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Author Topic: Is there an interdependence between seal populations and polar bear populations?  (Read 3107 times)

Offline CliffordK

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I looked up arctic seal populations tonight. 

Population estimates show nearly a quadrupling of the Harp Seal and Gray Seal Populations in the last few decades.


Estimated recent population trends of northwest Atlantic harp seals.

I'm not surprised as there may be increased habitat, and increased food available with recent arctic thawing. 

Shouldn't this have a positive effect on the Polar Bear population?


 

Online evan_au

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Has there been a change in the amount of hunting that is conducted over this time?
 

Offline CliffordK

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Ok,
So seal hunting regulations started being implemented around 1970, which would have been about the low point of the graph above.

One note also indicated that polar bear populations also hit a minimum around 1970 of about 5,000 bears, and have now increased to about 20,000 bears.

Nonetheless, it would seem that the increase in seals would be good for the bears.

Polar Bears are also hunted.
The estimates that I'm seeing lists the global number of polar bears at about 20,000 - 25,000.
Somewhere between 500 and 1000 bears are killed by humans each year, or about 3-5% of the total number.

2 cubs are born a year (sometimes every other year), and take about 4 to 5 years to reach maturity, and a maximum lifespan of about 25 years in the wild.  Although, fertility drops off as they age, and many cubs don't survive to maturity.

This paper discuses survival rates and fertility rates..  I get a little lost with the numbers, if 5% of the bears are shot each year, then over a 20 year lifespan, the chances of any individual bear being shot in its lifetime is very high.

Anyway, as far as I can tell, the numbers of bears is relatively stable, but perhaps the first step in conservation would be also to reduce the hunting of the bears to only allow nuisance hunting, or at least prohibit 100% of the non-native "sport" hunting.

How difficult would it be to say, only hunt those bears over 15  years old?  One could certainly tag as many cubs as possible, but it would be difficult to assess 15 yr old tags on bears before hunting them.
 

Offline Don_1

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I'm not surprised as there may be increased habitat, and increased food available with recent arctic thawing. 

Shouldn't this have a positive effect on the Polar Bear population?

I think the increase in seal numbers can only be attributed to their protection. The shrinking polar ice cap has probably resulted in the seals having to venture further north to take advantage of the northward movement of fish feeding on plankton in the richest parts of the Artic seas.

As for the Polar Bears, they are adversely affected by the shrinking polar ice cap. Summer is their time of poor hunting since they need sea ice to catch their prey. It is seals and their pups using blow holes in the sea ice which allows the Polar Bear the opportunity to catch the seals, whereupon the bear feasts on the rich oily blubber, leaving the rest of the carcase to scavengers such as the Artic Fox. The shrinking ice cap is making life difficult for the Polar Bear, driving them to find food elsewhere.

Polar Bears have been observed attacking Walrus, an extremely dangerous move for the bear, since the Walrus is so much bigger and around 3 times heavier than the bear and is armed with tusks up to 4ft long that could inflict life threatening injury to the bear. Polar Bears have even been known to attack Beluga Whales using blow holes in the artic sea ice. http://www.youtube.com/watch?v=lE-RKRNSG_c
 

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