Publication Abstract

A critique of methods for stockidentification in marine capture fisheries

M.G. Pawson and S. Jennings

Marinefishes rarely reproduce randomly with conspecifics throughout their geographical range.Rather, mating is confined to intraspecific stocks which have sufficient spatial andtemporal integrity to warrant consideration as self-perpetuating units. Recent debate onthe `stock' concept has largely focused on the extent to which `sufficient' implies totalor partial reproductive isolation and the timescales over which the unit may be consideredselfcontained. This debate has produced numerous sub-definitions of stocks, many of whichhave little relevance to fishery management problems.

At present, the majority of marinefisheries in the north-east Atlantic are monitored and regulated in areas which do notnecessarily have logical or consistent relationships with biological processes or fishmovements. As a result, several biological stocks of the same species may be exploitedwithin each management area, and stocks which enter a given area may have been exploitedby fisheries elsewhere. The yield dynamics of each stock may differ in respect of theirbiological productivity and the relative impact of fishing on growth, survival andreproductive capacity. Because stock assessments and fishery controls are considered toapply uniformly to species populations throughout each management area, it is possiblethat the exploitation rate affecting individual biological stocks cannot be determined andthat the potential yield from the fishery is not realised. The key factor is that thepopulation unit considered to be a stock responds largely independently to the effects ofexploitation, because recruitment, growth and mortality within the stock are of moresignificance than emigration from or immigration to the stock (Harden-Jones, 1968).

The conventional definition of a stock as amanagement unit is pertinent to the realities of contemporary fisheries management, whichis essentially short term.

Reference:

M.G. Pawson and S. Jennings, 1996. A critique of methods for stock identification inmarine capture fisheries. Fisheries Research, 25: 203-217.