Development of a Stock Profile for the Central....
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GRANT NUMBER:  NA66FD0057           NMFS NUMBER:  95-SWR-063

REPORT TITLE:  Development of a Stock Profile for the Central North Pacific Broadbill Swordfish (Xiphias gladius) Fishery

AUTHOR:  John Kaneko MS, DVM

PUBLISH DATE:  July 27, 1998

AVAILABLE FROM:  National Marine Fisheries Service, Southwest Region, 501 West Ocean Blvd., Suite 4200, Long Beach, CA 90802-4213.   TELEPHONE:  (562) 980-4001


The relationship between dressed body weight and methyl mercury (MeHg) concentration in the edible muscle of broadbill swordfish (Xiphias gladius) from the Central North Pacific fishery was evaluated. Swordfish ranging from 6 to 434lb. Dressed weight were sampled over an 18- month period between October 1996 and March 1998.  Swordfish landed in Honolulu by Hawaii-based longliners were sampled. Standard muscle samples were taken just posterior to the cleithrum ("fillet sample"). The correlation between dressed body weight with fillet MeHg content was highly significant (p<0.0001), resulting in the linear relationship, Y fillet MeHg (ppm) = 0.7847 + 0.0034 (X dressed weight in lb.). These results indicate that the MeHg content of Central North Pacific swordfish can be estimated from the dressed body weight. An alternative muscle sampling site was also evaluated. The MeHg content of muscle collected from just anterior to the caudal peduncle ("tail sample") was correlated with the dressed weight. This correlation was highly significant (p > 0.0001), with the linear relationship, Y tail Me Hg (ppm) = 0.6577 + 0.0036 (X dressed weight in lb.). Similarly, the correlation between the MeHg concentration if paired tail with fillet muscle samples was highly significant (p<0.0001). A paired t-test showed a highly significant difference (p<0.0001) between the MeHg concentrations between these two muscle sampling sites. Covariance analysis determined no significant difference (p<0.54) between the slopes of the two regressions. Based on these findings it was concluded that tail muscle samples could be used to make estimates of the MeHg content in the standard fillet sample. Sampling muscle from the tail site offers a suitable alternative to the costly standard practice of sampling from the prime portion of the musculature. 

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