This section does not include habitat loss or degradation from reduction of prey, pollution, or noise, which are discussed individually in other sections.
Sources of Habitat Loss or Degradation in Cook Inlet
In contrast to most beluga populations, which are observed seasonally in estuarine habitats, belugas in Cook Inlet are year-round residents (NMFS 2008a). With the CI beluga population decline in the mid-1990s, the spatial distribution of CI belugas in the summer contracted such that whales are primarily found in the upper portion of Cook Inlet (Rugh et al. 2010). Range contraction proportionate to population decline is consistent with the theory that populations tend to concentrate in areas of optimal habitat during periods of low abundance and expand outside those areas during increased abundance (MacCall 1990). Upper Cook Inlet would thus represent preferred habitat, with the suitability of that habitat depending on both biotic and abiotic characteristics.
Ecological changes such as increased water temperature, siltation, and salinity changes due to changing volumes of freshwater runoff may occur over the long-term in response to climate change. Such changes may also occur due to episodic events such as earthquakes or volcanic eruptions. Anthropogenic activities can result in substantial changes in habitat, or temporary or permanent loss of habitat. Such activities include in-water construction, port expansion, highway and bridge construction, culvert placement, changes in freshwater inflow from dams, dredging, and channeling (NMFS 2008a). Seasonal anthropogenic activities that disturb the substrate can re-suspend sediments and chemicals and also degrade the acoustic propagation characteristics of the habitat, whereas continuous activities, such as sewage outfalls, can alter the chemical composition, prevalence of pathogens, or temperature of the habitat, particularly in the immediate environment of the outfall. Permanent structures, such as docks, platforms, bridges, or trestles, alter localized water flow and characteristics as long as the structure exists. While losses of area from in-water fill may be quite visible, changes in benthic substrate and currents resulting from other types of human infrastructure are less obvious and may have significant impacts on available prey.
While some habitat loss or degradation within the core range of CI belugas is evident, the population level effects of this degradation are unknown. Habitat impacts of past activities are poorly documented, and impacts of current and planned projects are not fully understood. Anthropogenic causes of habitat loss or degradation tend to be localized, seasonal, and increasing in frequency, whereas natural causes (e.g., warmer water temperatures under climate change scenarios) may operate range-wide.
All of these factors may limit suitable habitat either directly through whale disturbance (e.g., chemical impacts to skin tissue) and reduction of fitness, or indirectly through impacts to prey populations and reduced carrying capacity of the environment. Many of the anthropogenic activities affecting CI beluga critical habitat are concentrated in the coastal areas and are often seasonal. Anthropogenic activities in Cook Inlet are increasing, and there is a high probability there will be more habitat loss or degradation in the future. Moreover, the contraction of the range of CI belugas into the upper Inlet has resulted in increased proximity to the developed areas around Anchorage. However, most of the beluga habitat in Cook Inlet is not degraded to the point that adverse effects to CI belugas are apparent. The extreme tidal ranges, land use patterns, and bathymetry of much of Cook Inlet may make it unsuitable for many types of development activities. Even though the majority of Cook Inlet is undeveloped, the loss or degradation of habitat is of medium relative concern for CI belugas due to a limited understanding of how this habitat might be altered by various factors and the resilience of this habitat.