The warming of Earth’s oceans due to climate change is affecting where the world’s fish live, eat and spawn — and often in ways that can negatively affect their populations. That’s according to a new journal paper Ecology and Evolution of Nature.
The researchers write that populations experiencing rapid range reductions are dramatic, up to 50 percent within a decade. The most affected populations are those living on the north poleward edges of their species’ range.
“There is a common wisdom among many climate change biologists that species that rapidly shift their ranges by moving northward must provide a mechanism to maintain healthy populations — that species migration is should be the winners of climate change. Our results show the exact opposite,” said paper co-author Jean-Philippe Lessard, a professor in the Department of Biology.
“Species that move their range quickly experience little change in their population size in their core range. But some of them experience large falls in their populations on the northern edges.
“In fact, population declines are mostly driven by north poleward populations,” he added. “We expect that many individuals from the core of the range will move north due to climate change and maintain these northern populations. But the northern populations are the ones most likely to collapse.”
Common patterns across species
The researchers combined data from two large databases to examine the population numbers of species that are changing range. They looked at 2,572 population-level time series involving 146 species, mostly living in temperate or subpolar regions.
Their analysis revealed that very fast poleward migration of species, defined as upwards of 17 kilometers per year, shows marked population declines, compared to negligible increases in populations that do not migrate.
“We have not yet identified any underlying mechanism that explains these results, but we can imagine that the populations that are rapidly declining are from species that are less plastic or less innovative to adapt to changing conditions,” says said Lessard. “It could be that they are both rapidly dispersing toward the colder water near the poles.”
It also showed that the correlation was maintained beyond the samplings used from small portions of extreme values, the location where range shift velocity estimates were measured and the use of negative range shift values, such as migrations toward the equator rather than the poles.
Additionally, the data showed that the relationship was not driven by some species with widely studied populations. However, this is largely driven by trends observed in the Northeastern Atlantic, where most of the data was recorded.
Multiple threats in combination
For species of economic value, the one-two combination of range shift and commercial fishing can potentially devastate local populations. Researchers point to the collapse of western Atlantic cod as an example of the dangers posed by vulnerable populations.
“Commercial fish show a similar pattern of population decline with rapid turnover, and are generally more likely to experience population decline than non-commercial species.”
