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Pacific white-sided dolphins (© Alexandra Morton)
white-sided dolphins (Lagenorhynchus obliquidens) are sporadic
residents on the B.C. coast. While their teeth are abundant in some
First Nation middens signifying several thousand years of presence,
they were absent from approximately 1915-1984. Seven showed in the
Broughton Archipelago in December of 1984. For the next few years
they appeared occasionally, always in winter. Then in 1992 hundreds
of dolphins appeared in the fall and stayed till spring in groups
of tens to hundreds. At the same time a small smelt called capelin
(Mallotus villosus) appeared, an Arctic population moving
south. The dolphins fed predominately on capelin and then when the
Pacific sardine or pilchard (Sardinops sagax) suddenly reappeared
in 1997 after a forty year absence in the Broughton area, the dolphins
fed on this species as well.
marine species pulse in and out of coastal areas in response to
oceanographic events, such as El Niņo, which increase or decrease
food resources. By examining seafloor core samples Baumgartner et
al. (1992) discovered sardines have crashed and flourished in Monteray
Bay on 50 - 70 cycles over the past 1,700 years. This pattern would
appear widespread and the reason the dolphins come and go from British
Research documented the most recent chapter in dolphin history and
has identified over 900 individual dolphins. Photo-identification
is a powerful tool to examine social structure and site fidelity.
Most groups seem flexible, but there are pairs and perhaps trios
of dolphins that have been photographed side by side years apart.
Most groups have tight coalitions of males (thick-based fins with
a bit of a forward hunch). Any photos from other areas are extremely
useful in mapping travel patterns and range.
dolphins are very aggressive towards other species chasing porpoises,
killing juvenile harbour seals, even harassing the fish-eating resident
orca (though they flee from the mammal-eaters). How do they tell
the difference? A silent orca is a dangerous orca, but by the time
they see the whale it can be too late! On occasion both Steller
and California sea lions have been sighted among the dolphins. Calves
are extremely rare in the Broughton.
white-sided dolphins can be distinguished from all other B.C. cetaceans
by their often large groups upto 1,000, their ability to jump several
body-lengths above the water and their grey and white streaking,
not black and white like Dall's porpoise.