Steves et al : Settlement and nursery habitats for demersal fishes 



181 



20 



18 



16 



^ 14 



S. 12 



E 



10 



Q B Jun1996 



60 80 100 



Distance offshore (km) 



120 



140 



Figure 8 



Bottom temperature by distance offshore for tlie center transect between June 1996 and June 

 1997. 



occur in the same area, include just a slight overlap 

 with one another, or may be entirely separate spatial 

 entities. Although association with settlement habi- 

 tat is not a given, an area in which postsettled juve- 

 nile fishes persist and grow prior to first spawning 

 must be considered to be nursery habitat. Evalua- 

 tion of nursery habitat quality requires the compari- 

 son of gi'owth rates among stations for individual 

 settlement cohorts (Sogard, 1992; Jenkins et al., 

 1993) — information not presented in our study. For 

 many species, however, growth certainly occurs on 

 the shelf after settlement (Figs. 4-6). 



For several of the species collected during this study 

 in the NYB, nursery and settlement habitats are syn- 

 onymous. For example, P. ferrugineus,E. i7iicrostomus, 

 and L. profundorum were limited in their distribu- 

 tions, remaining unchanged from settlement through- 

 out the first year of life (Fig. 7, A-C). Several other 

 species, M. bilinearis, C. arctifrons, and M. america- 

 nus (Fig. 7, D-F) showed some movement in depth 

 between settlement and nursery areas, as well as 

 some indication of within-nursery migi-ation across 

 the shelf Toole et al. ( 1997 ) observed similar migi'ation 



between the settlement and nursery areas of Dover 

 sole (Microstomus pacificus) and suggested that such 

 movements were actively pursued by the juveniles, 

 but the ultimate migratory cues remained unclear. 



Within the NYB, several environmental gradients 

 describe the spatial and temporal distributions of 

 settlement habitats. Species-environment relation- 

 ships from the ordination analysis reveal that tem- 

 perature and depth explain most of the among-species 

 variance in habitat associations. Previous studies of 

 adult fishes in the NYB have shown the importance of 

 temperature and depth in describing species assem- 

 blages (Colvocoresses and Musick, 1984). This is in 

 contrast to the west coast of the United States, where 

 fish habitat associations have been studies exten- 

 sively for rockfish (Sebastes spp.) and to a lesser 

 extent for flatfish. There, for many species, more 

 importance has been attributed to geological fea- 

 tures such as sediment size and bathymetric hetero- 

 geneity (Pearcy, 1978; Stein et al., 1992; Adams et 

 al., 1995). Considering the higher level of geological 

 diversity on the West Coast than in the NYQ, this 

 conclusion is not surprising. 



