Atlantic cod, Gadus morhua, was a heavily overfishing
species in Northern Atlantic fisheries to the point where any commercial
fishing of the species became unsustainable. Atlantic cod is on the
International Union for Conservation of Nature’s Red List Threatened Species. It
was thought that overfishing caused early maturation in smaller sized fish due
to the high selection of larger cod, which kept the populations from reaching
their growth potential. If it was believed that cod were not reaching growth
potential because due to fishing pressures populations genetics began favoring
the smaller sized individuals that reached maturity early and populations would
not reach original sizes. This study compared experimental and wild results of
Atlantic cod using a genomic-wide analysis of 346,290 loci observing single-nucleotide
polymorphisms (SNP). The genome of Atlantic cod was sequenced from archives of
Atlantic cod before intense fishing pressures and after extreme decline in
populations from overfishing using scales and otoliths. These archives revealed
the genomic variation of many generations that were kept for fisheries management.
The results revealed a large difference between experimental genomes and wild
genomes. The genomic range of wild Atlantic cod was found to be not genetically
limited in their environment due to overfishing; whereas, the selectivity of
cod generations in a controlled experimental environment produced more
significant genetic variation across generations. However, in the wild,
polygenic evolution can still occur in the genetic diversity of wild
populations due to long term environmental conditions and not fishing
pressures. Other marine species can be directly influenced by fishing pressures
and genetic loss can occur in Atlantic cod based on experimental results, but
the conditions for this to occur is still under research. Due to these results
from this study, it supports that Atlantic cod populations will reestablish
from significant decreases in fishing pressures because of no genomic variation
loss. A reason that the wild population results differ from the experimental
results is because wild Atlantic cod populations respond to pressures from
phenotypic plasticity and this is supported by density-dependent growth. Wild
populations are much larger than experimental populations because wild
populations will hold more genomic variation across more individuals within the
population carrying it on to future generations.
https://www.pnas.org/content/pnas/118/15/e2025453118.full.pdf
https://www.frontiersin.org/articles/10.3389/fncir.2019.00066/full
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