At this time, it is unknown what factor(s) continue to limit growth and recovery of CI belugas. It may be that the cumulative effects of multiple stressors are impeding recovery, whereas the effects of individual stressors in isolation would not impede recovery. Here we provide brief overviews of the ten potential threats identified and assessed in this recovery plan, based on current knowledge of threat factors.
Several natural factors may result in a catastrophic event with potential to adversely affect CI belugas, including effects from environmental or climatic changes, earthquakes, volcanos, novel disease outbreaks, mass strandings resulting in large numbers of mortalities, and failures of key salmon runs. Anthropogenic activities, such as oil spills and natural gas blowouts, among others, may also result in a catastrophic event with detrimental effects on CI belugas. Catastrophic events may also have significant effects on CI beluga prey, whether through changes to spawning or migration patterns, direct mortality, or potential long-term sub-lethal impacts. A catastrophic event on its own may not always directly adversely affect CI belugas; rather, it may lead to a mass stranding event, which could have catastrophic results if there are multiple mortalities as a result of the stranding. Mortalities associated with a live stranding event do not appear to be common. Effects from catastrophic events are variable, and in addition to mortality, may also result in compromised health or injury to individual whales, reduced overall fitness or resilience of the population, or reduced carrying capacity of the environment; however, depending on the location of the event, the exposure or effect to CI belugas will vary. Small populations, such as the CI beluga population, may be more susceptible to adverse effects resulting from catastrophic events than large populations. The reduced summer range of CI belugas into the upper Inlet makes them far more vulnerable to catastrophic events that have the potential to kill or injure a significant portion of the population. It is expected that most catastrophic events would be localized events, affecting only a portion of the CI belugas’ range. Past experience indicates the frequency of catastrophic events in Cook Inlet is low. Anthropogenic activity in Cook Inlet is increasing, however, and environmental and climatic conditions are changing. Thus the probability of adverse effects resulting from a future catastrophic event is thought to be medium to high. The magnitude of effect upon CI belugas of a catastrophic event is a function of several factors, including type of event, location of event, and exposure of whales to the event. However, given the history of live stranding-related mortalities and given the fact that mortalities can have an immediate and notable impact to the recovery potential of the population, we ranked the magnitude of the effects of catastrophic events as variable, but potentially high. We conclude the overall relative concern of the impact of catastrophic events on CI belugas is of high concern.
Cumulative Effects of Multiple Stressors
Multiple stressors occur continuously throughout the range of CI belugas. While it is difficult to quantify or characterize effects on CI belugas from individual stressors, it is even more difficult to characterize the potential cumulative effects from a combination of stressors. Exposure to any given stressor at a sub-lethal level may predispose individual belugas to greater susceptibility to mortality or long-term effects (for example, reproductive failure) from other stressors. Death can also result from different combinations and intensities of multiple stressors. Cumulative impacts have been a long-standing issue in the debate over noise effects on marine mammals; the additive effects of multiple noise sources, as well as the combination of noise and other stressors, are of particular concern. Perhaps most important are potential synergistic effects in which two stressors interact to cause greater harm than the sum of the effects of the stressors individually. For example, a stressor may increase cortisol levels, which in turn tends to reduce immune response. There are well-documented examples of multiple stressors in terrestrial species that individually have little impact, but, when combined, can have major, negative, synergistic impacts that may cause death. In the case of CI belugas, contaminants and predators (e.g., transient killer whales) may occur in the preferred habitat, creating a potential for synergistic effects if the contaminants make the belugas more susceptible to predation. CI belugas might be at risk from the negative synergistic effects from anthropogenic noise exposures coupled with other stressors such as widespread pollutants or the presence of transient killer whales (e.g., detecting their presence acoustically without the need of actual physical encounters). Accurate prediction of all the potential cumulative effects requires a reasonable knowledge of all the various contextual factors for each exposure and is therefore difficult. Stressors related to the current small population size of CI belugas, when combined with anticipated trends of increased anthropogenic impacts, can increase the likelihood of co- occurring and interacting multiple stressors, reducing the likelihood of population recovery in the near term. Of particular concern are the cumulative effects of multiple stressors (acoustic and non-acoustic), given the noisy environment of Cook Inlet. Given the growth of activities in Cook Inlet, the trend for cumulative effects is increasing over time, with a high probability that these effects will continue in the future. Uncertainty over the complexity of potential mechanisms and difficulty in detection of their impacts and their potential mitigation make the cumulative effects of multiple stressors a threat category of high relative concern regarding potential impediments to recovery of CI belugas.
