Considerable research has been devoted to finding out what stimuli
attract sharks and incite them to attack. Results are mostly
inconclusive, but some general principles have been advanced: Certain
types of irregular sounds - like those made by a swimmer in trouble or
a damaged fish - seem to attract sharks from great distances. Sound,
rather than sight or smell, seems to be a shark's primary cue for
moving into an area. Some scientific experiments indicate that sharks
can distinguish light colors from dark, and that they may even be able
to distinguish colors.
Yellow, white, and silver seem to attract
sharks. Many divers maintain that clothing, fins, and tanks should be
painted in dull colors to avoid shark attacks.
Great White (and not so great white)
Though blood itself may not attract sharks, its presence in combination
with other unusual factors will excite the animals and make them more
prone to attack. The most dangerous species in order of documented
attack records are: the great white shark, bull shark, tiger shark,
grey nurse shark, lemon shark, blue shark, sand tiger,
several species of hammerheads, and the mako. Some species such as the
nurse shark are extremely sluggish and have poorly developed teeth, but
even these have been known to attack man when excited or disturbed.
The barracuda (though divers claim its ferocious reputation is
undeserved), moray eels, octopuses, and sharp-spined sea urchins can be
dangerous to swimmers. The Portuguese man-of-war has tentacles up to 50
feet long with specialized cells that produce painful stings and welts
on contact by swimmers.
Pacific salmon is a generic term used to describe those members of the genus Oncorhynchus that die after spawning. At present, there are seven species commonly referred to as Pacific salmon. There are five species that occur on both sides of the Pacific Ocean:
Chinook salmon (Oncorhynchus tshawytscha) a.k.a. king salmon,
chum salmon (Oncorhynchus keta) a.k.a. dog salmon,
coho salmon (Oncorhynchus kisutch) a.k.a. silver salmon,
pink salmon (Oncorhynchus gorbuscha) a.k.a. humpback salmon, and
sockeye salmon (Oncorhynchus nerka) a.k.a. red salmon.
Two species occur only in Asia:
masu salmon (Oncorhynchus masou) a.k.a. yamame, and
amago salmon (Oncorhynchus rhodurus) a.k.a. biwamasu.
An excellent discussion of the varied life histories of these seven species can be found in C. Groot and L. Margolis [editors] 1991. Pacific Salmon Life Histories, University of British Columbia Press, 564 pp.
Almost always. Some straying has been documented, but it is
minor. Most spawning salmon return to the precise stream of their
birth, sometimes overcoming great distances and hazardous river
conditions to reach home.
(Salmo salar) is actually one species within the genus Salmo.
Pacific salmon are represented by seven different species,
see question above, and belong to the genus Oncorhynchus. The seven
Pacific salmon species have life histories that are extremely complex and vary
widely within and between species. However, all the Pacific salmon die shortly
after spawning. Atlantic salmon have a much less variable range of life
history strategies across the species and have high post spawning mortality but
are capable of surviving and spawning again.
Until 1988, steelhead (the anadromous form of rainbow trout) was classified in
the genus Salmo along with Atlantic salmon, brown trout, and several
western trout species. With additional osteology and biochemistry data,
biologists have now reclassified steelhead as members of the genus
Oncorhynchus. The reason for this is that new information suggested
that steelhead are more closely related to Pacific salmon than to brown trout
and Atlantic salmon. As such, the American Fisheries Society - American
Society of Ichthyologists Committee on Names of Fishes voted unanimously to
accept Oncorhynchus as the proper generic name. For full scientific
details, see Smith, G. R., and R. F. Stearley. 1989. The classification and
scientific names of rainbow and cutthroat trouts. Fisheries 14 (1): 4-10. As
such, the scientific name of steelhead was changed from Salmo gairdneri
to Oncorhynchus mykiss. The generic names of the golden, Mexican
golden, Gila, and Apache trouts were also changed to Oncorhynchus. Since all
of these western trouts including steelhead are biologically capable of repeat
spawning and do not die after spawning, it has been suggested this group be
called the Pacific trout.
The image of the
man-of-war warning sign is Copyright c 1986, Hawaiian Lifeguard
Barracuda and Salmon images courtesy of "Regulatory Fish Encyclopedia, Office of Seafood and
Office of Regulatory Affairs, Food and Drug