Seasonal Patterns of Fish Entrainment for Regional U.S. Electric Generating Facilities

Entrainment of fish eggs, larvae, and early juveniles at cooling water intakes occurs seasonally based on geography and fish community composition.  Seasonal rather than year-round operation of compliance measures may be used in some cases to reduce entrainment.  The timing and duration of the majority of entrainment was determined for a sample of 111 existing generating facilities from 11 regions.  The regions covered a wide range of ecosystems from coldwater and warmwater freshwater communities to marine and estuarine communities along the northern Atlantic and southern Atlantic coasts, the Gulf of Mexico, California and Hawaii.

Facilities located on freshwater required shorter periods to encompass the majority or entirety of entrainment, while facilities located on estuaries or marine systems required a longer period.  The relationship between entrainment and water temperature also suggested the potential use of a “threshold temperature”, above which entrainment levels might be expected to be elevated, and entrainment mitigation measures would be most effective.  A “safety factor” of an additional few weeks of the use of temporary entrainment reducing technologies could ensure that the desired entrainment reduction is achieved and might compensate for annual variations in species composition (dominance), water temperature, or other controlling environmental variables.