Growth, growth modelling and age determination of Pandalus borealis

Abstract

A growth model for pandalid shrimps accounting for seasonal variations in growth is presented based on successive additions of sigmoid functions along a basic von Bertalanffy growth (VBG) equation. Results obtained with this new model are compared with results from the VBG equation and from a VBG model modified by the addition of a sine function. Results show that growth of Pandalus borealis (Krsyer) from Gullmarsfjorden on the Swedish west coast is best described by the seasonal models. Of the 2 seasonal models, the new model gave a slightly better fit. Seasonal variations in growth are discussed in relation to the reproductive cycle of P. borealis. Differences in growth pattern between sexes were also found in a 4 yr series of data from the fjord. The main difference was that male growth declined earlier in the year (late summer-autumn) than female growth which declined later (autumn-winter) and for a longer period. Differences in growth rate between sexes are also discussed. Since Gullmarsfjorden contained 4 different periodically isolated P. borealis populations during the study period (1984 to 1987), the relationship between growth rate and mean ambient temperature could be investigated in the temperature interval of 4 to 6 C. No correlation between these 2 factors was found. Results also indicated that recurring immigrations of adult shrimp during late winter-early spring from the Skagerrak population did not significantly affect growth-rate estimates. Finally, sizes by age of P. borealis in the fjord did not dlffer s~gnificantly from reported sizes by age In other boreal populations.