Monday, April 18, 2011

The Deep Blue Sea

I grew up vacationing and fishing on a lake near Dayton, Ohio (Grand Lake St. Mary’s) that was about nine miles long by three miles wide and had a depth of less than seven feet.  So you can imagine my disconnect now when looking out our backyard and seeing humpback whales swimming past and ocean going cruise vessels entering  the Hilo Harbor.

"Valentine" in Backyard
This led me to wonder just how deep the ocean was off of our lanai, which in turn led me to the NOAA (National Oceanic and Atmospheric Administration) site which was brought to my attention by a friend of mine in Marine Science at the University of Hawaii - Hilo:  http://www.nauticalchartsonline.

So the ocean seems to be about 14 feet deep near our cliff, then increasing to 25 feet in depth and quickly to 34 feet.  Beyond that the water becomes about 90 feet in depth which must be fine for humpback whales.  It seems that humpback whales seem to prefer "shallow/protected" waters and spend the majority of their lives in waters that are 300 feet or less, and in this case, considerably less  than 300 feet.
Credit: Devany Vickery-Davidson

From deep water on the north, there is a ship channel to the inner harbor edge to the wharves in Kuhio Bay. A Federal project provides for an entrance channel 35 feet deep and a harbor basin of the same depth in Kuhio Bay. Channel and basin are maintained at or near the project depth. www.NOAA

As you can see, our weekly Tuesday visitor, the “Pride of America,” has a draft of only 26 feet.
Humpback whales and the cruise ships seem to coexist peacefully.  We have even seen whales swimming next to the ship and “porpoising” in and out of the water next to the boat. 
Interestingly, the 20-fathom depth (120 feet) curve is seldom more than one mile from shore in Hawaii and usually not far from the coral reefs that fringe much of the island coastline. The bottom generally pitches off rapidly to great depths from a narrow coastal shelf. Under normal conditions the color of the water changes from a deep blue in the open ocean to a blue-green between the 10- and 15-fathom (60 feet to 90 feet) curves; and bottom features become visible at 6 to 7 fathoms (36 feet to 42 feet).  www.NOAA