ALBACORE OCEANOGRAPHY OFF OREGON — 1970 



William G. Pearcyi 



ABSTRACT 



During July 1970, albacore boats trolling surface jigs (jig boats) had record catches 

 in an area off the mouth of the Columbia River. The jig fishery declined suddenly in 

 late July and was poor throughout the remainder of the summer. No obvious oceano- 

 graphic changes were correlated with these drastic changes in fishing success. Favorable 

 water temperatures extended through August, traditionally the month of highest 

 albacore landings in Oregon. 



Bait boats, which chum with live bait, had good fishing off Oregon from mid-August 

 to October, indicating that the poor success of jig boats during this time was caused 

 by the behavior of albacore relative to surface-trolled fishing gear. It is postulated 

 that albacore descended into subsurface water in response to a change in availability 

 of their preferred prey, the saury; here they were less accessible to jig boats than 

 bait boats. Saury were common in the stomachs of albacore during periods of good 

 jig fishing and were usually the dominant food where high albacore catches were 

 made by our research vessel. 



The first albacore catches of the season were probably from an area of warm 

 temperature and low salinity representing Columbia River plume water. The subsequent 

 migration to the north appeared to be along the oceanic edge of the plume. In 

 general, high catches by boats were not within the core of the plume but in 15.5 °C 

 water, especially in areas where a horizontal thermal gradient was apparent. 



During the summer season albacore {Thuuinis 

 alalunga) usually migrate into waters off the 

 Oregon coast where upwelling and Columbia 

 River water form a complex ecotone between 

 coastal and oceanic waters (Owen, 1968; Pearcy 

 and Mueller, 1970; Pearcy, 1971). The albacore 

 fishery here fluctuates greatly among years 

 as a result of variations of abundance and 

 availability of albacore and fishing effort 

 (Johnson, 1962). 



Marked fluctuations of catches may also 

 occur within a single summer and the 1970 

 albacore season off Oregon is a spectacular 

 example of within-season changes in fishing 

 success. The fisheiy got off to an early start 

 in mid-July and jig boats reported exceptionally 

 high catches (up to 1,400 fish/boat day) during 

 late July. Record landings of over 4,000 tons 

 were recorded for July. During late July and 

 early August, however, the jig fisheiy virtually 

 disappeared. Boats fishing in the region of 

 the Columbia River, where high catches of 



800-1,300 fish per boat day were reported on 

 30 July, averaged only 50 fish on 31 July.- 

 Although jig fishing continued to be poor 

 during the rest of the summer off Oregon, bait 

 boats enjoyed good fishing into October. 



The purpose of this paper is to describe 

 ocean conditions and albacore catches in Oregon 

 waters during the summer of 1970 in hopes 

 of better understanding the small-scale spatial 

 distribution of albacore tuna and the dramatic 

 changes in their availability that occurred 

 in 1970. 



SOURCES AND TREATMENT 

 OF DATA 



Catch data for the 1970 albacore season off 

 Oregon were derived from fish boat logs sent 

 directly to us from fishermen or obtained 

 through other agencies from fishermen. Thirty- 

 three jig boats and two bait boats submitted 

 usable records to us from our original dis- 



' Department of Oceanography, Oregon State Univer- 

 sity , Corvallis, OR 9733 1 . 



- Laurs. R.M. 1970. U.S. Bur. Commer. 

 Albacore Bull. No. 70-3 and 70-4, La Jolla, Calif. 



Fish. 



Manuscript accepted October 1972. 



FISHERY BULLETIN: VOL. 71, NO. 2, 1973. 



489 



