Springtime transport and retention of Calanus finmarchicus in Massachusetts and Cape Cod Bays, USA, and implications for right whale foraging

Abstract

The Massachusetts Bay (MB) and Cape Cod Bay (CCB) system is a unique coastal embayment, with CCB serving as a high-use feeding ground for endangered North Atlantic right whales Eubalaena glacialis during winter and early spring. We used a hydrodynamic model, observed Calanus finmarchicus (the preferred prey of right whales) abundance, and right whale sightings during 1997-2004 to examine the transport and retention of C. finmarchicus in MB-CCB and the implications for right whale activity. A particle-tracking program was embedded into the model to simulate the Lagrangian residual circulation, and the transport and retention of passive particles. The results indicate significant correlations in the inter-annual variability of coastal trans- port, circulation pattern, C. finmarchicus abundance, and right whale sightings in spring. In nor- mal years (with prevailing northwesterly winds), the monthly mean distributions of particles and Lagrangian residual currents show a coherent pattern with 2 particle retention areas in central CCB and central MB, respectively. The CCB retention area closely matches the area of high prob- ability of right whale occurrence and feeding activity, indicating that this is an area favorable to zooplankton aggregations. In other years (e.g. 2002), the coastal current is significantly reduced due to prevailing southwesterly winds, and the particle retention zone is shifted northward, coinci- dent with low C. finmarchicus abundance and whale sightings in CCB. The study also suggests that the North Atlantic Oscillation may influence C. finmarchicus abundance and distributions, and hence, right whale feeding activity in CCB through surface winds affecting MB-CCB circulation, and hence, zooplankton distributions.