DYNAMICS OF THE NOVA SCOTIA CURRENT AND LINKAGES WITH ATLANTIC SALMON MIGRATION PATTERNS OVER THE SCOTIAN SHELF

Abstract

Over the 2008-2015 period, the Ocean Tracking Network provided unprecedented spatiotemporal coverage of the hydrography and currents along the Halifax Line (HL) on the Scotian Shelf, using several different monitoring techniques (e.g., moorings and underwater gliders). The observations are analyzed here to provide an extensive description of the physical oceanographic conditions over the Scotian Shelf, as well as the spatiotemporal variability observed over this period. The analysis of observations identifies the distribution of key water masses present along the HL. The water mass analysis demonstrates that the large warming event observed in 2012 was primarily due to the advection of already anomalously warm water from the Shelf Slope. The ocean circulation along the HL during this period is examined, with a focus on the seasonal cycle and the inter-annual variability of the Nova Scotia Current (NSC). A conceptual model is developed to investigate the main mechanisms driving the NSC. The relative roles of buoyancy-driven and wind-driven flows to the NSC are estimated at the HL to study the seasonal variability of the forcing and the relative importance of these two mechanisms in driving the NSC. Generally, the NSC is dominated by the buoyancy-driven component of the current, throughout the year and at all four transects between Cabot Strait and Cape Sable. The relative contributions of buoyancy and alongshore surface winds to the NSC’s dynamics are remarkably similar across transects having the same coastal orientation, but significantly vary where the coastline orientation changes. The newly-acquired oceanographic knowledge along the HL is also combined with acoustic detections of Atlantic salmon postsmolts coming from the Penobscot River to study the temporal and spatial distribution of the migrating fish in the context of oceanographic conditions. It is shown that postsmolts tend to be in greater abundance in the colder and fresher coastal water mass, while the abundance is not related to the direction or magnitude of local currents.