683 



Abstract— Billfishps aro a component 

 ofoO'shore ecosystems; thus it is impor- 

 tant to quantify the impact of the tuna 

 fishery on these species in the world's 

 ocean. The aim of this study was to 

 assess the bycatch of billfishes gener- 

 ated by the tropical tuna purse-seine 

 fishery in the eastern Atlantic Ocean. 

 Information on bycatch was collected by 

 obser\'ers at sea during the European 

 Union Bigeye Program. With a total of 

 62 obser\ers" trips, conducted on Span- 

 ish and French vessels between June 

 1997 and May 1999. this project is the 

 biggest observer program ever carried 

 out in the European tuna purse-seine 

 fishery. This study showed that billfish 

 bycatch by the purse seiners is very 

 low (less than 0.021^:^ of the total tuna 

 catches and less than 10*^; of the total 

 billfish catches currently reported). A 

 Monte Carlo simulation was performed 

 to account for some uncertainties in the 

 fishing strategies of purse seiners oper- 

 ating in this ocean. One of the findings 

 of this study indicated that the tempo- 

 rary moratorium on fishing with FADs 

 (fish aggregating devices), adopted by 

 the European purse-seine fishery in 

 the eastern Atlantic Ocean, produced 

 a decrease in incidental catches of mar- 

 lins from 600-700 metric tons (t) to less 

 than 300 t. In contrast, this trend was 

 reversed for sailfishes, for which the 

 bycatch increased from 25 t to 45 t. The 

 difficulty of defining indices that express 

 the conservation status in marine fishes 

 and that gauge key ecosystem parame- 

 ters and the need to promote an ecosys- 

 tem approach for large-pelagic-resource 

 management which takes into account 

 biologic and socioeconomic criteria are 

 brieflv discussed. 



Bycatch of billfishes by the European tuna 

 purse-seine fishery in the Atlantic Ocean 



Daniel Gaertner 



Frederic Menard 



Carol Develter 



IRD (UR 109) Centre de Recherche Halieutique Mediterraneenne et Tropicale 



B.P 171 



34203 Sete cedex, France 



E-mail address (for D Gaertner) gaertner(Siird fr 



Javier Ariz 



Alicia Delgado de Molina 



lEO, Centre Oceanogralico Canarias 



Apdo 1373 



Santa Cruz de Tenerife 



Islas Cananas, Spam 



Manuscript accepted 27 May 2002. 

 Fish. Bull. 100:683-689 (2002). 



In the spirit of the code of conduct for 

 responsible fisheries it is important to 

 quantify discards and bycatches taken 

 by the main fishing fleets in the world's 

 ocean. Despite recommendations made 

 by different fishery agencies, such as 

 the tuna commissions, this information 

 is rarely reported by skippers in their 

 commercial logbooks. Thus the level of 

 catches of billfishes taken incidentally 

 by the tropical tuna purse-seine fishery 

 is not vifell-known. In contrast to the 

 recreational fishery, or to some specific 

 small-scale fisheries, billfishes are not 

 targeted by the purse-seine fishery but 

 they can be taken incidentally during 

 the setting operation. In the eastern 

 Atlantic Ocean, parts of bycatch, includ- 

 ing billfishes, are kept and are sold 

 in the local African fish market (Ro- 

 many et al., 2000). 



The purpose of this study was to es- 

 timate the amount of billfish taken as 

 bycatch by fishing modes (i.e. by FAD 

 [fish aggregating devices] sets, school 

 sets [sets without the use of FADs], and 

 seamount sets) and as bycatch by the 

 Spanish and the French purse seiners 

 in the eastern Atlantic Ocean. Because 

 bycatch information is not recorded 

 in commercial purse seiner logbooks, 

 observations collected by scientific ob- 

 servers aboard purse seiners appeared 

 to be a useful way to assess the amount 

 of bycatch taken by this fleet. Although 

 the European Union Bigeye Program 



focused on the study of the increase in 

 catch of bigeye tuna (Thunnus obesus) 

 by the European tuna-purse seiners in 

 the Atlantic Ocean (Ariz and Gaertner, 

 1999), information on bycatch was also 

 collected by observers on these purse 

 seiners. We used this data set to es- 

 timate the bycatch of billfish in the 

 European purse-seine fishery. These 

 estimates will contribute to the calcu- 

 lation of the total bycatch of billfishes 

 taken in the Atlantic Ocean. 



Materials and methods 



Data 



A total of 62 observer trips (44 for the 

 Spanish fleet and 18 for the French 

 fleet) were conducted opportunistically 

 between June 1997 and May 1999, 

 except from November 1998 through 

 January 1999, a period when there 

 was a moratorium on the use of FADs 

 in fishing operations. In spite of this 

 limitation, this project was the largest 

 observer program ever carried out in 

 the European tuna purse-seine fishery 

 (a total of 2706 fishing days, with 1884 

 observed sets). The catch of commercial 

 tunas reached 34,693 t, whereas dis- 

 cards (composed mainly of small tuna 

 species or of juveniles of commercial 

 tuna species) were estimated at about 

 737 t and total bycatch (billfishes. 



