FISHERY BULLETIN: VOL. 79, NO. 4 



Table 4. — Distribution of reported 1968-79 fishing effort for 

 thread herring among the three principal fishing zones on the 

 Pacific coast of Costa Rica and percent of total effort expended in 

 zones two and three. Source: Oficina de Pesca, Ministerio de 

 Agricultura y Ganaderia, Puntarenas, Costa Rica. 



'Total effort includes a small amount of fishing in zone 4 whicfi is not shown 

 in this table. 



registered in 1973 or later (Table 5). At least one of 

 the newer vessels was equipped with directional 

 sonar equipment, an addition which greatly aids 

 in the location of schools. 



Table 5. — Characteristics of purse seine vessels and gear which 

 constituted the Costa Rican thread herring fleet in 1979. Vessels 

 are ranked according to net tonnage and fall roughly into two 

 groups according to size, horsepower, and the size of the net used 

 by each vessel. Source: Oficina de Pesca, Ministerio de Agri- 

 cultura y Ganaderia, Puntarenas, Costa Rica. 



'This vessel was lost at sea in October 1979. 



Original 1974-79 effort data were adjusted (Ta- 

 ble 6) to account for increased search time by in- 

 creasing observed effort in five S'^ annual incre- 

 ments beginning in 1975 and by a constant 25% 

 annual increment to account for increased fishing 

 power beginning in 1974. The first adjustment was 

 based on the presumption that no more than 5 h in 

 an average 12-h day (or 50% of the total fishing 

 time after deducting 2 h for travel to and from 

 port) were spent searching for fish in the early 

 years of the fishery when fishing was concentrated 

 primarily in the Gulf of Nicoya (Table 4), whereas 

 9 out of 12 h ( 75% ) may have been spent searching 

 for fish in 1979, assuming that the fish were less 

 abundant and that vessels which travelled longer 

 distances to and from fishing grounds in zones two 

 and three devoted most of their daylight transit 

 time to searching. This last assumption has in fact 

 been confirmed by vessel captains. Observations 

 made aboard vessels fishing near Puntarenas in 

 1980 during only 11 d (Table 3) showed that 63% of 

 the daylight hours were devoted to searching. 

 Since catch data originally collected for individual 

 vessels and trips were no longer available when 

 this assessment was conducted, the relative fish- 

 ing power of individual vessels and the factors 

 affecting vessel performance could not be deter- 

 mined. 



Yield Analyses 



Maximum equilibrium yield {Yg) and its corre- 

 sponding effort (/s) were estimated by applying the 

 linear and exponential forms of the surplus pro- 

 duction model to annual catch and effort data 

 compiled during 1969-79. These data were col- 

 lected beginning in 1968 when fishing began and 

 represented fishing activity during an initial 

 period of high CPUE and low effort, an inter- 

 mediate period when larger vessels were built and 



Table 6. — Annual 1974-79 catch, adjusted effort and adjusted catch per unit effort ( CPUE) statistics for three species of thread herring 

 captured on the Pacific coast of Costa Rica. Original effort data were adjusted to account for a presumed 25*7^ annual increase in vessel 

 fishing power beginning in 1974 and an additional 5% annual increment to account for a presumed increase in search time per day 

 at sea beginning in 1975. 



Year 



Catch 

 Ct 

 (t) 



Original effort 



ft 



(d at sea) 



Correction factor 

 xt 



Adjusted effort 



xtft 



(standard d) 



Adjusted CPUE 



Ctlxtft 

 (f/standard d) 



Average effort 



"2(Xf/f + Xf_1^f-1) 



(Standard d) 



1974 

 1975 

 1976 

 1977 

 1978 

 1979 



'xfff in 1973 was 1.0(501 d) = 501 d. 



694 



