Euphausiid transport in the Western Arctic Ocean

Euphausiids are commonly found in the stomachs of bowhead whales Balaena mysticetus hunted near Barrow, Alaska; however, no evidence exists of a self-sustaining population in this region. To explain euphausiid presence near Barrow, their transport from the northern Bering Sea was investigated through particle tracking experiments using velocity fields from an ocean general circulation model in 4 contrasted circulation scenarios (1997, 1998, 2002 and 2003). Euphausiids were released during their spawning season (April-June) in the bottom and surface layers in the northern Bering Sea, their endemic region, and tracked through the Chukchi-Beaufort Sea. Results show that both Anadyr Gulf and Shpanberg Strait are potential regions of origin for euphausiids. Topographically steered bottom particles have 4 to 5 times higher probability of reaching Barrow than surface particles (ca. 95% versus 20% of particles). As euphausiids are often found near the bottom on the northern Bering shelf, this suggests a very high probability of euphausiids reaching Barrow, making this location a privileged area for whale feeding. The main pathways to Barrow across the Chukchi Sea shelf are Central Valley (CV) and Herald Valley (HV). The transit to Barrow takes 4 to 20 mo. Arrivals at Barrow have 2 peaks at ca. 200 d (fall, CV particles) and 395 d after release (spring, mixed CV and HV) on average, because of the seasonal cycle of the Chukchi Sea currents. Elevated euphausiid abundance in the fall at Barrow is favored by a high Bering Strait northward transport and by southerly winds, driving organisms through CV rather than through the HV pathway.