Application of Numerical Simulation for Analysis of Sinking Characteristics of Purse Seine

This study applies the mass-spring system to model the dynamic behavior of a submerged net panel similar to the shooting process in actual purse seine fishing operation. Modeling indicates that there is insufficient stretching with the net panel under the floatline in the prophase of the shooting process. Sinkers at different locations along the leadline descend successively after submergence, and the sinking speed decreases gradually with elapsed time until attainment of a stable state. Designs with different current speeds and sinker weights are executed to determine the dimensional shape and sinking characteristics of the net. The net rigged with greater sinker weight gains significantly greater sinking depth without water flow. Compared with the vertical spread of the net wall in static water, the middle part of the netting presents a larger displacement along the direction of current under flow condition. It follows that considerable deformation of the netting occurs with higher current speed as the sinkers affected by hydrodynamic force drift in the direction of current. The numerical model is verified by a comparison between simulated results and sea measurements. The calculated values generally coincide with the observed ones, with the former being slightly higher than the latter. This study provides an implicit algorithm which saves computational loads for enormous systems such as purse seines, and ensures the accuracy and stability of numerical solutions in a repetitious iteration process.

Evaluation of FAD-associated purse seine fishery reduction strategies for bigeye tuna (Thunnus obesus) in the Indian Ocean

In the Indian Ocean, bigeye tuna supports one of the most important fisheries in the world. This fishery mainly consists of two components: longline and purse seine fisheries. Evidence of overfishing and stock depletion of bigeye tuna calls for an evaluation of alternative management strategies. Using an age-structured operating model, parameterize dwith the results derived in a recent stock assessment,we evaluated the effectiveness of applying constant fishing mortality (CF) and quasi-constant fishing mortality (QCF) strategies to reduce fishing effort of purse seining with fish aggregating devices (FADs) at different rates. Three different levels of productivity accounted for the uncertainty in our understanding of stock productivity. The study shows that the results of CF and QCF are similar. Average SSB and catchduring simulation years would be higher if fishing mortality of FAD-associated purse seiningwas reduced rapidly. The banning or rapid reduction of purse seining with FAD resulted in a mean catch, and catch in the last simulation year, higher than that of the base case in which no change was made to the purse seine fishery. This could be caused by growth overfishing by purse seine fisheries with FADs according to the per-recruit analysis. These differences would be more obvious when stock productivity was low. Transferring efforts of FAD-associated purse seining to longline fisheries is also not feasible.Our study suggests that changes are necessary to improve the performance of the current management strategy.

The effectiveness of light emitting diode(LED)lamps in the offshore purse seine fishery in Vietnam

Fishing with artificial light has become one of the most advanced,efficient,and common methods for the night-time purse seining in Vietnam.This study evaluated the radiation spectrum,CIE chromaticity coordinates,correlated color temperature(CCT),catch rate,fuel consumption,and CO_(2)emissions when using Light emitting diode(LED)lamps(0.196 kW)in comparison with the use of metal halide(MH)lights(1 kW)in the offshore purse seine fishery in Quang Tri province,Vietnam.The fishing efficiency of the purse seine fishing boats using LED lamps has increased 1.58 times in catch rate than MH lights,although the energy consumption of LED lamp is 4 times smaller.Fuel consumption of boats per trip using LED lamps was one third of that using MH lights.The use of LED reduced the radiation spectrum,especially the intense UV radiation which negatively affects the health of fishermen.This study also showed the potential of CO_(2)emission reduction up to 1.09 tons of CO_(2)per trip per boat from the use of LED lamps in the offshore purse seine fishing boats.

Use of light-emitting diode(LED)lamps in combination with metal halide(MH)lamps reduce fuel consumption in the Vietnamese purse seine fishery

The use of high-power lights during night-time purse seining is common in Vietnam.Typically,metal halide(MH)lamps are used in the commercial fishery to attract fish,however these lights require more energy,have a shorter lifespan,and lower chromatic performance than light emitting diode(LED)lamps.This study examined catch efficiency and fuel consumption when using LED lamps in combination with reduced numbers of MH lamps(10.24 kW),compared to conventional lighting(28.6 kW),used during purse seining off the coast of Ninh Thuan province,Vietnam.The economic performance associated with using LED lamps in this fishery was also assessed.We found no significant differences in catch rates between the different light treatments,however fuel consumption was significantly reduced.Fuel consumption per nightly trip using LED with MH lamps was 70.8 l(11.1 l/h)compared to114 l(17.45 l/hr)using MH lamps alone,an estimated 37.9%reduction in fuel consumption.An investment in LED lamps by a fishing enterprise will require additional initial costs,however our analysis revealed the financial break-event point can be reached after approximately 101 nightly trips when the fuel price is at the 2015 level of USD$0.74 per l.Fishing enterprises can increase their profitability,and reduce CO2 emissions,by using LED lamps in the Vietnamese purse seine fishery.