Current Biology 2021 May 17;S0960-9822(21)00614-X. doi: https://doi.org/10.1016/j.cub.2021.04.067
The North Atlantic right whale (Narwhale, NARW) is a medium-sized toothed whale that lives year-round in the Arctic waters around Greenland, Canada, and Russia. It possesses a large tusk from a protruding canine tooth. NARW born in recent years have experienced stunted growth, and over the same period have experienced increasing rates of entanglement in fishing gear. As a result, NARW appear to have less energy to devote to early growth. A portion of the estimated length reduction was directly attributable to entanglements.
These researchers evaluated changes in body lengths of NARW over a 20-year period. They combined age and length data collected from crewed aircraft in 20002002 and from remotely operated drones since 2016 to generate a growth model. The ages of measured whales ranged from <1 to 37 years old. They find that body lengths have been decreasing since 1981 and entanglements in fishing gear are associated with shorter whale lengths. Birth year had the greatest effect on the estimated length of NARW. Known energy-consuming entanglements of a whale with attached gear and also entanglements of its mother during nursing had negative effects on expected maximum length. The effect of entanglement as appeared to have a continuous effect, so that whales with longer entanglement durations had even greater reductions in length.
NARW have been declining in abundance since 2011 due primarily to vessel strikes. They are now protected from direct harvest but numbers remain far below their historical abundances. Climate-driven changes result directly in mortality. But it also impacts on life history, individual fitness, and population viability. Arrested growth may lead to reduced reproductive success and increased probability of lethal entanglements. These results show that sub-lethal stressors threaten the recoveries of vulnerable whale populations even in the absence of direct harvest.