Human‐induced gradients of reef fish declines in the Hawaiian Archipelago viewed through the lens of traditional management boundaries

Abstract

1. Large declines in reef fish populations in Hawai'i have raised concerns about the sustainability of these resources, and the ecosystem as a whole. To help elucidate the reasons behind these declines, a comprehensive examination of reef fish assemblages was conducted across the entire 2500 km Hawaiian Archipelago.2. Twenty-five datasets were compiled, representing >25 000 individual surveys conducted throughout Hawai'i since 2000. To account for overall differences in survey methods, conversion factors were created to standardize among methods.3. Comparisons of major targeted resource species (N = 35) between the densely populated main (MHI) and remote north-western Hawaiian Islands (NWHI) revealed that 40% of these species had biomass in the MHI below 25% of NWHI levels. In total, 54% of the species examined had biomass <50% of NWHI biomass. 4. The moku or district was a basic unit of resource management in pre-contact Hawai'i and was used as a unit of spatial stratification for comparisons within the MHI. Biomass of resource species was negatively correlated with human population density within moku boundaries, with extremely low biomass in areas with highest human population densities. No such relationship was found for species not targeted by fishing. 5. A number of remote areas with small human populations in the MHI still support high standing stock of fished species, and these areas are likely important refugia for maintaining fisheries production and biodiversity functioning.6. These results highlight the large gradient of human impacts on fish assemblages across the Hawaiian Archipelago and the potential in using landscape and seascape units, such as those that are watershed and bio-physically-based, when managing in part based on a framework of traditional ecological knowledge.

Characteristics of effective marine protected areas in Hawaiʻi

“…If a calibration factor could not be calculated at the combined family–trophic level, then a global calibration was used that considered all species pooled for each method. For all subsequent analyses, density estimates were based on calibrated densities of raw data (Friedlander et al, , table S3).…”

“…Fishes were categorized into four trophic groups (piscivores, invertivores, planktivores, and herbivores) after DeMartini, Friedlander, Sandin, and Sala () and Sandin et al (). Resource species were defined either as those species having ≥450 kg of average annual commercial or recreational harvest from 2000 to 2010 or as recognized species that are important to the local subsistence or cultural sectors (Friedlander et al, ).…”

“…Human population density was used as a proxy for isolation and human impacts associated with MPAs. Total human population based on 2010 census data (www.census.hawaii.gov) within each moku (traditional Hawaiian district) was divided by the shoreline length of that moku to provide an index of human population pressure (Friedlander et al, ).…”

“…Reef fish populations and their associated fisheries have declined dramatically around Hawaiʻi over the past 100 years due to a growing human population, destruction of habitat, introduction of new and unsustainable fishing techniques, and loss of traditional conservation practices (Friedlander et al, ; Smith, ). Today in Hawaiʻi, resource (food) fish biomass is low in areas near large human populations; however, remote areas with small human populations in the main Hawaiian Islands (MHI) still support high standing stock of important fisheries species (Friedlander et al, ; Williams et al, ).…”

Seascape models reveal places to focus coastal fisheries management

“…Impacts from fishing have been inferred by comparing fish populations in populated vs. remote areas (e.g., Friedlander et al. ) and by using proxies such as local human population density and distance to markets (Williams et al. , Cinner et al.…”