Coastal Fish Populations Fluctuate Independent of Once-Through-Cooling Water Use in Southern California: The SONGS Case

Power plant once-through-cooling has been a contentious issue since the 1972 passage of the Federal Clean Water Act. The greatest debate centers around the impacts of impingement and entrainment of marine life, especially fishes, on the natural environment and source populations. Considerable work has been done to document the impingement and entrainment at a specific or suite of power plants using statistical modeling and often temporally brief studies. Few monitoring programs, however, have been maintained over extensive periods to document long-term (decadal or greater) trends in both impingement and entrainment, but also natural variation in the source populations and the environment. Of studies that meet these criteria, few encompass substantial changes in cooling water flow volumes. Southern California is unique in the presence of an extensive time series of juvenile/adult fish entrapment monitoring at local power plants and an independently executed ichthyoplankton sampling program. Both of these time series overlap the commercial startup of the San Onofre Nuclear Generating Station’s (SONGS) Units 2 (1983) and 3 (1984), which resulted in an additional 2400 million gallons of daily cooling water circulation without an immediate reduction in the remaining facilities with offshore intakes in southern California. By utilizing ichthyoplankton data from the extensive California Cooperative Oceanic Fisheries Investigations (CalCOFI) nearshore station sampling (1950-2009) and brief (1978-1986) sampling directly offshore of SONGS, we derived the long-term patterns in the 16 most common species occurring in both time series. Comparisons of these trends with long-term cooling water flow volumes resulted in clear evidence of no relationship between ichthyoplankton densities and cooling water flow volumes. Extrapolating the larval densities recorded at the CalCOFI nearshore stations in 2006 indicates ~ 9 trillion larvae were along the southern California coast. We chose 2006 as this was the year that the majority of studies were completed from which the State Water Resources Control Board compiled an overall statewide estimate of 19 billion larvae entrained by once-through-cooling. Based on these estimates, ~0.08% of the source larvae was entrained by southern California’s offshore once-through-cooling intakes.