Sport Fish Contain Toxin Produced During Algal “Blooms”Sea Grant to Study Anglers’ Exposure

February 16, 2006

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

SANTA CRUZ - Sport fish caught from the Santa Cruz Wharf can become contaminated with a potent neurotoxin, two UC Santa Cruz scientists have found.

Mary Silver

Professor Mary Silver (left) of the Ocean Sciences Department at UC Santa Cruz says that the algal toxin, domoic acid, has been detected in the viscera (guts) of two popular sport fish - white croaker and staghorn sculpin. The toxin has not been detected in muscle tissue of either fish.

A person could dramatically reduce the risk of poisoning by removing a fish’s head, tail and viscera before cooking and eating it. Silver, however, is cautious about drawing too many conclusions or raising any red flags about the public’s risk from exposure to the toxin because only a limited number of fish have been collected and tested. Additionally, the toxin has been detected in fish only during the relatively infrequent times when it is also present in seawater.

The preliminary findings, however, do present compelling evidence of the need for further study, as domoic acid was found in white croaker specimens four of the 13 times the fish were caught off the wharf. The toxin was found in staghorn sculpin on only one of the 10 sampling dates. It was not detected in any samples of surfperch or bocaccio, the only other sport fish sampled in numbers sufficient for scientific analysis.

Silver and her graduate student Spencer Fire, also at UC Santa Cruz, recently published their findings in a report for the California Department of Fish and Game.

Sick Sea Lion: Domoic acid causes
painful seizures and even death to sea lions. Credit: Francis Gulland, Marine Mammal Center, Sausalito, Calif.

To expand the study and more fully document public health risks, California Sea Grant has awarded a research grant to Silver, Sea Grant marine advisor Carrie Pomeroy, a social scientist with an expertise in fisheries and Raquel Prado, a statistician at UC Santa Cruz. Besides analyzing many more fish, the investigators will begin to quantify toxin exposure rates for different sub-groups of anglers at the wharf. Motivating the study is the concern that consumption patterns and cooking methods vary significantly along socioeconomic and cultural lines. As a result, some people may be ingesting toxins in amounts exceeding federal safety limits.

“Domoic acid has been studied in the natural environment but there is no systematic understanding of people’s risk from consuming contaminated fish,” said Pomeroy, who will be leading a pilot survey of anglers’ seafood consumption patterns. “We want to look at what people are catching and what they are eating,” she said. “There may be people who are at risk because of the way they prepare and consume what they catch.”

Pseudonitz.jpg: Diatoms of the
genus Pseudonitza produce domoic acid.

Domoic acid is an algal toxin produced by diatoms of the genus Pseudo-nitzschia that has caused die offs of marine mammals and sea birds in California and elsewhere. The toxin is ingested by fish and is poisonous to people. Cooking does not denature the toxin.

Although commercially sold fish and shellfish are tested for domoic acid, similar safeguards for protecting public health are not in place for recreationally caught fish. In fact, very little is known about how much domoic acid recreational fishers consume. Culinary practices, however, are thought to play a large role in exposure rates, Silver said. In some cultures, anchovies and other fish are eaten whole. Crab “butter” (the liver) is also prized in some cultures and could be a source of toxins. Even cooking techniques influence toxicity, she said. While boiling can help remove domoic acid, assuming the broth is not consumed, frying does not. Stir-frying in a wok can thus seal in toxins.

“Once we figure out the cultural and economic dimensions of the situation, we can work with health officials and community groups to target public education efforts,” Pomeroy said.

Investigators:

Mary Silver
Ocean Sciences Department,
UC Santa Cruz,
msilver@ucsc.edu, T. 831-459-2908

Caroline Pomeroy
California Sea Grant Extension Program,
UC Cooperative Extension,
Santa Cruz County, cmpomeroy@ucdavis.edu,
T. 831-763-8002

Raquel Prado
Department of Applied Mathematics and Statistics,
UC Santa Cruz,
raquel@ams.ucsc.edu,
T. 831-459-1488

NOAA's California Sea Grant is a statewide, multi-university program of marine research, extension services, and education activities. It is the largest of the nation's 30 Sea Grant programs and is headquartered at Scripps Institution of Oceanography at the University of California, San Diego. The National Sea Grant College Program is part of the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce.