Relationships between High River Discharge, Upwelling Events, and Bowhead Whale (Balaena mysticetus) Occurrence in the Central Alaskan Beaufort Sea

Aerial surveys of bowhead whales have been conducted in September in the central Alaskan Beaufort Sea (144°W-150°W) for several decades. These surveys, co-managed by BOEM and NOAA, have documented bowhead whale distribution that is almost exclusively on the continental shelf, generally from <1 to 70 km from shore. Most whales observed in September are actively migrating and swimming in a westerly direction, with feeding behavior occasionally observed. In September 2014, several hundred bowhead whales were observed feeding on several occasions within a few kilometers of local barrier islands. This is an unusual situation that has been observed in September in only one other year (1997). To investigate local conditions that might be conducive to increased bowhead whale occurrence, freshwater discharge data from the Sagavanirktok and Kuparak rivers, surface wind data, and suspended sediment data obtained from MODIS satellite imagery were analyzed and compared to bowhead whale observations for September 1989-2014. Results indicate that anomalously high freshwater river discharge coupled with prior upwelling events, based on surface winds >5.4 m s^-1, may combine to promote the aggregation of bowhead whale prey on the shallow shelf. When these two conditions were met, whales were sighted more frequently, were more likely to be in groups of ≥2 animals, and be closer to shore. Conversely, when either of the two conditions was not met, whales were sighted less frequently, more likely to be single animals, and be farther from shore. These results underscore annual variation during the bowhead whale fall migration and the physical oceanography processes that may be related to whale distribution and behavior.