The acoustic environment of Cook Inlet is naturally noisy, complex, and dynamic. Natural sources of noise are particularly abundant and loud in the CI belugas’ range and include: bottom substrate being transported by high currents; sand and mud bars generating breaking waves during low tide/high current periods; river mouths becoming rapids at low tide periods; and fast and pancake ice being formed during winter months and under continuous mechanical stress by high tide oscillations and currents. The effects of these natural conditions, while difficult to quantify, may compromise CI beluga acoustic communication and echolocation, particularly as the sound transmission distance increases. However, CI belugas have presumably adapted to accommodate such noise. The addition of anthropogenic noise, to which the whales have not necessarily adapted, may have negative effects. Due to the highly concentrated human population in the current range of CI belugas, a wide variety of anthropogenic noise sources that may affect fitness are present in CI beluga habitat, especially in the upper Inlet. Most sources of anthropogenic noise in Cook Inlet are seasonal and occur during the ice-free months, although some sources are present year-round. Sources of anthropogenic noise in Cook Inlet include: propeller cavitation, engines, sonar, dredging, pile driving, military detonations, aircraft, seismic air guns, drilling, geophysical and geotechnical equipment, and other mechanical noise. The effect of anthropogenic noise, particularly the combined effect of different sound sources occurring simultaneously or consecutively, has the potential to affect beluga acoustic perception, communication, echolocation, and behavior. In the long term, anthropogenic noise may induce chronic effects altering the health of individual CI belugas, which in turn have consequences at the population level (i.e., decreased survival and reproduction). Despite the fact that direct and indirect effects of these sounds on CI belugas have not been analyzed and are currently unknown, there is enough evidence from other odontocete species (including other beluga populations) to conclude that a high potential exists for negative impacts. Anthropogenic noise also has the potential to indirectly affect the survival and reproduction success of CI belugas by having negative effects on their prey. Depending on the source, a noise can be localized or occur rangewide. While noise may result in compromised communication and hearing of CI belugas and may contribute to habitat degradation, the magnitude of the impact of noise on CI belugas is unknown, but potentially high. There is a high probability that anthropogenic noise in Cook Inlet will continue and increase in the future, and given that the natural noise is already limiting, the threat to CI beluga recovery due to anthropogenic noise is of high relative concern.
Disease Agents (Pathogens, Parasites, Harmful Algal Blooms)
Potential sources of disease-causing agents exist in and around Cook Inlet. Disease agents may include pathogens (such as bacteria, viruses, and fungi), parasites, and harmful algal blooms (HABs). The necropsy record of stranded CI beluga carcasses shows only low levels of parasitism, and parasites that were present did not appear to have a significant negative impact (i.e., were not attributed to be the cause of death). Additionally, parasites most likely would only have detrimental effects at the scale of individual whales, with population-wide effects unlikely. Thus, the threat of parasites is currently of low relative concern for CI belugas. Although HABs have the potential to detrimentally impact a large portion of the population, the reported incidence of HABs in Cook Inlet has been very low to date. However, there is evidence that HAB toxins are present throughout Alaska waters at levels high enough to be detectable in marine mammals; moreover, current climate trends may result in conditions favorable to the growth of HABs, increasing the health risks to marine mammals. In addition to the potential prevalence of HABS, climate change is rapidly altering the global movement of pathogens, bringing diseases to new areas. Small populations, such as CI belugas, are susceptible to population-wide disease outbreaks. A population-wide outbreak of a novel (new) disease could be catastrophic to CI belugas. Based on the number of whales photographed in Eagle Bay in 2011 with indications of past infection, we assume disease of some sort is present in the population at unknown levels, and recognize there is a medium to high probability that disease will increase in the future. Currently, the incidence of disease as a factor in the deaths of CI belugas appears to be low, and there is little evidence to suggest diseases of concern are present in other mammals in the area. As such, while current incidence of disease and parasitism is a low relative concern, the threat to CI beluga recovery due to increases in HABs or a disease outbreak associated with novel pathogens in the future is of medium relative concern, and the overall threat posed by disease agents is of medium relative concern.
