[Coral-List] Predator fish disappearing: what effects on coral reefs and related ecosystems

Douglas Fenner douglasfenner at yahoo.com
Sat Feb 26 21:21:28 EST 2011

The newspaper article concentrates on the large pelagic predatory fish like 
tuna, as most likely the original study did.
     On coral reefs, large reef fish are at low abundances most places anywhere 
near people, around the world.  In recent years a series of papers have 
documented amazing high abundances of large apex predatory fish on remote, 
nearly-pristine reefs.  They often compose about half the total fish biomass, 
and the fish biomass is much larger than on reefs near people, on average.  It 
is well known that fishing removes the largest fish first, and the extirpation 
of some large reef fish by fishing has been documented, such as the bumphead 
parrotfish that filled fish markets in Fiji when night time spearfishing was 
introduced, and which are now locally extinct on some islands in Fiji and 
ecologically extinct on most or all of Fiji's islands.  The largest fish are 
highly vulnerable to fishing, if you go to www.fishbase.org, and look up a few 
reef fish species, some large and some small, you will see the quantitative 
vulnerability number they give for large species is much higher than for small 
fish.  The principle reasons I know of are because big fish are smaller in 
number than small fish like damsels (even though the total biomass of the large 
fish is larger, because larger fish have so much more biomass), they generally 
have long lifespans, late reproductive maturity and some like sharks produce 
very few young, and the payoff for fishers in either food or money is usually 
much greater when they can catch large fish.  I was told recently in Guam by a 
fisherman that he spearfishes at night at around 230 feet deep for large fish, 
and that humphead wrasse bring $11.95 a pound in the market in Guam.  Thus, a 
100 pound fish can get him $1000, and he does get them.  Humphead wrasse can get 
to 229 cm and 191 kg according to the Lieske and Myers ID book "Coral reef 
fishes."  That size is very rare indeed, by my calculation that would bring 
$5021 in Guam.  In Hong Kong or Taiwan, a very large live fish would go for much 
more than that, maybe $20,000 or more.
     No other threat to coral reefs, such as sediment runoff, nutrients, coral 
bleaching, etc. removes large fish more than small fish.  Because in the Pacific 
the large fish include elasmobranchs, a wrasse, a parrotfish, a trevally (jack) 
and groupers, and they all have very different biology and different 
requirements, it is highly unlikely that environmental threats or habitat will 
cause all of them to be at low levels.  The differential removal of all large 
fish species is a fingerprint of fishing, and often their decline from 
spearfishing can be documented.
     The large reef fish are about 50% of the reef fish biomass on near-pristine 
reefs, and near zero on reefs near people.  They are ecologically extinct most 
places where there are people.  (There are a few exceptions, such as Wake 
Island, which has people, but it is a military base and fishing is strictly 
prohibited.)  An entire guild or size class on most of the world's coral reefs 
has been driven to ecological extinction.  And it is a very large guild indeed, 
representing about half of the total fish biomass.  If half the corals on our 
reefs were suddenly missing, we'd notice it and be very concerned.  But until 
recently, the loss of these fish wasn't realized.  They were removed gradually, 
not suddenly, and since they were the first to be removed, they were removed 
long ago some places, and few reef biologists have ever seen anything remotely 
close to a pristine reef (shark populations are now down on the GBR and falling 
fast, so even the GBR isn't a pristine area for sharks).  We have all been 
subject to massive shifting baselines on this one, and only the remote 
near-pristine reefs shows us the reality of what a near-pristine reef is really 
like, and just how much we have lost.  It is worse than most have realized, when 
it comes to reef fish.
    To quote an article on diving in the Northwestern Hawaiian Islands (which 
have no permanent resident humans):

       “Indeed, on almost every dive, Galapagos sharks were omnipresent during 
the decompression.  On one particularly memorable dive- at almost the exact same 
spot of our aborted Midway dive in 1989- I lost count at over 80 Galapagos 
sharks surrounding us!”  (emphasis as in original article) 

Pyle, R. L.  2010.  Natural Science: Deep discoveries in the Papahanaumokuakea 
Marine  National Monument.  P 8-10 in Ka’Elele, The Messenger, The Journal of 
Bishop Museum, Fall, 2010.      (Midway is in the Northwestern Hawaiian 

