Modelling Seasonal Distribution of Pelagic Marine Fishes

The distribution of pelagic marine fishes and invertebrates varies seasonally. However, information on the seasonal variation of the distribution of most pelagic marine fishes and invertebrates is scarce. In this paper, seasonal changes in distribution ranges of commercially exploited pelagic fishes and invertebrates are predicted based on the existing Sea Around Us Project distribution, a prediction algorithm, the correlation between seasonal changes in northsouth boundaries and sea surface temperature. In the northern hemisphere, in summer (July to September), mobile pelagic marine species tend to migrate to the northern part of their distribution range to avoid excessive temperature near the equator, while in winter (January to March), the same species will migrate southward to avoid the low temperature at higher latitudes. The converse applies to the southern hemisphere. The resulting distributions can improve the prediction of temperature preference profile of pelagic species which are important in evaluating the effects of global warming on their distribution ranges. However, this method of predicting summer and winter distributions of pelagic species can only be considered as an approximation as other factors such as food availability, salinity, rainfall and current are not included. On the other hand, such approximation appear reasonable, given the global scope of the application of the predicted seasonal distributions and the large number of evaluated species (> 16o). INTRODUCTION Temperature is a key factor affecting the physiology (e.g., reproduction, growth) and spatial and temporal distributions of marine fishes and invertebrates. For instance, Pörtner et al. (2001) shows that growth rates and fecundity decrease with higher latitude in the case of Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus). Thus, marine ectotherms generally inhabit areas where temperature is favorable for their physiological processes. Also, the northern and southern boundaries of a particular species are determined by the water temperatures suitable for survival and reproduction. Such boundaries may fluctuate according to seasonal changes in temperature. Thus, in the northern hemisphere, the northern boundaries may shift southward in winter and northward in summer (Hutchins 1947), and conversely, in the southern hemisphere. The correlation between distribution ranges and water temperature is a major factor determining the fluctuation in distributions of the highly mobile pelagic fishes and invertebrates. Many pelagic fishes and invertebrates have the ability to migrate over long-distance to find suitable habitats. As sea water temperature fluctuates seasonally and inter-annually, these species migrate to maintain physiologically suitable temperature in their surrounding water. For instance, Sardinella and 2 Cited as: Lam, V.W.Y., Cheung, W.W.L., Close, C., Hodgson, S., Watson, R. and Pauly, D. 2008. Modelling seasonal distribution of pelagic marine fishes and squids, p. 51-62. In: Cheung, W.W.L, Lam, V.W.Y., Pauly, D. (eds.) Modelling Present and Climate-shifted Distribution of Marine Fishes and Invertebrates. Fisheries Centre Research Report 16(3). Fisheries Centre, University of British Columbia [ISSN 1198-6727].