Ask Dr. Pauly
Dr. Daniel Pauly is the founder and principal investigator of the Sea Around Us project at the University of British Columbia’s Institute for the Oceans and Fisheries, as well as an Oceana Board Member.
How is global warming affecting fisheries? The news about the impact of global warming on the oceans — or, more precisely, of ocean warming and deoxygenation — are gradually becoming more serious and wideranging, so much so that a brief review of the issues involved may be helpful. Here, contrary to my earlier columns, I will add a number of scientific or other references to the summary below of these issues, so that readers get a feel of the existing literature. My excuse for being associated with several of these references is that I do work on these topics. 1. Elevated temperatures increase the oxygen requirements of fish while decreasing the oxygen content of the water1 (see also Oceana
Magazine, Winter 2015). This effect is worse in oxygen-poor zones of the ocean, which are spreading². One major effect of these challenges is that the maximal size that fish and invertebrates (such as lobsters and squids) can reach declines, along with the size at which they become mature¹, which reduces the number of eggs they can produce; 2. Another major effect of increasing ocean temperatures is that fish populations (which usually occur over a range of latitudes) do well on the cool edge of their distributions and badly on the warmer edge3. Thus, rising ocean
Atlantic cod sizes in higher versus lower temperatures 180
Total Length (Centimeters)
160
Iceland (1-10° C or 33.8-50° F)
140 120
Northeastern France (5-15°C or 41-59° F)
100 80 60 40 20
Atlantic cod
0 0
5
10
15
20
25
Age (Years) The above graph – adapted from one that appears in reference 1 – shows how water temperature affects the growth and size of Atlantic cod in two different regions. In Iceland, they reach much larger sizes than in French waters.
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