     Not all reefs that have had their large fish mostly removed have collapsed, 
and for those that have the causes can mostly be found elsewhere, in the removal 
of herbivores, or sedimentation, nutrients, mass coral bleaching, etc, the usual 
suspects.  That does not mean that the removal of half of the reef fish biomass, 
all in one size guild, does not have major effects.  But those effects are not 
yet obvious.  The removal of apex predators can have major effects called 
"trophic cascades" in other ecosystems.  Removing wolves in North America can 
actually shift the course of streams.  Because wolves influence where elk drink 
from the streams, and the elk trampling of banks affects stream courses.  A 
classic marine tropic cascade has sea otters at the top.  They eat urchins, 
which eat kelp (algae).  When the sea otters are removed (almost all were shot 
on the west coast of North America for their soft fur), the urchins explode, and 
eat all the kelp, producing "urchin barrens."  Since sea otters are eaten by 
killer whales, there is another predator above them..  For reefs, trophic 
cascades are rarely demonstrated on coral reefs.  In one case it was.  On the 
GBR, there is a hook and line fishery for "coral cod" which is a species of 
grouper, which of course is predatory.  The study looked at the species they 
prey on, and compared no-take zones to areas open to fishing.  Indeed, the prey 
species were more abundant in the areas open to fishing (which thus had less 
predators).  Likely trophic cascades are more common on reefs than we know.
      The big reef fish are likely "sleepers."  Before the phase shift from 
coral to algae on north shore Jamaican reefs, we didn't realize how critical 
herbivory is to the maintenance of a healthy reef.  Those Jamaican reefs were 
overfished for over a hundred years before the phase shift happened, and no one 
knew the phase shift was going to happen.  It was an accident waiting to happen 
because there was just one species of herbivore left, the black urchins, 
Diadema.  Not long ago a paper reported an experiment on the GBR where 
herbivores were caged out of small areas of reef for 3 years.  A forest of tall 
brown algae, Sargassum, grew.  When they removed the cages, they set up video 
cameras to see who would eat the algae.  No one would ever guess which fish ate 
them, that species wasn't even known to be a herbivore!!  Batfish ate them.  So 
it was a sleeper.  If a reef has had its batfish removed, it won't look any 
different from any healthy reef, until something happens that leads to a forest 
of Sargassum.  Then there will be no one to eat it, and the reef will be stuck 
as an algae bed.  No one would have predicted or known.  Can we say for sure 
that something as massive as removing half of all the reef fish biomass, all in 
one size class will not have some drastic affect in a way we don't yet know?  

"If  the biota, in the course of aeons, has built something we like but do  not 
understand, then who but a fool would discard seemingly useless  parts? To keep 
every cog and wheel is the first precaution of  intelligent tinkering."  Aldo 

   A note: in the Pacific, not all large reef fish are in a single trophic 
guild.  The sharks, large grouper and giant trevally are all apex predators, 
primarily picivores, but humphead wrasse are invertivores, and bumphead parrots 
eat algae and coral.  FishBase gives the trophic level for each species.
  Much more information documenting much of this and a long list of references 
are available in an article available on the internet, "The largest fish on 
coral reefs were the first to go."



Douglas Fenner, Ph.D.
Coral Reef Monitoring Ecologist
Dept Marine & Wildlife Resources
American Samoa

Mailing address:
PO Box 3730
Pago Pago, AS 96799

work phone 684  633 4456

Figures on Global Climate Show 2010 Tied 2005 as the Hottest Year on Record

"New government figures for the global climate show that 2010 was the wettest 
year in the historical record, and it tied 2005 as the hottest year since 
record-keeping began in 1880.  It was the 34th year running that global 
temperatures have been above the 20th-century average; the last below-average 
year was 1976. The new figures show that 9 of the 10 warmest years on record 
have occurred since the beginning of 2001." 


From: RainbowWarriorsInternational <southern_caribbean at yahoo.com>
To: coral-list at coral.aoml.noaa.gov
Sent: Fri, February 25, 2011 5:43:36 AM
Subject: [Coral-List] Predator fish disappearing: what effects on coral reefs 
and related ecosystems

Predator fish in oceans on alarming decline, experts say
By Marc Kaufman
Washington Post Staff Writer

Sunday, February 20, 2011; 8:13 PM


What are the direct medium and long term effects on coral reefs and related 
ecosystems if large predator fish disappear?

Milton Ponson, President
Rainbow Warriors Core Foundation
(Rainbow Warriors International) Tel. +297 568 5908
PO Box 1154, Oranjestad 
Aruba, Dutch Caribbean 
Email: southern_caribbean at yahoo.com    http://www.rainbowwarriors.net

To unite humanity in a global society dedicated to a sustainable way of life

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