Study Urges Protection of Big Fish

SAN DIEGO, California, October 18, 2006 (ENS) - Commercial fishing does not just threaten targeted stocks by reducing the overall number of remaining fish, according to a new study. Researchers have found that fishing puts populations at greater risk of collapse because it tends to remove older, stronger, bigger fish, leaving behind younger, smaller fish less capable of surviving natural changes in the ecosystem.

The study, published in this week's edition of the journal "Nature," indicates fishery managers should consider adjusting quotas and regulations to protect larger fish.

"We found that the variability of the targeted populations was much higher, meaning that fishing tends to amplify both the peaks and the valleys of population numbers," said study coauthor George Sugihara, a co-author of the paper and an oceanographer at Scripps Institution of Oceanography at the University of California at San Diego. "Fishing can potentially not only lead to declining stock levels, but cause populations to fluctuate more through time, which could put them at greater risk of collapse than previously thought."

The study warns that catching too many large fish puts targeted species in double jeopardy. (Photo by Jorge Sierra courtesy WWF-Canon)

The study is based on data obtained by the California Cooperative Oceanic Fisheries Investigations (CalCOFI), a 50-year study of the ecological conditions of the California Current - the large current originating in the northern Pacific Ocean that flows along the western coast of North America.

The researchers differentiated between environmental and fishing impacts by analyzing the populations of exploited versus unexploited species living in the same environments.

Normally this comparison cannot be made with traditional fisheries data based on "landings" records, as there are no landings records for unfished species.

But the CalCOFI data was unique in this regard because it contains information on larval abundances of both fished and non-fished species.

Larval abundance is an indicator of adult abundance. The study analyzed the quantity of larval fish recorded during research expeditions to study current.

Its shows that fishing amplifies the highs and lows of natural population variability because it selectively culls the larger, older individuals, thereby removing the fish that are more able to buffer random environmental variation and the ones that tend also to be more the most reproductively active.

"This suggests that fisheries need to be managed not only to maintain a harvest target or total biomass level, but also to maintain a certain age structure in the stock," said Sugihara.

The fluctuations identified precede systematic declines of populations, he explained, and can be viewed as a kind of early warning sign prior to collapse.

"This study shows that there is significant value in conducting long-term ecological research in the oceans," added Philip Taylor, director of National Science Foundation's Biological Oceanography Program, which funded the research along with the foundation's Long-Term Ecological Research Program.

"There are risks in not taking fish population variability and fish population age structure into account because they impact the resilience of future fish generations," Taylor said. "A ton of fish of the very largest sizes has far more value to future populations if preserved than a ton of smaller fish, which contribute far less to reproduction."