Title

Habitat Use in Marine Fish: A Test of Three Current Theories

Date of Completion

January 2011

Keywords

Biology, Ecology|Biology, Oceanography|Agriculture, Fisheries and Aquaculture

Degree

Ph.D.

Abstract

Understanding how animals select habitat is important for conservation and for management of exploited species such as marine fish. Three theories of habitat use have been proposed for marine fishes, the Constant Density Model, the Proportional Density Model, and the Basin Model. Each makes different predictions of changes in the occupied range and fitness of a species as the population grows. The Constant Density Model predicts that local population density is constant and the range occupied by the species expands as the population grows. Fitness is dependent on location and not on population size. The Proportional Density Model maintains that range does not change and that local population density is a fixed proportion of the whole. As in the Constant Density Model, fitness is site dependent and not population size. The Basin Model predicts that both range and local population density change with increases in global population size and that fitness is inversely correlated with population size. ^ I have examined patterns of habitat use at three different spatial scales, using three different species at different life history stages to determine whether the patterns of habitat use are consistent with the Constant Density Model, the Proportional Density Model, or the Basin Model. I have looked at habitat use in juvenile fish in the nearshore zone, spawning habitat selection by winter flounder (Pseudopleuronectes americanus), and the distribution of yellowtail flounder (Limanda ferruginea) on Georges Bank. ^ Two habitats in the nearshore zone were identified by the different assemblages of juvenile fishes they contained. One of the species in the assemblage ( Tautoga onitis) expanded their range when populations were higher. Fitness, as measured by growth rate, was not significantly different in the two habitats. Spawning habitat for winter flounder in Milford and New Haven Harbors seemed to be more related to current patterns rather than substrate type or depth. Egg mortality rate, a proxy for fitness, was higher in Milford Harbor. I found evidence of range expansion and, site dependent habitat use, and density dependent habitat use in the yellowtail flounder population on Georges Bank. ^