NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
May 2 – 25, 2004
Mission: Swordfish Assessment Survey
Geographical Area: Hawaiian Islands
Date: May 10, 2004
Lat: 18 41 N
Long: 158 19 W
Sky: Sunshine with scattered cumulus; beautiful day.
Air temp: 27.3 C
Wind: 68 degrees at 8 Knots
Relative humidity: 47.9%
Sea temp: 27.1 C
Depth: 1674m (at 1800 hours, Lat 18 25N, Long 158 27W)
Sea: A few white caps tonight. What might they foretell?
Science and Technology Log
Pretty good day on the line. We tagged a yellowfin tuna (on board) and a broadbill swordfish (in the water). In the latter case, the tag was attached by sort of harpooning it into the animal from deck. We also pulled in a snakefish (head only), a big eye tuna, 2 escolar, a barracuda (of no interest so simply cut off the line) and 3 blue sharks. One was too large to safely bring aboard; it was cut loose. The two others were brought on board. From one we took blood and fin clips after which it was released. One fish was brought in by trolling today.
As you have noticed water temperature here would be quite comfortable for us (but we are not taking afternoon swims). Rich explained to me that here there is mixing of the surface layers such that the surface temps. I have been reporting would apply to a depth of about 100 meters. Then between there and 400 meters we would see about a 10 degree C drop. While some fish stay in the upper layers others hang in the depths or make regular vertical transgressions across these zones.
Fish are generally regarded as having body temperature at or very near ambient. Any heat produced in the muscles by aerobic respiration is picked up by the blood and circulated through the gills where that heat is dumped efficiently to the environment. Some saltwater fish (no freshwater ones) including tunas and some sharks have developed a kind of heat exchange system. Heat from venous blood is passed to arterial flow in order to keep certain muscles and organs above ambient temp. by as much as 20 degrees C in large fish. This allows body tissues and organs to work more efficiently.
Billfish such as swordfish also have a heat exchange system but it is located only around the eye and brain. Here certain eye muscle is reduced to little more than a container for mitochondria which generate lots of heat. The heat exchange system then only serves this region of the body keeping it above water temp. Still busy at Cross Seamount. The fishermen must be having a big time up there. We are setting at Swordfish again tonight. (Lat 18 17N Long 158 22W at finish of set)
Those oily escolar are not being kept for consumption. This morning we took one’s eyes and made a short incision along the belly just to take some muscle tissue In returning the escolar bodies to the sea I have scored their diving entries 1-10 as in competitive events. Most have been dropped straight in, but this morning I thought of trying something with a higher difficulty factor — a one and half back flip with tail entry. But on its first rotation, a bit of the entrails was ejected shipward striking me on the shoulder before falling to the deck. Unfortunately, this was not captured on film for replay tonight on “Funniest Ship Videos”, but for those present, it provided a good bit of humor to start the morning. Hereafter, we might just stay with the less ambitious dives. Spectators were glad it was I and not they.
Later I made my debut as a shark wrestler. As a rookie I was given the tail end. Even though the blues are comparatively tame once on board, the strength in the animal’s body was very evident as it tried to move – – not so sure I care to deal with the other end of these babies!
This question relates to paragraph two of the science log. What is the thermocline within a body of water? How would you expect a temperature profile to change through the seasons in a deep lake in central Pennsylvania?
Any questions from you folks???