Sexual HealthDid The North Atlantic Fisheries Collapse Due To Fisheries-Induced Evolution?
The Atlantic cod has, for many centuries, sustained major fisheries on
both sides of the Atlantic. However, the North American fisheries have now
largely collapsed. A new paper in the open-access, peer-reviewed journal
PLoS ONE from scientists at the University of Iceland and Marine Research
Institute in Reykjavik provides insights into possible mechanisms of the
collapse of fisheries, due to fisheries-induced evolution.
Cod fishing is of highest intensity in shallow water in Iceland and it
selects against genotypes of cod adapted to shallow water. The PLoS ONE
paper
reports a significant difference in Darwinian fitness (relative survival
rate) between shallow-water and deep-water adapted cod. The shallow-water
fish have only 8% of the fitness of deep-water fish. This difference can
lead to rapid elimination of shallow-water fish in only a few generations
with drastic effects on the population and the fishery.
Using molecular population genetics, the authors reports steep changes in
the frequency of genotypes at a single genetic locus with depth: a
gradient
of nearly one half percent drop in frequency per meter. The genotypes at
the locus are directly related to behavioral types that select deep vs
shallow water habitat by genotype.
"There is no direct targeting of specific genotypes. Instead the intense
selection results from the interaction of fish that select their habitat
by
genotype and fishermen choosing to fish in the preferred habitat of the
fish," said Einar Arnason, professor of population genetics and lead
author.
In addition to the molecular results, the study also demonstrates that the
length and age at which the fish become mature have decreased. So-called
"probabilistic maturation reaction norms" show that the length at which
there is a 50% probability of becoming mature, has, on average, decreased
nearly one centimeter per year. The changes observed very likely are
evolutionary genetic changes and not simply plastic phenotypic responses
to the
environment. They are comparable to changes that preceded the collapse of
northern cod at Newfoundland.
This finding further supports the hypothesis of an imminent collapse of
Icelandic cod due to the intense fisheries-induced selection. The cod
fishery
at Iceland is one of the world"s few remaining cod fisheries. The study
appears to have met all criteria for concern that this fishery is
threatened.
"Can anything be done to avert collapse?" the authors ask. A strategy that
would remove selection pressures against shallow-water adapted fish
would seem to be the answer. The authors speculate that immediate
establishment of large no-take reserves might be the right strategy by
relieving
selection pressures on all genotypes.
The findings provide general lessons for population and conservation
genetics that anthropogenic changes in habitat can lead to intense
selection even
if the mortality is non-selective in the habitat in which it occurs. The
study highlights the importance of applying Darwinian principles and
evolutionary thinking to fisheries and conservation science.
The study was funded by grants from the Icelandic Research Fund and
res from the Marine Research Institute and the University of
Iceland.
Specimens were obtained during Marine Research Institute Surveys. The
funders had no role in study design, data collection and analysis,
decision to
publish, or preparation of the manuscript.
Citation:
"Intense Habitat-Specific Fisheries-Induced Selection at the Molecular Pan I Locus Predicts Imminent Collapse of a Major Cod Fishery."
ērnason E, Hernandez UB, Kristinsson K (2009)
PLoS ONE 4(5): e5529. doi:10.1371/journal.pone.0005529
Plos One