Fish studies questioned

Posted: Friday, September 26, 2008

The Peninsula Clarion's recent article "China's bad air affects Alaska" (Aug. 8), greatly interested me. I became concerned about methyl mercury levels in halibut after reading the article Alaska fish receive clean bill of health published in 2003 in the Anchorage Daily News (ADN) and subsequently reviewed Oct. 10, 2004, in the Clarion. These articles, based on an Alaska Department of Environmental Conservation (DEC) studies, suggested Alaska's seafood is free from contamination levels anywhere near numbers that should raise public health concerns.

I my opinion, data in those studies not analyzed adequately. Halibut sample data were combined over age/size groups; results presented were average group values. Halibut samples more appropriately should have been stratified (separated) into age or size groups for analyses. By combining data from young (small) halibut with that from old (large) halibut, potentially higher levels of mercury in older fish were diluted by lower levels in young fish.

It is common knowledge that mercury accumulates in edible tissue of fish. Mercury levels increase with age of fish. Older fish have accumulated more mercury and have higher levels. Early studies (Hall 1976) showed mercury contamination in southeastern Alaska caught halibut increased with age of fish, older fish contained higher levels of methyl mercury than younger fish.

I question why data collected in 2003 studies were not stratified (separated) by age/size of halibut prior to statistical analyses. Results more appropriately should have been presented by fish age/size classes.

In more recent DEC studies (2007), reported on in the August 2008 Clarion, halibut data were analyzed by age/size and showed that older/larger halibut (90-plus pounds) contain levels of methyl mercury that may be of health risk to humans.

Did mercury levels in halibut change greatly from 2003 to 2007?

This recent study lead the Alaska Department of Health & Social Services and the Alaska DEC to issue guidelines for human consumption of halibut over 90 pounds. This study indicated that most commercially caught halibut weigh an average of 33 pounds and can be safely consumed up to four times a week.

When consumers are in the fish market selecting fish for consumption how do they know if they are purchasing halibut less than 90 pounds? Should it be comforting to know the average commercial size halibut is 33 pounds; when all the halibut they purchase may be from fish over 90 pounds? How does the consumer determine whether he is purchasing small (less than 90 pounds) or larger halibut or an unacceptable contaminated proportion in between?

Should consumers be concerned about average values? If halibut less than 90 pounds are unhealthy and mercury levels increase with age; what are mercury levels in halibut greater than 150 pounds; double that of a 90-pound halibut? Should larger, more contaminated, more productive (few males are more than 100 pounds) halibut be released and only smaller less contaminated, less productive halibut be marketed for human consumption?

Ron Modafferi

Lake Tahoe, Calif.

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