Historical changes in genotypic frequencies at thePantophysinlocus in Atlantic cod (Gadus morhua) in Icelandic waters: evidence of fisheries-induced selection?

Abstract

The intense fishing mortality imposed on Atlantic cod in Icelandic waters during recent decades has resulted in marked changes in stock abundance, as well as in age and size composition. Using a molecular marker known to be under selection (Pan I) along with a suite of six neutral microsatellite loci, we analysed an archived data set and revealed evidence of distinct temporal changes in the frequencies of genotypes at the Pan I locus among spawning Icelandic cod, collected between 1948 and 2002, a period characterized by high fishing pressure. Concurrently, temporal stability in the composition of the microsatellite loci was established within the same data set. The frequency of the Pan IBB genotype decreased over a period of six decades, concomitant with considerable spatial and technical changes in fishing effort that resulted in the disappearance of older individuals from the fishable stock. Consequently, these changes have likely led to a change in the genotype frequencies at this locus in the spawning stock of Icelandic cod. The study highlights the value of molecular genetic approaches that combine functional and neutral markers examined in the same set of individuals for investigations of the selective effects of harvesting and reiterates the need for an evolutionary dimension to fisheries management.

Settling-depth vs. genotype and size vs. genotype correlations at the Pan I locus in 0-group Atlantic cod Gadus morhua

“…Pan I AB heterozygotes were intermediate in length of the 2 homozygotes. Similar features were recently reported from Icelandic waters (Jakobsdóttir et al 2011), although growth−genotype relations there have previously been reported to vary among spawning sites (Jónsdóttir et al 2008). Reports on individual length in NCC and ANC populations, classified by otolith typing, showed no difference in growth between the 2 populations (Berg & Albert 2003).…”

“…The coexistence of migratory and stationary stocks of Atlantic cod has been reported from different regions of the North Atlantic (e.g. Robichaud & Rose 2004, Jakobsdóttir et al 2011), but nowhere so well defined and with such abrupt differences at the Pan I locus as between ANC and NCC.…”

Historical DNA reveals the demographic history of Atlantic cod (Gadus morhua) in medieval and early modern Iceland

“…Fisheries pose strong predation pressure on fish populations and may cause evolutionary change [72]. Two recent studies indicate fisheries effects on the relative frequencies of inshore (Pan I AA ) and offshore (Pan I BB and Pan I AB ) genotypes in the Icelandic Atlantic cod population [9,18]. The frequency of the offshore Pan I B allele in the historical samples is low (table 2) in comparison with samples from modern-day inshore spawning stock [9].…”

“…Archived material from fisheries surveys has revealed the history of many commercial fish populations, although the samples commonly include only few generations [17][18][19]. Atlantic cod vertebrae have accumulated at historical fishing sites in the North Atlantic since the beginning of commercial fishing [20,21] and in Iceland since the early settlement [22,23].…”

Consequences of fisheries-induced evolution for population productivity and recovery potential

“…It should also be borne in mind that even if fisheries-induced changes in life histories did not affect population growth rate directly, they may still affect a population's ability to cope with environmental fluctuations [59]. In cod, for instance, a population of early-and small-maturing individuals has been hypothesized to be more vulnerable to climate change [60,61]. All such features need to be carefully accounted for when evaluating conservational consequences of anthropogenic evolution [62].…”