#26: Climate Change effect on right whale prey abundance

Global climate change has become a growing concern all over the world. Data suggests global temperatures will increase by 1.4-5.8 C by the end of the 21st century. The increase in global temperature will affect every part of the world. Coastal communities will be affected as sea level rises 13-95cm due to the Antarctic and Greenland ice caps melting as well as the thermal expansion of seawater. Global mean precipitation will rise by 5-20%, particularly in the higher latitudes, resulting in increased freshwater runoff from rivers to oceans. This will reduce salinity in these areas and may increase the prevalence of red tides. Areas not afflicted by excess precipitation will likely experience longer periods of drought.

In the ocean, as temperatures rise and salinity decreases, significant changes in ocean biology are likely, although we can only guess the effects on such a small population like the North Atlantic right whale. A climate change related shift in hydrographic factors has the potential to affect the abundance and quality of Calanus finmarchicus, a planktonic copepod that is the primary food source of the North Atlantic right whale. Calanus copepods are about the size of a grain of rice, and are the dominant zooplankton species found the western North Atlantic. Right whales consume between 0.6-6.4% of their body weight in calories per day, or as many as 2.6 billion C. finmarchicus! But because copepod development is temperature dependent, warming oceans could affect plankton population dynamics. A shift in C. finmarchicus abundance in right whale feeding grounds may cause right whale numbers in these areas to drop considerably. Salinity can also alter food for right whales. In the 1990's, arctic freshwater currents made their way down into the Gulf of Maine leading to changes in salinity and stratification that favored large increases in smaller species of zooplankton, most of which were not a suitable substitute as right whale food.

For right whales, climate change could mean shifts in the ranges and abundance of preferred food (Calanus copepods), shifts in species composition from copepods to other smaller less suitable prey species, and increases in red tides (which are known to be eaten by right whales accidentally).The reduction of suitable prey could pose a number of threats to right whales. Strong correlations have been made between C. finmarchicus abundance and right whale reproductive success, so reduction in prey abundance could lead to a decline in the number of calves. Reduced food can also lead to malnourishment, and increased susceptibility to disease, and increased mortality.

Not everything is so bleak though. One of our right whales, "Porter" travelled from Cape Cod Bay one spring to Norway by September, and returned to the Gulf of Maine the following year. Another whale was seen in the Bay of Fundy last summer, and in the Azores last month! These travels suggest that the capacity of this species to adapt to environmental changes, whether anthropomorphic or natural, may be greater than heretofore believed. Perhaps these travelers have carried the right whale population through tough times, and the long-distance travels of individually-identified right whales have shown they may not be as habitat restricted as has been believed.


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