With few exceptions, belugas inhabit isolated areas subject to seasonal ice cover that are not frequently used as shipping lanes. The southernmost beluga stock, however, inhabits the St Laurence River in Canada, one of the busiest shipping routes in the world. Here they are subject to high levels of noise, both from ships and whale-watching operations (McQuinn et al. 2011). The population-level consequences of this to this threatened population are unknown, however belugas do appear to become habituated to some levels of noise over time.
Moreso than for other Arctic marine mammal species, the beluga whale is susceptible to contaminant exposure because of its habit of occupying river estuaries during parts of the summer. Rivers carry pollutants from inland and therefore tend to be more contaminated than offshore marine areas. One population particularly susceptible to marine contaminants is the St Laurence River stock, because its habitat is the densely populated and heavily polluted St Lawrence River basin (DFO 2012). However some other stocks, particularly those inhabiting northeastern Russia, may also be exposed to high levels of contaminants.
Belugas are top predators in the marine food web and therefore tend to accumulate relatively high levels of some contaminants in their tissues. Particularly high levels of organic contaminants, such as pesticides, are found in the fatty blubber layers, to the extent that beach-cast belugas in the St Lawrence must sometimes be treated as toxic waste.
Contaminants can affect survival in several ways, including increasing the rates of chronic diseases such as cancers, and disrupting the immune system and increasing vulnerability to pathogens and parasites. They can also disrupt the reproductive system and decrease reproductive success (DFO 2012). While the extent to which contaminants are actually affecting the survival and reproduction at the population are not known, contaminants are considered to be a major threat to the St Lawrence population (DFO 2012). A relatively high incidence of cancerous tumours has been observed in beach-cast carcasses, leading some to link this to environmental contamination (Martineau et al. 2002); however this conclusion remains controversial mainly because the incidence of cancer in the general population is difficult to infer from the incidence in carcasses (Hammill et al. 2003).
Photo: Courtesy of Aboriginal Affairs and Northern Development Canada
In recent years, the eastern part of Baffin Bay and Davis Strait has had lighter pack ice cover during the winter and spring. Beluga have responded to this by extending their winter distribution farther west and north. This also affects the success of hunters in West Greenland: they must range further from the coast to gain access to beluga in light ice years. These effects demonstrate the influence of climate change on this stock of beluga (Heide-Jørgensen et al. 2010).
Like narwhals and bowheads, belugas are susceptible to occasional entrapments in sea ice which can, if prolonged, lead to their death by starvation, suffocation, predation or human harvesting (Heide-Jørgensen et al. 2002, see also here). While this is a form of natural mortality that belugas as a species have survived throughout their history, it is possible that human activities, particularly seismic exploration within beluga habitat, might disrupt migration timing or routes in such a way as to increase the frequency of entrapments. Possible incidences of this have been observed for narwhal (Heide-Jørgensen et al. 2013) and similar occurrences are possible for belugas. In addition, climate change might also disrupt migration patterns in such a way as to change the frequency of entrapments.
Most beluga stocks inhabit areas with little or no commercial fishing. Again, the St Laurence River stock is exceptional in this regard as it lives year-round in an area with heavy commercial fishing (DFO 2012). Declines in several fish stocks, some of which are important in the beluga diet, have been documented in this area, but it is not known if this is having a population-level effect on the stock.
Commercial fisheries, primarily for Greenland halibut (Reinhardtius hippoglosoides), have expanded into Baffin Bay and Davis Strait, which provides the overwintering habitat for some stocks of belugas (DFO 2007, Laidre et al. 2004). While Greenland halibut are a primary prey species for narwhal, they are less important for belugas which tend to consume more pelagic prey species.