Analysis On The Effect Of Fish Aggregation Devices(FAD)measures In The Western And Central Pacific Ocean

Tuna and other pelagic fish can be attracted by floating objects to form floating-object-associated school.Taking advantage of this behavior,drifting fish aggregation devices(FAD)were developed to attract fish to form aggregations.In the Western and Central Pacific Ocean,skipjack tuna Katsuwonus pelamis and adult yellowfin tuna Thunnus albacores were the main species in Fish Aggregation Devices(FAD)sets,meanwhile juvenile bigeye tuna Thunnus obesus and yellowfin tuna were two major bycatch species by FAD.On the one hand,FAD can greatly improve fishing efficiency and increase the output,which made their application rapidly popularized and developed in the global tropical waters.But on the other hand,the increase of the amount of FAD had a potential ecological impact on the tuna stock,and it also seriously threatened juvenile bigeye tuna and yellowfin tuna in the western and western Pacific,and now it has caused bigeye tuna appeared be overfished.That was why the Western and Central Pacific Fisheries Commission(WCPFC)had developed several conservation and management measures about FAD moratorium.The history of Chinese tuna purse seiners was relatively short,and most of their fishing vessels were second-hand vessels.In addition,captains were lack of fishing experience,that was why they preferred to use FAD to catch associated schools because there was a high rate of empty net when fishing for free swimming schools.Therefore,these conservation and management measures about FAD moratorium propoesd by WCPFC in recent years may have a serious impact on Chinese tuna purse seiners.Our study mainly focus on the following three issues:(1)The impact of FAD moratorium measures on fishing efforts of Chinese tuna purse seiners;(2)The impact of FAD moratorium measures on non-target species(i.e.bigeye tuna)catches;(3)The impact of FAD moratorium measures on target species(i.e.skipjack tuna)catches.This study indicated that :(1)In this study,the fishing effort of Chinese tuna purse seiners was measured by the number of operating days and fishing nets,both of which can effectively reflect the size of the fishing vessels.We also used some other indexes such as the proportion of associated school sets and monthly associated school school sets per vessel to compare the changes in fishermen’ operating patterns during the study period.This study indicated after 2012,the level of associated school sets of Chinese tuna purse seiners did decrease,which may be the result of the extension of FAD moratorium by one month from 2013.Although Chinese purse seiners had shown some discomfort in the face of the measure of extending FAD moratorium by one month,they still actively adjusted their fishing strategy to increase the rate of searching for free swimming schools to counteract the negative impacts of restriction on fishing efforts by FAD moratorium.In addition,during the study period,the average number of associated school sets after FAD moratorium were higher than that before FAD moratorium.These phenomena may be due to FAD and other floating objects had a good fish gathering effect under the long moratorium,which encouraged fishing vessels to prefer to catch associated schools after FAD moratorium.(2)The main purpose of the FAD moratorium measures was to protect the juvenile bigeye tuna in the Western and Central Pacific Ocean and to improve their status of being overfished.So,it was an important indicator to assess the effectiveness of the measure by determining whether the catch level of juvenile bigeye tuna declined.In order to evaluate the impact of FAD moratorium measures on bigeye tuna catches,bigeye tuna was divided into two categories: juvenile bigeye tuna and adult bigeye tuna(the weight of juvenile bigeye tuna were less than or equal to 9 kg,while that of adult bigeye tuna were more than 9 kg).The analysis indexes included the proportion of juvenile bigeye tuna accounted for the total catches of bigeye tuna,average catch per vessel and average catch per set.The results showed that since 2012 the proportion of juvenile bigeye tuna accounted for the total catches of bigeye tuna has been decreasing,and regardless of the total bigeye tuna or the juvenile bigeye tuna,their average catch per vessel and average catch per set both have been declined,in particular during FAD moratorium,the decline was particularly pronounced.Besides,the average catch per vessel and average catch per set of bigeye tuna increased dramatically in the first month at the end of the FAD moratorium(i.e.,November)from 2013 to 2016.Based on the above results,we support that the FAD moratorium has a certain effect on bigeye tuna catches of Chinese tuna purse seiners.(3)As a result of skipjack tuna cannot be isolated from associated schools,whether the FAD moratorium will have a negative impact on skipjack tuna catches,which has been in good resource condition,while reducing juvenile bigeye tuna catches,has become another issue of concern.The proportion of skipjack tuna accounted for the total catches,average catch per vessel and average catch per set were analyzed to assess the impact of FAD moratorium measures on skipjack tuna catches.The results indicated that the proportion of skipjack tuna accounted for the total catches of the Chinese purse seiners from 2012 to 2016 were more than 80%,that represented skipjack tuna was always the primary target species in purse seine fishery.After 2012,we notably observed a decrease both in the average catch per vessel and per set of skipjack tuna,that maybe relate to the extension of FAD moratorium measures.In addition,during the study period,the average catch per vessel and average catch per set after FAD moratorium were both higher than that before FAD moratorium.Furthermore,both of them approached their highest level in the first month at the end of the FAD moratorium.Based on the above results,we support that the FAD moratorium has a negative effect on skipjack tuna catches of Chinese tuna purse seiners.