Conservation genetics considerations in fishery management

TLDR: It is argued that assessments of acceptable levels of introgression should be made on the basis of spontaneously occurring gene flow estimated from genetic data using parameters such as Fst or similar ones, and it is concluded that although the fitness approach may appear attractive it is not compatible with the more general objective of maintaining genetic diversity between and within populations.

Abstract: This paper discusses three aspects of genetic conservation relating to fishery management and fish culture, namely (1) the goal for conservation (what to conserve), (2) a guideline for assessing acceptable levels of gene flow among populations. and (3) the effect on the genetically effective population size resulting from stock enhancement. Goal for conservation: The goal for genetic conservation is to maintain genetic variability between and within populations. It has been suggested recently, as an alternative to that goal, that in the context of fisheries management conservation should strive at maintaining the variance or the distribution of fitness. The characteristics of this model are discussed from the perspective of population genetics. It is concluded that although the fitness approach may appear attractive it is not compatible with the more general objective of maintaining genetic diversity between and within populations. Acceptable levels of gene, flow: A tension exists between the need for protection of natural fish populations and the rapidly expanding levels of aquaculture causing increased migration into those populations. Guidelines are needed for assessing levels of introgression that are acceptable in the context of genetic conservation. To avoid unrealistically restrictive recommendations it is suggested that acceptable levels of introgression are related to those occurring naturally. It is argued that assessments of acceptable levels of introgression should be made on the basis of spontaneously occurring gene flow estimated from genetic data using parameters such as Fst or similar ones. Stock enhancement and effective size: In the context of genetic conservation previously published recommendations on stocking have focussed on the need to identify the genetic structure within the region in question to ensure that the appropriate population is targeted for propagation and release. There is, however, an additional aspect that appears to have been largely unrecognized: the reduction of the genetically effective size of the total population that may result from breeding-release programmes aimed at supporting wild stocks. The details of this problem are introduced and discussed.