Abstract:
Effective conservation of upper trophic level marine predators requires a comprehensive
understanding of their distributions and of the underlying biological and physical processes
that drive these distributions. We investigated the spatial distributions of marine mammals
and seabirds off Cape Hatteras, NC, in relation to positions of the shelf break and Hatteras
Front system. We conducted transect surveys with synoptic, fine-scale oceanographic
sampling in August 2004, and derived the daily position of the Hatteras Front from
temperature, salinity, and pressure data collected by a scanfish. To account for the correlated
and autocorrelated nature of the environmental data, we assessed the influence of the Front
on species distributions using a suite of Mantel’s tests. Pure partial Mantel’s results show
that marine mammal distribution over all survey days was influenced by salinity. Results of
the daily Mantel’s tests show that no one variable consistently influenced the distribution of
marine mammals. Pure partial Mantel’s results show that seabird distribution over all survey
days was influenced by depth, distance from shelf break, fluorescence, and space. The
significance of space indicates that another variable or variables with spatial structure
influenced the distribution of seabirds but were not tested. Results of the daily Mantel’s tests
show that different combinations of environmental variables influenced the distribution of
seabirds on different days. However, one variable consistently influenced seabird
distribution – fluorescence. These findings enable consideration of spatially explicit
approaches to the conservation of marine mammals and seabirds and other upper trophic
level predators in this region.
Keywords: marine mammal distribution; seabird distribution; spatial analysis; Hatteras Front
