Cook, A. F., N. E. Stacey, and R. E. Peter. 



1980. Periovulatory changes in serum Cortisol levels in 

 the goldfish, Carassius auratus. Gen. Comp. Endocri- 

 nol. 40:507-510. 



Hirose, K. 



1976. Endocrine control of ovulation in medaka (Oryzias 



latipes) and ayu (Plecoglossiis altivelis). J. Fish. Res. 



Board Can. 33:989-994. 

 Jalabert, B. 



1976. In vitro oocyte maturation and ovulation in rain- 

 bow trout (Sal mo gairdneri), northern pike (Esox lucius), 

 and goldfish (Carassius auratus). J. Fish. Res. Board 

 Can. 33:974-988. 



Kaya, C. M., A. E. Dizon, and S. D. Hendrix. 



1981. Induced spawning of a tuna, Euthynnus a/finis. 

 Fish. Bull., U.S. 79:185-187. 



Matsumoto, W. M. 



1966. Distribution and abundance of tuna larvae in the 

 Pacific Ocean. In T. A. Manar (editor), Proceedings, 

 Governor's Conference on Central Pacific Fishery Re- 

 sources, p. 221-230. State of Hawaii. 



Mazeaud, M. M., F. Mazeaud, and E. M. Donaldson. 



1977. Primary and secondary effects of stress in fish: 

 Some new data with a general review. Trans. Am. 

 Fish. Soc. 106:201-212. 



Strange, R. J., C. B. Schreck, and J. T. Golden. 



1977. Corticoid stress responses to handling and temper- 

 ature in salmonids. Trans. Am. Fish. Soc. 106:213-218. 

 Sundararaj, B. I., and S. V. Goswami. 



1977. Hormonal regulation of in vivo and in vitro oocyte 

 maturation in the catfish, Heteropneustesfossilis (Bloch). 

 Gen. Comp. Endocrinol. 32:17-28. 

 Witschi, E., and C. Y. Chang. 



1959. Amphibian ovulation and spermiation. In A. 

 Gorbman (editor), Comparative endocrinology, p. 149- 

 160. Wiley, New York. 

 Yoshida, H. O. 



1971. The early life history of skipjack tuna, Katsuwonus 

 pelamis, in the Pacific Ocean. Fish. Bull., U.S. 69:545- 

 554. 



Calvin M. Kaya 



Southwest Fisheries Center Honolulu Laboratory 



National Marine Fisheries Sennce, NOAA 



Honolulu, HI 96812 



Present address: Department of Biology 



Montana State University 



Bozeman, MT 59717 



Andrew E. Dizon 



Sharon D. Hendrix 



Thomas K. Kazama 



Martina K. K. Queenth 



Southwest Fisheries Center Honolulu Laboratory 

 National Marine Fisheries Service, NOAA 

 Honolulu. HI 96812 



ESTIMATING AND MONITORING 



INCIDENTAL DOLPHIN MORTALITY IN 



THE EASTERN TROPICAL PACIFIC 



TUNA PURSE SEINE FISHERY 



Each year the purse seine fishery for yellowfin 

 tuna, Thunnus albacares, in the eastern tropical 

 Pacific is responsible for the incidental kill of 

 thousands of small cetaceans, 1 primarily dol- 

 phins or "porpoise." Yellowfin tuna are often 

 associated with small cetaceans in this region 

 and fishermen have used this association since 

 1959 to catch tuna(McNeely 1961; Perrin 1969; 

 Fox 1978). During the purse seining operation, 

 cetaceans encircled with yellowfin tuna by the 

 net may become entangled and accidentally 

 drown. In such cases, the fishermen retain the 

 tuna and discard the cetaceans at sea. 



The Marine Mammal Protection Act of 1972 

 requires the tuna fishery to be managed so that 

 the dolphin populations are maintained at spe- 

 cific population levels and that incidental mor- 

 tality be reduced to insignificant levels. The 

 National Marine Fisheries Service (NMFS) has 

 the responsibility of monitoring the dolphin mor- 

 tality and of assessing the impact of dolphin 

 mortality on dolphin populations. NMFS carries 

 out research on the abundance and distribution 

 of dolphins, their biology, the level of incidental 

 mortality, and methods for reducing incidental 

 mortality. 



Beginning in 1971, the NMFS regularly 

 placed observers on purse seiners to collect data 

 on the incidental mortality of dolphins. Prior to 



1974, however, only a few observers were hired 

 to collect data; the amount of data collected, 

 therefore, is too small to produce a precise esti- 

 mate of total incidental mortality. Most estimates 

 from this period place the total at about 300,000 

 to 500,000 animals/yr. Estimates for 1974 and 



1975, which are more precise, are 140,000 and 

 157,000 animals killed, respectively, for the U.S. 

 fleet (Smith 2 ). 



After a U.S. District Court ruling in 1976, the 

 NMFS set an annual quota of 78,000 animals for 



'Dolphin, in this paper, is used as a general term referring to 

 all small cetaceans impacted in the fishery. Mortality or kill 

 refers to dolphin mortality incidental to the catch of yellowfin 

 tuna. The unit of fishing effort "set" is defined as a single 

 deployment of a purse seine net around an aggregation of dol- 

 phin or tuna. Tuna catches are expressed in the unit short tons, 

 as it is the most common form in which these statistics are re- 

 ported. 



2 Smith, T. D. Report of the status of porpoise stock work- 

 shop. Southwest Fish. Cent. Adm. Rep. LJ-79-41, 120 p. 



396 



