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The St. Lawrence beluga has been legally protected from hunting since 1979. Yet, the St. Lawrence population does not appear to be recovering despite the fact that this activity has been abandoned. The beluga inhabits an area where numerous human activities may be impeding recovery. The St. Lawrence Beluga Recovery Team has identified seven potentially limiting factors*.
Disturbance Habitat degradation Competition for food resources Incidental catch Genetic diversity Catastrophic events * Translated from St. Lawrence Beluga Recovery Team. 1995. St. Lawrence Beluga Recovery Plan. Department of Fisheries and Oceans of Canada and World Wildlife Fund WWF-Canada. 73p.
ContaminationThe examination of carcasses retrieved from the shores of the St. Lawrence since 1982 has revealed high levels of PCBs, DDT, Mirex, mercury and lead, as well as signs indicating exposure to PAHs. These substances are well-known for their toxic effects on animal life and for interfering with reproduction and resistance to diseases. Due to its eating habits and its place in the food web, the beluga accumulates large concentrations of contaminants. It feeds on small and medium-sized fish as well as invertebrates that live near sediment. Thus, the beluga ingests concentrated contaminants and becomes a reservoir of sorts for these persistent products. Despite recent reductions in the discharge of these toxic compounds, contaminant levels in the tissues of belugas have responded slowly to changes in loading. Adults continue to be exposed through their diet, while calves are receiving extremely elevated doses during lactation. This transfer of contaminants from mother to calf hampers the decontamination process for the beluga and probably slows down recovery. The diseases observed in dead belugas are compatible with the known effects of these substances on other species of marine mammals. Also, the cancer rate is much higher in St. Lawrence belugas than it is in the much less contaminated Arctic belugas, or in any other wild mammal species. Moreover, the frequency of these diseases suggests that the St. Lawrence beluga’s immune system may have been weakened by exposure to toxic chemicals. Finally, carcass analysis suggests that contamination could affect the beluga’s reproductive system, reducing calving rates and consequently slowing down population recovery. DisturbanceHeavy shipping traffic in the area where St. Lawrence belugas and other marine mammals spend much of their time is a potential source of disturbance. This shipping traffic includes several thousand ships that navigate up and down the St. Lawrence and Saguenay rivers, ferries, fishing boats, private yachts of all description and whale-watching boats. The number of whale-watching excursions has increased rapidly since the early 1980s and also includes airplane and helicopter tours for tourists. The movement of boats could interfere with the beluga’s daily activities, such as foraging, travelling, its social behaviour and cow-calf bonding. The presence of boats also increases the risk of ship strikes. Belugas are likely more vulnerable to whale-watching boats and private yachts—which change direction and speed frequently—than they are to merchant fleet vessels. The beluga’s natural curiosity for these types of boats contributes to its vulnerability. Belugas may also be affected by the noise generated by commercial shipping, whale watching, pleasure boating and aerial tours. Recent studies have shown that noise produced by maritime traffic is so intense that there is a real risk of harm to the ears of belugas living in the St. Lawrence. This whale possesses a highly developed hearing and echolocation system that is essential for finding food, navigating and communicating. Habitat degradationBelugas spend a lot of time close to shore. During summer months, they show strong site fidelity towards different bays and islands in the Estuary as well as in the Saguenay Fjord. These habitats expose belugas to coastal human activities such as damming, the construction of marinas and wharves, dredging and other projects related to the expanding tourism industry. Although no single case of desertion has been properly documented, it has been suggested that the absence of belugas in the area of the Manicouagan Banks might have been related to changes in the habitat following damming of the Manicouagan and Outardes rivers for hydroelectric power in the 1960s. Unfortunately, the impacts of damming are impossible to evaluate since information on past and present St. Lawrence beluga distribution is insufficient. A similar hypothesis was formulated to explain the absence of belugas in Tadoussac Bay—a site previously frequented by belugas—which has undergone numerous changes since the development of a major tourist industry. Dredging—typically carried out to increase the width and depth of navigation channels and in conjunction with marine construction projects such as marinas—can result in the release of contaminants contained in the sediments. Dredging and dumping have been going on every year close to a site frequented by belugas near the wharf at Rivière-du-Loup and throughout the St. Lawrence. Considering the size of the ships that travel in and out of the St. Lawrence, the amplitude of these dredging projects is not likely to decrease. Competition for food resourcesThe impact of fishing operations on belugas is not known. However, following the decline of commercial fish stocks, a shift to low trophic level species could exert pressure on the beluga’s food sources. Similarly, the recent increase in populations of grey and harp seals may affect the availability of prey items. There is also concern about increasing competition for prey if climate change were to extend the season favourable to seabirds and other animals not adapted to ice conditions in the St. Lawrence. But without reliable data on the diet of beluga and other marine mammals, the degree of competition for food is difficult to estimate. Incidental catchFishermen in the Gulf of St. Lawrence regularly report accidental entanglement of harbour porpoises and occasionally other species of cetaceans in fishing gear. Accidental entanglement in fishing gear is rare in the beluga’s summer range. Since the establishment of the St. Lawrence beluga stranding network in 1982, four cases of belugas stranded in fishing gear have been reported in the St. Lawrence Estuary. The low frequency of beluga entanglement more likely reflects the small size of the Estuary fishing industry or the low use of gill netting. Nevertheless, risks of entanglement could be much higher for animals that travel out of their usual area, where fishing activities are more widespread. Genetic diversitySmall populations are often characterized by low genetic diversity. The small size of the St. Lawrence beluga population raises the question as to whether reduced genetic diversity has contributed to the apparent lack of recovery of the population. Recent analysis of St. Lawrence beluga DNA has indicated a lower level of genetic variation when compared to Arctic belugas. Reduced genetic diversity is suspected of decreasing metabolic, reproductive and immune function efficiency. It is still not clear if St. Lawrence belugas suffer from their low genetic diversity. The possibility of importing belugas from Arctic populations to increase genetic diversity comes with risks that overshadow potential benefits. This solution has thus been set aside. Conservation efforts have been concentrated on other factors that are more worrying, such as contamination, disturbance and habitat degradation. Catastrophic eventsOil spills and epidemics are two catastrophes that could affect the St. Lawrence beluga population. To date, few major oil spills have occurred in the St. Lawrence. The Estuary is a partially closed habitat. Consequently the effects of a spill here could be more serious than if it were to occur on the open sea. Among other potential problems the release of toxic vapours through evaporation could damage sensitive tissues. Harmful oil could even be swallowed if the whales were to consume contaminated prey. Risks of contact with oil are increased in winter. Conditions in winter are such that spilled oil tends to accumulate at the ice edge where animals like belugas spend much of their time. The greatest risk of a disease outbreak is likely to come from viruses. One virus in particular, the morbillivirus, has caused the deaths of hundreds, even thousands of seals and cetaceans around the world in recent years. Although seals from the St. Lawrence examined before 1999 had antibodies for the seal morbillivirus (signs of exposure to the virus) none of the belugas examined during the same time period had the antibody. There are two possible explanations for this: beluga whales have not yet been exposed to the virus or they are resistant to it. In the first case, the St. Lawrence beluga population would be extremely susceptible if they were to come into contact with the virus. Due to the small size of the population, if the beluga is not resistant to the virus an epidemic caused by the virus could bring about its extinction. Also, considering the possibility that the beluga immune system, has been affected by several contaminants , their vulnerability to this type of disease could be higher than anticipated. |