Habitat Loss or Degradation
Concurrent with the CI beluga population decline in the mid-1990s, the spatial distribution of CI belugas contracted such that whales are found primarily in the upper portion of Cook Inlet near Anchorage during the summer. Climate-driven increased water temperature, siltation, changes in volume of freshwater runoff, and reduced salinity may occur gradually. However, when they result from episodic events, such as earthquakes or volcanic eruptions, effects may be immediate. Examples of anthropogenic activities that can result in substantial changes in habitat, or temporary or permanent loss of habitat, may include in-water construction, port expansion, highway and bridge construction, dredging, changes in freshwater inflow from dams, and river dredging or channeling. These types of anthropogenic threats tend to be localized, seasonal, and increasing in frequency, whereas natural threats may operate range-wide at either unknown or increasing frequency (e.g., warmer water temperatures under climate change scenarios). Both natural and anthropogenic factors may limit suitable habitat either directly in the form of whale perturbation and reduction of fitness (e.g., chemical impacts to skin tissue), or indirectly through impacts to prey populations and reduced carrying capacity of the environment. Most of the anthropogenic activities disturbing CI beluga critical habitat are concentrated in the coastal zone and are often seasonal. Although most of the beluga habitat in Cook Inlet is not degraded to the point that adverse effects to CI belugas are apparent, anthropogenic activities in the Inlet are increasing, and there is a high probability there will be more habitat loss or degradation in the future. Concurrent with increasing anthropogenic activities in Cook Inlet, the trend of habitat loss or degradation for CI belugas is also increasing over time, and the contraction of their range into the upper Inlet has resulted in increased proximity to the developed areas around Anchorage. Due to a limited understanding of how this habitat might be altered by various factors and its resilience to perturbations, the loss or degradation of habitat is of medium relative concern for CI belugas.
Reduction in Prey
The impact of reduction of available prey on CI belugas is poorly understood and may have several effect pathways including: changes in the total availability, quality, species composition, and seasonality of prey. While the potential exists for human fishing pressure to dramatically change the abundance, seasonality, or composition of beluga whale prey, for targeted species, fisheries in Alaska are managed with in-season reductions or closures if those fish stocks appear to be weak. However, not all fish stocks are assessed, and it is unknown whether management of fisheries for optimal returns provides sufficient densities in beluga feeding areas for efficient foraging by belugas. It is likely there is interspecific competition for limited prey resources between CI belugas and other predators in Cook Inlet (e.g., harbor seal, harbor porpoise). Habitat modification may result in changes in species availability and/or species composition throughout the range distribution of CI belugas. Depending on the source, a reduction of prey can be a localized event or occur Inlet-wide, with a variable frequency of occurrence. While reduction of prey may result in reduced carrying capacity of CI beluga habitat or reduce CI beluga fitness, the magnitude of the impact of a reduction of prey on CI belugas is unknown, as is the trend and future probability. As such, the threat to CI beluga recovery due to the reduction of prey is of medium relative concern.
In certain instances, NMFS may authorize or permit directed or incidental “takes” of CI belugas under the MMPA and ESA. These authorizations undergo extensive reviews prior to issuance. Authorized takes are not considered to be a population-level threat to CI belugas. Activities which result in harassment or harm to CI belugas but which NMFS has not authorized (i.e., unauthorized take) may result in changes in CI beluga behavior, displacement of CI belugas from important areas, or injury or mortality to CI belugas. Some activities with potential to result in unauthorized take include entanglements from fisheries operations, strikes from vessel activities, unanticipated harassment or mortalities from research activities, mortalities or injuries from poaching and intentional harassment, and other adverse outcomes (e.g., displacement) associated with miscellaneous activities such as whale watching.
While there have been sporadic reports over the years of individual belugas becoming entangled in fishing nets, the only known fishery-related mortality in recent years was one yearling CI beluga carcass recovered in 2012 from a set net. Ship strikes have not been confirmed in a CI beluga death, but there are two instances where death by ship strike was highly probable given the blunt trauma sustained by the whales. Scarring consistent with non-lethal propeller injuries has also been documented in the CI beluga photo-identification catalog.
