The order Cetacea includes over 80 species of whales, dolphins and porpoises and can be divided into two distinct suborders; Mysticeti and Odontoceti. The North Atlantic right whale (NARW) (Eubalaena glacialis) belongs to the Mysticeti suborder, in the Balaenidae family under the Eubalaena genera. It is one of three right whale species on earth; the other two being the North Pacific right whale (Eubalaena japonica) and the southern right whale (Eubalaena australis).
Previously, the North Atlantic and North Pacific right whales were classified as the
same species under the term Eubalaena glacialis, but a recent study has revealed that the North Pacific and North Atlantic right whale are genetically distinct from one another. Furthermore, it was established that North Pacific right whales and the southern right whales were more closely related than the North Pacific and North Atlantic species (Rosenbaum et al. 2000).
The North Atlantic right whale (NARW) (Eubalaena glacialis) is considered the most endangered of all large cetaceans in the world. With a population of approximately 450 individuals, and little sign of recovery despite over 75 years of international protection, the survival of this species is precarious.
Right whales are rotund whales, weighing in at 36,000-72,000 kg. The average size of a fully grown adult NARW is 14 meters with females being 1 meter larger than males. These whales often appear to be upside-down due to their bowed lower jaw and narrow, arched upper jaw (rostrum) which holds 205-270 baleen plates on each side that can reach lengths of 2-2.8 meters (figure 2). Baleen plates are only 18 cm wide, are usually black in colour and contain fine fringes to filter copepods from water. The NARWs head makes up about 25% of its body length.
Right whales are black in colour and occasionally have white blotches on their chin and belly. Raised and thickened skin patches, known as callosities, are present on various points of the head and face including the rostrum, around the eyes, behind the blowhole, and around the jaw, chin and lips. Soon after birth, cyamid crustaceans or whale lice, infest these raised skin patches giving them a creamy-yellow colour (figure 1).
Several other physical features also make the right whale easily identifiable in the field. These features include the absence of a dorsal fin, two blowholes arranged in a V-shape (figure 3), and broad, black flippers and fluke.
Distribution and Range
Right whales are migratory, spending part of the year feeding in colder waters before migrating to warmer waters to calve. The NARW inhabits the mid-Northern Hemisphere from the Gulf of Mexico to Iceland and Norway. Five critical habitats currently exist where numerous individuals congregate at various times of the year (figure 4). They include the South Eastern United States (SEUS), the Great South Channel (GSC), Cape Cod Bay (CCB), the Bay of Fundy (BOF), and the Roseway Basin (RB). Most females migrate to the SEUS (coastal waters of Florida and Georgia) during the winter months to calve; this is currently the known calving ground for the species. Occasionally, non-pregnant females and males are also found here, some remain in CCB, Jeffery’s Ledge and Jordan Basin, others can be found in the Gulf of Maine (the possible long elusive breeding ground), but most migrate to areas unknown. During the months of spring, they can be found in the GSC, CCB and Massachusetts Bay, before pressing even further north during the summer months to the BOF and the RB.
The average age at which NARW females reach sexual maturity is nine years of age. Most females produce their first calf around 10 years of age, although some females have produce their first calf as young as five years or as old as 21 years. Right whales are capable of producing a calf once every three years and gestation lasts approximately one year. Calves are born during the winter with the majority born between December and March. At birth, NARW calves are already 4-5 m in length and by the time they are weaned, at 11 months of age, they will have almost doubled in size (figure 5). Following weaning, cows spend one year building up their energy reserves to support the next pregnancy.
Male right whales are assumed to reach sexual maturity at eight years of age, although no males under 10 years have sired a calf and most are 15. There is a significant skew in male reproductive success, with numerous males having sired no calves or multiple calves and few males having sired a single calf. This suggests that right whales have evolved pre- and postcopulatory mechanisms into their mating system. Intense sperm competition is hypothesized to be of great importance as male right whales have the largest penis length (up to three meters) to body length ratio and testes weight (980 kg) to body weight ratio of any baleen whale species. Older males may have higher rates of reproductive success do to higher androgen levels which could allow for continued testicle development and higher rates of spermatogenesis. Another explanation for higher rates of reproductive success in older males could be greater strength, endurance or skill in surface active groups.
