Slow dating beluga
The blubber often results in lumpy sides and undersides, especially in large males (Reeves et al., 2002).
Belugas lack a dorsal fin, possessing instead a dorsal ridge (O'Corry-Crowe, 2002).
Delphinapterus leucas fossils, less than 2 million years old and found in northeastern North America, show that the distribution of the beluga changed as the glacial cover of the oceans altered (Berta and Sumich, 2003; O'Corry- Crowe, 2002).
Belugas are found only in the Northern Hemisphere—in Arctic and subarctic waters.
The summer habitats of belugas generally include an estuary.
Belugas show a high degree of philopatry, or site tenacity/fidelity, with stocks returning to the same estuaries year after year (COSEWIC, 2004).
Genetic evidence also suggests that the stocks have been visiting separate estuaries for long periods, perhaps since glaciers receded at the end of the last Ice Age, with only limited exchange between the different groups (O'Corry-Crowe, 2008). This behavior is tied to the seasonal epidermal molt of the beluga (Smith et al., 1992).
Diet varies with season and location, and food intake changes with water temperature (Balsiger, 2003).
These patterns indicate that belugas possess an ability to move freely between salt and fresh water, an ability that most other cetaceans do not have (Martin, 1996).
In addition, belugas have been sighted in various waters of various depths from extremely shallow waters to deep underwater trenches (Schreer and Kovacs, 1997).
Around 35 million years ago, both odontocete and mysticete cetaceans evolved and diversified rapidly; most likely due to new food resources resulting from oceanic change (Fordyce, 2002).
The earliest fossil monodontid is that of an extinct beluga (Denebola brachycephala), which lived along the coast of Baja California, Mexico, about 10 million years ago (O'Corry-Crowe, 2008).