B_MSY = 1.40, F₂₀₂₀/F_MSY = 0.62) showed that the state of this stock may be healthy. Changes in the catch time series did not affect CMSY results but did affect BSM. The present study confirms that prior information for BSM and SPiCT models is very important in order to obtain reliable results on the stock status. The results of JABBA-Select showed that different selectivity coefficients can affect the stock status of a species, as observed in the present study. Based on the optimistic stock status indicated by the best model, JABBA, a higher catch is allowable, but further projection is required for specific catch limit setting. Results suggested that, as a precautionary measure, management would be directed towards maintaining or slightly reducing the fishing effort for the sustainable harvest of this fish stock, while laying more emphasis on accurately estimating prior input parameters for use in assessment models.

Japanese sardine (Sardinops melanostictus) is a significant small pelagic fish and a valuable resource that plays an essential ecological role in the marine ecosystem. It is present in the far Eastern Asian maritime waters, including the Pacific Ocean, Sea of Japan, and the East China Sea. Encircling nets, particularly purse seines, are the most used fishing equipment to catch this species. Their fishing grounds are located entirely in coastal areas. Japanese sardine catches have shown varying trends over the last five decades, with a high frequency of captures occurring in the 1980s before collapsing in the early 1990s. The economic and ecological importance of this species has prompted much research, which provided additional information about their spawning migration, distribution, fisheries, and biology. This research was mostly undertaken in the Sea of Japan and its adjacent waters spanning in the north Pacific Ocean. Despite all this research and the importance of this species in its habitats and in commercial fisheries, there is a lack of a recent review presenting the status of global fisheries and biological information for this species. This paper summarizes and updates information on the global geographical distribution, biological aspects, trends in catches, stock fluctuations and assessment, and management measures of the Japanese sardine population. This paper also summarizes information related to the influence of environmental factors on the occurrence of this species and also identifies information gaps. Further research directions are also discussed in this work, which may help improve the knowledge of Japanese sardine and establish rational management measures for their conservation.