No matter how many Talk and Walk presentations I attend, I am
constantly amazed at the breadth and depth of knowledge that people freely and
generously give.
April was a case in point when Jim Cosgrove, former head of
Natural History Collections at RBCM, agreed to come out to Metchosin to give a
talk on octopuses.
His enthusiasm and fondness for these sea creatures was evident
throughout the evening as he informed and amused with his twenty plus years of
research and experiences with these mollusks.
And it is octopuses, not octopi (which is a pie of eight
servings...).
These amazing and intelligent creatures are cephalopods, in the
same phylum, Mollusca, as squid and cuttlefish and their terrestrial relatives
of which we are more familiar, slugs and snails.
Two of the world's 300 plus octopus species are generally found
off BC's shores. The Ruby octopus (Octopus rubescens) only weights 100 to 400 grams, with arms that reach
thirty to forty cm. The Giant Pacific Octopus (O. dofleini), with a range from California to Korea, is
considered the largest of all octopuses. Jim once found a specimen that
measured almost seven metres across (twenty-two feet) and weighed over seventy
kilograms (156 lbs). Wikipedia reports the largest ever found weighed 600 lbs
and had an arm spread of thirty feet (that’s 272 kilograms and over nine
meters)! Generally they mature at thirty-five lbs, about sixteen kg, with an
arm span of fourteen feet, a little over four metres.
Octopuses do not have tentacles, they have eight arms, covered
with 200 very sensitive suckers per arm. Fifty percent of their nerves are
located in their arms, which have enormous strength, one sucker (3.5 to 4
inches across) can lift thirty-five lbs (sixteen kg), times 200 suckers,
well...that is brute strength ...you can't pull them from their dens. The
suckers are used to explore their world, tasting whatever they touch.
Besides humans - harbour seals, sea lions, some beaked whales,
ling cod and halibut are their usual predators - creatures that use their
visual sense to hunt. Octopuses have developed a range of strategies in order
to evade capture. Specialised cells in their skin, called chromatophores, which
can change colour and texture in a fraction of a second, are an effective,
primary means of avoiding predation, when they appear to disappear. Hiding in
rocks, shells and crevices, fleeing at great speed, and of course, shooting
jets of "ink" are all in their arsenal of survival techniques. Their
eyes are not restricted by any bone structure, so they can move anywhere in
their head, giving them a further advantage in eluding predators.
They generally propel themselves by pushing their arms back or
through "jet propulsion", where they take in water and forcefully
release it through a siphon.
As predators, octopuses gather their prey into the upper part of
their arms, the interbrachial web, which can form a large sac. An anesthetic is
injected into this area, immobilising their prey. They can then either use
their rasp-like tongue to drill into a shell, or their powerful beak to break
it apart; their salivary glands reduce the meat into a fluid they can ingest.
At dawn and dusk, Giant Pacific adult octopuses hunt crabs and clams, but will
also hunt and consume larger species such as dogfish. Recently, a story and
photos of an octopus catching a gull off the rocks at Ogden Point in Victoria
has garnered international attention.
An octopus has a short life span, often only two or three years,
although the Giant Pacific Octopus can live up to five years, which is remarkable
when you consider their amazing intelligence and the fact they do not receive
any knowledge directly from their parents. They learn through trial and error,
although octopuses in neighboring tanks have learned from observing each other.
There are many documented instances of a captive octopus leaving
it's supposedly secure tank, slithering across aquarium and lab floors,
entering other fish tanks and consuming the fish, then returning to their own
tanks. Staff would be scratching their heads, wondering how all the fish had
disappeared without a trace with no intruder alarms sounding. It wasn't until
videos were installed to watch the suspicious night-time activities that the
true culprit was identified.
In another show of their intelligence, an octopus was placed in
a tank with a jar, which it was left to explore for several days. Eventually
the scientists placed a crab in the jar, and within a short period of time, the
octopus was able to remove the crab. Then they put a cork on the jar and within
a few minutes, the octopus was able to pop the cork and again remove the crab.
They continued to make it harder and harder for the octopus to get at the crab
in the jar and each time the octopus was able to open the jar and remove the
crab. It could remember this even after months had gone by. I only wish my own
memory was half as good! With another octopus test subject, the octopus was one
step ahead of the scientists and as soon as it saw them enter the room, it
would enter the jar and wait for the crab!
I think all parents have considered at one time or another that
they have made great sacrifices for their children, I'm convinced that the
worry of my children's teenage misadventures has probably reduced my life
expectancy by a number of years....
We hold no candle to a mother octopus though! When a female
Giant Pacific Octopus is ready to
reproduce, at three to four years, she gives off a pheromone to attract a mate.
The male will transfer a sperm sac which she will store for about a month as
she searches for the perfect den, usually under an overhanging boulder. She
will then amass a large pile of rocks and eventually seal herself into the den.
She individually fertilizes each one of her 55,000 to 75,000
eggs and glues them onto strings holding about 175 eggs each, which she
attaches to the ceiling. When this has been accomplished, over approximately
one month, she devotes her attention to keeping them groomed and clean of algae
and bacteria, or anything else that might hinder their development. She continually
blows air around the eggs, to provide a constant supply of oxygen. The minute
(.028 gram) babies, called paralarvae, only the size of a grain of rice, hatch
in 240-270 days. Again the mother works tirelessly to help her babies by
blowing water and thrashing the eggs, which aids them in their escape from
their embryonic sacs. Without this motherly intervention, most babies would not
be able to hatch. During this entire time the mother has not left her nest, or
eaten - losing half to three quarters of her weight. She dies 220 to 270 days after reproduction, which can mean
that some mothers might die before their young have fully developed and
hatched. Even with a successful brood, it's estimated that only two, of her
75,000 octopus babies, will survive to adulthood.
Males are sexually mature at three and a half years, after
mating they will live only a short period, becoming senescent and displaying
inappropriate behaviour....sometimes crawling onto land and following people.
Octopuses are fascinating creatures, living in a marine world
that is alien to most of us. Their adaptable minds and bodies have evolved
survival mechanisms far outside of our terrestrial adaptations. But no amount
of evolutionary success will enable them to withstand the effects of shipping
accidents and oil spills and the over-harvesting of our oceans.
picture from: http://www.fantasy-art-workshop.com/free-animal-clip-art-s-t.html
