North Atlantic right whale (Eubalaena glacialis) recovery strategy: chapter 10

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1. Background (cont'd)

1.8. Threats

Since whaling ended in the 1930s the most obvious threats that are potentially depressing the growth rate of the North Atlantic right whale population are strikes by vessels and entanglements in fixed fishing gear.  Of 75 reliably documented right whale deaths between 1970 and January 2007, eight (~11%) were traced to entanglements in fishing gear, 28 (37%) were traced to collisions with vessels, 21 (28%) were attributed to "unknown causes" and 18 (24%) to "neonatal mortality" (Knowlton and Kraus 2001 and NEAq unpublished data).  Twenty-one of the 28 known ship strikes (75%) have occurred over the period 1991 through January 2007 and represent 50% of the known right whale mortalities for this period.  The actual total number of deaths resulting from human activities is unknown; however, it is almost certainly higher than the observed number because not all carcasses of right whales are found.  For example, carcasses of right whales that die as a result of entanglements in fishing gear may be more likely to sink at sea because of the decreased health of the animals and subsequent loss of blubber mass and thus it has been suggest that up to two-thirds of human-caused right whale deaths may go undetected (Moore et al. 2007).

The only "natural" mortality currently observed is neonatal mortality, though it should be presumed that natural deaths from old age occur as well.  The category of “unknown” deaths includes those animals for which the carcass was not retrieved, the carcass was too decomposed to identify a causal factor, or no obvious factor was found despite a detailed necropsy.

The mortality from vessel strikes and entanglements would be particularly significant if it was biased toward females. Given that females accompanied by calves are usually observed in coastal waters where fishing gear and ships are more common, it is plausible that adult females would be more vulnerable to the threats of ship strike and entanglement.  Overall, known deaths in the last five years reflect a female bias (NEAq unpublished data).

1.8.1.    Historical threat - whaling

Right whales played a large role in the development of the whaling industry in eastern North America.  The name of the right whale may have come from whalers who thought that it was the "right" whale to kill from an economic perspective, although the exact origin of the common name is unknown. They were easy to approach, floated after death and provided large amounts of products such as oil and baleen.  As a consequence, the population was reduced to very low levels and was commercially extinct in the 19^th century.  The population was legally protected from commercial whaling in the 1930s.

As early as the 14^th century, Basque ships were whaling off the waters of Atlantic Canada and are thought to have targeted species such as right whales.   Whaling in the United States was the centre of the world whaling industry during the 18th and 19th centuries.  In the western North Atlantic, right whales were hunted in coastal waters from Florida to Labrador, including the Strait of Belle Isle and Gulf of St. Lawrence (Aguilar 1986, Reeves et al. 1999, Reeves 2001).  They were also encountered and hunted during the summer in pelagic waters, particularly near the eastern edge of the Grand Bank and in an area directly east and southeast of Cape Farewell, the southern tip of Greenland (Reeves and Mitchell 1986).  There is only limited evidence of historical whaling for right whales the present-day high-use areas; the Bay of Fundy (Reeves and Barto 1985), the Scotian Shelf (Mitchell et al.1986), and the Great South Channel (Reeves and Mitchell 1986, Reeves et al.1999). 

It is interesting to note that no right whales have been reported for more than a century in the supposed historical Basque whaling grounds in the Strait of Belle Isle between Labrador and Newfoundland, where the species’ range is believed to have overlapped that of the bowhead whale (Aguilar 1986, Cumbaa 1986). It has generally been assumed that the balaenids hunted in summer in this region were right whales, while those hunted from late autumn through spring were bowheads (Tuck and Grenier 1981, Cumbaa 1986, Reeves and Mitchell 1986). Recent analyses of DNA extracted from bone material indicate that a very high proportion of the whales taken by the Basque whalers at Red Bay, Labrador, were bowheads rather than right whales (Rastogi et al. 2004 and (Frasier et al. 2007).These results contradict earlier views that Basque whalers harvested equal proportions of right whales and bowhead whales in that area, in turn suggesting that the right whale population has been relatively low since before commercial hunting (Frasier et al. 2007).

