Fluctuations in year-class strength of cod and pollack in southeastern Norwegian coastal waters during 1920-1969
Abstract
TVEITE, S. 1971. Fluctuations in year-class strength of cod and pollack in southeastern
Norwegian coastal waters during 1920-1969. FiskDir. Skr. Ser. HavUnders., 16: 65-76.
From 1920 a small beach seine has every September-October (except 1940-1944)
been worked at selected localities along the Norwegian Skagerack coast. The catch
per beach seine haul of 0-group cod agree fairly well with catch per trap per week
of the same year-class as I-, II-, III- and IV-group and may thus be used as estimate
of the strength of each year-class. There are two marked periods with rich year-classes,
one before 1930 and one after 1950. In the intermediate period the only rich year-classes were 1938 and 1945. The fluctuations are generally similar in all districts.
There has been increase in relative abundance in the most open areas compared to the
more landlocked ones. By the present method no effect of the liberation of cod larvae
has been revealed.
The catch per beach seine haul of 0-group pollack is less reliable as estimates of
year-class strength. Two rich periods, however, one before 1931 and one after 1953, are shown by the material. In the last period the average relative number is below that of
the first period. Again, 1938 and 1945 are the only years in the intermediate period
which gave rich broods.
Covariation between year-class strength of pollack and cod excist to some extent,
but not all years with rich year-classes of one of the species showed a similar year-class strength of the other species.
Publisher
[Fiskeridirektoratets havforskningsinstitutt]Series
Fiskeridirektoratets skrifter, Serie Havundersøkelservol 16 no 2