Interannual variability of dolphin habitats in the eastern tropical Pacific. II: Effects on abundances estimated from tuna vessel

Stephen B. Reilly Southwest Fisheries Science Center. National Marine Fisheries Service. NOM P. O. Box 27'. La Jolla. CA 92038 Interannual variability of dolphin habitats in the eastern tropical Pacific. II: Effects on abundances estimated from tuna vessel sightings, 1975-1990 Abstract.-The results of a canonical correspondence analysis (CCA) of data from research vessel surveys of the eastern tropical Pacific were applied to time series of estimated dolphin abundances from tuna vessel sightings. The research vessel survey data consisted of daily dolphin school sightings and concurrent environmental variables for August-November of 1986 through 1990. Seasonal fields of habitat quality for 1975-90 were calculated from historical bathythermograph data by using the CCA ordination results. For spotted (Stenella attenuata) and eastern spinner (S. longirostris orientalis) dolphins, annual abundance estimates or interannual changes in those estimates are significantly correlated with habitat quality. This effect is at least partly due to expansion of high quality habitat beyond the geographic ranges assumed for the abundance estimate. We discuss ways that environmental data could be used to reduce error in dolphin abundance estimates.