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.
Posted by Jan T at 10:37 AM
Labels: Conservation, Fisheries, Marine Issues, Oceanography, Reefs, Sharks, Weather, Zoology
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