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K. H. Postuma, On the Abundance of Mackerel (Scomber Scombrus L.) in the Northern and North-Eastern North Sea in the Period 1959–1969, ICES Journal of Marine Science, Volume 34, Issue 3, October 1972, Pages 455–465, https://doi.org/10.1093/icesjms/34.3.455
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Abstract
Although fishing intensity on North Sea mackerel during the years 1959–1966 was estimated to be very low as indicated by a low total mortality-rate (Z = 0·28), the abundance of the mackerel as measured by the catch-per-unit-effort in the Dutch trawlfisheries declined due to a failing recruitment. Recruitment to the North Sea population was poor after the strong year-class 1958 appeared in the trawl-fisheries in 1962. The combined effect of a very moderate fishing intensity and poor recruitment, gave the mackerel population the appearance of an old accumulated stock by the middle sixties.
Since the introduction of the purse-seine fishery in 1964 the total international catch of North Sea mackerel started to rise, reaching an unprecedented level of about 900000 tons in 1967.
As a result of these substantial catches mortalities rose to an average of Z = 0·80 in the late sixties. In 1968 and 1969 mackerel abundance in the North Sea dropped to a very low level as a consequence of the high fishing intensity and the persisting failure of recruitment to the now decimated stock.
Although the yield curve in mackerel does not suggest large gains from protection measures such as minimum size or effort restriction, the danger of an unlimited fishery on a stock of small sized mackerel are discussed.