Modelling seasonal catchability of the southern rock lobster Jasus edwardsii by water temperature, moulting, and mating

Abstract

Seasonal variation in catchability of legal-sized male and female southern rock lobster Jasus edwardsii in a scientific reserve in south-east Tasmania, Australia, over a 15-month period was described by modelling the effects of water temperature, moulting and mating. Seasonal changes in water temperature described 62% of the variation of catchability for males, but were a poor predictor of catchability for females outside winter. Both moulting and mating was highly synchronised, although males and females moulted at different times of the year. This had a significant sex-specific effect on catchability, because the models developed here indicate that feeding and therefore catchability is decreased during moulting and mating and followed by an increased food consumption to compensate for the lack of feeding during these periods. Gaussian probability density functions were used to represent the timing and intensity of moulting, mating and subsequent compensation periods, and were combined with the description of seasonal temperature changes. Four Gaussian functions in agreement with independent biological data considerably improved the model fits for the catchability of males (R2=0.84). Adding a single Gaussian function to the temperature model, representing a combined moulting and mating period, provided a good fit to the variation in catchability of females (R2=0.90). However, the biological relevance of this model remained unclear during a second period of moulting and mating where empirical observations were missing.