Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,11/7/2009,#,按一下以編輯母片標題樣式,按一下以編輯母片,第二層,第三層,第四層,第五層,*,按一下以編輯母片,第二層,第三層,第四層,第五層,*,按一下以編輯母片標題樣式,Exploitation of small tunas by a purse-seine fishery with fish aggregating devices and their feeding ecology in an eastern tropical Atlantic ecosystem,F.M,nard,A.Fonteneau,D.Gaertner,V.Nordstrom,B.Stquert,and E.Marchal,ICES Journal of Marine Science,57:525-530.2000,圍網使用人工聚集器對於小型鮪類的開發及在熱帶東大西洋攝食食性之研究,Reporter:謝佳樺,第1页，共29页。,What is a FAD？,第2页，共29页。,For centuries,men have noticed that fish tend to gather around objects floating on the surface of the ocean,such as logs,debris,etc.This natural phenomenon has been exploited by fishermen for a long time to help them detect and catch fish.Fishermen then started to build artificial floating objects(buoys,rafts,etc.).,第3页，共29页。,WCPFC,WCPFC,WCPFC,第4页，共29页。,(FADIO/IRD-Ifremer/M.Taquet),(FADIO/IRD-Ifremer/D.Itano),(FADIO/IRD-Ifremer/D.Itano),(FADIO/IRD-Ifremer/D.Itano),第5页，共29页。,Western and Central Pacific Fisheries Commission,SCG2,a)FADs increase the efficiency of purse seine effort for tuna including skipjack.,圍網漁業使用FAD作業會提昇鮪類捕獲效率,b)The species composition of purse seine sets on floating objects(including FADs)is different to those on unassociated tuna schools.In particular the proportion of bigeye tuna in the catch is much higher for FAD-sets than unassociated sets,圍網使用FAD補獲之漁獲物，其魚種組成及混獲種類較捕撈浮水群複雜，特別是大目鮪幼魚混獲比率會提高,c)Purse seine and other fishing around floating objects results in juvenile bigeye tuna being fished by multiple gears.,大目鮪幼魚隨漂浮物洄游，造成多種漁法可捕獲大目鮪幼魚,d)The deployment of FADs has compounded the difficulties of assessing CPUE trends for purse seine fisheries and hence undertaking stock assessment for skipjack,bigeye and yellowfin,tuna,.FAD的使用導致評估圍網漁業CPUE變動趨勢的準確度，並致使無法準確估計正鰹、大目鮪、及黃鰭鮪的資源,e)Purse seine sets around floating objects have much higher catches of non-target species(both,in terms of species diversity and total weight)than purse seine sets on unassociated tuna schools.,圍網使用漂浮物捕撈鮪類，其非目標魚的比例增加,f)FADs may alter the movements,feeding and other behaviours of tuna resulting in a range of either negative impacts(e.g.tuna may become“trapped”in unproductive waters,on small and/or large spatial and temporal scales,reducing growth and possibly increasing mortality)or positive impacts(e.g.FADs may provide additional meeting points that assist in schooling and spawning).,FAD可能會改變鮪類洄游、攝食及其他行為，使在FAD周圍洄游魚群成長減緩及死亡率增加，而對資源產生負面影響;但FAD的聚集效果使魚群容易成群並增加生殖機會,Impacts on fisheries,第6页，共29页。,Why do fish aggregate under FADs?,Hypotheses on FADs,1.Shelter from predator,:The object can be used by the prey as a refuge.,2.Concentration of food supply,:A floating object or a seamount aggregates prey in,its close vicinity on which large fish could feed.,3.Indicator log,:Natural floating objects are often indicators of productive areas.,4.Spatial orientation,:Floating objects,underwater structures or seamounts provide,spatial references around which fish can orient in the otherwise,unstructured pelagic environment.,5.Meeting point,:Tuna can make use of floating objects to increase the encounter,rate between isolated individuals or small schools and other,schools,to form larger schools.,From:FADIO,第7页，共29页。,Outline,Background,Objectives,Material&Method,Result,Discussion and Conclusions,第8页，共29页。,Background,第9页，共29页。,1.There had been no surface fishing activity in the area until 1975.,Since 1991,fishing operations on schools of tuna associated with,FADs has become widespread and this offshore area has developed,into a major fishing zone.,Background,第10页，共29页。,Figure 1.Mean annual catch(t)associated with FADs per 1 square of yellowfin,skipjack,and bigeye,19911996.,Background,第11页，共29页。,Background,第12页，共29页。,Objectives,第13页，共29页。,To,give an overview of the FAD tuna purse-seine fishery in the SSA.,To estimate the by-catch using scientific observer data collected during 1998.,To,describe the feeding ecology of tunas associated with FADs based on stomach content data.,Objectives,第14页，共29页。,Material&Method,第15页，共29页。,1.Fishery data were obtained from logbooks of purse seiners operating in the Eastern Atlantic Ocean from 1991 to 1997.,2.We used data obtained during the European Union bigeye research program by French scientific observers to estimate by-catch and discards generated by FAD fishing during 1998.,3.The length of each fish sampled was measured and the stomach was preserved in formalin or deep-frozen.Stomach contents were sorted,identified to the lowest possible taxa,counted,and weighed.,Material&Method,第16页，共29页。,Results,第17页，共29页。,1.Purse-seine catches in South Sherbro area,Mean FAD catch per fishing season represented 27000 t of the total average catch of 40000 t in the SSA(1991-1997),Fig 2.Monthly mean purse-seine catches in the South,Sherbro area(bars)and proportion of FAD-associated catches,(line).,Results,第18页，共29页。,Fig 3.Size distribution of catches of skipjack and of yellowfin