Mating is speculated to occur in surface active groups (SAG), which consist of two to 40 individuals (figure 6 and 7). A single female who remains inverted at the surface, turns over every minute to breathe, giving the male who has competed for a position closest to her breeding rights. SAGs can last an hour in duration meaning that females may breed with multiple males up to 60 times. These groups occur all throughout the year with most observed in late summer rather than in winter, when conception is thought to occur, which could imply that either delayed implantation occurs in this species, the gestation period is longer than 12-13 months, or these groups form to fulfill social functions, help with mate selection, and allow individuals to practice their courtship behaviours before the breeding season begins. SAGs are not always indicative of reproductive intentions; 20% of SAG consists of all females, all males, or juvenile individuals.
Past and Present Threats to Recovery
While the southern right whale population has significantly recovered over the years, the North Atlantic population continues to struggle. Below are some examples of some of the threats, past and present, which has or is contributing to the lack of recovery.
As their name implies, right whales were
considered the “right” whales to hunt because the slow speed at which they swim made them easy to catch and their abundant blubber stores allowed them to float once dead, making them easy for whalers to render (figure 8).
In 1935, right whales were granted international protection, but by this time the NARWs effective population size was estimated at 85 individuals. While whaling was partially responsible for the diminished population, genetic profiling of a 16th century NARW bone suggests a major population decline predated the whaling boom.
In 1935, right whales were granted international protection, but by this time the NARWs effective population size was estimated at 85 individuals. While whaling was partially responsible for the diminished population, genetic profiling of a 16th century NARW bone suggests a major population decline occurred before Basque whaling began.
While the threat of whaling has long since passed, right whales still find themselves in deadly encounters with humans. Right whales live in coastal waters making them highly susceptible to ship strikes, and the NARW in particular often find themselves in the midst of high volumes of ship traffic. Frequently, right whales are observed with deep gashes from the propeller blades of the boats they collide with (figure 9). These collisions can also result in fractured bones and internal bleeding. Between 1970 and 2005, at least 19 out of 34 NARW deaths were marine vessel related. In 2003, a major shipping route in the Bay of Fundy was rerouted to decrease the number of vessel related injuries and fatalities after right whale density models showed a significant overlap with the shipping route (figure 10 and 11). Except for research vessels, those given permission by the NOAA and commercial fishing ships hauling in gear, it is illegal for marine vessels to come within 500 yards of a right whale.
Right whales also fall victim to entanglement in fishing gear resulting in severe mutilation and even starvation. Over 75% of right whales exhibit scars consistent with entanglement (figure 12) and numerous right whales have been seen with coils of rope constricting their body, flippers and tails. Sometimes, ropes even become lodged in their baleen plates or wrapped around their jaw which hinders their ability to feed and results in starvation. In this case, individuals often sink after death, as they become emaciated, and are never seen again. Ropes have been known to cut flippers to the bone and penetrate thick layers of blubber to cut through muscle tissue if not removed quickly. Sometimes whales are able to disentangle themselves and other times a team of whale rescuers are called in to attempt to aid entangled whales (figure 13). However, disentangling a right whale is a difficult and dangerous process as they are often difficult to find or approach. Right whales are also incredibly strong and un-cooperative, and their aggressive thrashing makes it dangerous for the whale rescue team to work.
Unlike the southern right whale population which is increasing at a rate of 7% per year, the NARW population recovery rate ranges from -0.02-2.5% per year and this is partially due to reproductive dysfunction. While right whales are capable of producing a calf once every three years, the NARWs calving interval is highly variable. Between 1993 and 1998 the average length of calving intervals had significantly increased to 5.3 years. Then, during 2004 and 2005, calving intervals sharply declined to 3.2 and 3.5 years, respectively.
