Right whale numbers improving, but the pace remains slow

First published in the MLA Newsletter, July, 2011.

This summer the National Marine Fisheries Service (NMFS) will hold a series of public scoping meetings in Maine to discuss options to reduce the risk of entangling endangered whales in lobster gear, specifically, vertical lines. These meetings are part of a multi-year process through which NMFS will devise new whale rules that will go into effect in 2014. To raise awareness about the importance of these meetings and help lobstermen understand why they are happening, the MLA newsletter will run a series of articles on endangered whales and the laws in place to protect them. The second installment of this series explores reproduction strategies and how the birth rate influences the population growth.

There are only about 450 North Atlantic right whales left in the world. Some scientists believe that these whales could be extinct in 200 years if birth rates continue to be low and accidents with ships and fishing gear continue. While deaths from ship strikes have declined, population growth is still relatively low. “Population rate and birth rate are two different things,” explained Scott Kraus, vice president of research at The New England Aquarium. “Population rate is all births minus all deaths.” Right now, the population rate is at one to two percent growth per year. Compared to the rate of the healthy right whale populations in the southern hemisphere, which are growing at six to seven percent a year, it looks as if the population in the north is barely growing. However, if you look just at birth rate, the number of babies born each year to northern whales has increased. In the 1980s, the average number of calves born each year was twelve, then it dropped in the 1990s to an average of ten, despite an increase in adult females. Calf production then rebounded starting in 2001, and for the last ten years, an average of 24 calves have been born each year. Unfortunately, this is about 15-20 fewer calves than would be expected of the current population. “Calving only happens every three years for females if all goes right,” said Kraus. And it’s easy to see why so few calves are born when you realize what the whales go through to have babies.

“The size of the male’s testicles usually grabs people’s attention,” said Kraus. Right whales have the heaviest testes of any mammal, weighing in at nearly 2,000 pounds. The males rely on the amount of sperm they can produce to successfully mate with a female rather than displays of aggression or color. Males don’t fight each other for the attention of a female like some animals do, they don’t show off flashy colors like many birds, nor do they protect a territory to prove that they are dominant. Instead, they put their energy into sperm production in hopes of successfully mating with a female. But the females certainly don’t make it easy for the males.

Courtship occurs at the surface in what are termed Surface-Active Groups (SAG). “The female doesn’t know who is a good mate,” explained Kraus. “SAGs test his lung capacity and strength. Females make it difficult in order to really test the males.” The female initiates the event by calling to males with a groan that resembles a cow mooing. The males swim to the female, eager to be the first to reach her. However, once they do reach her, the female rolls onto her back, keeping her genitals out of the water, all while swimming in large circles. But the males still have a chance; the female has to roll back over in order to breathe. “Copulations occurs every time she breathes, so mating opportunities for males appear perhaps 60 times an hour,” Kraus said. “The more sperm a male can release into the female, the better the probability that he will be the one to impregnate her.”

However, it seems that not all SAGs are formed in order to mate. Females typically give birth to calves in January after a gestation period of 12-13 months. But SAGs have been observed throughout the year. “SAGs are the most important behavior in the North Atlantic right whale,” said Kraus. Since females only give birth every three years, there is “a mismatch between the numbers of sexually mature males and females,” Kraus explained. This creates extreme competition for the few fertile females that are available each year. SAGs may take place year-round because it is important for the male whales to practice mating behavior, therefore increasing their chances of successfully fertilizing a female.

Producing and caring for offspring is physically draining for female right whales. Pregnancy lasts 12-13 months and results in the birth of a single calf, weighing between 1,500 and 2,000 pounds and measuring between 15 and 20 feet in length. The calf will grow quickly while nursing, measuring between 28 and 30 feet after a year with its mother.  This year of nursing drains the mother of her nutrients and fat stores, requiring her to take at least a year to replenish her health and condition before mating again.

Even though there are approximately 85 more North Atlantic right whales now then there were just four years ago, the birth rate is still far below what researches expect it to be. “In healthy populations, such as in the southern hemisphere, if there are 100 sexually mature females, we would expect to see about 33 calves a year. In the North Atlantic we have about 120 adult females, and right now we see the number of calves in the low to mid-20s,” reports Kraus. Last year there were 21 calves born, far fewer than the average of 40 expected to be seen in a healthy population. “There are two parts to the equation,” he explained.

“We see diminished reproduction and increased mortality from human interactions.”

Two of the biggest threats to right whales are ship strikes and entanglement in fishing gear. “We’ve seen a reduction in kills from ships since they have been slowed down, but it’s too early to tell if gear changes are helping,” said Kraus. Over 80% of this endangered species have scars indicating fishing gear entanglement. Kraus said the number of entanglements ranges from 20-80 each year. The rate of entanglements seems to be staying the same but the severity is increasing. “This may be because rope has gotten stronger,” Kraus speculated, “and the further offshore people fish, the bigger their rope gets so the whales are having a harder time breaking free.”

Kraus said he knows it isn't easy for the fishermen to make changes to their gear, especially when most people don’t see the whales near where they fish. “This is a classic conservation dilemma. The chances of fishermen seeing a right whale are low; most guys won’t ever see one. Nevertheless, 80% of the whale population will encounter lobster gear. If we could figure out how to make fishing gear that won't kill the whales, then the occasional gear entanglement wouldn’t be such a big problem.”

“We have seen a lot of success involving fishermen in this process,” said Kraus. “They are making a great effort to be involved and many have been great, willing to test our crazy ideas to reduce lethal entanglements.”