1.8.2.    Vessel strikes

The importance of vessel collisions as the leading cause of mortality for right whales has been recognized since the 1970s (Reeves et al. 1978, Kraus 1990, Kraus et al. 2005, Moore et al. 2007).  Since 1970, there have been 75 carcasses reported, at least 28 of which have died as a result of a ship strike (Knowlton and Brown 2007).  Twenty-one of the 28 ship strikes (75%) have occurred over the period 1991 through January 2007 and represent 50% of the total right whale mortalities for this period.   In addition to the outright mortality, about seven per cent of the living population was seen to have “major wounds” on the back or tail peduncle caused by propellers.  Thus the actual total number of deaths resulting from vessel strikes is unknown; however, it is almost certainly higher than the observed number because not all injured right whales are found and the poor condition of some carcasses prevents conclusive determination of the cause of death (Moore et al. 2007). Moreover, the morbidity, lowered productivity and decreased longevity of animals with “nonfatal” or “possibly fatal” injuries (e.g., propeller cuts, deep gashes, severed flukes) must be taken into account when evaluating the total impact of vessel collisions.  Seven of the 28 (25%) fatalities traced to vessel strikes are known to have taken place in Canadian waters between 1987 and 2006. 

The mechanisms involved in a whale’s ability to detect and take evasive action to prevent being struck by a vessel are poorly understood. Evidence suggests that the hearing range of right whales encompasses frequencies produced by vessels (Knowlton and Brown 2007). However, it may not be too surprising that right whales do not always take successful evasive action when vessels approach them, since the sound produced by most vessels propagates toward the rear and sides of the vessel; the area forward of the bow may be the quietest location. The effect of noise masking by meteorological conditions (wind, waves and precipitation) is not known. It has also been argued that for an animal with such a long lifespan, there has been no opportunity to evolve a response to vessels, since vessel traffic is a relatively new addition to their habitat, and vessel speeds have increased in the past several decades.

Most of the areas heavily used by right whales in the western North Atlantic are in or near major shipping lanes serving ports in the eastern United States and Canada (Knowlton and Kraus 2001).  There are, however, stewardship measures at our disposal that will help reduce the threat of vessel strikes in Canadian waters. For example, researchers used evidence from extensive survey work in the Bay of Fundy and limited radio tracking to show that right whales were found most frequently and in highest concentrations in the deepest part of the Bay of Fundy, which placed them in or near the Bay of Fundy Traffic Separation Scheme (Knowlton and Brown 2007, Mate et al. 1997, Vanderlaan et al. 2008). As the whales are highly mobile, their wanderings frequently take them across other shipping routes, including Roseway Basin on the western Scotian Shelf and ones east of Halifax (Mate et al. 1997). The Bay of Fundy Traffic Separation scheme was amended to reduce the relative probability of vessel/right whale interaction (e.g., see Knowlton and Brown 2007).  Vanderlaan et al. (2008) estimate that the probability of interaction in the outbound traffic lane has been reduced by an average of 90%. 

Recent investigations seek to understand the influence of both vessel size and vessel speed on injury or mortality of right whales. It is known that both small and large vessels can cause death and life-threatening injury to right whales, such as the observed morbid condition of a whale that had been struck by a 12.8 meter long recreational vessel (Knowlton and Brown 2007). As more strikes are documented where the vessel speed is known, findings suggest that vessels traveling at less than 13 knots (26 km/h) may provide right whales with a greater likelihood of avoiding serious injury or death (Knowlton and Brown 2007). Vanderlaan and Taggart (2007) analyzed right whale vessel strike data and concluded that at vessel speeds above 15 knots (28 km/h), lethality to whales approaches 100%. Conversely they found that for whale strikes by vessels travelling at less than 11.8 knots (22 km/h), lethality dropped below 50%.

