HABITAT USE AND BEHAVIOR OF THE PACIFIC SAND LANCE (AMMODYTES HEXAPTERUS) IN THE SHALLOW SUBTIDAL REGION OF SOUTHWESTERN VANCOUVER ISLAND

Abstract

The Pacific Sand Lance (Ammodytes hexapterus) is an important Pacific Northwest prey species for marine predators. In our study along the West Coast Trail, southwestern Vancouver Island, British Columbia, we examined shallow subtidal habitat selection of juvenile and adult Sand Lance with respect to sediment characteristics, and also examined aggregation behavior. Analysis of presence or absence using a classification tree showed that Sand Lance avoided sites with no subtidal sediments, preferred sites with mean sediment particle sizes ≤ 1290 μm and preferred mixed sediments (sorting values >3.09 standard deviations; standard deviation of particle size used as a heterogeneity index of the substrate grain size). The regression tree analysis explained 99% of the variation in abundance based on the effects of mean particle size, particle sorting and presence or absence of sediments, but the model showed evidence of over-classification due to small sample sizes. Nevertheless, the model indicated environmental factors that are important for Sand Lance habitat use. Behavioral analysis showed that Sand Lance aggregated into larger schools to feed and these schools tended to occur in the mid-water column compared to non-feeding schools which remained closer to the seafloor. Near the beaches, 0-year (young-of-the-year) Sand Lance were found in deeper water compared to older Sand Lance (1 -year classes). Together these data suggest that Sand Lance using the shallow subtidal show some indication of habitat use based on particle size and sorting, and aggregation differences based on behavior and age class.