Standardized Catch Per Unit Effort of Swordfish (Xiphias gladius) for the South African Longline Fishery

Swordfish, Xiphias gladius, is a target species in the South African pelagic longline fleet operating along the west and east coast of South Africa. A standardization of the CPUE of the South African swordfish directed longline fleet for the time series 2004-2019 was carried out with a Generalized Additive Mixed Model (GAMM) with a Tweedie distributed error. Explanatory variables of the final model included Year, Month, geographic position (Lat, Long) and a targeting factor (Fishing Tactic) with two levels, derived by clustering of PCA scores of the root-root transformed, normalized catch composition. Vessel was included as a random effect. Swordfish CPUE had a definitive seasonal trend, with catch rates higher in winter (July - October) than the rest of the year. Standardized CPUE peaked in 2008 (530kg/1000 hooks) and was lowest in 2014 (262kg/1000 hooks). The results indicate that the swordfish catch rates in the South African pelagic longline fishery have recently stabilized after an initial period of decline during 2004 to 2012.