Species composition and diversity of pelagic fishes based on a longline fishery catch in the North Pacific Ocean

Evaluation of spatial-temporal variability of species composition and diversity in oceanic ecosystems is not easy because it is usually difficult to obtain sufficient data quantifying such variability.In this study,we examined pelagic species diversity indicators,species richness,Shannon-Wiener index of diversity and Hurlbert's species evenness,for fish assemblages from two areas(north and south) in the North Pacific Ocean(2°±12°N,178°E±165°W) during May±July 2008.The assemblages were based on data collected by an onboard scientific observer during a commercial longline fishing trip.The species richness and Shannon-Wiener diversity index of fish assemblages in the northern area were slightly higher than those in the southern area,although these differences were not significant(t test,P.0.05).Non-parametric multidimensional scaling and analysis of similarities indicated that there were significant differences in fish assemblages between the two areas(P,0.01).

Dynamic Simulation of Pelagic Longline Retrieval

To improve fishing gear efficiency, it is important to understand the interactions among sea current, fishing vessel, line hauler, and catches during pelagic longline gear retrieval. In this study, fishing gear configuration parameters, operational parameters, and 3 D ocean current data were collected from Indian Ocean. Dynamic models of pelagic longline gear retrieval were built using the lumped mass method and solved using the Euler-Trapezoidal method. From the results, the pulling force of line hauler exerted on the gear was 2800–3600 N. There were no significant differences(P > 0.05) between the time of the hook retrieval measured at sea and that obtained from the simulation. The absolute values of the movement velocity at representative nodes along the X, Y, and Z axes were 0.01–25.5 m s^(-1). These results suggest that the dynamic model of longline fishing gear retrieval can be used to analyze the interactions among sea current, fishing vessel, line hauler, longline gear, and catches, and to acquire the basic data for optimizing the design of the line hauler. Moreover, the model can serve as a reference to study the hydrodynamic performance of other fishing gears during the hauling process.

The Development and Operational Testing of an Underwater Bait Setting System to Prevent the Mortality of Albatrosses and Petrels in Pelagic Longline Fisheries

Longline fisheries for tunas and tuna-like species present an existential threat to many populations of albatrosses and petrels worldwide. To prevent this form of mortality we developed a new technology designed to deploy baited hooks underwater beyond the dive depths of?seabirds (6 - 10 m for the species most commonly caught). The underwater bait setter is a stern-mounted, hydraulically-operated and computer-controlled?device that catapults?baited hooks underwater in a steel capsule?connected to hydraulic winches by Spectra®rope. Baits are flushed from the capsule by water pressure through a spring-loaded bait release door. The chief engineering challenges in the developmental stageswere ensuring:?1) bait delivery?to target depths with cycle times (time from release to recovery) that were practical for fishing operations;?2) bait retention in the capsule (no drop-outs) on the descent phase of the cycle;?3) baits, upon?release at target depth, were not drawn up the water column on the capsule recovery phase (from possible hook-ups and/or suction);and?4) the retention of baits?on?hooks post-release from the capsule was not affected by the mechanical release underwater. Operational trials with the final version of the capsule yielded?satisfactory cycle times to depths of 6 - 10 m. All baits were retained?in the capsule on the descent and?released as required?at target depths (n = 606 deployments). Bait retention on hooks post release from the capsule and retention on hooks hand-set at the surface (the conventional method) were statistically indistinguishable.?The underwater bait setter is modular in construction and can be fitted to all types of vessel sterns.

Study on the catch,bycatch and discard of Chinese pelagic longline fisheries in the Atlantic Ocean

Catch,bycatch and discard information is important for the assessment and management of fisheries.Using Chinese pelagic tuna longline observer data from 2010 to 2018,we studied the catch composition in the Chinese pelagic tuna longline fisheries in Atlantic targeting bigeye tuna(Thunnus obesus)and bluefin tuna(Thunnus thynnus),and analyzed the survival status and discard rates of common bycatch species.A total of 55 species,including tunas,billfishes,sharks,sea turtles,cetaceans,seabirds,and other pelagic species,were observed.The results indicated that the catch composition of the Chinese pelagic tuna longline fishery targeting bigeye tuna was significantly different from that targeting bluefin tuna.The annual discard rates of common species decreased over this period.Discard rate by length and discard mortality for common species were varied among species.This is the first study to estimate catch,bycatch,and discard using Chinese pelagic tuna longline observer data in the Atlantic Ocean,which is important for the management of Chinese tuna longline fisheries in Atlantic Ocean.

Developing a longline/jig sentinel survey program for an area with limited monitoring and fishing efforts

Areas,such as coastal eastern Gulf of Maine(GOM),perceived to have low density of target fish species and having high density fixed gear,are often subject to low fishing pressure and not well monitored.This can lead to a shortage of information regarding the fine scale dynamics of groundfish populations.Sentinel surveys are commonly developed for such areas with little monitoring and commercial fishing activity as a cost effective way to collect relevant data for monitoring the dynamics of fish stocks.In this study,we outline an approach that utilizes information from other survey programs and pilot study for designing a survey that satisfies both the wish of fishermen participants to contribute their knowledge and experience in determining groundfish abundance and distribution and the statistical rigor required for stock assessments.Through an analysis of spatial and density distribution of groundfish populations based on data from pilot seasons of the sentinel survey and other monitoring programs,we designed a survey that has good spatial and temporal coverage and captures the spatial variability in species composition and size structure of key species.The spatially explicit data collected in the program can contribute to a better understanding of groundfish stock status in the eastern GOM.The approach,although developed for the coastal eastern GOM,is also applicable to other areas with similar issues.

Modeling the Hook Depth Distribution of Pelagic Longlining in the Equatorial Area of Indian Ocean

A survey was conducted in the equatorial area of Indian Ocean for a better understanding of the dynamics of hook depth distribution of pelagic longline fishery. We determined the relationship between hook depth and vertical shear of current coefficieney, wind speed, hook position code, sine of wind angle, sine of angle of attack and weight of messenger weight. We identified the hook depth models by the analysis of covariance with a general linear model. The results showed that the wind effect on the hook depth can be ignored from October to November in the survey area; the surface current effect on the hook depth can be ignored; the equato- rial undercurrent is the key factor for the hook depth in Indian Ocean; and there is a negative correlation between the hook depth and vertical shear of current and angle of attack. It was also found that the deeper the hook was set, the higher hook depth shoaling was. The proposed model improves the accuracy of the prediction of hook depth, which can be used to estimate the vertical distribution of pelagic fish in water column.