Spatial scaling of recruitment in four continental shelf fishes

With the recent decline of several exploited populations of northwest Atlantic fishes, effort has been directed toward understanding the scales at which recruitment varies along with the deterministic processes underlying this variability. Using surveys from 3 research submersible cruises (1994, 1997, 1998), we examined the distributions of 4 species of recently settled groundfish in relation to spatial scale on the New York Bight region of the continental shelf (USA). A hierarchical sampling design was used to calculate the percent variability in abundance partitioned over 4 nested scales: submersible transect (~100 m), site (~10 km), shelf zone (~25 km), and sampling line (~100 km). For all years, early juveniles of Limanda ferruginea (yellowtail flounder) were highly concentrated at the shelf-zone scale, where abundance followed the thermal contours of a mid-shelf cold pool of remnant winter water. Conversely, Hippoglossina oblonga (fourspot flounder) and Citharichthys arctifrons (Gulf Stream flounder) were highly site-dependent, bounding the distribution of L. ferruginea at inner and outer shelf sites, respectively. Merluccius bilinearis (silver hake) exhibited moderate to high variability partitioned over several scales. For all species, the absence of sampling-line variability suggested that settlement patterns were consistent across the breadth of the shelf, while substantial residual variance suggested that microscale-level processes generated additional variability. Annual settlement of these early juveniles is highly specialized and cued to distinct aspects of the physical and biological setting of the New York Bight. Conceptually, these local habitat parameters can be used to link nodes of high variability with the possible deterministic processes modifying recruitment. Our results underscore the critical contribution juvenile nursery habitats may have to the subsequent survival and growth of continental shelf species.