Yearclass strength of north-east Arctic cod at the 0-group stage. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983

Abstract

On the basis of recent developments in artificial propagation of cod fry it has been suggested that propagated cod fry may be released in the Barents Sea and the Svalbard region, the feeding areas of North-East Arctic cod. The aim would be to improve the periodical bad state of this stock. The North-East Arctic cod is spawning from February to April, and the first abundance index of a new yearclass is assessed at an age of six months by midwater trawl survey. Estimates of year class abundance (VPA) vary between 115 and 1818 million fish at age 3, a much smaller range than indicated by the 0-group survey indexes for six months old cod. In August/September the 0-group cod are distributed in the Barents Sea, around Bear Island and along West-Spitsbergen. Strong yearclasses have a much wider distribution than poor ones. Information from this survey may be used in planning the release of artificially propagated cod fry , which could then take place in September. Because of lack of reliable basis for estimating the natural mortality of cod; especially on the younger age groups, the number of cod fry in September cannot be precisely estimated. However, for areas on able range of natural mortalities, the number of fry needed to raise a poor year class to a strong one at the 0-group stage would be in the order of 2600-5200 million. Artificial propagation of cod fry would have to start in March, but it may be stopped later in years with high natural production of fry in order to reduce the effects of density dependent growth. Artificially propagated fry should have to be released in the most suit able areas. Observations on hydrographical and food conditions are therefore needed for the most suitable time. In order to avoid a high degree of cannibalism, the distribution of l-3-group cod would also have to be taken into account. A programme for artificial propagation of North-East Arctic cod fry would be justifiable in years or periods with low potential yearclass strength. However, our state of knowledge about the many factors involved does not at present justify such an extensive programme.