LAIRS iind LYNN SEASONAL MIGRATION OF THUNNUS ALALUNC I 



being taken before the vessel departed the area on 

 5 June. The 1955 scouting effort may have been 

 too early by a matter of days to weeks to locate 

 substantial numbers offish. In 1957, a BCF fishery 

 research vessel (John R. Manning! scouted to the 

 north and east of this area in late June (Callaway 

 and McGary 1959). Small to modest catches of 

 albacore were made by trolling and in gill net sets 

 in and about the Transition Zone, but the area 

 which we have found to have a center of high 

 relative abundance was not scouted. 



Extension in Space and Time of 

 U.S. Albacore Fishery 



The cooperative NMFS-AFRF albacore re- 

 search surveys have demonstrated the feasibility 

 of extending the U.S. fishery for albacore in space 

 and time. Albacore were caught by chartered 

 fishing vessels in commercial concentrations con- 

 siderably farther offshore than where the albacore 

 fishery has traditionally taken place and up to 6 

 wk prior to the usual beginning of the fishing 

 season. Noncharter commercial albacore fishing 

 vessels, attracted to the early season offshore 

 fishery by the research survey findings, have 

 begun operating in this fishery in increasing 

 numbers. 



While fishing results of the AFRF-chartered 

 and the nonchartered fishing vessels indicate that 

 commercial amounts offish can be caught earlier 

 and farther offshore than the usual fishing season, 

 additional experience is needed to examine the 

 variability of this extension of the fishery, espe- 

 cially in terms of timing and availability, in order 

 to judge properly whether it can provide a depend- 

 able contribution to the U.S. fishery. If in the 

 long-run the early season offshore fishery proves 

 viable, its development could be an important fac- 

 tor in reducing annual fluctuations in the catch of 

 albacore. According to Clemens (1962) large an- 

 nual fluctuations in catch are a prominent feature 

 of the U.S. albacore fishery. Stabilization of catch 

 among years could contribute significantly to the 

 proper utilization and ultimately to the effective 

 management of the resource. 



The fishing success by charter and noncharter 

 albacore commercial fishing vessels in 1972-74 is 

 in contrast to an earlier attempt to establish com- 

 mercial fishing in waters offshore from where the 

 U.S. fishery has historically operated. According 

 to McGary et al. (1961), an unsuccessful gill net 

 and trolling effort was made in the summer of 



1958 by a chartered commercial fishing vessel in 

 areas of the central North Pacific where albacore 

 were caught during research surveys conducted in 

 summers of 1955 and 1956. The failure to catch 

 albacore in amounts sufficient to support commer- 

 cial fishing may have been an accidental event 

 related to intense anomalous oceanic conditions 

 which occurred ocean-wide and affected numerous 

 fisheries in 1957-58 (Sette and Isaacs 1960). 



Association of Shoreward Albacore 



Migration With Transition Zone 



and Possible Mechanisms 



Shoreward Migration and Transition Zone 



Based on association of albacore distribution 

 and relative abundance with the Transition Zone 

 and its frontal boundaries, we conclude that the 

 shoreward migration of albacore is linked to the 

 Transition Zone and that variations in the pattern 

 of migration occur in response to variations in the 

 character and development of the Transition Zone 

 and its frontal structure. When the Transition 

 Zone is narrow and its fronts are well developed, as 

 in 1972 and 1973, the migration pattern of the fish 

 is narrow and relatively well defined. In contrast, 

 when the Transition Zone is broad and its fronts 

 weakly formed, as in 1974, the migration pattern 

 offish is wide and less well defined. 



There is also some suggestion that the strength 

 and continuity of the Transition Zone fronts in 

 offshore waters may affect the timing of arrival of 

 fish in nearshore waters. When the fronts are well 

 developed, fish appear to aggregate in their vicin- 

 ity, resulting in a tendency for the fish to remain in 

 offshore waters for periods of time that delay their 

 arrival in the nearshore fishing grounds. How- 

 ever, when the fronts are weak the fish appear to 

 move through offshore waters with less delay and 

 arrive earlier in nearshore waters. Initial showing 

 offish in nearshore waters during the years of the 

 surveys supports this speculation. The nearshore 

 commercial fishery and sport fishery off southern 

 California commenced several weeks later in 1972 

 and 1973 than in 1974. 



Possible Mechanisms tor Association of 

 Albacore With the Transition Zone 



The mechanisms responsible for the relation- 

 ship between albacore and the Transition Zone 

 and its frontal boundaries may result from a 



817 



