Publication Abstract

Temporal variations in the fecundity of Arcto-Norwegian cod (Gadus morhua) in response to natural changes in food and temperature

Temporal variations in the fecundityof Arcto-Norwegian cod (Gadus morhua) in response to natural changes in food andtemperature

O.S. Kjesbu, P.R. Witthames, P. Solemdal and M. Greer Walker

Sexually mature Arcto-Norwegian female cod, Gadus morhua, were sampled offnorthern Norway either during spawning migration (Vesterialen) or at spawning sites(Lofoten) from 1986 to 1996. This period comprised a dramatic, nearly cyclical change inthe Barents Sea ecosystem. The stock of the main food item, viz. the Barents Sea capelin Mallowvillosus villosus, changed from a low (1986), to a high (1991) and again to a low(1994) level of abundance while the climate changed from a cold (< 1989) to a warmregime. The relative annual potential fecundity (i.e. number of vitellooenic oocytes per gprespawning fish) increased by approximately 40% from 1987 to 1991. However, informationfrom a back-calculation technique calibrated in the laboratory using spawning fishindicated that this change might have been as high as 80 to 90%. Ovaries were analysed bythe gravimetric, the automated particle counting and the stereometric method (modified touse with ovaries too large to section whole). All three methods gave similar fecundityestimates. The latter method was applied to quantify atresia of developing oocytes in thegood-condition year of 1991. Atresia was rare, occurring in only 30% of the ovaries andwhere it was present in only 1 to 4% of the vitellogenic oocytes. Spawning females sampledfrom 1991 to 1996 gradually produced fewer eggs and demonstrated clear interannualvariations in vitellogenic oocyte mean size and distribution thought to reflect a delicatereproductive tactic to minimise negative nutritional effects on egg size and egg quality.Estimates of annual potential fecundity for the duration of the study were significantlypositively correlated with environmental temperature and the availability of capelinduring vitellogenesis.

Reference:

O.S. Kjesbu, P.R. Witthames, P. Solemdal and M. Greer Walker, 1998. Temporal variations inthe fecundity of Arcto-Norwegian cod (Gadus morhua) in response to natural changes in foodand temperature. Journal of Sea Research, 40: 303-321.

O.S. Kjesbu, P.R. Witthames*, P. Solemdal and M. Greer Walker*

Journal of Sea Research, 40: 303-321