The bongo net (shown here) has been the standard CalCOFI sampler since 1978. Ships retrieve the nets at an oblique angle to collect fish larvae. CalCOFI sampling and equipment specifications must meet and follow rigorous standards.
Two independent long-term time series show four decades of declines within fish populations in the California Current, with no sign of reversal.
The data set from the California Cooperative Oceanic Fisheries (CalCOFI) and the data set from the power plant cooling water intakes (PPI) were taken from five sites along the California Coastline. Both sets exhibited dramatic declines from the 1970s to the 2000s: 78% for fishes entrapped by the power plants and 72% for the overall abundance of larval fishes in the CalCOFI time series.
“It is notable that these two very distinct data sets tell us that the larval fish populations collected by CalCOFI and near shore fish species observed by PPI data are both declining at nearly the same rates,” said Scripps researcher John McGowan, one of the authors of the study published in Marine Ecology Progress Series on October 28, 2015.
Overall, fishes with an affinity for cool-water conditions, such as northern anchovy, Pacific hake, and several rockfish and midwater fish species are among the most abundant in the California ecosystem. These have declined most dramatically off southern California with initial declines deepening after the 1989 to 1990 regime shift, when warm waters intensified, severely reducing the productivity of many coastal species.
The study’s conclusion: One of the most striking aspects of this study is the strong coherence between these two independent time series and the nearshore and offshore fish communities that they represent. Cool-water marine ecosystems are generally more productive than warm-water ecosystems, and it is apparent that changing ocean conditions have produced far more losers than winners across a range of fish communities in the southern California Current System over the past 40 years. Without the CalCOFI and PPI time series, such dramatic changes would likely not have been possible to document, as they are not observed so clearly in the commercial fishery data. Whether this is due to a movement of cool-water species northward or an overall decline throughout the California Current is a key question for future investigation.
References
J. Anthony Koslow,Eric F. Miller, John A. McGowan, Dramatic declines in coastal and oceanic fish communities off California
Mario Aguilera, California’s Fish Populations Are Declining, Oct 29, 2015
Jason Waite, Climate Change and the Central California Current System
Images
The bongo net (shown here) has been the standard CalCOFI sampler since 1978, CalCOFI