Despite broad "dolphin safe" practices, fishing activities have continued to restrict the growth of at least one Pacific Ocean dolphin population, a new report led by a researcher at Scripps Institution of Oceanography at UC San Diego has concluded.
Populations of dolphins in the Eastern Pacific were expected to increase in abundance after successful regulations and agreements were enacted to reduce dolphin deaths as a result of fishing "bycatch," cases in which animals are caught unintentionally along with intended targets.
But the new study, published in the October issue of Marine Ecology Progress Series, reveals that negative impacts from fishing activities remain. Instead of reducing numbers through direct mortalities, the study by Katie Cramer of Scripps Institution of Oceanography and Wayne Perryman and Tim Gerrodette of the National Oceanic and Atmospheric Administration's (NOAA's) Southwest Fisheries Science Center shows that fishing activities have disrupted the reproductive output of the northeastern pantropical spotted dolphin. The researchers note that reproductive output of the eastern spinner dolphin also declined, but a direct link to fishing effort was inconclusive.
"The results of this study clearly show that depleted dolphin populations have failed to recover in part due to a decline in reproductive output, and that fishing has had an effect on reproduction," said Cramer, a graduate student researcher in the Scripps Center for Marine Biodiversity and Conservation. "This shows that the fisheries indeed are still having an impact."
The new conclusions are based on broad surveys conducted by NOAA Fisheries Service between 1987 and 2003 designed to assess the size and health of dolphin populations in the eastern Pacific Ocean. The surveys included military reconnaissance camera images of more than 20,000 animals.
Cramer, who participated in helicopter surveys between 1998 and 2003, and her
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University of California - San Diego