The average age a first parturition in the NARW is also variable with some females producing their first calf as young as five or as old as 21. Between 1980 and 1992, the average age of a female at first parturition was calculated to be 7.57 years, but this number increased to 9.53 years during the five year period between 1993 and 1995. By 2007, the average age at first parturition had increased again and was calculated to be 10.1. Additionally, 12% of sexually mature females at this time were considered nulliparous. Furthermore, the number of calves born each year is also highly variable. Only one calf was observed in 2000, while thirty-nine were observed in 2009 and only six were born in 2012 with one dying shortly after birth. In 2007, 300-350 individuals made up the total NARW population with an equal number of males and females. Given that 60% of females were expected to be sexually mature and normal calving intervals were expected to be 3 years in duration, then 30-35 calves should have been born every year. However, the average observed number of calves born each year was nearly three times lower than what was expected with an average of only 13 calves born each year.
The highly variable, longer than normal calving intervals, variable age at first parturition, and variable number of calves born each year are consistent with failed conception, spontaneous abortion, and neonate mortality (figure 14). Numerous factors may be contributing to low reproductive rates and include climate change, prey resources, toxins, parasites and low genetic variability.
Climate Change and Prey Abundance
Right whales have evolved to live in cold waters (average of 12.3⁰C) as they have a blubber layer which can reach 20 cm in thickness. However, global temperatures are on the rise and while, historically, right whales have lived through periods of warming and cooling, this period of global warming is occurring at a much faster pace. As such, right whales may begin to suffer the effects of heat stress unless their distribution changes. Calving grounds are predicted to shift northward to historical calving grounds which are currently rarely used.
Climate change has a wide range of indirect effects on the NARW population. For example, climate change has been associated with changes in prey resources which affects calving intervals and the number of calves born each year. The primary prey of the NARW is Calanus finmarchicus (figure 15) and their population size is strongly influenced by the North Atlantic Oscillation (NAO) cycle and the NW Atlantic’s coupled slope water system (CSWS). In the 1980s, when C. finmarchicus were abundant, the NAO was mainly in a positive state and the CSWS was mainly in maximal mode. This resulted in more calves produced per year and stable calving intervals. Then as the CSWS returned to its minimal mode in the years after 1980, C. finmarchicus populations declined as did calving rates, only to recover again when the CSWS reversed its mode during the mid-90s, before again falling with the occurrence of a minimal CSWS mode.
Pollution, Biotoxins, and Parasites
Some studies have suggested that organochlorine (OC) accumulation in baleen whales is minimal making it unlikely to cause any significant biological problems. However, other researchers suggest that OC exposure may be contributing to the low reproductive rates exhibited by the NARW.
Marine biotoxins, which include a wide range of toxins produced by various algal species, have been implemented in the deaths of numerous humpback whales and reproductive failure in seal lions, but their effects on right whales are unknown. What is understood is that areas where harmful algal blooms occur overlap with the NARW population. Many of these toxins are transferred through the food chain and C. finmarchicus is known to ingest large quantities of Alexandrium spp. which is a major producer of saxitoxis.
Parasites are also contributors of low reproductive rates in many terrestrial and marine animals. Right whales have the highest rate of Giardia and Cryptosporidium compared to any other whale and could be an indicator of a compromised immune system. Both these parasites cause gastrointestinal illnesses in humans although their health affects in the NARW are unknown.
Low Genetic Variability
Low genetic variation in a population has been correlated with reduced reproductive success. NARW have low levels of variability at minisatellite, microsatellite and mitochondrial loci. Additionally, they have
lower levels of variability at major histocompatibility complex (MHC) than many terrestrial levels. The MHC is involved in immune response and there is evidence to suggest that certain species chose mates with genotypes which are different from their own as heterozygosity increases survival. However, as of yet, no evidence has been found to associate MHC haplotypes with female reproductive success or survival rates in the NARW.
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