Food Chain and whales

From: Kim Marshall-Tilas (kimm@oceanalliance.org)
Date: Thu May 16 2002 - 16:07:25 EDT


Question: hi, i`ve been trying to find information about the importance
whales have in the food chains, and why are they so important.

Reply:
Hello Javier,

Whales are important to the oceanic food chain as is every other animal
because it is sort of a chain and if links are broken the chain breaks
apart. The larger baleen or toothless whales eat small creatures such as
krill and sand eels which bloom during summer months in cold waters in the
number of hundreds of thousands to millions. The life cycles of these small
animals and the large whales are linked together much as the lives of any
prey-predator situation. In many prey species, if the number of predators
decreases, the number of prey generally increases until the prey species
begins to overuse its resources. The population of the prey then plummets.
Conversely, if the number of prey decreases, the predator species have a
harder time finding food. The prey and the predator situation generally
keeps the populations level, thereby making sure that other resources are in
adequate supply.

We are finding that whales are a good indicator of the health of the seas.
Whales (especially toothed whales such as sperm or killer whales) are top
order predators, meaning that they eat the large fish which eat the smaller
fish and so on down the food chain to the primary producers. In all, they
top about seven levels of prey items, as do humans. The oceans have been
contaminated by human-created chemicals. Because these chemicals are not
found in nature, animals have not had time to adapt to break them down.
Instead, they accumulate in the fats of animals. When a predator eats a
prey item, it ingests all of the toxins that that animal has ingested
through its lifetime. It is estimated that the levels of toxins in animals
increases tenfold for every step in the food chain, so a whale (or human)
eating at the top can ingest 10 million times the toxins that the first
animal ingested. These chemicals are also passed from mammal mother to
child through the fats in her milk, so young animals start out in life with
approximately the same level of toxins in their bodies as their mothers had.
In the US, we consider anything with 50 parts per million of organohalogens
(a toxicant) to be toxic waste. Beluga whales in the St. Lawrence river
have been found with 6900 parts per million in their bodies and must be
disposed of carefully.

As we learn more about whales, we also learn more about our oceans and the
threats we humans are posing to life in the oceans and to ourselves.

Thank you for your question and please review the information about whales
on WhaleNet at http://whale.wheelock.edu.

Kim

---------------------------------------------------------------------
Kim Marshall-Tilas
Executive Director
Ocean Alliance
(Encompassing the Whale Conservation Inst. & the Voyage of the Odyssey)
191 Weston Road, Lincoln, MA 01773
781-259-0423 x 14 fax: 781-259-0288
www.oceanalliance.org www.pbs.org/odyssey



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