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Thursday, July 29, 2010

Palmyra Atoll: Why so many predators?

Palmyra Atoll
Source of image:
http://www.wildlifeextra.com/go/news/pacific-monument.html#cr

To read an interesting article which discusses why there seem to be so many predators
in the  Palmyra Atoll (which is located here):




 please click on the following link:

http://scientistatwork.blogs.nytimes.com/2010/07/29/why-so-many-predators/

I have done some research online to determine in my own mind why Palmyra Atoll has more
predatory species existing there than in nearby areas. Here is what I have discovered:

What is an atoll?
---------------
An atoll  is an island of coral that encircles a lagoon partially or completely. Charles Darwin
classifyed "the atoll" as a unique type of island, Darwin understood the creation of an atoll as having
 its roots in volcanic activity. The basis for his theory came from personal observations that Darwin
made during a six-year voyage around the southern section of the Pacific Ocean.
According to Darwin, the atoll was the result of the gradual sinking of a volcanic island that has long since cooled, leaving behind an open crater in the middle section of the island. As the island begins to sink, the surrounding territory of the island falls beneath the surface of the water. At the same time, the coral reef that is found around the fringes of the island remains and gradually is built up through the natural practice of the accumulation of marine organisms that become part of the reef. This creates a barrier reef around the remaining section of the island, forming the perfect conditions for the development of a lagoon. Once the lagoon is formed and is more or less encircled by the barrier reef, an atoll is the final product of this gradual metamorphosis."(source:  http://www.wisegeek.com/what-is-an-atoll.htm )

Facts about the Palmyra Atoll:
------------------------------
"About halfway between Hawai‘i and American Samoa lies Palmyra Atoll. Palmyra consists of a
circular string of about 50 islets nestled among several lagoons and encircled by 15,000 acres
 of shallow turquoise reefs and deep blue submerged reefs. It is the northernmost atoll in the
 Line Islands in the equatorial Pacific." (source:http://www.fws.gov/palmyraatoll/ )

"Palmyra.is an incorporated atoll administered by the United States federal government.
The atoll is 4.6 sq mi (12 km2), and it is located in the Northern Pacific Ocean. Geographically,
 Palmyra is one of the Northern Line Islands (southeast of Kingman Reef and north of
Kiribati Line Islands), located almost due south of the Hawaiian Islands, roughly halfway between
Hawaii and American Samoa. Its 9 mi (14 km) of coastline has one anchorage known as West
 Lagoon. It consists of an extensive reef, two shallow lagoons, and some 50 sand and reef-rock
 islets and bars covered with vegetation—mostly coconut trees, Scaevola, and tall Pisonia trees."

"Palmyra was first sighted in 1798 by an American sea captain, Edmund Fanning of
Stonington, Connecticut, while his ship the Betsy was in transit to Asia, but it was only later—
on November 7, 1802—that the first Western people landed on the uninhabited atoll. On that
date, Captain Sawle of the United States ship Palmyra was wrecked on the atoll..In December
 2000, most of the atoll was purchased by The Nature Conservancy,"

"On January 18, 2001, the  U.S. Secretary of the Interior signed an order designating
Palmyra’s tidal lands, submerged lands, and surrounding waters out to 12 nautical miles
 from the water’s edge as a National Wildlife Refuge.
 (source:http://en.wikipedia.org/wiki/Palmyra_Atoll)."

According to the document :https://darchive.mblwhoilibrary.org/bitstream/handle/1912/2051/
StevensonetalCoralreefs.pdf?sequence=1


"On coral reefs in Palmyra—a central Pacific atoll with limited fishing
pressure—total fish biomass is 428 and 299% greater than on reefs in nearby
Christmas and Fanning Islands. Large apex predators –groupers, sharks, snappers, and
jacks larger than 50 cm in length- account for 56% of total fish biomass in Palmyra on
average, but only 7% and 3% on Christmas and Fanning."

"With minimal historical and current population (two resident refuge managers and up
to ten visiting scientists or volunteers), Palmyra has never had the extensive local
fisheries of the more populated Line Islands."

"The shallow reefs at Palmyra Atoll (2-10 people, no fishing allowed on
reefs because of marine protected area status) sustain 428% and 299% more fish
biomass per 200 m2 than Christmas"

According to the document: "Trip Report from December 2008 Pangaea Research
Expedition",
http://www.igfa.org/PDF/PANGAEA_EXPEDITION_REPORT_DEC08.pdf


"Our findings to date have helped to describe the
dynamics of this unique ecosystem, which is relatively free of human influences"

We determined bonefish at Palmyra to have much higher natural mortality rates compared
 with other locations that have been investigated (Friedlander et al.2004, 2007), most
 likely a consequence of the large number of apex predators at Palmyra (e.g. sharks and jacks).
These predator-dominated ecosystems are rare owing to the extirpation of 
large apex-predators from most reefs worldwide
(Friedlander and DeMartini 2002, Sandin et al. 2008)."

"Understanding the role that sharks and other apex predators play is becoming even more
 important due to recent reports that predator populations are declining due to over-fishing,
and it is unclear what effect this may have on prey populations and other dynamics of the
 marine communities (Baum et al., 2003)"

"In addition to bonefish, we have intensively studied movements and feeding habits of the
most common predator in the lagoon ecosystem at Palmyra, the blacktip reef shark (Carcharhinus melanopterus). Our data indicates that blacktip reef sharks show site fidelity to certain lagoon areas,
 and that movements are focused along the edges of the sand flats (Papastamatiou et al. in press).
 Using fractal analysis, we surmised that blacktips patrol these edges to intercept prey species
that may move to and from the lagoons and sand flats with the tides. The only other study of movement patterns of blacktip reef sharks, at Aldabra atoll, Indian Ocean, also suggested that blacktips
 showed site fidelity to core areas of a reef, and that movement patterns were influenced
by tidal currents (Stevens 1984).
----------------------------------------------------------------------------------

So  I  come to  the following conclusion which seem to indicate why there are more predators
 in Palmyra Atoll than in surrounding atolls and areas :
The atoll has limited  or no fishing pressure from humans, partially due to the fact that no fisheries are
present in this area and  due to the fact that no fishing is  allowed on reefs because these areas
have been designated as having  "marine protected area" status. The fact that the United
States Government has also designated Palmyra’s tidal lands, submerged lands, and surrounding
 waters out to 12 nautical miles  from the water’s edge as a National Wildlife Refuge is another reason
why there are more predators found in this atoll.

Because more fish exist, this means that predators have a larger food supply in this
area, which they have come to know, and therefore they will obviously continue to reside in
 an area where their dietary needs can be fulfilled. Because the predator fish and animal species
 in this atoll have not been over-fished by humans, this means these populations of these fish
 have been allowed to increase in size.

In the following video
Senior Scientist and Cultural Advisor for the Nature Conservancy Hawai'i, Sam Ohu Gon,
 shares why Palmyra is so special and why Hōkūle'a was allowed to visit this protected atoll:





Here is a video which shows some pictures taken of Palmyra Atoll from Google Earth
by Youtube member Tautvis17 source of video:


http://www.youtube.com/watch?v=uiAiuIL4Ico




The "Nature Conservancy created  this next video of the waters off of Palmyra Atoll
(source:http://www.youtube.com/watch?v=lHkQIXQTaxg



Lastly, here is a website which gives you more information about the Atoll:

Here is a webpage devoted to discussing this area:

I hope you enjoyed learning about Palmyra Atoll and also learning why more predatory life-forms
are found in this Atoll! I sure have!

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