Distribution of marine predator hotspots explained by persistent areas of prey

Abstract

Investigations of distributional and density patterns of marine predators often reveal areas where high abundances of one or many species overlap in space and time (‘biological hotspots’); however, mechanisms underlying hotspot formation are often unclear, leading to difficulties determining spatial and temporal boundaries of protected areas. On the northeast Newfoundland coast, I previously described annually persistent aggregations of a key forage fish species, capelin (Mallotus villosus): (1) two pre- and post-spawning staging areas in deep (>150 m) bathymetric channels, (2) a cluster of four persistently used demersal spawning sites (17–40 m), and (3) a coastal migratory route (<50 m). Through at-sea surveys repeated over 8 years (2000–2003, 2007, and 2009–2011), I show that the majority of predator hotspots identified were spatially associated with (i.e., within 10 km) these persistent capelin areas for breeding seabirds (common murre: 85.2 ± 4.6 %; northern gannet: 66.9 ± 6.6 %), overwintering seabirds (great and sooty shearwaters: 88.0 ± 6.9 %), and baleen whales (humpback, minke, and fin whales: 86.8 ± 8.6 %). Most predator hotspots were closer to the spawning (3.8–14.0 km) relative to the staging areas (13.1–27.6 km), especially for murres and shearwaters. Interspecific differences were attributed to variation in maximum dive depths and dietary preferences. Predators only aggregated within the spawning area, while capelin were spawning, suggesting that interannual variation in association with predator and capelin hotspots was attributed to variation in survey timing relative to capelin spawning. As these areas of persistent capelin are bound by static bathymetric and large-scale oceanographic features and can be delimited in time based on the capelin spawning period, they may be important candidate areas for protection.