Research activities not targeting belugas, such as research activities studying CI beluga prey or habitat, may incidentally harass CI belugas, and if not authorized by NMFS, these are unauthorized takes. NMFS has authorized take associated with several directed CI beluga research projects over the years, including capture, tagging, biopsies, and aerial and boat-based surveys, but recent authorizations have not allowed for mortality. It is possible that three CI belugas died (an unanticipated outcome) as a result of a capture and satellite tagging research project in 2002. With the exception of an effort to apply acoustic recorders to the whales via suction cup tags and a biopsy feasibility project, all other directed research activities have involved non-invasive techniques (e.g., passive acoustic recordings; aerial, boat, and land-based observations; photographic studies) with a low potential to adversely affect CI belugas.
There is little information available to suggest illegal hunting or harassment is currently occurring, perhaps in part due to increased awareness of the status of CI belugas and the prohibitions against hunting, shooting, or harassing the whales. The lack of reports to NMFS regarding illegal hunting attempts; the near absence of conviction by the NOAA Office of Law Enforcement for suspected cases of illegal hunting and harassment; the lack of mortalities associated with firearms for over 15 years; and the lack of fresh injuries documented through photo-identification studies leads to a conclusion that the threat of illegal hunting or harassment has decreased in recent years, and currently occurs at levels at or near zero. There is a medium probability that unauthorized takes will occur to some degree in the future, but the magnitude of the impact to CI belugas is variable, depending upon the effect. If the effect is displacement or a short-term change in behavior, the magnitude of the threat on CI belugas population is low, but if the effect is mortality, then the magnitude is high. The overall relative concern of the impact of unauthorized takes resulting from activities such as fisheries, vessel operations, research, whale watching, and other miscellaneous activities is medium.
CI belugas may be exposed to contaminants through direct contact in the water; inhalation of contaminants in the air; or ingestion of contaminants found in prey, mud, or silt. Pollution often enters the water from a specific source (e.g., a sewage outfall pipe; in-water construction site; etc.); these sources of pollution may result in localized effects. Other sources of pollution in Cook Inlet occur over broader geographic areas and can ultimately have rangewide effects (e.g., runoff from roads, airports, agricultural sites, military training areas; etc.). Thus, depending on the source of the pollution, the extent of the effect may be either localized or rangewide, with a variable frequency of occurrence. Given the increases in the human population and development of Cook Inlet, it is likely that the level of pollution entering Cook Inlet is increasing and will continue to increase in the future. However, if the Asplund Wastewater Treatment Facility, Alaska’s largest wastewater treatment facility, is upgraded in the future from a primary treatment facility to a secondary treatment facility the overall pollution entering Cook Inlet could stabilize or decline in the near term. It is possible that CI belugas have been chronically exposed to low levels of contaminants in Cook Inlet for some time. For the contaminants that have been studied, CI belugas have generally had lower contaminant levels than did belugas from other populations, and thus the magnitude of the threat to CI belugas from pollution is assumed to be low. Even though the available data do not include assessment of all possible contaminants to which belugas may be exposed, the comparatively low levels of contaminants documented in CI belugas, as well as in Cook Inlet waters and sediments analyzed, suggest that known and tested contaminants are in general of low relative concern.
Transient (mammal eating) killer whales are known to prey on CI belugas, however, there have only been 9–12 CI beluga mortalities since 1982 suspected to be a direct result of killer whale predation. In addition to directly reducing CI beluga abundance via mortality, the presence of killer whales in Cook Inlet may increase beluga live-stranding events. It appears that only a small group of transient killer whales may occasionally prey seasonally on the belugas in upper Cook Inlet. Killer whale sightings in upper Cook Inlet reported to NMFS have been infrequent. The shallow, highly turbid, and restricted waters of the upper Inlet may lead to killer whales stranding, and may reduce the benefit of preying on belugas in that region. Although predation on CI belugas by sharks has been postulated, there is no conclusive evidence that shark predation on CI belugas occurs. There is a medium probability that a low level of predation by sharks will occur at some point in the future, but if the trend remains stable, the magnitude of the effect upon CI belugas is low. Overall, predation is currently of low relative concern for the recovery of CI belugas.
In the 1990s, legal subsistence hunting of CI belugas by Alaska Natives had a direct negative impact on belugas in Cook Inlet; however, subsistence hunting is currently conservatively managed, and no harvests are authorized through 2017. Harvests after 2017 will only be considered if specific population size parameters are met and if it is determined that allowing a mortality will not jeopardize the continued existence of CI belugas. As such, there is no immediate threat to CI belugas or their recovery as a result of legal subsistence harvests, and the relative concern from subsistence hunting is low.