Population dynamics, diet and trophic positioning of three small demersal fish species within Porsangerfjord, Norway

Abstract

In today’s society, one often stumbles over the quote “you are what you eat”. Diet is closely related to fish size and physical conditions, so in order to understand the food web one must first understand the population dynamics of the fish. Three demersal species in the northern hemisphere are; Artediellus atlanticus, Myoxocephalus scorpius and Leptagonus decagonus. The study was undertaken in 2009-2011, within the inner basin of Porsangerfjord (70oN 25oE) through the project ‘Ecological Processes and Impacts Governing the Resilience and Alternations in the Porsangerfjord and Hardangerfjord’. The study objectives were to provide basic information about these species population dynamics and feeding ecology. The length distribution varied between both sex and species, whereas the age structure was the same. The growth were different for L. decagonus but not for A. atlanticus and M. scorpius. The dominant prey found in A. atlanticus was Polychaeta, whereas M. scorpius fed on fish, and L. decagonus had fed on Copepoda. Correlations were found within the species diets, but not between any of these species. The stable isotope analysis showed that L. decagonus had a pelagic related diet whereas the A. atlanticus had a benthic related diet and M. scorpius demonstrated a mixed benthic-pelagic diet signature. The study found that the three species had different diets but similar trophic positions. Thus, indicating that they had individual food chains within the food web of inner Porsangerfjord.