James Parrish

Habitat characteristics affecting fish assemblages on a Hawaiian coral reef

Habitat characteristics of a reef were examined as potential influences on fish assemblage structure, using underwater visual census to estimate numbers and biomass of all fishes visible on 42 benthic transects and making quantitative measurements of 13 variables of the corresponding physical habitat and sessile biota. Fish assemblages in the diverse set of benthic habitats were grouped by detrended correspondence analysis, and associated with six major habitat types. Statistical differences were shown between a number of these habitat types for various ensemble variables of the fish assemblages. Overall, both for complete assemblages and for component major trophic and mobility guilds, these variables tended to have higher values where reef substratum was more structurally or topographically complex, and closer to reef edges. When study sites were separately divided into five depth strata, the deeper strata tended to have statistically higher values of ensemble variables for the fish assemblages. Patterns with depth varied among the various trophic and mobility guilds. Multiple linear regression models indicated that for the complete assemblages and for most trophic and mobility guilds, a large part of the variability for most ensemble variables was explained by measures of holes in the substratum, with important contributions from measured substratum rugosity and depth. A strong linear relationship found by regression of mean fish length on mean volume of holes in the reef surface emphasized the importance of shelter for fish assemblages. Results of this study may have practical applications in designing reserve areas as well as theoretical value in helping to explain the organization of reef fish assemblages.

Temporal dynamics of fish communities on an exposed shoreline in Hawaii

Environmental conditions on higher latitude coral reefs can be extremely variable, and may structure fish communities in ways not previously observed in the more stable, low latitude locations where communities have usually been studied. Temporal changes in fish community structure were examined in an intensive two-year study of the reef fishes of Hanalei Bay, Kauai, Hawaii. Hanalei Bay is directly exposed to winter swells with high surf, as well as frequent heavy winter rainfall and high river discharge. Twenty-two transects (25 × 5 m) were established in a wide variety of habitats and censused monthly (N = 1052 censuses). Over 121 000 sightings of individuals from 150 species were made during the study. Seasonal patterns in number of species, number of individuals, species diversity, and evenness were observed, with winter values usually lowest. Values of these ensemble variables tended to be higher at deeper sites and at sites with greater habitat complexity. Surf height and degree of wave exposure were negatively correlated with several measures of community organization. Groups of fishes with different levels of spatial mobility tended to occupy depths consistent with their various abilities to respond to events of heavy weather. The rank abundance of fish taxa tended to be more stable seasonally at sites with less exposure to high wave energy. These seasonal effects may suggest some type of short-range movement from more exposed and monotypic habitats to locations that are deeper or otherwise provide refuge from seasonally heavy seas.

Fisheries harvest and standing stock in a Hawaiian Bay

Abstract An 18-month study at Hanalei Bay, Kauai provided unusually valuable quantitative fishery data and concurrent estimates of natural density of reef fish for a complete, small, subsistence/recreational/artisanal fishery on a small, remote island in the tropical mid-Pacific. Catch and effort data were collected using a stratified random sampling design. The commercial surround net fishery targeted mainly coastal pelagic species and accounted for over 70% of the catch. Most other fishing was for recreation or subsistence. Line fishing from shore and boats accounted for much of the effort but produced some of the lowest catches per unit effort (CPUE). The cast net and spear fisheries had CPUE values of more than 1 kg per gear-hour and caught a wide diversity of reef-associated species. Standing stock of reef-associated fishes was estimated from 516 underwater visual censuses. Mean biomass ranged from over 16 kg/100 m 2 in shallow complex habitats to less than 1 kg/100 m 2 in monotypic reef flat habitats. These densities, which are higher than those reported from some more populated, similar areas in Hawaii, may reflect lower fishing pressure in Hanalei. Yield estimates from Hanalei Bay are very low compared to those from many other locations in the Pacific. The small fraction of the overall standing stock that is harvested annually (~ 1.3%) suggests that most of the fish community is not being severely overfished. Parrotfishes, goatfishes, and surgeonfishes were important components of the fisheries and of the censused communities, suggesting that these target species have not been seriously depleted. The small sizes at which some valued species are caught is a matter of concern for management of these stocks.

Piscivory in a coral reef fish community

The community of demersal, resident reef fishes of the Northwestern Hawaiian Islands was studied to determine the various roles of fishes within the piscivorous trophic subweb. Relative abundance estimates for 160 fish species were made on the basis of extensive visual censuses and four chemical collections. Diet information was collected by gut analysis of 52 piscivorous species from 16 families. Twenty species were termed major piscivores and 32 minor piscivores. Twelve to 31% of the biomass of the entire fish community at the four chemical stations was piscivorous. The Apogonidae, Labridae, Mullidae, Scorpaenidae, Pomacentridae, Holocentridae and Gobiidae were the most important prey families, providing over 70% of all prey. The families producing largest piscivorous impacts were the Muraenidae, Synodontidae, Congridae, Labridae, Scorpaenidae, Holocentridae, Priacanthidae and Cirrhitidae. Several families contained a number of intermediate level species whose combination of relatively high abundance, moderate degree of piscivory, and substantial vulnerability to predation gave them a wide trophic scope and an important place in the total trophic activity. The quantitative approach used here to analyze community trophics by estimating predation by and upon whole interacting populations offers promise for improved understanding of these complex systems.

Community structure and habitat associations of parrotfishes on Oahu, Hawaii

Despite their ecological importance as bioeroders and their economic importance in commercial, artisanal, and recreational fisheries, there have been relatively few studies on parrotfish (Scaridae) ecology in Hawaii. Belt transects were conducted around the island of Oahu to survey current parrotfish distributions, size structure, species composition and associated habitats. Scarid communities in this heavily fished region are dominated by smaller species and smaller individuals within all species. Specific habitat characteristics such as rugosity, substrate diversity, and percent live coral cover were positively correlated with scarid numerical abundance. Scarids, however, were patchily distributed and were often absent from preferable habitats, suggesting that intense fishing pressure may be an important factor preventing these fish from fully exploiting available habitats. This study is the first thorough, broad-scale investigation of scarid community structure in Hawaii, and provides important information that has management and conservation implications for parrotfish in Hawaii and throughout tropical coral reef ecosystems.