News
Seabirds
Other Sea Animals
Where To Find Seabirds
Pelagic Trips
Reports
Breeding Colonies
Conservation
Mail Box
Links
Wandering Birder
References

Sea Conditions

Comments
 

Finding The Birds and Other Sea Animals By Emmalee Tarry

The Continental Slope showing Norfolk Canyon.

Finding The Birds and Other Sea Animals

On a map the ocean is blue.  It would seem that birds and animals would be dispersed evenly across the beautiful expanse of the ocean.  Any fisherman can tell you this is not the case.  Animals go where there is food and  food is not evenly distributed across the ocean.

Ocean Zones
The ocean can be divided into 4 zones:

In this map of the Gulf of Maine and the area directly south of Cape Cod, shallow areas are lighter blue.  The darker the shading, the deeper the water.  The continental shelf edge south of Cape Cod is labeled "The Canyons".  During the last ice age when the ocean was some 300' lower, the continental shelf was dry land.  The canyons were formed by rivers that flowed into the ocean. Banks are shallow areas some of which were formed by glacial deposits.   Cape Cod was the terminal morraine of a large glacier.  It is still above water.  Stellwagen Bank which is the "C" shaped area just north of the lower arm of Cape Cod is also a glacial deposit that is now covered with water. Other banks represent rocky ridges on the ocean bottom.  Jeffreys Ledge the light blue snake like area off the coast of New Hampshire is such a ridge.

What is Necessary for Life?
Life needs energy.  Food.  Plants take carbon dioxide, water and sunlight and make plant parts.  To do this they also need certain minerals such as Iron, Potassium, Nitrogen etc. Minerals that gardeners frequently add as fertilizer to their gardens. These salts and minerals are found in the land and they wash into the oceans from run off and rivers.

 Animals eat plants or they eat other animals that eat plants so they must go where plants can grow.

The problem in the ocean is that when a plant or animal dies, the minerals make their way to the bottom of the ocean.  Here there is no light and no plant can utilize the minerals. They remain unavailable to plants.  There are animals that live on the bottom of the very deep ocean.  They must depend upon dead plants and animals that sink to the bottom.

So the problem is the fertilizer in the ocean is near the bottom where the plants can't get it.  The light only penetrates a few hundred feet into the ocean. Plants need both fertilizer and light. So much of the ocean is lifeless.

Upwellings
Certain structural features of the ocean bottom cause bottom water to rise to the top.   These upwelling bring bottom water containing minerals into the light zone where they can be utilized by plants. Here where phytoplankton grows we find birds, mammals, and fish.

Upwellings can be caused by an underwater current flowing into a ridge or mountain on the ocean bottom.  Like wind hitting a tall building, the current is deflected toward the surface. Upwellings can also be caused by a cold current meeting a warm current. The colder water slides under the warm water causing the warm water carrying minerals to rise. When the water rises it brings nutrients to the surface where small plants (Phytoplankton)  get sunlight and  can utilized the nutrients to carry on photosynthesis. As these small  plants grow they feed small animals which in turn feed large animals and up the food chain.

Stellwagen Bank This computer generated map is used with permission of Rich Signell of the U.S. Geological Survey at Woods Hole. See their web page for more interesting computer images. http://crusty.er.usgs.gov/rsignell.html The dark blue area to the left (west) of Stellwagen Bank is known as Stellwagen Basin. The depth in the basin is over 300 feet. Once you cross over the banks the depth decreases to 70 - 100 feet. Stellwagen Bank is steeper on the west side than it is on the east side. As your boat leaves the harbor of Boston or Gloucester, it will cross the blue area that is Stellwagen Basin.  Here you will see few birds or mammals simply because there is little food.   Abruptly you will arrive on the bank and if it is going to be a good day, you will start to see birds.  The birds and mammals are feeding on Sand Lance a small fish that like sandy bottoms.