Sunday, April 5, 2015

Fisheries science challenged: Little fixes won't do.

We assume that a high human population like O`ahu’s is why that island’s fisheries are depleted—more fishing, more activities destructive of reefs,  more development and the associated toxic runoff.

But the science is more sobering. 

(Image: The Hawaiian parrotfish uhu-uliuli, or Chlorurus perspicillatus. Parrotfish are among the first species to be fished heavily and to suffer significant population declines on human-impacted reefs. Credit: Dr. Dwayne Meadows, NOAA/NMFS/OPR.)

It doesn’t take near that many people to have deeply destructive impacts on coastal marine life. And the first impacts of human activity significantly change mix of reef inhabitants.

A new study from researchers at the University of Hawai`i’s School of Ocean and Earth Science and Technology (SOEST) looked at nearly 2,000 sites on 40 islands and atolls around the Pacific. Among its conclusions is that a pattern of fishing regulation might not be as valuable in protecting reef resources as complete bans in some areas--what the authors refer to as "full protection over large areas."

They found that deep declines in fish abundance occur at pretty low human population densities. Sure, O`ahu and Guam are marginally worse, but human impact on reef populations is severe right from the start, and then declines at lower levels as human populations rise dramatically.

But the team also found that just because there’s no human impact, it doesn’t mean a particular reef will be amazingly productive. There are significant natural differences in reef productivity.

“Our results emphasize that coral reef areas do not all have equal ability to sustain large reef fish stocks, and that what is natural varies significantly amongst locations,” the authors wrote'

"It is...important to recognize that among islands and regions there are substantial differences in reef habitats and structure that are likely independent of human impacts, as well as in potentially influential oceanic factors such as wave energy, water temperature, and oceanic productivity that confound our ability to understand what might be considered ‘natural’ for a particular region or reef," they wrote.

The paper was published in the journal PLOS One by a team led by SOEST researcher Ivor Williams, along with Julia Baum, Adel Heenan, Katharine Hanson, Marc Nadon and Russell Brainard, under the title “Human, Oceanographic and Habitat Drivers of Central and Western Pacific Coral Reef Fish Assemblages.”

If you have swum some of the really impressive waters of productive tropical coral reef ecosystems, it’s not safe to assume, for example, that subtropical Hawai`i ever had that kind of assemblage of marine life.

“Perhaps the most important component of this study is the demonstration of the extent to which coral reefs’ capacity to support large fish populations varies among what we assume are relatively unimpacted reef areas,” they wrote.

“In our study, oceanic productivity appeared to be a key driver of those differences, but clearly there are also other factors driving differences among and within island reef ecosystems. We caution against any assumption that the spectacular high biomass fish assemblages seen at some remote reefs represent a natural level that all reefs would attain in the absence of humans.”

To assess impacts of human activities, the researchers looked at uninhabited islands like Jarvis and Kingman Reef, lower population islands like Ni`ihau and Samoa’s Ofu and Olosenga, and higher population islands like O`ahu, Tutuila in Samoa and Guam. A lot of the data was collected from 2010 to 2013 as part of the Pacific Reef Assessment and Monitoring Program (Pacific RAMP).

“Sharp declines in fish biomass at the low end of that human population scale are consistent with earlier smaller-scale studies on human impacts to coral reef fishes along fishing-intensity and population gradients in Fiji and the Seychelles,” they wrote.

Sharks and parrotfish are the first to go, along with total reef biomass. And this kind of removal has an impact. Groupers

“There is strong evidence that key aspects of reef fish assemblages including total biomass, top-predator density, and grazing potential, are highly susceptible to even low levels of human impacts, and therefore that full protection over large areas is probably necessary for a natural coral reef ecosystem to persis,” they wrote.

© Jan TenBruggencate 2015

Citation: Ivor D. Williams, Julia K. Baum, Adel Heenan, Katharine M. Hanson, Marc O. Nadon, Russell E. Brainard (2015) Human, Oceanographic and Habitat Drivers of Central and Western Pacific Coral Reef Fish Assemblages. PLOS ONE, DOI: 10.1371/journal.pone.0120516.

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