FISHERY BULLETIN: VOL. 79, NO. 4 



monthly length-frequency distributions compiled 

 from commercial landings by the Costa Rican 

 Ministry of Agriculture during 1975-77. 



Attempts to determine the age and growth of 

 Opisthonema spp. based on apparent scale annuli 

 and length-frequency analyses have not produced 

 very satisfactory results, presumably since 

 growth rates and recruitment are more or less 

 continuous throughout the year. Reintjes'* re- 

 ported that few Atlantic thread herring live be- 

 yond age 4, and Sokolov and Wong^ speculated 

 that there were three adult year classes of O. liber- 

 tate within the harvestable size range ( 5-26 cm SL) 

 in the Gulf of California. Paez Barrera (footnote 3) 

 reported a minimum length at maturity of 13-14 

 cm SL for O. libertate in Mexico. Houde (1976) 

 reported that age 1 Atlantic thread herring mea- 

 sured approximately 13 cm SL. Length-frequency 

 distributions for Opisthonema spp. sampled from 

 commercial landings in Costa Rica were com- 

 monly characterized by a single predominant size 

 group at 18-20 cm SL, but occasionally included a 

 second group at 12-16 cm SL. 



Although he presented no information for Opis- 

 thonema, Beverton (1963) indicated that most 

 clupeid and engraulid species are short lived (5 yr 

 or less) and are generally characterized by high 

 growth and mortality rates. Furthermore, these 

 fish mature at relatively early ages (age at 

 maturity/maximum age = 0.30-0.37) and grow 

 very little after maturing (length at maturity/ 

 maximum length = 0.65-0.80) compared with 

 other taxonomic groups. High mortality rates (Z 

 = 0.5-3.0) can be largely attributed to the active 

 predation on these fish by man, birds, and other 

 fish. Highly variable recruitment has contributed 

 to the decline of many stocks of small pelagic fishes 

 for which recruitment appears to be independent 

 of spawning stock size over a wide range of stock 

 sizes (Murphy 1977). 



The most important thread herring fisheries are 

 conducted on the Pacific coast of Central and 

 South America. Most of the 1972-77 catch of Pacific 

 thread herring was landed in Ecuador (Table 1) 

 where landings increased by 700% during this 



■•Reintjes, J. W. 1979. A review of the clupeoid and carangid 

 fishery resources in the western central Atlantic. Inter- 

 regional Project for the Development of Fisheries in the Western 

 Central Atlantic (WECAF), 49 p. 



^Sokolov, V. A., and M. I. Wong. 1973. Informe cientlfico de 

 las investigaciones sob re los peces pela'gicos del Golfo de Califor- 

 nia (sardina crinuday anchoveta) en 1971. Inst. Nac. Pesca, Inf. 

 Cien. 2,41p. 



Table l. — Annual 1972-77 landings (thousand metric tons) of 

 Pacific thread herring in Ecuador, Panama, and Mexico. 

 Sources: FAO Yearbook of Fishery Statistics ( 1979) and In.stituto 

 Nacional de Pesca, Mexico. 



Country 



1972 



1973 



1974 



1975 



1976 



1977 



1,100 1.750 2,250 3,830 



367 201 166 234 



22 32 35 65 



1,489 1.983 2,451 4,129 



6-yr period. Panama and Mexico accounted for 

 <W7c of the total reported landings in 1976 and 

 1977. Thread herring are harvested with the 

 Pacific sardine, Sardinops sagax, in Mexico and 

 are utilized both for human consumption and for 

 fish meal. Thread herring are harvested inciden- 

 tally to the anchoveta, Centengraulis mysticetus, 

 in the Gulf of Panama and reduced to meal. 

 Thread herring fisheries do not presently exist in 

 any of the remaining Central American countries 

 except Costa Rica where, by law, the total produc- 

 tion is canned for human consumption. 



Thread herring have been harvested on the 

 Pacific coast of Costa Rica since 1968. The fleet 

 expanded steadily from a single vessel in 1968-69 

 to nine vessels in 1975. At present the fleet consists 

 of 10 vessels, although only half the fleet may be 

 active at any one time. Most of the fish landed 

 during 1968-73 were harvested in the outer Gulf of 

 Nicoya (Figure 1) and from coastal waters im- 

 mediately to the south. Purse seiners and trawlers 

 have been prohibited from fishing in the interior of 

 the Gulf of Nicoya since 1975. The fishery ex- 

 panded as far south as Golfo Dulce near the 

 Panamanian border in 1972. Total catch reached a 

 maximum of 7,500 t in 1975 and declined to about 

 5,000 t in 1978 and 1979, while total catch per day 

 at sea peaked in 1971 (Figure 2). Catch in the Gulf 

 of Nicoya peaked at 5,000 t in 1972 (Figure 3) and 

 at 2,800 t in Golfo Dulce during 1975 (Figure 4). 



The thread herring resource supports a small 

 but important industry in Costa Rica. Landings in 

 1978 accounted for 36% of all fish and shellfish 

 landed by the domestic fleet and $76,635 in ex- 

 vessel revenue. Most of the herring canned in 

 Costa Rica is sold domestically. A small quantity 

 (9% in 1977) is exported to other Central American 

 countries. There are three canning plants in the 

 country, two in Puntarenas and one in Golfito. 

 Eight of the existing 10 vessels are based in Pun- 

 tarenas. 



The objective of this study was to determine, 

 from historical catch and effort data compiled by 



690 



