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Ask The Expert
Set 3, posted October 2, 1998
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Question:

Dear people at NOVA and company, Hi! My name is [withheld by request] and I'm 13 years old. I was looking at your Web site when I noticed that sharks aren't as bad as I thought. Well I finished reading so now I would like to ask a few questions:
  1. I was looking at the scientific names and when I was starting think those would be cool to say when talking about those species of shark I noticed something. When you use the scientific name of the mako shark you abbr. (in Isurus sp.). What does the sp. mean?

  2. How long have you been in the shark business?

After every section of the Web page I told mom (or somebody) about what I had read and acknowledged. My mom got really disgusted when I told her every thing I learned too!!!!! Well I hope you write back with answers. Gotta Go!!!

(name witheld by request)



Response from Dr. Klimley:

"Sp." is placed after the genus, if the identifier of the shark is uncertain as to the species. The shortfin and longfin mako sharks are in the family Isurus, a name formed by the Greek prefix, "iso", and suffix, "tail" that refer the tails equal upper and lower lobes. I have been studying sharks for 25 years. My career began upon joining the master's degree program at the Rosenstiel School of Marine and Atmospheric in 1973. My thesis research was directed at describing the properties of sounds that frightened sharks. In 1977, I entered the Ph.D. program at Scripps Institution of Oceanography and described the social organization of hammerhead shark schools for my doctoral thesis. I stayed on at Scripps to further elucidate how hammerhead sharks navigate in the ocean. In 1987, I moved to the Bodega Marine Laboratory, which is in Central California where my interest turned to the behavior and ecology of white sharks.



Question:

Is the species Carcharodon carcharias restricted to certain depth ranges, salinity and temperatures within the ocean? Are Great White Sharks considered resident animals due to the fixed location of their food sources, or do they share the migratory behaviour of other sharks? Could it be possible that there are Great White sharks that are either migratory or resident, as displayed by Orcas?

(name witheld by request)



Response from Dr. Klimley:

White sharks have been tracked with depth-sensing beacons near seal and sea lion colonies at Dangerous Reef, South Australia and Southeast Farallon Island, Central California. When near these islands, the sharks often swam near the bottom, looking upward and searching the surface for object that might be prey. They dash upward to seize these objects, and once they have them in their jaws, decide whether or not to eat them. While feeding, they can swim very fast at the surface with a third of their body at times breaching the surface. A possible reason for swimming near the bottom at pinniped colonies is that their dark back blends with the dark rocky background, making the shark difficult to see for seals and sea lions swimming above. Thus, the "white" shark's color and swimming behavior make it easier to ambush prey. It might be more appropriate to call the species the "black" shark based upon its mode of feeding.

A shark was tracked away from a pinniped colony over the continental shelf from Montauk Point, New York to Hudson Canyon. This shark swam up and down in a "yo-yo" fashion, staying near the thermocline, a zone of rapidly changing temperature at a depth of 10 meters, occasionally making dives to the bottom.

The white shark is an inhabitant of the coastal zone, favoring the waters adjacent to seal colonies, and does not generally enter estuaries and rivers with low salinities as does the bull shark, Carcharhinus leucas. In fact, 80 percent of attacks on seals observed from a hill at Southeast Farallon Island occurred within 450 miles from shore.

White sharks may be either resident or nomadic, visiting pinniped for periods ranging from a few days to three weeks. For instance, observation of sharks with identifiable natural marks a short-term tracking of a single male shark tagged with an ultrasonic transmitter indicates that some white sharks are nomadic, remaining only one to four days in the area, while others are resident up to two weeks at Southeast Farallon Island. At Ano Nuevo Island, also in Central California, five white sharks were tracked by an array of three sonobuoys for periods of up to three weeks. The sharks spent an average of a third of the day within a kilometer of the island, being present equal times during day and night.

It is not yet known where white sharks are when not at seal and sea lion colonies. One idea is that they move widely, feeding along the western coast of North American upon whales that die naturally on their extensive migration from the Gulf of Alaska to the Baja Peninsula. This may provide an explanation of their highly acute sense of smell. Their olfactory bulb is highly developed. Their high olfactory sensitivity may enable them to locate whales from long distances by orienting to the long slicks of body fluids emanating from the whales.



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