Rutgers University researchers have for the first time sequenced genomes from Atlantic cod, drawing information that may have implications for other fish maturing earlier as a result of fishing.
Author Malin Pinsky, an associate professor in the School of Environmental and Biological Sciences at Rutgers-New Brunswick, says there is evidence that many species of fish are maturing earlier as a result of fishing, including haddock, European plaice, whiting, American plaice, sole and sockeye salmon.
The study, led by Rutgers and the University of Oslo, concludes that overfishing likely did not cause the Atlantic cod to evolve genetically and mature earlier.
“Evolution has been used in part as an excuse for why cod and other species have not recovered from overfishing,” Pinsky said. “Our findings suggest instead that more attention to reducing fishing and addressing other environmental changes, including climate change, will be important for allowing recovery.”
Atlantic cod may be about eight million years old. Pacific cod split off from Atlantic cod evolutionarily some three to four million years ago when some stray fish swam through the then-open Bering Strait from the Atlantic Ocean.
There has been much debate over the last few decades about whether cod have evolved in response to fisheries, a phenomenon known as fisheries-induced evolution. Atlantic cod, for example, now mature at a much earlier age, and this is a concern because cod populations that mature later can produce more offspring and more effectively avoid predators, said Pinsky. They are also better protected against climate variability, more stable and less likely to collapse, he said.
Both theory and experiments have suggested that fishing can lead to an earlier maturation age, but up until now no one had tried to sequence whole genomes from before intensive fishing to determine whether evolution had occurred.
“It’s like putting a jigsaw puzzle back together again,” Pinsky explained. “That’s where computation comes in. We compare the genome of historic cod against the genome for modern cod. We are looking for areas that have changed or been lost.”
“One of the concerns is that over the last couple of decades Atlantic cod don’t get as big as they used to, and they reproduce earlier, at a much younger age,” Pinsky added.
“Because of these changes the populations are less stable and more vulnerable to predators and more subject to climate change,” he said. “If these changes are permanent, it may be difficult for these populations to recover, but our research shows they have not lost the ability to recover to (a) larger size.”
For this study researchers sequenced cod ear bones and scale from 1907 in Norway, 1940 in Canada and modern cod from the same populations. The northern Canadian cod had collapsed due to overfishing in the early 1990s and the Norwegian cod had faced high fishing rates, although with smaller declines, the study notes.
Researchers concluded that the cod likely did not evolve in response to fisheries.
There were no major losses in genetic diversity and no major changes that suggested intensive fishing induced evolution. While evolution cannot be entirely ruled out, it’s more likely they are developing earlier in response to their environment and would be able to mature later if the environment changes, benefitting the species, Pinsky said.