243 



Abstract.— This study examined the 

 relative rates of billfish bycatch and 

 target species catch by areas ( r\ 2°, and 

 5 latitude and longitude) and months 

 m the catch data reported in mandatoi-y 

 log books kept by U.S. pelagic-longline 

 fishermen in order to identify potential 

 time-area strata that could reduce bill- 

 fish bycatch. The 1986-91 mean per- 

 centages identified month-area strata 

 with high percentages of sailfish and 

 marlin bycatch and marlin only bycatch. 

 The analyses indicated that the elimi- 

 nation of effort in cells selected accord- 

 ing to percentages of billfish in the 

 catch could have reduced the 1986-91 

 billfish bycatch by 509; and the target 

 species from 13.9 to 19.2%, depending 

 on the spatial resolution employed. The 

 corresponding analysis of marlin only 

 indicated a 509f reduction in marlin 

 bycatch could have been attained and 

 a 16.4-20.7'? reduction in the target 

 species catch. The time-area closures 

 identified in the 1986-91 logbook data 

 were applied to the data for 1992-95 

 and provided a test of the spatial and 

 temporal stabilities of these results. For 

 the evaluation of sailfish and marlin 

 combined, the reductions in both bill- 

 fish bycatch and target species catches 

 averaged less than the predicted val- 

 ues, but in all cases billfish were selec- 

 tively protected. For the evaluation of 

 marlin only, the reduction of sailfish 

 bycatch was less than the predicted 

 amount and the reduction of the target 

 species was slightly greater than the 

 predicted value. The agreement be- 

 tween the predicted level of protection 

 for billfish or marlin and the mean 

 value for the 1992-95 test period in- 

 creased with increasing size of the grid. 

 At the 5'cell size, the mean reduction 

 was 22.8% for the targeted species and 

 48.6% for marlin (compared with pre- 

 dicted values of 20.7 and 50% respec- 

 tively). These results suggest that time 

 and area restrictions on fishing could 

 significantly reduce the bycatch of 

 billfishes in the pelagic-longline fish- 

 eries without equivalent reductions in 

 the catch of target species. 



An analysis of the possible utility of time-area 

 closures to minimize billfish bycatch by 

 U.S. pelagic longlines 



C. Phillip Goodyear 



415 Ridgewood Road 



Key Biscayne, Florida 33149 



E-mail address phiLgoodyear g email msn com 



"Manuscript accepted 22 June 1998. 

 Fish. Bull. 97:243-255 (1999). 



The U.S. Fisheries Management 

 Plan for Atlantic Billfishes ( sailfish, 

 blue and white marlin, and spear- 

 fish) reserves billfish stocks for 

 recreational use; their commercial 

 hai^vest by U.S. fishermen has been 

 prohibited since the plan became 

 effective in 1988 (SAFMC, 1988). 

 The most recent stock assessment 

 for billfishes found that, over the 

 Atlantic as a whole, blue and white 

 marlin stocks are seriously over- 

 fished (Anonymous, 1996). Their 

 stocks were at about 21 and 24%, 

 respectively, of the biomass needed 

 to support maximum sustainable 

 yield ( MSY) at the beginning of 1996 

 (Anonymous, 1996). Fishing-in- 

 duced mortality was estimated to be 

 3.19 times higher than that which 

 would produce MSY for blue mar- 

 lin, and 1.88 times higher than that 

 which would produce MSY for white 

 marlin. Most of the fishing mortal- 

 ity on these species is the result of 

 bycatch in the pelagic-longline fish- 

 eries that target other species, par- 

 ticularly tuna and swordfish. 



Many authors have promoted the 

 concept of marine reserves (also 

 called marine protected areas or 

 MPAs) as management tools to 

 enhance conservation of fishery 

 resources (Bohnsack, 1994; Shackell 

 and Wilson, 1995; Hutchings, 1995, 

 1996; Allison et al., 1998; Lauck et 

 al., 1998). Closed areas have been 

 used in many parts of the world to 

 control bycatch mortality (Alverson 

 et al., 1994). Hutchings { 1996 ) noted 

 that MPAs might have considerable 



merit in reducing bycatch when as- 

 sessed against the effectiveness of 

 other forms of regulatory control 

 such as bycatch limitations and 

 catch quotas. Often, however, the 

 concept of marine reserves is re- 

 stricted to closures of particular habi- 

 tats or portions of habitats. Kench- 

 ington (1990) noted that such 

 marine reserves would be of little 

 use for species such as billfish that 

 have both pelagic larvae and highly 

 pelagic adults. Among other options 

 for reducing bycatch, Alverson et al. 

 (1994) observed that time-area 

 control of fishing activity offers an 

 opportunity to reduce unwanted 

 bycatch. The main objective of 

 employing time— area strategies is 

 to take advantage of variation in the 

 degree of co-occurrence between tar- 

 get and bycatch species (Murawski, 

 1992). The effectiveness of such 

 controls obviously depends on the 

 degree of overlap between the 

 bycatch and the targeted species 

 (Adlerstein and Trumble, 1992). 



Cramer ( 1996 ) used logbook data 

 on U.S. large pelagic fish (data that 

 have been mandatory since October 

 1986) in order to evaluate the 

 spatial distribution of the catch of 

 undersized swordfish by the long- 

 line fishery in strata of 1° latitude 

 and longitude by season and area. 

 Her study evaluated the implica- 

 tions of removing time-area strata 

 with high swordfish discard rates on 

 the total catch of the longline fish- 

 ery. The present study uses the same 

 data set to evaluate the degree of 



