STEVENSON and CARRANZA: MAXIMUM YIELD ESTIMATES FOR OPISTHONEMA SPP. 



Table 2. — Annual 1968-79 catch, effort, catch per unit effort, 

 and average effort statistics for three species of thread herring 

 captured on the Pacific coast of Costa Rica. Catch and effort data 

 were compiled from sales receipts. Source: Oficina de Pesca, 

 Ministerio de Agricultura y Ganaden'a, Puntarenas, Costa Rica. 



Rican vessels and sold for canning in these two 

 ports. Effort was estimated from sales receipts as 

 the number of calendar days at sea and recorded as 

 the difference between the dates of departure and 

 arrival in port. One day at sea was considered to 

 include only 12 daylight hours since no fishing was 

 conducted at night. Effort measurements included 

 any daylight time spent in transit to and from 

 port, time actually spent setting and retrieving 

 the net,, time spent searching for schools of fish, 

 and any time lost for vessel repairs or other ac- 

 tivities unrelated to the capture offish. 



Some information on the division of total effort 

 was available from Ministry of Agriculture 

 biologists who observed vessel activities during 

 five fishing trips in the Gulf of Nicoya during Au- 

 gust and September 1980 (Table 3). During a total 

 of 95 h absent from port, 60 h (63%) were spent 

 searching for fish, 23 h in setting and retrieving 

 the net, and 12 h were lost in transit and other 

 activities unrelated to fishing. An average of 8.6 h 

 were spent working per calendar day. The fourth 

 trip was the most productive trip in terms of catch 



per day, catch per hour search, and catch per total 

 hours, but the first and second trips were the most 

 productive in terms of catch per hour fishing. 

 These observations tended to confirm the assump- 

 tion that search time was the most significant 

 component of total effort and indicated that catch 

 per day, the index of CPUE (catch per unit effort) 

 used in this assessment, compared more closely to 

 catch per hour search than to catch per hour fish- 

 ing with the net. Although these observations 

 were recorded for a very short period of time and 

 did not represent average fishing conditions for 

 the entire fishery during that time, they do give an 

 idea of how time at sea was apportioned for vessels 

 fishing close to Puntarenas during trips of 2-3 d 

 duration in 1980 when catches were poor. 



The original 1974-79 effort data (Table 2) were 

 adjusted to account for a presumed increase in the 

 proportion of a 12-h day spent searching for fish as 

 stock abundance declined and an improved cap- 

 ture efficiency associated with the construction of 

 larger, more powerful vessels using larger nets. In 

 the absence of reliable information on the decline 

 in resource availability or increased vessel fishing 

 power, the standardization procedures which were 

 applied were very approximate, but served in some 

 degree to counteract the probable underestima- 

 tion of real fishing effort during the later years of 

 the fishery as measured simply by the number of 

 days at sea. The year 1974 was selected as the 

 critical year to initiate effort standardization 

 since it was in 1974 that the fleet, in response to 

 declining yields in the Gulf of Nicoya, expanded 

 operations in earnest to more distant fishing 

 grounds (Table 4) and increased in size from five 

 active vessels to seven. The fleet continued to 

 exploit more distant fishing grounds during sub- 

 sequent years and expanded to nine active vessels 

 in 1975-77. Most of the larger vessels were first 



Table 3.— Detailed catch and effort information recorded by observers aboard thread herring vessels fishing 

 in the Gulf of Nicoya, Costa Rica, during Augu.st and September 1980. Source; Oficina de Pesca. Ministerio 

 de Agricultura y Ganaderia, Puntarenas, Costa Rica. 



'Calendar days absent from port. 



^Estimated by captain. 



^Two days were spent tuna fishing. 



"Trip terminated early morning of day 3 due to equipment failure. 



693 



