2012 to 2003 Movement and Dive Behavior of Beluga Whales in Cook Inlet Alaska
Beluga whales (Delphinapterus leucas) in Cook Inlet are the most geographically and genetically isolated of the five stocks recognized around Alaska (OCorry-Crowe et al. 1997, Laidre et al. 2000). Their isolation, in combination with high site fidelity in summer (Rugh et al. 2000, 2005, 2010), makes them particularly vulnerable to both environmental (Moore et al. 2000) and anthropogenic impacts (Hill 1996). The population of Cook Inlet belugas declined by nearly 50% between 1994 and 1998 to an estimated 347 whales (Hobbs et al. 2000). Despite cessation of the Alaska Native subsistence hunt in 1999 of approximately 70 animals per year (Mahoney and Shelden 2000), the abundance estimates of belugas in Cook Inlet have remained low (321 and 340 animals in 2009 and 2010 compared to 653 in 1994) with no notable signs of recovery (Hobbs and Shelden 2008). In recognition of the low numbers of belugas remaining in Cook Inlet, the U.S. government listed this isolated population as endangered under the U.S. Endangered Species Act in October 2008.
The summer distribution and habitat of belugas has been well documented from annual aerial surveys (Rugh et al. 2000, 2004, 2005; Goetz et al. 2007, 2012). During this time, belugas concentrate in the upper reaches of the Inlet in shallow bays and river mouths where fish runs are abundant (Lensink 1961, Moore et al. 2000, Goetz et al. 2012). Prior to biologging technology, the winter distribution of Cook Inlet belugas was poorly understood and considered enigmatic. Calkins (1983) hypothesized that belugas left Cook Inlet during the winter, especially when heavy ice was present. Sporadic sightings outside of Cook Inlet have occurred in all seasons; however, these sightings of belugas are considered rare relative to the survey effort and hundreds of thousands of other cetacean sightings documented for the Gulf of Alaska and adjacent inside waters (Laidre et al. 2000).
In addition to sighting small, scattered pods of belugas during February-March 1997 surveys of Cook Inlet (Hansen and Hubbard 1999), numerous opportunistic sightings have been reported throughout the year (NMFS unpubl. data). Belugas were also observed every month except February during monthly aerial surveys conducted in 2001-2002, suggesting that at least part of the beluga population remains in the Inlet over winter (Calkins 1983). During these surveys, there were fewer beluga sightings in the winter (10 in January) than the summer (204 in August), which may be linked to the inability of observers to detect belugas amongst heavy ice (Rugh et al. 2004).