Report of the North-Western Working Group, 1968

Statistics relating to the landings of Iceland cod have been brought up to date in Tables 1 to

3. Total landings have continued to decline and in 1966 amounted to 357,000 tons. The catches per

unit effort by both English and Iceland trawlers decreased but this was due to the fact that much of

the German trawler effort was directed to catching redfish. Estimates of total effort in English

trawler units showed a decline in 1966,

Fluctuations in t4e total yield of Iceland cod cannot be interpreted directly in relation to

•fluctuations in fishing effort, however. This is because landings are also influenced by the level of

recruitment. This is illustrated by the data in Figure 1. These show the tctal landings of Iceland

cod for the past thirty-five years. Also shown are the contributions to the landings (in millions of

fish) of the year classes spawned eight years previously. The agreement is good, In particular it is

seen that the high yield from 1930 to 1933 was associated with the good year classes of 1922 and

1924, Again, in 1954 landings were very high and can be associated with the good year class of

1945, Since then there have been fluctuations due to fluctuations in the level of year class strength,

and for the future it is known that all year classes after 1959 are poor or very poor in Iceland

experimental trawling material (Jonsson, unpublished data), These results show that fluctuations in

year class strength can cause fluctuations in the landings large enough to mask the possible effects

of changes in fishing effort. Assessments of the effects of changes in fishing effort cannot therefore

be obtained from commercial statistics directly, but have to be obtained indirectly. This is done

by first estimating the level of mortality in the stock due to fishing. The effect of changes in this

fishing mortality on the expected yield can then be calculated and this is the method of assessment

used in this r~port.