SKIPJACK VELOCITY, DWELL TIME AND MIGRATION

Apparent velocities (distance travelled/time at liberty) of tagged Pac ific skipjack tuna, Katsuwonus pelamis, observed over the 1978 to 1982 Skipjack Survey and Assessment Program (SSAP) of the South Pacific Co mmission (SPC) were very low (less than 10 cm s(-1) in 90% of observat ions) compared with the minimum swimming speed of skipjack tunas of 70 -100 cm s(-1). Such low apparent velocities are not biologically meani ngful and therefore the extrapolation of biological properties from ma thematical models, such as diffusion and advection models, based on th e tagging data is difficult, if not impossible. This paper explores al ternative approaches to the 1978 to 1982 SSAP data set. Dwell time and migration analysis indicate a north to south seasonal migratory patte rn with the skipjack home range located along an arc from the Solomon Islands, through Fiji and Samoa, to the Marquesas. Ancillary evidence supports a purposeful rather than advective migration pattern that osc illates between southern feeding areas and northern breeding areas.