A Predictive Sub-Tidal Habitat Model of the Forage Fish Pacific Sand Lance (Ammodytes hexapterus) – A Study in Progress, Salish Sea, USA and Canada

The Pacific sand lance (PSL or Ammodytes hexapterus) is a major forage fish in the Salish Sea, as sand lance are in much of world’s oceans.  PSL are preyed upon by many species of birds (e.g., tufted puffins, rhinoceros auklets), fish (e.g., lingcod, rockfish, salmon), and mammals (e.g. minke whale) among other animals. Until recently little or nothing was known about its sub-tidal habitat, or even if it had a sub-tidal habitat. However, our recent investigation into the benthic habitats of PSL through imaging the seafloor using mulitbeam echosounder (MBES) techniques and tank experiments indicates that PSL prefer to burrow into medium- to coarse-grain sand (0.5 mm or 1 phi to 2 mm or -1 phi in size) at depths up to 80 m. Although PSL appear to be capable of burrowing into substrate types that range from mud (0.002 mm or 9 phi) to fine gravel (2-3 mm or -1 - -1.5 phi), where present it appears to prefer dynamic bedforms such as sediment wave fields of sand and gravel.

We sampled for both grain size and fish using a Van Veen grab sampler, which is capable of obtaining a maximum sample of ~0.5 m³ of sediment. In one of our grabs we collected as many as 70 PSL, alive and healthy, from our referenced sand wave field in San Juan Channel, WA. We use the reference field to determine presence or absence of PSL in the Salish Sea region, occupation by life stage, egg presence or absence, abundance, and duration of occupancy. From these data we have generated a geomorphic model (bathymetric image) that most probably represents PSL potential habitat. Tentatively, this model looks like a sediment wave field of well-sorted sand and gravel with wave heights on the order of 0.25-0.5 m and wavelengths of 3-4 m.