The relationship between seal abundance and cod worm (Phocanema decipiens) infestation in cod in Norwegian coastal waters

A sample of 52 cods, Gadus morhua, caught close to a grey\nseal, Halichoerus grypus, haul out site, and a total of 652\ncods from 18 commercial catches (average sample size 36\ncods) were examined with regard to cod worm infestation.\nThe sampling was carried out from July 1978 to January 1981\nin Norwegian coastal waters between 62° and 66° North. The presence of larval cod worm was recorded in 64% of the\nexamined fishes, and the average infestation in all 704\nfishes was 8.5 cod-worms per fish. However, the\ninfestation decreased significantly with increasing\ndistances from the haul out sites of grey seals and common\nseals, Phoca vitulina. The heaviest infestations were\nrecorded in cod from the outern part of in shore waters,\nand slightly decreasing towards the fjords, fitting well to\nthe observed distribution of seals. A substantial decrease\nwas also recorded with increasing distance (and depth) off\nshore from the mentioned grey seal haul out site.