Approaches to assessing stocks of Loligo gahi around the Falkland Islands

Management of the Falkland Islands Loligo gahi fishery is by a combination of effort control and in-season assessment of the state of the stock in relation to biological reference points. There are two fishing seasons, from February to May and from August to October inclusive. There appear to be at least two, and sometimes three cohorts that recruit to the fishery over a year, in January, April/May and October. The fishing seasons therefore do not directly coincide with the separate cohorts; the second cohort is caught in both the first and second seasons. Assessments of the cohorts were made using a Delury depletion model. In situations when a Delury could not be fitted satisfactorily, an extension was developed in which annual trends in catchability coefficients were used together with individual vessel CPUE data to estimate stock size. The Delury and its extension enabled both first and second cohorts to be assessed for all years from 1987 to 1996 Results indicated that the cohorts have different dynamics and should be considered as separate stocks. Both cohorts have been declining in size over the last several years. The significance of a transition between two distinct stocks in a single fishing season is discussed in the context of real-time management of this fishery. (C) 1998 Elsevier Science B.V. All rights reserved.