Gimme Shelter: the Importance of Crevices to Some Fish Species Inhabiting a Deeper-water Rocky Outcrop in Southern California

Federal law governing fisheries management recognizes the role habitat plays in structuring fish assemblages and achieving sustainable fisheries. However, in most instances it is not known which aspects of habitat are important to the lives of fish species. In 2004, we examined the importance of sheltering sites (crevices) to fishes living along low ledges in deeper waters off Anacapa Island, southern California. We found that patterns of fishhabitat relationships varied among the eight most abundant species. Three species, bocaccio (Sebastes paucispinis), vermilion (S. miniatus), and flag (S. rubrivinctus) rockfishes, had densities one to three orders of magnitude greater in the deep crevice habitat compared to low relief rock or shallow crevice habitats. Density and mean size of the two most abundant fishes, halfbanded (S. semicinctus) and squarespot (S. hopkinsi) rockfishes, generally increased as complexity of rock habitat increased. Not all species had the highest densities in deep crevice habitat. Greenspotted rockfish (S. chlorostictus) and blackeye goby (Rhinogobiops nicholsii) showed no significant difference in density among rock habitats. Pink seaperch (Zalembius rosaceus) were absent in the deep crevice habitat and abundant only in low relief rock habitats. Our study implies that it is not sufficient to distinguish only between soft and hard bottom types when using habitat to guide fisheries management strategies. Finer-scale investigations of fish-habitat relationships, paired with habitat mapping and groundtruthing, aid in the design and positioning of Marine Park Areas (MPAs) and are necessary to facilitate understanding of how a particular MPA may contribute to fisheries management. INTRODUCTION In recent years, studies have begun to illustrate the role that habitats play in structuring fish assemblages. Much of the impetus for this research derives from the Sustainable Fisheries Act of 1996, which reauthorized and amended the Magnuson-Stevens Fishery Management and Conservation Act. The amended Magnuson-Stevens Act made habitat characterization and conservation central tenets and created the concept of Essential Fish Habitat (EFH) and Habitats of Particular Concern (HAPCs). In addition, the establishment of Marine Protected Areas (MPAs), as a tool of fishery management (e.g., the Pacific Coast Rockfish Conservation Areas created by the Pacific Fishery Management Council, www.pcouncil.org/reserves/reservesback.html) and a protector of ecosystem function and structure (e.g., as delineated in the California Marine Life Protection Act, http://www.dfg.ca.gov/mrd/mlpa/), has demonstrated that understanding habitat preferences of fish species is crucial if we are to protect various life stages. However, as noted by Lindeman et al. (2000), in most instances it is not known which of the “finer scale, structural habitat types” are important to the lives of fish species and “characterizing structural and water-quality attributes influencing behavior of settlement-competent stages is fundamental to identifying primary nurseries and EFH-HAPCs.” In general, the habitat preferences of deeper-water (below scuba-diving depth) fishes along the Pacific Coast have been characterized at the megahabitat (e.g., sediment-covered seafloor) and mesohabit (e.g., rock outcrops, boulders, and cobble fields, sensu Greene et al. 1999) levels (Stein et al. 1992; Yoklavich et al. 2000; Nasby-Lucas et al. 2002). One issue is that, while within many larger habitats fishes may associate with smaller macroand microhabitats (e.g., cracks, crevices, and substrate-forming invertebrates), these relationships are often difficult to discern in complex habitats, particularly in waters below scuba-diver depth where experimentally altering habitat (e.g., Matthews 1990) is problematic. In 2004, surveys conducted using a manned submersible allowed us to examine the importance of sheltering sites, one aspect of complex habitats, to fishes living along low ledges in deeper waters off Anacapa Island, southern California. Although limited in scope, our surveys indicate that finer-scale investigations of fish-habitat relationships, paired with habitat mapping and groundtruthing, aid the design and positioning of Marine Park Areas (MPAs) and facilitate understanding of how a particular MPA may contribute to fisheries management. 119 119-126 Love bl 11/19/06 1:38 PM Page 119