Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8722
Title: Fishing and environmental influences on herbivorous fish biomass across the Hawaiian Archipelago
Author: Jason Helyer, J. F. Samhouri
Publication Year: 2017
Journal: Marine Ecology Progress Series
Volume: 575
Pages: 1-15

A longstanding goal in coral reef ecology is to estimate the baseline states of ecological communities and the extent to which human activities have perturbed them. Multiple studies have established baselines for fish communities using observations from remote, uninhabited coral reefs, highlighting drastic differences in the composition and abundance of fish communities compared to coral reefs near populated areas. However, previous studies have focused on island- and archipelago-wide comparisons of reef communities that mask finer-scale spatial variability of coral reef communities within remote, unpopulated reef systems. Here we describe spatial patterns of herbivorous fish biomass across fished and unfished regions of the Hawaiian Archipelago to evaluate whether accounting for environmental variability between these regions alters estimates of unfished biomass (Bunfished) and fisheries depletion. We found environmental factors were strongly associated with four measures of herbivorous fish community biomass (total, scraper, grazer, and browser) and failure to account for these influences on unfished biomass resulted in different conclusions about herbivore depletion in Hawaii.  Overall, depletion estimates that controlled for environmental differences indicated that biomasses of the four herbivorous fish groups across much of Hawaii are near or above a commonly used sustainability reference point (0.5*Bunfished). However, scraper and browser biomass on Oahu, the island with the highest human population density, were near or below 15% of Bunfished, highlighting the potential importance of spatial and functional group variability when assessing fishing effects on coral reefs. These findings are at once useful for resource managers in Hawaii and applicable to other reef systems where embracing spatial variability can aid in identification of conservation targets on coral reefs.

Theme: Ecosystem approach to improve management of marine resources
Foci: Provide scientific support for the implementation of ecosystem-based management
Assess ecosystem status and trends.