1.8.3.    Entanglement in fishing gear

Entanglement and entrapment of right whales (and other cetaceans) in fixed fishing gear (and other lines in the water) has been known as a hazard for decades. For example, as early as 1909, a young right whale became entangled in a fish-trap in Provincetown Harbor (Massachusetts), allowing local fishermen to kill it with a bomb-lance (Allen 1916). Reports in the 1970s of whales entangled in netting and lobster lines, and trapped in herring weirs, were regarded as "exceptional" events by Reeves et al. (1978).  But the more rigorous evaluations since then by Kraus (1990), Kenney and Kraus (1993), and Knowlton and Kraus (2001) have shown that interactions with fishing gear are considered a major source of serious injury and mortality and an important factor in slowing the right whale population's recovery (Kraus et al. 2005).

The most recent analysis of scarring showed that more than 75% of right whales have scars indicative of an entanglement at some time in their lives and that the rate of scar accumulation increased in the 1990s (Knowlton et al. 2005).   While no sex bias was apparent, there is an age bias: juvenile right whales experienced a disproportionately higher number of entanglements than adults (Knowlton et al. 2005). The attribution of entanglements to a particular geographical location or gear type is difficult to determine because the whales are highly mobile and the entangling gear retrieved is often unmarked. However, it has been shown that the types of fishing gear most often implicated in right whale entanglements are the vertical and horizontal lines used in fixed gear fisheries (i.e. gillnets and pot gear) in Canadian and U.S waters (Johnson et al. 2005).  There is little information regarding the risk of entanglement in gear associated with aquaculture operations, although there is one known instance of an entanglement that occurred in 1990 (DFO and NMFS unpublished data).

Since 1988, at least two right whale mortalities from entanglement can be attributed to fishing gear traced to Canadian fishing operations (Knowlton and Kraus 2001, NEAq unpublished data). The actual total number of deaths resulting from entanglements range-wide is unknown.  However, it is almost certainly higher than the observed number in Canadian and US waters as indicated by the analysis of entanglement data from 1980 through 1999 that documented eight right whales, that were last seen alive but with potentially fatal entanglements, that are presumed dead (Knowlton and Kraus 2001).

In Atlantic Canadian waters, researchers are using right whale sighting data and logbook data from the fixed gear fisheries to determine where there is a seasonal overlap between the whales and fishing operations (Taggart et al. 2005). In the past, most fishing activity was thought to occur at a time of year when right whales were not present (WWF/DFO 2000). However, due to more comprehensive sighting data, examination of fishing gear retrieved from entangled right whales, and the emergence of new fixed gear fisheries that are carried out in the summer and autumn, it is clear that there is a greater risk for right whale entanglement in Canadian waters than was previously thought.

Disentanglement efforts in Canada and the United States have resulted in the freeing of some right whales and the release of a few entrapped in herring weirs (NEAq, PCCS unpublished data). Disentanglement of free-swimming right whales is notoriously difficult, often unsuccessful and does not guarantee survival of the whale in question; however, these efforts should continue even when changes in fishing practices are implemented that are successful in eliminating severe entanglements.

1.8.4.    Disturbance and habitat reduction or degradation

General references have been made to the possibility that habitat degradation is contributing to the North Atlantic right whale population’s failure to recover more rapidly (Reeves et al. 1978, Kraus 1985, Gaskin 1987, Kraus et al. 2005, Kraus and Rolland 2007). The concept of habitat quality reduction or degradation includes a host of short- and long-term phenomena from exposure to contaminants from marine and land-based activities, as well as exposure to excessive noise, and to changes in the food supply as a result of human activities.

Two points must be made when discussing habitat degradation in the context of right whale recovery strategies. First, it cannot be assumed that right whales simply relocate once a threshold of disturbance has been reached in a part of their range. The cost of such relocation is likely to take the form of reduced reproductive success or increased mortality, or both. Second, the effects of various types of degradation are likely to be cumulative or synergistic, or both. While cumulative and synergistic effects are potentially important, (Bunch and Reeves 1992, Pearce and Wallace 1995, Mangel et al. 1996), it is extremely difficult or impossible to document and describe these effects using empirical data.

