Asymmetry in Latitudinal, Longitudinal and Bathymetric Distribution of Marine Fishes and Invertebrates

D. Pauly, W. W. L. Cheung, C. Close, S. Hodgson, V. W. Y. Lam, R. Watson, (2008). “Asymmetry in Latitudinal, Longitudinal and Bathymetric Distribution of Marine Fishes and Invertebrates.,” Fisheries Centre Research Report No. 16 (Fisheries Centre, University of British Columbia, Vancouver, Canada

The distribution ranges of organisms, and marine animals in particular, are a manifestation of their environmental requirements, although they are often modified by the dynamics of prey and predators. Distribution range maps can also be used to infer where an activity occurs which requires the presence of a set of species, e.g., a fishery which targets them. The distribution of marine fishes and invertebrates serves as the basis for the mapping of fisheries by the Sea Around Us Project. Thus, accurate range maps are extremely important, and an earlier contribution by Close et al. (2006, FCRR 14(4): 27-37) reviews the step-by-step approach, and the assumptions used to predict the distribution of relative abundance of marine fishes and invertebrates from broad geographical limits, e.g., ocean basins, latitudinal limits, depth limits, etc., to relatively narrow polygons surrounding a number of ½ degree lat.-long. cells. Once established, such distributions, at least those referring to demersal fishes and invertebrates, can be interfaced with a map of sea bottom temperature, and inferred temperature preference profiles (TPP). These can be used, among other things, to verify the distribution ranges as predicted distributions should generate unimodal TPP, with the bulk of the distributions spanning a narrow range of temperature (~100 Celsius). As a relatively large fraction of the TPP that we obtained at first appeared bimodal, or exhibited a strong kurtosis, the assumption was revisited that the distribution of a species with regard to latitude can be simulated by an equal-sided triangle. It is shown here, for the cod (Gadus morhua), and generally for all our over 900 demersal species, that assuming a skewed triangular distribution, whose degree of skew is proportional to the temperature gradient from low to high latitude, generates more realistic distributions when compared to observed species distribution maps, although the narrowing of the uni-modal temperature probability distributions is relatively small. This correction will be implemented in all distribution ranges of demersal fishes and invertebrates in the Sea Around Us database, and used for catch allocation, and inferences on climate shifted distributions due to climate change.