Pacific sand lance (Ammodytes hexapterus) inhabit subtidal sediment wave fields
in the San Juan Islands of Washington state. Although they are an important forage fish,
serving as a trophic link between zooplankton and larger organisms, very little is known
of the life history of subtidal sand lance in the sediment wave fields. Here, I hypothesize
that spatial and temporal patterns of sand lance abundance are influenced by a variety of
physical factors, including sediment grain size and tidal currents. Using a Van Veen grab
sampler to collect sand lance in the sediment fields, and an ADP to measure current
velocities over two, 3 hour sampling periods aboard the R/V Centennial, I found
anomalously high numbers of sand lance in the sediment during slack before flood tides
when northward velocities measured between +/- 15 cm s-1. In contrast, negative
anomalies that occurred during weak ebb tides of -20 to -40 cm s-1. This suggests fine
scale temporal variation in sand lance presence in the sediment fields may be tied to tidal
cycles, and that sand lance may enter and leave the fields during the fall and early winter.
The sediment fields near Sucia Island composed of large (1mm) shell hash,
contained only mature fish, while the finer grained (1/2 mm) sediments of the San Jean
Channel wave field had larger proportions of juveniles less than 90 mm in length,
suggesting a relationship between sediment grain size and life stage. Other factors
including depth and tidal mixing may also play a role in the spatial distribution of sand
lance
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