Low effective population size and evidence for inbreeding in an overexploited flatfish, plaice (Pleuronectes platessaL.)

Abstract

Overexploitation and subsequent collapse of major worldwide fisheries has made it clear that marine stocks are not inexhaustible. Unfortunately, the perception remains that marine fishes are resilient to large population reductions, as even a commercially 'collapsed' stock will still consist of millions of individuals. Coupled with this notion is the idea that fisheries can, therefore, have little effect on the genetic diversity of stocks. We used DNA from archived otoliths collected between 1924 and 1972 together with 2002 juvenile's tissue to estimate effective population size (Ne) in plaice (Pleuronectes platessa). Ne was estimated at 20 000 in the North Sea and 2000 in Iceland. These values are five orders of magnitude smaller than the estimated census size for the two locations. Populations examined between 1924 and 1960 were in HardyWeinberg equilibrium, whereas populations examined after approximately 1970 were not. Extensive testing was performed to rule out genotyping artefacts and Wahlund effects. The significant heterozygote deficiencies found from 1970 onward were attributed to inbreeding. The emergence of inbreeding between 1950 and 1970 coincides with the increase in fishing mortality after World War II. Although the biological mechanisms remain speculative, our demonstration of inbreeding signals the need for understanding the social and mating behaviour in commercially important fishes.

Genetic panmixia and demographic dependence across the North Atlantic in the deep-sea fish, blue hake (Antimora rostrata)

“…We found a non-random distribution of individuals in relation to size and sex, and relatively high F IS levels within most sample-sets. This suggests that standard population comparisons may not be appropriate in this species and that some kind of temporal Wahlund effect may be operating (Hoarau et al, 2005), for example, because of sweepstake effects (in which most surviving larvae are from a relatively small number of females) every breeding season (Hedgecock, 1994). In common with previous studies of A. rostrata, we found that samples from off Greenland contained both males and females, whereas samples from elsewhere consisted almost entirely of females.…”

Demographic and genetic factors shaping contemporary metapopulation effective size and its empirical estimation in salmonid fish

“…Interestingly, Hoarau et al (2005) reported that their low N e /N ratio for North Sea plaice could be explained by inbreeding. This inference may essentially be correct, with the distinction that population subdivision (that is, inbreeding), may have introduced a downward bias into N e , in addition to inbreeding effects reducing N e through biological processes.…”

Population genetics of cobia (Rachycentron canadum) in the Gulf of Thailand and Andaman Sea: fisheries management implications

“…At present, there is no regular collection of data to show changes in the level of genetic diversity of cobia over time. Additionally, it has been shown that a high or unchanged level of genetic diversity may not be able to fully reflect the status of population exploitation if the effective population size of the species is large (Hoarau et al 2005). However, due to the small and undervalued domestic market for cobia, it is possible that cobia fisheries in Thailand may not yet be overexploited.…”