Publication Abstract

Growth, sexual maturation and spawning in central North Sea plaice (Pleuronectes platessa L.), and the generation of maturity ogives from commercial catch data

Growth, sexual maturation and spawningin central North Sea plaice (Pleuronectes platessa L.), and the generation ofmaturity ogives from commercial catch data

P.J. Bromley

This paper investigates sexualmaturation in North Sea plaice using data from the commercial catch of plaice landed onLowestoft fish market from 1983-1996, along with data from the English summer groundfishsurveys from 1977-1993. Two offshore spawning areas were identified in the central NorthSea - central-northern and central-southern. A general linear model (GLM) showed plaicesexual maturation was influenced by body weight, age and geographical location and wassubject to annual and seasonal variation. Few three year old female place appeared tospawn in the central North Sea, similar to the situation early in the 20th century. Thecondition factor of plaice peaked at the start of spawning and declined sharply duringspawning, with older females investing the most heavily in reproduction, both in absoluteand relative terms. The loss of older females through fishing is, therefore, likely tocompromise the overall reproductive fitness of the remaining population, comprising ofyoung females. The reproductive fitness of the males was also compromised, since youngmales tended to be in running condition for about a month less than older males.Reproductive investment in females was about twice the level found in males. There wasevidence that plaice in the northern North Sea matured at a slower rate than fish in thesouth. From the mid-1980s until the mid-1990s there was an increase in the proportion ofyoung plaice reaching sexual maturity, following an earlier decline from the late 1970s.Problems with using maturity ogives derived from market sampling data in order to assessthe proportion of spawning plaice in the North Sea are discussed.

Reference:

P.J. Bromley, 2000. Growth, sexual maturation and spawning in central North Sea plaice(Pleuronectes platessa L.), and the generation of maturity ogives from commercial catchdata. Journal of Sea Research, 44(1-2): 27-43.

P.J. Bromley*

Journal of Sea Research, 44(1-2): 27-43