Entangled Right Whale: an Extra Weight to Tow
Over 75% of North Atlantic right whales show injuries or scars caused by fishing gear. A study conducted by the Woods Hole Oceanographic Institution recently specifically addressed the issue of the extra weight towed by these entangled whales over long distances.
A heavy weight to carry
Over 75% of right whales, young individuals especially, show injuries or scars caused by fishing gear. Buoy ropes, gillnet panels, floating longlines and ghost nets are most often involved, but right whales have also been reported to run afoul of longlines, cod traps and herring weirs. They usually get caught by the mouth, fins or tail. Some of these entanglements result in the animal’s death. Whales can survive however with lines wrapped around their bodies, occasionally dragging nets, lines, buoys or traps for months or even years on end. The weakening of the animal caused by infected injuries as well as the loss of efficiency for swimming, diving, hunting and other behaviours are difficult to measure.
A research team led by the Woods Hole Oceanographic Institution (WHOI), in collaboration with the Center for Coastal Studies (CCS) and the National Oceanic and Atmospheric Administration (NOAA), has specifically addressed the issue of extra weight towed by entangled whales for months, even years, before being released by a specialized team, shedding the gear on their own or perishing. The results of the study were published on December 9, 2015 in the journal Marine Mammal Science.
To quantify this additional drag, researchers used a tensiometer to measure the dynamic forces (tension/compression) of various types of fishing gear towed by a boat at various speeds and depths. Sixteen sets of fishing gear were tested: ten longlines between 25 and 200 m, five with buoys and one with a two-brick lobster trap.
On average, fishing gear is believed to increase the drag of a whale 1.5 times more than that of a free-swimming whale. Entangled animals spend twice as much energy to swim at the same speed. In the long term, or if the whale becomes entangled multiple times, such incidents may significantly harm its migration, diet and even the growth of its young. Additionally, emaciated individuals have been documented in 56% of cases of entanglement-related mortalities. These results go to show that the efforts made to release a whale from its ropes are certainly not in vain. If the animal is not completely freed, cutting some of the ropes can reduce the drag by up to 85%.
An urban whale
North Atlantic right whales spend the summer in the Gulf of St. Lawrence, the Bay of Fundy and the Scotian Shelf region in Canada, and in the Gulf of Maine and off Cape Cod in the United States. In the fall, they head south along the US East Coast toward the waters of Florida and Georgia. During this long journey, they cross major shipping lanes and several fishing grounds. Numerous measures have been implemented to try to reduce the risk of ship strikes and bycatch, but to date, mortalities continue. In addition to being dangerous if not deadly for whales, these entanglements are costly for fishermen, who must replace lost or damaged ropes and traps.
With an estimated population of 526 individuals in 2014, the North Atlantic right whale is one of the most endangered species in the world. Every birth therefore represents a faint hope for survival.
To learn more:
Drag from Fishing Gear Entanglements Quantified, Study Focused on North Atlantic Right Whales
North atlantic right whale
Recovery strategies, North Atlantic right whale
Incidental catches in fishing gear