Eddy retention and seafloor terrain facilitate cross-shelf transport and delivery of fish larvae to suitable nursery habitats

For marine fish with ontogenetic shifts in habitat requirements, survival is dependent upon oceanographic transport of pelagic larvae from spawning locations and the arrival of settlement-stage larvae to nursery habitats. Settlement success for fish with nurseries on the continental shelf, such as many flatfish, relies on routes of transport that facilitate the delivery of larvae from offshore to suitable inshore habitats. To address spatial and temporal coupling between spawning, transport, and settlement, we utilized an individual-based biophysical model for the years 2000–2011 in combination with a juvenile habitat suitability model for arrowtooth flounder (Atheresthes stomias), an abundant predatory flatfish in the oceans off Alaska. Settlement success was inversely related to the availability of nursery habitat, but oceanographic variability dictated interannual patterns in larval supply to nurseries. Paradoxically, the majority of larvae were advected offshore and arrived to nurseries on the continental shelf. Shoreward bathymetric steering through glacial troughs that resulted in directed transport to nurseries was minimal despite the high proportion of larvae that accessed trough features. Based on modeling results and empirical observations, mesoscale eddies and retention near suitable settlement habitats enhanced settlement and recruitment magnitude. In advective ecosystems such as the Gulf of Alaska, settlement success and cross-shelf transport are augmented by transient retentive features that influence recruitment by facilitating the delivery of larvae to nursery habitats on the continental shelf.