Thursday, February 18, 2010

Great Whites: new Insights!

Unbelievably cool stuff!

I just got this synopsis of this year's International Great White Symposium in Hawaii.
It's a PdF document with the title Selected Highlights from the International White Shark Symposium February 7-10, 2010 that features no author, and I herewith apologize profusely for breaching any copyright and citing it verbatim in its entirety - but it's absolutely fascinating stuff and it would be a great shame if it remained reserved for the select few Shark scientists and not communicated to the many GW enthusiasts at large.

So without further ado: this is what we've learned about the life cycle of the Great White Shark.
Absolutely stunning!

In the past two decades, fish biologists have gained considerable knowledge about the great white shark, Carcharodon charcharias.
Many more investigations, however, are still necessary in order to understand the comprehensive biology and life history of this ecologically important and charismatic apex predator. Below are the some of the information presented as new or reviewed at the symposium:

A. White Shark population in the NE Pacific region:

1. Adult population size estimated to be between 200 to 300 individuals in the NE Pacific. Worldwide population is still not known

2. Females give birth (live birth) near shore in the Southern California coastal region; between Malibu, California and Vizcaino Bay, Baja California

3. White sharks copulate, have internal fertilization, the gestation period is about 18 months, and the pups at birth are about 4.5 to 5 ft long

4. White sharks are warm blooded and the young tend to congregate in near shore warmer waters: theoretically, the smaller size sharks need warmer water to assist in thermoregulation

5. Young white sharks feed primarily on fish, ignoring humans and other mammals near the coast

6. Young white sharks migrate 1000 km between the Malibu Coast and Vizcaino Bay. They are protected in Baja (like California), but the Mexican government does not enforce conservation. Thus, many of the young sharks in Mexico are being poached for food to feed the indigenous people while their fins are sold off lucratively. Scientists are analyzing the effect on the NE Pacific population resulting from this practice.

7. When the young sharks grow to about 9 to 10 feet long, they begin to feed on marine mammals plus other larger prey and start to migrate to the northern and colder regions of the
Pacific. At this size, their thermoregulatory mechanism is well developed.

8. Genetic studies (using mitochondrial DNA) demonstrated that the NE Pacific white shark population is derived from the population in Australia/New Zealand. This NE Pacific group split off tens of thousands years ago.

B. Great White Shark Café:

1. The Café encompasses a region in the NE Pacific primarily between ...W to ...W and ...N to ...N where the adult white sharks migrate from the US west coast during winter to aggregate.

2. Some of these sharks, mainly males, go as far SW as the Big Island and as far NW as Midway Island. White Sharks have been tracked throughout the Hawaiian Islands

3. Great debate regarding the ‘purpose’ of the Café: food or sex or both?? One scientific group favors the view that the animals go there to feed and another sees it as an area for mating. Only circumstantial evidence is available to support either role.

4. Females and males appear to segregate at the Café. Each sex has its own preferred section. Males to the W-NW and females to the SE

5. Studies showed that the white sharks swim on the surface non stop between the US west coast the Café, crossing > a thousand miles of ocean (Adult white sharks have been found to be able to travel up to ~5,000 miles.)

6. Upon arrival at the Café, white sharks dive down and come up again continuously. They go from the surface and straight down to as deep as 800-1,200 meters, from 25 degrees C at the surface to 4 degrees C at depth. Again, this seems to be a non-stop, 24/7 activity.

7. Other marine life found at the Café: sperm whale aggregation and 3 species of squid, including the giant squid. Reproduction of all squid species has been observed here.

8. Although no similar Café has been described in detail as for the NE Pacific region, similarly tropical migrations during the winter have been found for the South Africa, Australia and New Zealand, and West Atlantic populations:

a) The New Zealand adult white sharks migrate to the New Caledonia region
b) The South African adult sharks migrate to the Mozambique coast and west Seychelles area

c) Australian white sharks migrate between S of the Sydney area in New South Wales up to tropical Queensland region

d) N Atlantic white sharks migrate from the Maritime Province area to Florida. These are known to have fed primarily on whale carcasses before conservation practices. Now that the gray seal population has bounced back near Cape Cod, after conservation is enforced after the enactment of Marine Mammal Protection Act in the 1970s, white sharks have begun preying on the seals in this region.

C. Other interesting information:

1. Scientists have not yet been able to witness the white shark mating/copulation act, not for the lack of trying. Must be an impressive sight as the scar patterns on head region of the adult females would indicate

2. Male adult white sharks (NOT female adults) appear to have a strong propensity to feed on newborn white shark pups. This could be the reason why male and female adult white sharks have different migration routes to the tropics

3. Intrauterine cannibalism of younger embryos by older ones has been documented for the white shark

4. Largest white shark caught and measured is > 7,000 lbs with its liver weight at 1,000 lbs.

5. Controversy over the evolutionary origin of the white shark: Megaladon (extinct ancient shark species) versus a Mako shark lineage.

6. Many of the studies that acquired the above information utilize dorsal fin tags that transmit data to satellites either when the sharks are at the surface or after timed-release of the tags

Is this cool, or what?

The question is, is there really a need to deploy more tags, especially those cruel SPOT, in the Pacific? How about taking that money and sending a ROV into the Café instead?

And who's gonna finance the same effort in the Mediterranean?

Always stirring the pot, am I...

1 comment:

Nathaniel said...

This is awesome info, thanks for sharing. I want more!