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
ABSTRACT

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.