Assessing Essential Fish Habitat for a Marine Pelagic Fish

Essential Fish Habitats are often defined by the structural (‘substrate’) components of the environment. In open pelagic ecosystems, habitats are also highly structured by the physical, chemical and biological properties of the water that drive or limit fish production. Habitat for a pelagic fish is often complex and spatially dynamic. For example, due to short and long-term changes in circulation patterns and climate drivers, the open pelagic habitat can shift its geographic location. How do we better define habitat quality and dynamics for pelagic fishes to delimit essential fish habitat and define linkages between habitat drivers and species production that can aid managers?  We use growth rate potential as a spatially-explicit and quantitative measure of fish habitat quality.   Examples from the North Pacific Ocean (adult chinook salmon) and the Gulf of Mexico (bluefish and striped bass) demonstrate that; 1) essential fish habitat can be quantitatively defined and is critically dependent on species-specific bioenergetics and feeding behavior, 2) physical, chemical and biological drivers are nonlinear and interactive and 3) changing environmental conditions (such as ocean circulations, climate and evolving hypoxia) can be used to better isolate fish responses to changes in habitat conditions, stressors and species management decisions.