Contaminants

As specialists that prey only on relatively small zooplankton that are low in the food web, right whales are less prone than most other baleen whales to accumulate large body burdens of organic contaminants (Woodley et al. 1991). Moreover, baleen whales generally have lower contaminant concentrations in their tissues than the toothed whales (O’Shea and Brownell 1994). If contaminants are affecting the survival or reproductive success of any baleen whale population, the effects have yet to be detected and described. It is important to emphasize that this does not mean there is no effect. It is extremely difficult to prove a causal link of this kind in a large, rare, wild mammal, for which standard experimental or epidemiological approaches are impossible. Even if there were no direct adverse effects on right whales from exposure to contaminants, the possibility of indirect effects brought about by their food supply could not be ruled out.

While the number of harmful algal blooms in the northwestern Atlantic has increased in recent years, and humpback whales (Megaptera novaeangliae) deaths in Cape Cod Bay have been attributed to biotoxins in their prey fish, to date there has not been a recorded case of toxic algal blooms affecting right whales (Rolland et al. 2007). In theory, saxitoxins – organisms responsible for paralytic shellfish poisoning – pose a risk to right whales. The whales’ feeding mechanism, filtering their plankton prey through baleen, is likely to prevent the small algal cells from being ingested (Rolland et al. 2007).

The risk posed to right whales from endocrine disrupting chemicals has not been investigated.  Because of their use of coastal habitats, it is possible that right whales are exposed to some of these chemicals from run-off, sewage outflows or other sources. Exposure to endocrine-disrupting chemicals during early development has been shown to alter reproductive and immune system function in lab and domestic animals, humans and wildlife (Colborn et al.1993). Some of the current use chemicals of possible concern for right whales include: the polybrominated diphenyl ethers (flame retardants), phthalate esters (plasticizers), alkylphenol ethoxylates (surfactants) and organotin compounds (anti-fouling agents: Reeves et al. 2001).

Organochlorines, especially toxaphenes, DDT, and PCBs are present in the blubber of right whales in the western North Atlantic, but the levels are not considered high enough for great concern (A. Westgate, pers. comm.). The trends of organochlorine concentrations follow the typical cetacean pattern, with low levels in calves, slightly higher levels in juveniles, highest levels in adult males, and low to medium levels in adult females (Woodley et al. 1991, A. Westgate pers. comm.). Females offload organochlorines to their calves during gestation and lactation. Males, in contrast, continue to accumulate these compounds throughout their lives.

In Atlantic Canada there are several existing and potential point and non-point sources of contaminants. These include vessel discharges, aquaculture operations, land run-off, oil and gas activities, and dredging (through remobilization of contaminants) to name a few.  Gaskin (1987) called attention to the fact that current circulation in both the Bay of Fundy and Gulf of Maine, where right whales feed, is semi-enclosed for at least part of the year. This means that contaminant gradients could become established from the inshore to the offshore regions. Recent reviews of information on contaminants in the Bay of Fundy have shown clear cause for concern (Percy et al. 1997). A wide array of contaminants, including those described above, are present in the environment and in the food web. 

Acoustic disturbances

For right whales, like all baleen whales, hearing is critical to their ability to communicate, navigate and locate food. While extensive research has been conducted on the sound production and behaviour of humpback whales and southern right whales, it is only recently that greater focus has been placed on these aspects of North Atlantic right whale ecology (Parks and Clark 2007). While ambient noise levels in right whale habitat can at times be high, for example due to storm and wave activity, increasing levels of human-caused noise are a cause for concern. The two relevant components of noise are duration and intensity. Some sounds are very loud but of short duration (for example some kinds of sonar or seismic activity), while other sounds are loud and also of long duration (e.g. commercial shipping traffic) (Parks and Clark 2007).

The effects of increased noise on marine mammals are varied and may include habituation, behavioural disturbance (including displacement), temporary or permanent hearing impairment, acoustic masking, and even mortality (Richardson et al. 1995). Increased noise can mask important social communication (e.g. mating calls, mother-calf interactions), limiting the range over which right whales can communicate (Parks et al. 2006), which in turn may reduce mating opportunities (e.g. beluga, Delphinapterus leucas, Erbe and Farmer 1998). 

