| New study: Fishing Has Major Impact on Fish Declines
Largest-scale assessment of main Hawaiian island coral reef fishes to date
(Honolulu – October 29, 2008) Fishing pressure may be far more important in the decline of Hawaiian nearshore fisheries than coastal sedimentation, pollution and other impacts of human population density, according to a new study by six Hawai'i fishery scientists.
“This study shows that the reef fishes most coveted by fishers, such as uhu, ulua and redfish, are severely depleted, and it points to fishing as the main driver of those declines,” said Ivor Williams, lead author of the study published in the current issue of the scientific journal Environmental Conservation.
The scientists compared fish populations at 89 sites throughout the main Hawaiian Islands, including heavily urbanized areas, remote and rural regions, and areas in between. In areas with more people and fewer overall fish, they found that the species in decline are the ones that fishers target. Species that are not popular food fishes, like hawkfishes, butterflyfishes and some of the small triggerfish and surgeonfish species, are faring better.
“If the chief cause of fish declines was habitat loss or environmental degradation related to development and pollution, then we would have seen fish declines across the board,” said Williams, a scientist with the University of Hawaii’s Cooperative Fishery Research Unit. “Instead, fish declines along human population trends were only really apparent for species preferred by fishers.”
Study authors came away very concerned about steep declines in one group of fishes, uhu (parrotfishes), which as herbivores are critical to maintaining reef health by controlling the growth of algae. Williams said, “We found that herbivores are enormously depleted. The biomass on Oahu reefs is only about three percent of that in remote parts of the state. Parrotfishes are massively impacted by fishing.”
Co-author Alan Friedlander of the Oceanic Institute and NOAA National Ocean Service said 75 percent of main Hawaiian island fishes previously examined are in critical or depleted condition, with an additional 11 percent below desired level. He said this latest study adds to growing evidence that “local fish populations are in poor condition and protected areas can ensure the sustainability of fisheries.” He added, “Stronger fisheries regulations and enforcement are also needed, especially on the use of fishing methods such as laying gill nets and fishing on SCUBA that result in too many fish being taken at once.”
Additional study authors included William Walsh and Kosta Stamoulis of the Hawaii Division of Aquatic Resources (DAR), and Robert Schroeder and Benjamin Richards of the University of Hawaii's Joint Institute for Marine and Atmospheric Research (JIMAR).
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In developing the study, the scientists already knew the impacts of heavy fishing pressure from earlier studies that showed that fish populations are higher when fishing is restricted. But they also knew that human activities on land can have significant effects on the coastal environment. "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. Degraded reefs…have much lower capacity to support diverse and abundant fish populations," the paper says.
To separate fishing impacts from other human impacts on reef fishes, the team studied 2005-2006 DAR and NOAA data from 128 surveys of fishes at 89 sites on seven islands. The paper reports that, “The extent of the impact of increasing human population density on local fish populations was substantial: total fish biomass at two remote locations was nearly three times that at the two most populous locations.”
But generally, in areas with lower overall fish numbers (Oahu and around Hilo), it wasn’t all fish whose numbers were lower; it was the ones fishers target, such as uhu (parrotfishes), sought-after redfish (bigeyes, some soldierfishes, and some squirrelfishes) and predators like ulua (jacks). Species rarely targeted by fishers, such as some triggerfishes, hawkfishes, butteflyfishes, small wrasses and some of the small surgeonfishes, were not impacted by human population density.
The scientists said it would seem unlikely that coastal pollution would only affect prized fishing species and not less targeted ones. The researchers also found that in a couple of areas with fairly high human populations, but where fishing access is difficult - such as on the Hamakua coast, and parts of Northeast Maui where there are high shoreline cliffs - the most sought-after fish species were not so depleted.
 
“It did not seem that proximity to human populations by itself was associated with fish population declines, but rather that the crucial factor was proximity to human populations who were able to readily access, and therefore fish, nearshore waters,” they wrote.
The research team acknowledges that coastal pollution and the resulting loss of reef habitat is having an impact on the health of fish populations in Hawaii, but they say fishing pressure may be a bigger factor. “Where significant habitat or environmental degradation occurs around heavily populated locations, its likely effects will be to exacerbate already severe impacts of intensive fishing, rather than being the main driver of any local declines in target fish stocks,” the paper says.
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25-second rip and read: A new scientific study points to fishing as the top threat to popular reef fish such as uhu, ulua and redfish. This largest-ever assessment of Hawaii’s coral reef fish provides evidence that the fish in steep decline in populated areas are the ones that fishers target, while non-food fishes are faring better. The six local scientists conclude that fishing is having a bigger impact on fish declines than shoreline development, sedimentation and pollution.
Note to editors: Through its commitment to International Year of the Reef, The Nature Conservancy of Hawaii is disseminating the latest marine science news to the public. To arrange interviews with study authors, for the full text of the paper, and for more charts and photos, contact Shannon Crownover, 808-587-6250, scrownover@tnc.org
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