Catckper-effort and Stock Status in the US . North Pacific Albacore Fishery : Reappraisal of Both

-on reexami?ing a m tine procedure for reporting catchper-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, positive bias in the routinely reported CPE has produced an optimistic, upwaid 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 conditions of an increasing ability of fishermen to locate concentrated patches of albacore. We present evidence 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 population has undergone a more severe decline than is shown by that series. Manuscript accepted 11 February 1991. Fishery Bulletin, US. 89379-386 (1991). Catckper-effort and Stock Status in the US. North Pacific