A range of anthropogenic noises in the marine waters of Atlantic Canada produce underwater sounds within the frequency range detectable by right whales (estimated to be 12 Hz to 22 kHz, with fundamental frequency of sounds produced by right whales primarily between 50 Hz and 2 kHz; Parks 2003). Within the high-use right whale habitat areas in Canada the sources of noise of most concern to date have related to commercial transport and whale watching vessels, nearby or potential oil and gas exploration, naval activities such as detonations, the use of harassment devices in aquaculture operations, marine construction, and on-shore detonations. Several kinds of sonar are operated in right whale habitat areas, including both active and passive military sonar, fish-finding sonar, and bottom mapping sonar.

It has been suggested that the constant noise from shipping in the North Atlantic has habituated right whales to ship sounds, making them less likely to avoid oncoming vessels resulting in collisions. It is also argued that right whales have no reason to avoid vessels, since they have no natural predators and these vessels are a recent introduction to their habitat, on the time scale of right whale generations. Nowacek et al. (2004) equipped several right whales with multi-sensor acoustic recording tags to measure the whales' responses to passing ships, and to test the whales' response to controlled sound exposures including recordings of ship noise, right whale social calls, and a signal designed to alert the whales. Nowacek et al. (2004) found that the whales reacted strongly to the alert signal, mildly to the social sounds, but showed no response to the sounds of approaching vessels.

No direct studies have been undertaken in Canadian waters to investigate the effects of non-vessel noise on right whales. Seismic air guns used in petroleum exploration are a source of loud noise that is a potential concern for right whale conservation. In a preliminary study, baleen whales have been observed changing their behaviour in the presence of seismic airgun noise (DFO 2004). Noise from offshore hydrocarbon production platforms and exploration drilling may also be of concern (Richardson et al. 1995), as they generally tend to be of low frequency (<500 Hz). Previous studies have demonstrated avoidance of odontocete species to acoustic harassment devices (e.g. Morton & Symonds 2002), but no data exists on baleen whale responses. Previous studies indicate that blasting for marine construction can lead to damage of ear structures in baleen whales (Ketten et al. 1993).

Vessel presence disturbance

Aside from acoustic disturbance, the presence of vessels - ranging from large commercial ships, to whale watching vessels through small recreational, scientific and fishing boats – in right whale habitat raises several concerns. In addition to noise pollution and the risk of vessel strikes, which have been described earlier, the presence of vessels in important habitat areas may affect right whale behaviour by disturbing social interactions like nursing, or displacing them from rich food patches (e.g. such as has been documented for gray whales, Eschrictius robustus; Bryant et al. 1984).

Changes in food supply

The question of whether right whales in the western North Atlantic are undernourished is closely linked to the quality of their habitat and their ability to use suitable habitat without being seriously disturbed by human activities. This issue was initially addressed by Kenney et al. (1986), who suggested that inadequacy of food resources could lead to either a reduction in individual growth rates, thus lengthening the time required for sexual maturation, or insufficient blubber reserves in females to sustain pregnancy or lactation, resulting in high calf mortality. It is uncertain, at present, whether either of these changes is occurring in the North Atlantic right whale population.

Blubber thickness may be a useful index of body condition in right whales. Scientists who observe right whales in the western North Atlantic regularly see a qualitative difference in the appearance of these whales and Southern Hemisphere right whales, the latter appearing broader bodied and more robust (with a “collar of fat” in the dorsal neck region). An analysis of blubber thickness in North Atlantic right whales compared blubber thickness in different classes with reproductive success (Angell 2005). It showed that blubber thickness and dorsal body shape were indices of right whale energy balance and that the marked fluctuations in reproduction likely have a nutritional component.

Global climate change could be affecting both the local spring and summer distribution of right whales in the Gulf of Maine (Kenney 1998b) and the calving rate of the North Atlantic population (Kenney 1998a).