Loss of microsatellite diversity and low effective population size in an overexploited population of New Zealand snapper ( Pagrus auratus )

Abstract

Although the effects of overfishing on species diversity and abundance are well documented, threats to the genetic diversity of marine fish populations have so far been largely neglected. Indeed, there seems to be little cause for concern, as even ''collapsed'' stocks usually consist of several million individuals, whereas population genetics theory suggests that only very small populations suffer significant loss of genetic diversity. On the other hand, in many marine species the genetically effective population size (Ne), which determines the genetic properties of a population, may be orders of magnitude smaller than the census population size (N). Here, microsatellite analyses of a time series of archived scales demonstrated a significant decline in genetic diversity in a New Zealand snapper population during its exploitation history. Effective population sizes estimated both from the decline in heterozygosity and from temporal fluctuations in allele frequency were five orders of magnitude smaller than census population sizes from fishery data. If such low Ne͞N ratios are commonplace in marine species, many exploited marine fish stocks may be in danger of losing genetic variability, potentially resulting in reduced adaptability, population persistence, and productivity.

Panmixia in the European eel: a matter of time…

“…On the other hand, these figures may not be unrealistic, as the estimated effective size of marine fishes can be several orders of magnitude less than the actual number of adults present in the population (Hauser et al 2002). The genetic 'sweepstake' hypothesis (Hedgecock 1994), which has affinities with the ecological match/mismatch hypothesis (Beaugrand et al 2003), was proposed to explain extremely low effective-to census-size ratios in highly fecund marine species, and states that many families do not recruit because their larvae do not end up in the right environment at the right time to survive critical life stages.…”

Temporal changes in allele frequencies but stable genetic diversity over the past 40 years in the Irish Sea population of thornback ray, Raja clavata

“…In a review of 192 studies, Frankham (1995) established that, on average, N e is nine times smaller than the census population size (N). In marine teleosts this ratio can be much smaller, generally estimated at about 10 À5 (Hauser et al, 2002;Hutchinson et al, 2003;Hoarau et al, 2005;Poulsen et al, 2006), though Turner et al (2002) estimated 10 -3 in red drum Sciaenops ocellatus. Hence, N e is an important parameter in population risk assessment.…”

A bias correction for estimates of effective population size based on linkage disequilibrium at unlinked gene loci*

“…Researchers still debate whether the ratio of effective to census population size (N e /N) is constrained within certain limits (Nunney 1993;Frankham 1995) or can be orders of magnitude smaller for some species (Hedgecock 1994;Turner et al 1999;Hauser et al 2002). Because of the difficulty of obtaining adequate demographic data to compute N e , several genetic methods for estimating effective size have been proposed.…”