posted on October 01, 1989 04:21
Department of Fisheries and Oceans, Science Branch
Northwest Atlantic Fisheries Centre, P. O. Box 5667
St. John's, Newfoundland, Canada A1C 5X1
Source - Journal of Northwest Atlantic Fishery Science, Volume 9(1): 45-52
Means of vertebral numbers in cod samples collected in 1947-71 from the eastern Newfoundland and Labrador area were compared by length-ranges.
In NAFO Div. 2GHJ and 3KL, the northern-type high-vertebral means (usually over or slightly below 55) were usually present at the length-ranges of lesser length, declining toward lower means at greater sizes. The high-vertebral-type mean extended to higher length-ranges northward than southward. In coastal areas of Div. 2GHJ and 3K, the means at the same length-ranges tended to be somewhat lower than offshore. Means at the same length-ranges for the above areas were usually a little higher in the earlier period, 1947-55, than in the later period, 1958-71. Throughout the area (not including Div. 3M) offshore and inshore vertebral means at the same length-range and period were typically lower in the southern than in the adjacent northern area. The vertebral means of the relatively isolated cod stock on Flemish Cap (Div. 3M) were intermediate between the northern- and the southern-types, and on the southern Grand Bank (Div. 3NO) the means (usually below 54) were typically the lowest in the eastern Newfoundland area. Within each of these areas (Div. 3M and 3NO), means did not differ greatly by length-range and from the earlier to the later period.
It appears that stock mixing is the primary mechanism causing the observed, relatively large, variations in mean vertebral number of the larger compared with those of the smaller fish. The lack of seasonal variation in mean vertebral numbers in offshore northern areas indicates that straying of larger fish from more southern or inshore stocks accounts for decreasing vertebral number with size. However, larval drift and mixing from seasonal migration are important causative factors of differences found in other areas. Differential fishing pressure on stocks could be the cause of temporal trends in vertebral counts in mixing areas.
Language - English
Publisher - Northwest Atlantic Fisheries Organization (NAFO), Dartmouth, N.S., Canada
Publication Date - September 1989
Publication Type - Journal Article