On Dynamic Interactions Between Some Fish Resources and Cetaceans off Iceland Based on a Simulation Model

Abstract

Twelve species of cetaceans are regarded as regular inhabitants in Icelandic and adjacent waters. Based on available estimates of the total food consumption of the cetaceans in the area, this paper explores potential interactions between three baleen whale species off Iceland and the relevant fish resources that constitute a part of their diet prey. The three species of whales are fin whale (Balaenoptera physalus), the largest cetacean consumer in this area, feeding mainly on krill (Meganyctiphanes norvegica) but also preying on some fish species like capelin (Mallotus villosus); minke whale (Balaenoptera acutorostrata), taking krill as well as a variety of fish, including capelin and gadoids (e.g. cod, Gadus morhua); and humpback whale (Megaptera novaeangliae) assumed to be feeding mainly on capelin. The study is based on a variety of assumptions regarding stock sizes, food preference, potential rates of increase and harvesting strategies. A single-species model developed for investigating the effects of different utilization policies of the Icelandic cod stock is combined with a crude multispecies model and these are used to study the potential impacts on capelin and cod stocks by various developments of the whale stocks under consideration. A Pella-Tomlinson like model is used to describe the whale stocks. The population and fisheries dynamics for shrimp (Pandalus borealis) and capelin (both important food items for cod) are described using simple models. Thus, only aggregates such as total, recruiting or adult numbers or biomass are considered as opposed to the fully age-class based cod model. The results indicate that both minke and humpback whales may have significant direct impact on the status of the capelin stock. The effects of fin whale predation on the capelin stock seems less significant unless such consumption occurs outside the sampled area, which is quite possible. The impact of the three baleen whale species on the development of the cod stock is uncertain, but may be considerable.