Do diet of long rough dab (Hippoglossoides platessoides) differ between fjords with and without red king crab (Paralithodes camtschaticus)? A study of summer diet

Abstract

The purpose of this study is to describe the diet of long rough dab in three different fjords with and without red king crab. The hypothesis is that red king crab are influencing the diet and possible also growth of long rough dab. By the applying objectives it is assumed to give an answer to if red king crab is influencing different aspects of the diet and growth in long rough dab. By the applied frequency of occurrence and weight % analyses there were found small differences in the long rough dab diet. There was a dominance of different Crustacea and some Polychaeta prey groups. The main differences between the fjords was high dominance by fish, Bivalvia and Pandalidae in Porsanger, and little dominance of fish and Bivalvia prey groups in Balsfjord. A diet shift with increased predator length were recognized in both Balsfjord, Kvænangen and Porsanger long rough dab diet. The shift in Balsfjord were from a Crustacea dominance to Polychaeta and Crustacea dominance. Kvænangen with the opposite result. Porsanger having the most diverse diet in regard to prey groups contributing to the energy budget. The diet shift is towards a more fish and Pandalidae dominated diet. There were found small differences in growth in the three populations of long rough dab, with Porsanger material being in slightly better condition. There is by this study not found indication of an impact of red king crab on diet and growth in long rough dab. Though there is assumed that the low size of the cod stock in Porsanger, might let the long rough dab to include more fish and Pandalidae into their diet. This is relative high energetic prey which might held the growth rate up in a situation where the ecosystem are in change. In a situation with a large cod stock in a fjord area, there might possible be a larger influence of red king crab on the diet and growth in a population of long rough dab. Keywords: Long rough dab, Hippoglossoides platessoides, diet, growth, red king crab influence.