Birth rate decline, fish net entanglements threaten recovery
Some whale populations have recovered strongly since end of the whaling era, but North Atlantic right whales are still struggling and their recovery is in doubt. More and more, the marine mammals are getting entangled in nets, and their overall birth rate has declined by 40 percent since 2010, marine researchers reported this week in the journal Frontiers in Marine Science.
About 500 North Atlantic right whales still survive after two decades period of modest annual growth, but even that was slow compared to other species — 2 to 3 percent a year compared to 6 to 7 percent in other regions, the study found. One recent study found that a different species of right whale is currently making a comeback around New Zealand, with pioneers from Antarctic waters once again visiting the island’s sandy bays to reestablish breeding grounds.
“Right whales need immediate and significant management intervention to reduce mortalities and injuries from fishing gear,” the authors concluded in the study. “Managers need a better understanding about the causes of reduced calving rates before this species can be considered on the road to recovery. Failure to act on this new information will lead to further declines in this population’s number and increase its vulnerability to extinction.”
Right whales got their name because whalers considered them the “right” whales to kill because they stayed near shore, reachable by small boats, and floated when killed because of their large stores of blubber. The same characteristics that made them an ecological marvel also caused them to be sought by hunters.
Since 1935, when North Atlantic right whales neared extinction and whaling for this species became illegal, right whales rebounded to about 295 living whales in 1992. The number of whales then increased by about 2.8 percent a year, to an estimated 500 right whales in 2010.
But the numbers of calves born each year dropped dramatically in the following five years. Kraus said researchers haven’t yet pinpointed the exact cause of the declining birth rate, buts suspects that non-lethal entanglements could be stressing the animals with long-term physical and reproductive health effects.
Other information shows that prey species have been shifting due to climate and environmental changes, potentially making harder for right whales to feed adequately. Finally, there is some concern over the potential for long-lasting implications from a disease event in the 1990s.
The new study analyzed the rising numbers of right whales that died due to human action. From 2009 to 2013, an average of 4.3 right whales died each year, mostly due to deadly entanglements in fishing ropes and gear, according to 2015 National Marine Fisheries Service data. By comparison, between 1970 and 2009, 44 percent of right whales died from ship strikes and 35 percent died from entanglements. New research on ropes that break more readily when whales become entangled may help.
Recent US and Canadian governmental action to slow ships and to move shipping lanes out of migratory paths of whales have been successful at reducing ship strikes.
In January 2016, the National Oceanic and Atmospheric Administration (NOAA) suggested that the species’ population decline was reversing, and there were signs of recovery. But, Dr. Kraus and his fellow authors believe that the opposite might now be true. “In contrast to this optimistic view of right whale recovery, our review of the recent science suggests that fishing gear entanglements are increasing in number and severity, and that this source of injury and mortalities may be overwhelming recovery efforts.”