Environmental Conservation: page 1 of 12 © 2008 Foundation for Environmental Conservation doi:10.1017/S0376892908004876 Assessing the importance of fishing impacts on Hawaiian coral reef fish assemblages along regional-scale human population gradients I. D. WILLIAMS 1,2 ∗ , W. J. WALSH 2 , R. E. SCHROEDER 3 , A. M. FRIEDLANDER 4 , B. L. RICHARDS 3 AND K. A. STAMOULIS 2 1 Hawaii Cooperative Fishery Research Unit, Department of Zoology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA, 2 Hawaii Division of Aquatic Resources, Honokohau Marina, 74-380B Kealakehe Parkway, Kailua-Kona, Hawaii 96740, USA, 3 Joint Institute for Marine and Atmospheric Research (JIMAR), University of Hawaii and Coral Reef Ecosystems Division (CRED) NOAA, National Marine Fisheries Service, Pacific Islands Fisheries Science Center, 1125B Ala Moana Boulevard, Honolulu, HI 96822, USA and 4 NOAA/NOS/NCCOS/ CCMA- Biogeography Branch and The Oceanic Institute, Makapuu Point/41-202 Kalanianaole Highway,Waimanalo, Hawaii 96795, USA Date submitted: 29 January 2008; Date accepted: 26 May 2008 SUMMARY Humans can impact coral reef fishes directly by fishing, or indirectly through anthropogenic degradation of habitat. Uncertainty about the relative importance of those can make it difficult to develop and build consensus for appropriate remedial management. Relationships between fish assemblages and human population density were assessed using data from 18 locations widely spread throughout the Main Hawaiian Islands (MHI) to evaluate the significance of fishing as a factor potentially driving fish trends on a regional scale. Fish biomass in several groups was negatively correlated with local human population density and a number of lines of evidence indicate that fishing was the prime driver of those trends. First, declines were consistently evident among fish groups targeted by fishers, but not among lightly fished or non-target groupings, which indicates that declines in target groups were not simply indicative of a general decline in habitat quality along human population gradients. Second, proximity to high human populations was not associated with low fish biomass where shoreline structure prevented ready access by fishers. Relatively remote and inaccessible locations within the MHI had 2.1–4.2 times the biomass of target fishes compared to accessible and populous locations, and may therefore function as partial refugia. However, stocks in those areas were clearly far from pristine, as biomass of large predators was more than an order of magnitude lower than at more intact ecosystems elsewhere in the Pacific. Keywords: coral reef, fishing, habitat, Hawaii, introduced species, natural refugia INTRODUCTION There is little question that even low levels of fishing can lead to substantial depletion of some groups of coral reef fishes (Jennings & Polunin 1996; Dulvy et al. 2004). More ∗ Correspondence: Dr Ivor Williams Tel: +1 808 327 6231 Fax: +1 808 327 6229 e-mail: ivor@hawaii.edu generally, coral reef areas within marine reserves tend to have two or more, sometimes up to 10 times, the biomass of targeted fishes when compared to nearby fished areas or pre-closure stocks (Russ & Alcala 1989, 2003; Polunin & Roberts 1993; Friedlander et al. 2007b; McClanahan et al. 2007). Furthermore, studies based around reserves will tend to underestimate the impacts of fishing, because marine reserves are generally too small or have insufficient compliance to effectively protect the wide-ranging and vulnerable taxa, such as sharks and other large apex predators, which make up the bulk of fish biomass in large, isolated and virtually-unfished areas (Friedlander & DeMartini 2002; Robbins et al. 2006). It therefore seems reasonable to suppose that, in most cases, coral reef fish stocks close to human population centres will have been substantially altered by fishing activities. High human population density and what accompanies it (for example urbanization, land- and watershed-alteration and associated increases in the input of sediment, nutrients and other pollutants into marine waters) can lead to the degradation of nearby coral reefs (Tomascik & Sander 1987; Hunter & Evans 1995; Edinger et al. 1998). Degraded reefs, on which coral cover and associated structural complexity has been lost, have much lower capacity to support diverse and abundant fish populations (Friedlander et al. 2003; Jones et al. 2004; Graham et al. 2006; Wilson et al. 2006). Therefore, coral reef fish stocks near human population centres are potentially affected by both fishing and anthropogenic environmental or habitat degradation. Although there is now widespread recognition that coral reefs and coral reef fish populations worldwide are under stress from overfishing and the consequences of coastal development, human population growth and climate change (Wilson et al. 2006; Kleypas & Eakin 2007; Newton et al. 2007), an essential first step towards developing effective management responses is to determine the importance of the various factors contributing to degradation in any particular situation. In particular, it is likely to be difficult to build support for appropriate remedial action if it is not possible to reach a consensus on the underlying cause(s) of resource declines. One means towards distinguishing the impacts of fishing on reef fish stocks from those due to habitat and other environmental degradation is to compare responses of