Hazards evaluation of a valuable vulnerable sand-wave field forage fish habitat in the marginal Central Salish Sea using a submersible

Abstract

The Salish Sea is a marginal inland sea of the NE Pacific (NW North America) that includes the Georgia Strait-Gulf Islands Archipelago of British Columbia, Canada and the San Juan Archipelago, Strait of Juan de Fuca, and the Lower Puget Sound of Washington State, USA. This marginal seafloor has been extensively mapped and according to criteria presented and discussed at GeoHab conferences critical marine benthic habitat types are identified. One such habitat that is the focus of this paper is the deep-water sub-tidal habitat of Pacific sand lance (PSL). The PSL (Ammodytes personatus) is a critical forage fish for a variety of mammals, birds and fish including minke whales and salmon as it preys upon zooplankton and acts as an energy transfer species from the lower to higher trophic levels. Pacific sand lance seeks refuge and overwinters in sand-wave fields consisting of dynamic bedforms. The species prefers loosely packed, well-aerated, well-sorted, medium- to coarse-grain (∼1 phi [φ], 500 µm) sand that it can burrow into easily. Such geomorphic features as active dynamic bedforms provide preferable habitats for PSL and depends on specific and unique oceanographic processes that can maintain the habitat's morphology and grain sizes. Understanding these processes is essential in forecasting alteration or destruction of such features, including changes that may be brought about by sea level rise. Using the five-person submersible Cyclops 1, we recently examined a well-studied sand-wave field in the San Juan Archipelago of Washington State, USA, which has been reported to harbor up to 12 million PSL. Observations, video recordings, and photography from this vehicle allowed us to assess modern seafloor processes of the central Salish Sea that can be used along with fish and sediment sample data to determine physical preferences this fish needs to sustain its population. Changes in the seafloor current regime, sediment source, and anthropogenic disturbances can critically alter these dynamic bedforms. This research provides insight into the structure of these bedforms, their composition, their persistence, their resilience to disturbance, and the susceptibility as an impact and becoming impacted.