Silvertip Sharks – The Underwater Grizzlies of Cocos Island

Photo courtesy from Wikipedia

Silvertip Sharks (Carcharhinus albimarginatus)

Max. Length: 300 centimeters
Length at 1^st Maturity: 141.4 centimeters
Weight: 160 kilograms
a value: 0.00305
b value: 3.243
Depth Range: 1 – 800 meters (3 – 2,640 feet)
Frequency: Near threatened due to high demand in shark’s fin

One of the big boys patrolling the underwater habitats of Cocos Island are the Silvertip sharks where you can easily identify them through its unique silver undertone in its large triangular dorsal fin and a fine silvery white band on the rest of the fins. Silvertip sharks have a long and broad snout, eyes that are large, gill slits that are short and their jaws filled with 12 to 14 rows of triangular serrated teeth. Their robust body is colored blue-grey with a bronze shine and a white undertone in the belly.

But if you want to get rid of the species identification process where for a layman all sharks almost looks the same, then we suggest you go diving in Silverado where this shallow reef has become their sanctuary.

Territorial and Potentially Dangerous

Despite being highly mobile patrolling nearby waters, Silvertip sharks are like grizzly bears that inhabits a particular area and reports of territorial behavior has been observed. Like grizzlies, their territory covers a huge area where they can cover up starting from the shallow reef up to deep water environments where they are known to dive up to 800 meters (2,640 feet) which perfectly describes their thriving environment in Silverado reef.

Silvertip sharks also displays dominance to other shark species of the same size especially when it comes to food competition where they can easily dominate Galapagos and blacktip sharks.

Photo courtesy from Dave Harasti

The real threat for divers are solitary Silvertip sharks which are known to be aggressive. Some have reported to see a lone individual that is heavily scarred which is believed to be a result of a fight during mating or food. But in Silverado, Silvertip sharks usually aggregate in small groups where female sharks are seen swimming in the deep while males and some juveniles are seen in the shallow cleaning station.

Although their main diet is composed mainly of groupers, mackerels, small tunas and other fish, human attacks are very rare. But it is better to understand the attitude of this shark to prevent accidents. When pursued and provoked by divers, Silvertip sharks performs the so-called “stereotypical threat” where it prepares itself for an attack by swimming away from you and immediately turns back directly towards the subject. If you happen to see this kind of behavior, DO NOT GO UP OR ASCEND. Instead, stay as close to the reef while taking refuge from rocks and crevices. If you have a long stick, you can tap it in its outer jaw targeting the small pores called Ampullae of Lorenzini which are highly sensitive receptors. Just stay put, tack in your arms or any dangling objects and allow the shark to pass by as it immediately losses interest once it sees that there is no more threat. One more thing, do not feed it with anything, especially fish, as this can agitate them causing a frenzy to occur.

With all this knowledge gained, diving with silvertip sharks can still be an enjoyable and safe experience as long you do not anything untoward to the shark or perhaps pursue its swimming for a nice photograph. Just remember, it is their territory and not ours. So we have to respect them just like doing a grizzly bear interaction.

Reference

IUCN Redlist of Threatened Species: www.iucnredlist.org

Marine Bio: www.marinebio.org

Encyclopedia of Life: www.eol.org

Video courtesy from bdbenj

About Tristan Paylado
Tristan is a marine biologist and a CMAS 2-Star Dive Instructor
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