Spatial scaling of recruitment in four continental shelf fishes

With the recent decline of several exploited populations of northwest Atlan tic fishes,. effort has been directed toward understanding the scales at wh ich recruitment varies along with the deterministic processes underlying th is variability. Using surveys from 3 research submersible cruises (1994, 19 97, 1998), we examined the distributions of 4 species of recently settled g roundfish in relation to spatial scale on the New York Eight region of the continental shelf (USA). A hierarchical sampling design was used to calcula te the percent variability in abundance partitioned over 4 nested scales: s ubmersible transect (similar to 100 m), site (similar to 10 km), shelf zone (similar to 25 km), and sampling line (similar to 100 km). For all years, early juveniles of Limanda ferruginea (yellowtail flounder) were highly con centrated at the shelf-zone scale, where abundance followed the thermal con tours of a mid-shelf cold pool of remnant winter water. Conversely, Hippogl ossina oblonga (fourspot flounder) and Citharichthys arctifrons (Gulf Strea m flounder) were highly site-dependent, bounding the distribution of L. fer ruginea at inner and outer shelf sites, respectively. Merluccius bilinearis (silver hake) exhibited moderate to high variability partitioned over seve ral scales. For all species, the absence of sampling-line variability sugge sted that settlement patterns were consistent across the breadth of the she lf, while substantial residual. variance suggested that microscale-level pr ocesses generated additional variability. Annual settlement of these early juveniles is highly specialized and cued to distinct aspects of the physica l and biological setting of the New York Eight. Conceptually, these local h abitat parameters can be used to link nodes of high variability with the po ssible deterministic processes modifying recruitment. Our results underscor e the critical contribution juvenile nursery habitats may have to the subse quent survival and growth of continental shelf species.