Ship strikes and entanglement in fishing gear are threatening
the survival of the North Atlantic right whale, one of the most
endangered whales with an estimated population of about
350. With eight recorded deaths in the past 16 months and a
population growth rate that has declined since 1980, scientists say
that unless emergency management actions are taken the population will
face a catastrophic decline and become extinct.
A report in the July 22 issue of the journal Science says the recent loss of eight whales, six of them adult females and three carrying near-term fetuses, is unprecedented in 25 years of study of this species, Eubalaena glacialis. Four of the females were beginning to bear calves, and since the average lifetime calf production is as high as five calves, the deaths of these females represents a reproductive loss of as many as 21 animals.
After almost 1,000 years of whaling that brought the species close to extinction in the early 20th century, the North Atlantic right whale has been protected from commercial whaling since 1935 but has faced constant threats from human activities, mainly collisions with ships and entanglement in fishing gear. In contrast, southern right whales, Eubalaena australis, are thriving, with a population estimated at more than 10,000 animals and growing at more than seven percent each year.
According to the recent study, lead by Scott Kraus of the New England Aquarium, 50 right whales have been reported dead since 1986, at least half of them from human activities. At least 19 were killed by vessel collisions and at least six by fishing gear entanglement. In addition, there were 61 confirmed reports of whales carrying fish gear, with about half of those whales able to shed the gear or were disentangled by humans.
Study co-authors Hal Caswell and Michael Moore of the Woods Hole Oceanographic Institution (WHOI) emphasize the consequences for the population. “The bottom line is that human induced right whale mortality is currently exceeding a level that allows the population to grow,” said Michael Moore, a veterinarian and research scientist. “ It is fulfilling the prediction made by Hal Caswell and Masami Fujiwara that if this level of mortality continues, the likelihood of the species having a sustainable future is very low.”
Fujiwara, a co-author on this study, was a student in the MIT/WHOI Joint Graduate Program in Oceanography and Applied Ocean Sciences and Engineering and is now at the University of California, Santa Barbara. In addition to the WHOI scientists, the recent study included scientists from Cornell University, University of Rhode Island, Provincetown Center for Coastal Studies, University of North Carolina at Wilmington, Florida State University, and Duke University Marine Laboratory.
An analysis of right whale population data by Caswell and his collaborators Fujiwara and Christine Hunter shows that northern right whales will probably become extinct within 200 years if the environmental conditions experienced by the whales in recent years continues. Data show the female survival rate, especially for females that have just given birth, is going down at an alarming rate.
Calf production has increased recently, from an average of 12 calves per year prior to 2000 to between 16 and 31 calves per year from 2001 to 2005. While this may seem like good news, it is insufficient to reverse the population decline, let alone compensate for the recent increase in deaths. Caswell and his co-authors report that the increased reproductive output will increase population growth only about 1.6 percent per year, not enough to save a population that has been declining about two percent per year since 2000.
"The future of the right whale depends primarily on reducing deaths from human activities, "Caswell says. “ Steps have been taken to minimize risks to right whales, but more needs to be done. If mortality continues at the levels of the past year, this population will face extinction.”
"Because the population is so small, a single death represents a significant mortality rate," Caswell, a senior scientist at the Institution, says. "Preventing the deaths of just two females a year would make a huge difference. The eight deaths reported in the past 16 months is almost three times the average annual rate of mortality. If something isn’t done to turn this around this species will no longer exist in the not too distant future.”
The Science study recommends that federal officials implement emergency measures to reduce ship speeds and re-route commercial and military ships as recommended in 2004, and eliminate or minimize the amount of fixed fishing gear in the water column. Steps could include mandating changes in the pot-fishing industry (lobsters, crab, etc.) that will reduce gear in the water, requiring the use of different rope types to minimize entanglements, developing and implementing fishing methods that do not use vertical lines attached to surface buoys, and streamlining the current process for right whale research and gear modifications, which now takes years.
Right whales are distributed from the coast of northern Florida to the Bay of Fundy, with females and calves most often seen in winter months off the coast of Florida and Georgia, their only known calving ground. That area is also close to shipping lanes where large vessel traffic has increased since 1980. More than 60 percent of the North Atlantic right whales have scars from entanglement in fishing gear, such as lobster pots and sink gillnets. Cuts from ship strikes are also visible on many whales.
WHOI has a major right whale initiative underway through its Ocean Life Institute and is working with a number of research organizations and institutions on ways to reduce right whale mortality.
A North Atlantic right whale dives in search of food near Grand Manan Island in the Bay of Fundy, Canada. (Photo by Michael Moore, Woods Hole Oceanographic Institution)