While the recent downward trends in CI beluga abundance and range are well documented, little is known about the mechanisms impeding recovery. Previous hypotheses for the delay in recovery include: 1) reduced fecundity because the mature female segment of the population is depleted; 2) reduced fecundity or survival due to potential population-wide stressors such as reduced prey, contaminants, disease, or inbreeding effects; 3) loss of whales as a result of predation by killer whales or stranding events; and 4) risks associated with contracting range and grouping behavior of the whales (NMFS 2008a). A population model that implicitly considered the time lags inherent in long-lived populations where sexual maturity does not occur for many years (Litzky 2001; Hobbs and Shelden 2008) indicated that the depletion of females is an unlikely cause for the current continued decline. While concluding that other effects besides the subsistence hunt have contributed to the decline and failure to rebuild, the population model was unable to narrow down the causal effects using the available data (Hobbs and Shelden 2008). The model also projected population abundance into the future and demonstrated that extinction risk varied considerably under different scenarios of risk factors for CI belugas. A more recent PVA reached similar conclusions (Hobbs et al. 2015c).
The following section examines potential obstacles to the recovery of CI belugas. It is unlikely that all threats listed in this recovery plan impact CI beluga recovery equally, so ideally each threat would be investigated and either dismissed as insignificant or prioritized for action according to defined criteria. Table 6 lists each threat and summarizes our assessment of the major effect of the threat, its extent, frequency, trend, probability, magnitude, and rating of relative concern (among the threats identified) for CI beluga recovery (definitions of these terms are provided in Table 6). Assessments were made based on the information and data gaps presented in the Background section of this recovery plan.
Climate change, while considered a potential threat to CI beluga recovery, is not addressed as a separate threat in this recovery plan, but rather is discussed with respect to how it may affect each of the listed threats. Although climate change occurs naturally, the effects of greenhouse gas emissions are fundamentally changing global processes. This recovery plan does not attempt to identify the sources of such emissions or to assess the relative contribution of each potential source. Instead it focuses on the effects of a changing climate to CI belugas. For example, climate change may result in increased frequency and intensity of storms and droughts, and these events can have effects on belugas. Thus, since we are assessing effects of climatic changes to the species and not the causes of climatic changes, in many instances in this recovery plan climate change is referenced as a factor that affects natural events, even though we acknowledge that certain natural events may be exacerbated by human-induced climate change.
As previously discussed (see Section II.C.3. Small Population Dynamics), there are inherent risks associated with small populations, such as loss of genetic or behavioral diversity. The effects of threats on small populations may be greater than on large populations due to these inherent risks. Small populations may be more susceptible to disease, inbreeding, predator pits, or catastrophic events than large populations. In this section, we address ten principal threats to the CI beluga population and consider how they may be exacerbated by these types of inherent risks due to small population size.
Section 4(a)(1) of the ESA and the associated regulations (50 CFR Part 424) set forth the following considerations for the listing status of a species: 1) the present or threatened destruction, modification, or curtailment of its habitat or range; 2) overutilization for commercial, recreational, scientific, or educational purposes; 3) disease or predation; 4) inadequacy of existing regulatory mechanisms; or 5) other natural or human-made factors affecting its continued existence. In the 2008 decision to list CI belugas as endangered, NMFS cited all five ESA section 4(a)(1) factors (73 FR 62919). In Table 6, the ten threats identified below are associated with the relevant ESA section 4(a)(1) factors (identified as Factors A–E).
Table 6: Threats Summary
ESA § 4(a)(1) factor
|Catastrophic events (e.g., natural disasters; spills; mass strandings)||A, D, E||Mortality, compromised health, reduced fitness, reduced carrying capacity||Localized||Intermittent & Seasonal||Stable||Medium to High||V ariable Potentially High||High|
|Cumulative effects||C ,D, E||Chronic stress; reduced resilience||Range wide||Continuous||Increasing||High||Unknown Potentially High||High|
|Noise||A, D, E||Compromised communication & echolocation, physiological damage, habitat degradation||Localized & Range wide||Continuous, Intermittent, & Seasonal||Increasing||High||Unknown Potentially High||High|
|Disease agents (e.g., pathogens; parasites; harmful algal blooms)||C||Compromised health, reduced reproduction||Range wide||Intermittent||Unknown||Medium to High||V ariable||Medium|
|Habitat loss or degradation||A||Reduced carrying capacity, reduced reproduction||Localized & Range wide||Continuous & Seasonal||Increasing||High||Medium||Medium|
|Reduction in prey||A, D, E||Reduced fitness (reproduction and/or survival); reduced carrying capacity||Localized & Range wide||Continuous, Intermittent, & Seasonal||Unknown||Unknown||Unknown||Medium|
|Unauthorized take||A, E||Behavior modification, displacement, injury or mortality||Range wide, localized hotspots||Seasonal||Unknown||Medium||V ariable||Medium|
|Pollution||A||Compromised health||Localized & Range wide||Continuous, Intermittent, & Seasonal||Increasing||High||Low||Low|
|Predation||C||Injury or mortality||Range wide||Intermittent||Stable||Medium||Low||Low|
|Subsistence hunting||B, D||Injury or mortality||Localized||Intermittent||Stable or Decreasing||Low||Low||Low|
Definitions used in Table 6 – Summary of threats assessment for CI belugas:
ESA §4(a)(1) factor: The ESA factors NMFS relied upon for listing CI belugas (73 FR 62919, October 22, 2008),
- A: The present or threatened destruction, modification, or curtailment of its habitat or range
- B: Overutilization for commercial, recreational, scientific, or educational purposes
- C: Disease or predation
- D: The inadequacy of existing regulatory mechanisms
- E: Other natural or manmade factors affecting its continued existence
Major effect: A brief description of immediate/proximate/primary effect of the threat on a biological process or the mechanism by which it impacts belugas. Ultimately all threats have an impact on fitness, reproduction, and/or mortality, but often there is an immediate effect on a specific aspect of life history, which is listed here.
Extent: The portion of the CI beluga range over which the threat is found.
Range wide: The threat occurs throughout the CI beluga distribution.
Localized: The threat is primarily found in only a portion of the range, or is present at low levels throughout the range but is greatest in discrete areas.
Frequency: The occurrence/regularity of the threat over time.
Continuous: The threat is relatively constant through the year.
Seasonal: The threat is greatest during specific seasons, but may occur at other times of the year.
Intermittent: The threat may occur at any time of the year or at irregular/sporadic intervals not associated with specific seasons or time frequencies.
Trend: The change in frequency or intensity of a threat over time; described as increasing, decreasing, stable, or unknown.
Probability: Qualitative description of the chance of a threat occurring in the future.
Magnitude: Describes the perceived qualitative impact of the threat (if it were to occur) on the CI beluga whale population.
Relative concern: The overall perception of how a threat affects CI beluga recovery, after accounting for other parameters listed in the table.
Threat Types Overview
The identified threat types and their level of relative concern are:
- Catastrophic events (relative concern: high);
- Cumulative effects of multiple stressors (relative concern: high);
- Noise (relative concern: high);
- Disease agents (relative concern: medium);
- Habitat loss or degradation (relative concern: medium);
- Reduction in prey (relative concern: medium);
- Unauthorized take (relative concern: medium);
- Pollution (relative concern: low);
- Predation (relative concern: low); and
- Subsistence hunting (relative concern: low).