Abstract. - On reexamining a rou- 

 tine procedure for reporting catch- 

 per-effort (CPE) in the North Pacific 

 albacore fishery, we found evidence 

 that CPE as an index of population 

 size has been subject to a changing 

 degree of bias. The increasing, posi- 

 tive bias in the routinely reported 

 CPE has produced an optimistic, up- 

 ward trend in this population index 

 during the past decade. A time series 

 of CPE, calculated in a different 

 way, trends downwards. We show 

 that both time series are subject to 

 increasing, positive bias under con- 

 ditions of an increasing ability of 

 fishermen to locate concentrated 

 patches of albacore. We present evi- 

 dence that this ability has grown 

 over the past decade, possibly as a 

 result of increasing availability of 

 satellite-based fishing advisories. 

 The divergence of the two time 

 series is explained by a model that 

 shows a different rate of increase in 

 bias in the two cases. The fact that 

 the bias is increasing in the new time 

 series implies that the true popula- 

 tion has undergone a more severe 

 decline than is shown by that series. 



Catch-per-effort and Stock Status 

 \n the U.S. North Pacific 

 Albacore Fishery: 

 Reappraisal of Both 



Pierre Kleiber 

 Christina Perrin 



La Jolla Laboratory, Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 P.O. Box 271. La Jolla. California 92038 



Manuscript accepted 11 February 1991. 

 Fishery Bulletin, U.S. 89:379-386 (1991). 



The Southwest Fisheries Science 

 Center (SWFSC) has been collecting 

 fishery statistics from the U.S. North 

 Pacific albacore fleet for a number of 

 years. Overall catch-per-effort (CPE) 

 and other summary statistics are in- 

 cluded in the deliberations of the In- 

 ternational North Pacific Albacore 

 Workshops (Bartoo and Watanabe 

 1989) and are used to indicate the 

 status of albacore stocks in the re- 

 gion. The history of these assess- 

 ments has been consistently a favor- 

 able outlook of increasing abundance 

 for the stocks, although in recent 

 years the workshop has underscored 

 the lack of detailed information about 

 albacore catch in the growing gillnet 

 fishery in the North Pacific. 



The U.S. North Pacific albacore 

 fleet consists primarily of jig vessels 

 which vary in length from 25 to over 

 100 feet. The effect of vessel length 

 on albacore fishing power was inves- 

 tigated by Laurs et al. (1976). They 

 reported significant variability be- 

 tween 10-foot length-classes of jig 

 vessels. Based on relative fishing 

 power estimates for each year, ad- 

 justed effort and CPE values were 

 calculated back to 1961. Since that 

 time the calculation of fishing power 

 and concomitant standardization of 

 effort and CPE has become a routine 

 part of reporting the albacore catch 

 and effort statistics by the SWFSC. 



In preparation for the 1989 North 

 Pacific Albacore Workshop, we re- 



visited the theory and rationale be- 

 hind the effort standardization and 

 calculation of CPE to see if the rou- 

 tine procedures continued to be ap- 

 propriate. We found that even with 

 standardization for fishing power, 

 there was a high degree of residual 

 variability in CPE within the fishing 

 grounds which was not being ad- 

 dressed. Recalculation of the time 

 series of CPE with a rough correc- 

 tion for such variability showed that 

 the optimistic upward trend over the 

 past decade in the original series was 

 replaced by a downward trend. In an 

 effort to reveal which of the two time 

 series is more representative of the 

 true course of the albacore popula- 

 tion, we explored the data in more 

 detail to find what might cause the 

 divergence in the two CPE series. 

 This paper is a report of our appraisal 

 of the routine procedure and our 

 reappraisal of the status of the alba- 

 core stocks. 



Description 

 of the fishery 



The U.S. North Pacific albacore fish- 

 ery is composed of several surface 

 fishing gears. Trolling vessels (jig 

 boats) are by far the most prevalent, 

 followed by baitboats. They operate 

 primarily in the eastern North Pa- 

 cific. Other North Pacific fleets that 

 harvest albacore include a Japanese 



379 



