[Coral-List] Atificial reefs

John McManus jmcmanus at rsmas.miami.edu
Tue Oct 22 13:50:16 EDT 2013

Regarding " However, there are non-fishermen citizens who thoroughly dislike
these artificial reefs because they make it easier to catch the fish. That's
a sociological side of the issue.", I would add that many fishery scientists
are cautious about these structures, who understand that;
1. many coral reef fish that are targets of fisheries are overfished,
2. in many cases, no legal and enforcement mechanisms to keep this fishing
under control are effective enough to do so,
3. and therefore, in many cases, an important rule in managing overfishing
is "do not make it easier to catch fish". 

Jeff Polovina brilliantly pointed out a fundamental flaw in the logic of
using such structures to enhance local fisheries in his short article
"Should anyone build reefs?" (Bulletin of Marine Science 1989
44(2):1056-1057). Given that overfishing implies a substantial reduction in
a fish population, which therefore frees up substantial habitat for newly
settling fish, why would anyone think that the best strategy to getting more
fish would be to create more habitat?

However, this does not in itself rule out the idea of creating new habitats
for reef fish far from existing reefs , as Gene implies. Clearly such
habitats do provide settling spaces for larvae that would otherwise not
survive. If anyone sees a large grouper (more than 5 years old) present
within a couple of years of establishing the structure, as is often the
case, then that is a sign that fish are being attracted to the structure
from other areas. As I have pointed out in previous years (see archives), it
would take either an extraordinarily large artificial structure (or tight
system of smaller ones) in terms of hundreds of thousands of sq. m., or an
extremely low level of fishing, for a fishery of snappers or groupers to
continue being viable based only on fish that have recruited to the
structures as juveniles. Obviously, the fish caught on most artificial
habitats in heavily fished areas and less than a few thousand sq. m. in area
are primarily coming from other habitats. Those structures are referred to
in fisheries science as "fish attracting devices (FADs)". It is feasible
that tight systems of oil rigs or large rock barriers may provide enough
habitat area to support a sustainable fishery of reasonable size with a net
gain to fish stocks. However, I am still waiting for appropriate
quantitative fishery analyses (Schaefer analysis, Beverton-Holt analysis,
VPA, etc.) to be done on fish dwelling in such structures.



John W. McManus, PhD
Director, National Center for Coral Reef Research (NCORE)
Professor, Marine Biology and Fisheries
Coral Reef Ecology and Management Lab (CREM Lab)
Rosenstiel School of Marine and Atmospheric Science (RSMAS)
University of Miami, 4600 Rickenbacker Causeway, Miami, 33149
jmcmanus at rsmas.miami.edu      http://ncore.rsmas.miami.edu/
Phone: 305-421-4814   

"Far better an approximate answer to the right question, which is often
   than an exact answer to the wrong question, which can always be made
     --John Tukey, Statistician, National Medal of Science and IEEE Medal of

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Eugene Shinn
Sent: Monday, October 21, 2013 1:22 PM
To: coral-list at coral.aoml.noaa.gov
Subject: [Coral-List] Atificial reefs

As co organizer of the first International Artificial Reef Symposium
(1973) in Houston, Texas, I have since had ample opportunity to follow the
subject of artificial reefs and categorize the various divergent views they
evoke. Basically there are two schools of thought that tend to correlate
with peoples socio/political views. In simple terms they consist of, (1).
Artificial reefs simply attract existing fish and therefore do not increase
the numbers of fish and at the same time simply provide a convenient way to
dispose of old boats, streetcars, building materials, culverts, rubber
tires, and oil platforms.(2). 
Artificial reefs actually increase fish productivity if placed in the right
locations regardless of the materials used. Of course there is truth in both
sides of the argument.

I first entered this field while diving (spearfishing and photography) under
offshore oil platforms off Louisiana and Texas. At the time I was a
geologist working for Shell Oil Co.Later when I was promoted from geology to
the environmental affairs department understanding the subject became part
of my daily job. Yes, we had old offshore rigs that needed disposal but
recycling the steel was more costly than purchasing new steel. If they could
be left in place or moved to established artificial reef sites there were
valid reasons to investigate their environmental functions.

What attracted my attention while diving under platforms was that those in
the northern Gulf were located on muddy bottom many miles from any natural
hard bottom. Surprisingly they were populated by an abundance of tropical
reef fish normally seen on Florida coral reefs.It became clear they had
arrived at the rigs as water borne larvae and encountered suitable refuge
and sources of food in the form of epiphytes, barnacles and other attached
organisms as well as an abundance of worms and shrimp in the surrounding
bottom sediment. Most of these fish larvae would likely have succumbed in
the hostile mud bottom environment of the northern gulf had they not
encountered these shelters. In addition there were lobsters living among the
cross beams well above the bottom. It seems unlikely that they arrived as
adults walking across many miles of muddy bottom. The sea floor beneath
these rigs consists of a thick layer of drill cuttings, fingernail-size bits
of rock, and yes, discarded debris, that also provide habitat for fish and
crustaceans. On the other hand the Jacks, Barracuda, and most
pelagic/migratory fish such as king mackerel that swarm around and under the
rigs, were likely attracted both for shelter and to prey on the other fish
that flourished there. 
Those observations provide evidence for those who favor the other side of
the artificial reef discussion. Clearly some of both sides of the discussion
are true.

What was most striking about the platforms however, is the range of habitats
they provide that is not available on natural reefs. Different habitats
range from the surface to the bottom and Red snapper generally occupy the
rigs from bottom to the surface. I had never dived deep enough to see a red
snapper off the Florida Keys whereas they range all the way to the surface
under the rigs. Of course huge groupers of many similar species may have
arrived as post larval adults and simply took up permanent residence. There
is food/prey and shelter beneath the rigs regardless how they got there.

That rigs are good places to fish is well known to fishermen and divers in
the Gulf of Mexico. However, there are non-fishermen citizens who thoroughly
dislike these artificial reefs because they make it easier to catch the
fish. That's a sociological side of the issue. And of course there are those
who seem to be born to hate oil companies and naturally see no good in
them.Off the east coast of Florida there is yet another issue; conflict
between divers and line fisherman. I never saw this as a problem around the
rigs but probably existed in some areas. To mediate this conflict the Dade
County artificial reef program sank some old vessels and other objects,
including surplus army tanks, in water to deep for divers. They became the
favorites among line fishermen. I examined many of these "reefs" using a
submersible to determine the optimum depth to alleviate this conflict. The
study found that it is essential to place such artificial reefs well away
from natural reef bottom. The artificial reefs serve best when not in
completion with natural hard or coral reefs. On all of these artificial
reefs we examined there was no simple way to determine if they simply
attracted existing fish or served as primary producers. However, it was
clear in all cases that fish were feeding on algae and any crustaceans
attached to the objects. They do provide food and shelter.

These basic arguments, attraction versus production, will likely continue
well into the future as evidenced from range of opinions evident from recent
coral list postings. Gene


No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
E. A. Shinn, Courtesy Professor
University of South Florida
College of Marine Science Room 221A
140 Seventh Avenue South
St. Petersburg, FL 33701
<eugeneshinn at mail.usf.edu>
Tel 727 553-1158
---------------------------------- -----------------------------------

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