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Christmas island - Crabs
the Red Crab Migration
by Bill Cain
I remember watching a Discovery Channel program several years ago that counted down the top 10 migrations around the world. As the countdown progressed, some of the more familiar animal species like the wildebeests of Africa and the swallows of Capistrano were highlighted. When the program reached the number one, and thus the greatest, migration of them all, imagine my surprise and probably that of most other viewers when that distinction was revealed to be the red crabs of Christmas Island – an exotic, far flung dot on the chart of the Indian Ocean! Right away I knew I had to witness this for myself.
Discovered by a British ship on December
25, 1643, the island changed hands several times before finally ending
up under the Australian flag in 1958. About the size of Martha’s Vineyard,
it lies 1,615 miles from the Australian mainland city of Perth, but just
a scant 223 miles from the Indonesian island of Java, and because only
twice-weekly flights connect from both Perth and Bali, Indonesia, careful
planning for a visit is necessary. Unlike its nearest island neighbors,
the Cocos, which are a series of flat atolls, Christmas has a rugged mountainous
and forested interior which give refuge to 14 different species of land
crabs, among which is the famous red crab found nowhere else in the world
and whose numbers on this relatively tiny island are staggering.
Though Christmas Island and its fledgling tourist bureau offer other reasons for visiting, the primary one from the end of October through the beginning of December each year is to witness an estimated 50 – 100 million red crabs which perform an incredible march from their inland burrows to the shore and back in order to satisfy their mating and reproduction ritual that was genetically programmed long before humans ever arrived.
Like most other naturally recurring events, the beginning of the migration and the different phases of the red crab’s movements and activities varies from year to year and is dictated by rain events as well as the phases of the moon and its effect upon ocean tides – an important factor when newly fertilized eggs are released into the ocean. The first and most spectacular stage of the migration is when all the crabs, prompted by biological programming, proceed to march to the sea en mass whereupon, after mating, the males replenish nutrients from the sea water and the females release their sacks of eggs. This part of the migration, however, lasts only 5-7 days between the end of October and the end of November. Consequently, it’s almost impossible to plan a trip to coincide with this small window of opportunity, especially from halfway around the world. As luck would have it, my recent visit was too late, as the main march in 2005 was unusually early.
For those fortunate enough to time it right, the extra diligence is especially rewarding as the spectacle is nothing short of astonishing. Like something out of a horror movie, millions upon millions of crabs, resembling an advancing red carpet in some places, literally run over, under and through everything that stands in their way to the coastline. Moving during the cooler mornings and late afternoons, they invade homes, back yards, commercial properties, parks, and the golf course. Residents take heed to keep their doors closed during this time, as it’s not unusual to open a closet only to find a stray crab staring you down. Sadly, however, the crabs must also pass over many roadways in their blind obedience to procreation.
Christmas Island redefines the term “road kill” and takes it to another level. Although the island’s park service has erected barriers, stalled grids along many of the roads and even closes some roads in an effort to minimize the yearly carnage, it’s simply not enough. All these attempts since 1980 when concerted efforts were begun to protect as many crabs as possible seem pitifully inadequate when the numbers are tabulated. Estimates suggest that about 1% of the island’s crab population, or between 500,000 and one million crabs, annually end up as motor vehicle fatalities.
Thousands of black smudge marks, indicating
where hits had taken place a couple of weeks before my arrival, could be
seen on many of the roads – some marks being no more than a few feet apart
and continuing in two parallel tire track lines for up to ¼ mile
in some places. Even though I missed the height of this gruesome aspect
of the great migration, enough stragglers were still marching on some of
the roadways during my visit. Dodging and weaving as best I could at slow
speed to avert further harm, there nevertheless were some areas where the
sickening crunching sound of car tire meeting crab shell was unavoidable.
It wouldn’t have been so disconcerting were it not for the fact that red
crabs are big, ranging in comparable size from that of a chipmunk to that
of a grey squirrel for some of the larger specimens.
For the next month or so, after completing their coastal encounter, the crabs begin their sporadic and much less impressive return migration to their homes in the interior.
Fortunately for the crabs, they are unsuitable
for human consumption. Otherwise, the commercial exploitation would certainly
have begun long ago and their numbers might be far fewer and less impressive
than they currently are. This is not the case, though, for some of the
island’s other land crab species, most notably the blue crab and the enormous
and colorful robber crab – both of which reportedly are delectable but,
because of their far fewer numbers, have been protected and designated
as endangered by the Christmas Island authorities.
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