343 Abstract–An investigation of skip- Assessment of skipjack tuna (Katsuwonus pelamis) jack tuna, Katsuwonus pelamis, spawn- ing activity was conducted to test an spawning activity in the eastern Pacifi c Ocean earlier established and widely accepted hypothesis that signifi cant spawning of skipjack does not occur in the east- Kurt M. Schaefer ern Pacifi c Ocean (EPO). Skipjack tuna Inter-American Tropical Tuna Commission ovaries were collected, from fi sh greater 8604 La Jolla Shores Drive than 50 cm in length, from commercial La Jolla, California 92037-1508 landings of purse seiners fi shing in the E-mail address:
[email protected] EPO during 1995. A total of 76 sam- ples, each consisting of approximately 25 females, were collected, processed, and analyzed. The characteristics used to classify the reproductive condition of the individual fi sh were the mean dia- meter of the oocytes of the most advanced mode and the presence or absence of residual hydrated oocytes. Results indi- cate that signifi cant spawning of skip- Skipjack tuna, Katsuwonus pelamis, however, hypothesized that “most skip- jack tuna, 50 cm or greater in length, are distributed throughout the Pacifi c jack taken by the eastern Pacifi c skip- occurs in areas of the EPO where sea Ocean in tropical and subtropical jack fi sheries originate in the central surface temperatures are equal to or waters, where they are a primary target Pacifi c.” His hypothesis was based on greater than 24°C. species of large-scale purse-seine fi sher- available evidence, at that time, from ies. Total estimated catches now exceed larval distributions, gonad indices, size one million metric tons.