Parasites of Northeast Arctic cod (Gadus morhua) in the Barents Sea: effects on reproduction

Parasites play a key role in the biodiversity and dynamics of an ecosystem, either by affecting host mortality and/or host reproduction. Spawning comes with a great cost in time and energy, and in times of poor conditions this time and energy is better directed into growth and survival to increase future success. The phenomenon of skipped spawning, where sexually mature fish skip a reproductive event, is a common occurence in the NEAC. Previous studies suggest that as much as 24-30% of females skip annual spawning, and instead remain at the feeding grounds. The causes for this is still unclear but it seems to occur in response to poor condition. As parasites, by definiton, have a negative effect on host fitness it is of finterest to see if parasites could affect the decision to skip spawning. In this study, we explore the effects of parasites on reproductive parameters in the Northeast Arctic cod (NEAC), the largest cod stock in the world. By comparing intensity of infestation in skippers and spawners we found that parasites do not seem to have an effect on the reproductive abilities of the NEAC. No significant differences in parasite intensity could be detected between skippers and spawners in any of the species included in our study. Nor were there any evidence to show that increase in parasite intensity were associated with decreased fecundity. Even an attempt to look at the effects of the whole parasite community by applying an intensity rank index did not find any correlation between infestation and reproductive parameters. However, caution must be made when making conclusions about parasites effect on host population dynamics. This demonstrates the importance of experimental studies of relationships between parasites and reproductive success. As well as look at parasite-induced host mortality in NEAC.