Environmental drivers of the presence and persistence of sand lance hotspots on the Northeast US Shelf

Northern sand lance (Ammodytes dubius) are critical prey for numerous top predators including humpback whales, bluefin tuna, and several seabird species on the Northeast US shelf. Our work aims to understand what drives the extreme spatio-temporal variability in adult sand lance abundance by coupling insights from stomach content and total lipid analyses of fish collected on Stellwagen Bank in 2018 and 2019 with catch anomalies in a broad-scale standardized survey. Stomach content analysis suggests that sand lance feed most heavily in the spring and early summer on Calanus finmarchicus copepods, after which they reduce feeding prior to spawning in November. Whole-fish lipid content exhibits significant intra-annual variability, peaking around June—likely a result of spring consumption of Calanus finmarchicus. Lipid content subsequently decreases in early fall through winter during the spawning period. Lagged abundance of Calanus in the Gulf of Maine correlates with sand lance abundance in the Northeast Fisheries Science Center bottom trawl survey, an association likely due to the influence of Calanus abundance on sand lance lipid levels and the subsequent use of lipids during gonad development. Deviations from this trend appear to be primarily driven by abundance of Atlantic herring, an intra-guild predator that may exert both competitive and top-down control of sand lance abundance. Further, the spatial distribution of sand lance correlates with the spring abundance of Calanus both on Stellwagen Bank and the larger Northeast US Shelf, corroborating the importance of Calanus to sand lance. However, the abundance of sand lance in hotspots such as Georges Bank and Stellwagen Bank exhibits inter-annual variability that is likely driven by changes in transport and retention of larvae. Future work will utilize coupled bio-physical individual based models to estimate the inter-annual differences in larval transport that may drive this intermediate scale of variability.