Application of lognormal and delta-lognormal linear models to standardise CPUE abundance indices (1994 to 2002) for orange roughy off Namibia

Abstract

GLM analyses are used to standardise the CPUE data for Namibian orange roughy. The possibility of there being a “learning” period of lower CPUE for a new vessel when it enters the fishery is taken into account. Alternative statistical approaches to deal with tows that record zero catch of orange roughy are considered. Further, to allow for areal expansion of the fishery at each aggregation, sub-aggregations are defined and CPUE trends estimated separately for each. Different methods for combining the results for the various sub-aggregations to provide a single index for an aggregation are considered. In broad terms standardised CPUE values for 2002 appear similar (with some slightly lower) to those for the previous year.