North Atlantic fish populations shifting as ocean tempera...(p The researchers looked at where the...)

The researchers looked at where the fish were caught and their biomass, or the estimated total weight of the population, in each year of the survey. For each stock they estimated the center of abundance, average depth, the range or area that the stock occupied, and the average temperature at which each stock was found.

They also took into account fishing pressures on the species over time, as well as natural cycles in ocean temperature. Ocean temperatures have increased since the 1960s and 1970s, and the authors found significant changes in species distribution consistent with warming in 24 of the 36 stocks studied.

Ten of the 36 stocks examined had significant range expansion, while 12 had significant range contraction. Changes in a species range can be affected by both temperature changes and fishing pressure, with heavily fished stocks appearing more sensitive to climate change and often showing a larger shift. Seventeen of the 36 stocks occupied increasingly greater depths, and three stocks occupied increasingly shallower waters. However, the temperature at which each stock was found did not change over time, suggesting that fish are moving to remain within their preferred temperature range.

Fish species can respond to changes in ocean temperature in a variety of ways. The stock can move poleward to avoid warmer water temperatures, or move into deeper waters than they have previously been found. If fish cannot change their geographic or depth distribution, there may be changes in growth, reproduction and mortality rates. As a result, the size of the population may increase or decrease depending on the temperature preference of the species. Most species in the study were found to be responding to warming ocean temperatures in one of these ways.

"The fact that we see responses in many species consistent with what you would expect with warming, but in different types of species that have experienced different histori
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