Five species of fish, Clinocottus analis, Girella nigdcans, Hypsoblennius gilberti, Gobiesox rl~essodon, and Gibbonsia elegans, conlmonly occur in southern California's rocky intertidal zone. To examine the extent to which tidepool habitat is segregated by the 5 fishes, habitat partitioning patterns among and within the species were determined at 2 sites in San Diego. Fish density, species composition, and fish size were measured in 105 tidepools every 3 mo from November 1996 to August 1997. Hypotheses were tested pertaining to the segregation of habitat among different species and different size classes within species relative to the tidepool characteristlcs of intertidal height, surface area, depth, rugosity, and percent algal cover. A manipulative field experiment was conducted to further investigate these results. Tidepools were partitioned among and within fish species. Tidepool characteristics most important in partitioning were intertidal height, depth, and rugosity, with the order of importance of these characteristics different for each species. Habitat part~t~oning between size classes within species, although not as great as partitioning among species, was also based largely on tidepool intertidal height and rugosity. Although fish abundance changed seasonally, species' distribution patterns, with the exception of C. analis, were seasonally stable. The seasonal change in C. analis distribution was due to the arrival of new recruits rather than a seasonal change in adult habitat. The use of different types of tidepools by different species and by different size classes within species serves to limit contact among these groups, and therefore both direct and indirect competition, during low tide.

No abstract

Stock enhancement of severely exploited, recruitment‐limited fisheries has been controversial for several reasons, one of which is the lack of information about competency, competitiveness, and survivorship of hatchery‐reared individuals released into the field. Because enhancement efforts have focused on finfish, even less information is available with which to assess enhancement potential of crustaceans. The Chesapeake Bay stock of blue crabs Callinectes sapidus has declined by more than 80% over the past 12 years and has exhibited recruitment limitation, leading to recent efforts to study the potential of enhancing populations with hatchery‐reared juveniles. To assess how hatchery‐raised juvenile blue crabs may fare after release into the Chesapeake Bay, we compared several aspects of hatchery and wild crabs. Hatchery crabs readily fed on natural prey, moved in the field similarly to wild crabs, and grew at rates similar to those of wild crabs; however, the two crab groups differed in other factors important to field survival. Prerelease and laboratory‐held hatchery crabs had different carapace morphology (smaller spines) than wild crabs, though spine lengths increased to normal proportions by several weeks after release. Hatchery crabs did not initially bury in sediment as often as wild crabs, suggesting inexperience with an important predator escape response. Hatchery crabs were also preyed upon at higher rates in the field than wild crabs. Conditioning experiments suggest that inexperience with sediment and low burial rates were not the main cause of higher predation. By identifying areas in which hatchery individuals may be relatively weak and deficits that can potentially be mitigated, studies such as this can lead to improving the success of hatchery‐raised individuals in the field. On a broader scale, such studies also contribute to determining whether stock enhancement is possible in the case of the Chesapeake blue crab.

No abstract

Intertidal organisms are influenced by the tidal, daily, and seasonal environmental variability of their habitat. Interannual variability, although often less severe than shorter-scale variability, may also be important in structuring intertidal systems. This study compares the magnitude of changes in a rocky intertidal fish guild occurring on a seasonal scale with those occurring during an El Niño Southern Oscillation (ENSO). I examined tidepool fish assemblage structure and habitat use in two southern California sites approximately every 3 months from 1996 to 2000, a period including non-ENSO conditions, the 1997-1998 El Niño, and the 1998-1999 La Niña. During each sampling period, I censused fish abundance in 105 tidepools of differing intertidal height, depth, and surface area. Several aspects of habitat use varied seasonally for the four most common species: Clinocottus analis (woolly sculpin), Girella nigricans (opaleye), Gobiesox rhessodon (California clingfish), and Hypsoblennius gilberti (notchbrow blenny). All four species migrated vertically within the intertidal zone on a seasonal scale, corresponding to seasonal changes in sea level. The assemblage dominant, C. analis, occupied tidepools of different sizes depending on season. Although seasonality in habitat use suggests an influence of environmental variability on seasonal scales, fish habitat was generally not altered by temperature and sea level changes imposed by the El Niño. Species assemblage, however, differed among climate conditions. C. analis declined in abundance during the El Niño because of lack of recruitment but increased immediately after its conclusion. Paraclinus integripinnis (reef finspot), usually rare, was more abundant during the El Niño. Effect of the El Niño on the other four species was not detected. Assemblage changes suggest that although intertidal fishes regularly experience large tidal, daily, and seasonal environmental fluctuations, interannual changes in environmental factors, even when relatively small in magnitude, can perturb the system. Perturbations in the present system, however, did not persist beyond the end of the El Niño event as they often do in lower-latitude nearshore areas.