Inter-American Tropical Tuna Commission c/o Scripps Institution of Oceanography
8604 La Jolla Shores Drive
La Jolla, California 92037-1508 USA
1 Full paper to be published elsewhereA simple procedure is described for directly estimating diffusion coefficients, which may vary both spatially and temporally, from changes in the spatial distribution of an index of abundance. Estimates of distributions of mobile organisms are not usually known with great accuracy, but the speed of individuals places a constraint on changes in distribution. This constraint can be used to revise the estimates of distribution. Estimates of the matrix of diffusion coefficients are used to re-evaluate the distribution of abundance by explicitly linking the estimation of movement and distribution in a single program. It is possible to infer estimates of distribution and movement in periods for which particular zones are not sampled.
These methods have been developed as part of a study of yellowfin tuna in the eastern Pacific Ocean, and are illustrated with data from that fishery. The same method could be applied to study other fisheries and organisms.