NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
May 2 – 25, 2004
Mission: Swordfish Assessment Survey
Geographical Area: Hawaiian Islands
Date: May 19, 2004
Lat: 19 15 N
Long: 157 14 W
Sky: Cloudy all day with light to moderate rain showers throughout the day after longline retrieval. Ended by supper time, but the sky remained overcast.
Air temp: 23.6 C
Wind: 106 degrees 16 at knots
Relative humidity: 73.4%
Sea temp: 26.2 C
Depth: 3959.8 m
Sea: Swells less than a meter.
Science and Technology Log
Not a big catch today, but everything we did catch came at once resulting in a flurry of activity for a short time. A blue shark was kept, and our largest swordfish so far came up dead. Too bad as it would have been an excellent one to tag.
For today’s in depth science report, I will refer to a couple of papers both coauthored by our chief scientist, Rich, relating to vertical movements of some of the species we have seen. Some fish tend to stay within particular vertical realms while others traverse them. What factors influence the animals’ movements?
One seems to be temperature. In a study of yellowfin tuna, blue marlin and striped marlins, all three were found to descend to depths where water is no more than 8C below surface temperature. Where oxygen levels in the water are not a factor, all three of these species seem to be restricted by the effects of water temperature on cardiac muscle function.
Bigeye tuna as you will recall stay deep (500m) by day and rise to the surface waters at night. At depth the animals are exposing themselves to ambient temperatures that are up to 20C colder and oxygen levels much lower than in the upper layers. Swordfish and bigeye thresher sharks exhibit patterns similar to those of the bigeye tuna.
What about those heat exchange mechanisms described in earlier issues of my log? Shouldn’t they, if present, allow a fish to tolerate a wide temperature range? While indeed they are present in some species, they are not working to keep blood warm as it goes to and through the heart. Any heat left in the blood on its return to the heart is lost as it passes through the gills. Since the heart is “downstream” of the gills, cardiac muscle remains within 1C of ambient temp. Studies show that temp. reductions cause heart rate and output to decrease.
Yellowfin tuna and the marlins seem to have no ability to increase heart rate or cardiac output following sudden temperature reductions. Consequently, they stay within that 8C window of surface temp.
So how do the bigeye tunas and others manage to negotiate these temperature realms with apparent ease? The question remains, the full story unknown so untold. Perhaps by the time you are here as a teacher at sea you can fill us in with the details. I’ll be waiting!
I’ll complete this look at physiology tomorrow with a bit more to relay about the oxygen issue.
I usually have a good start on the log by supper time but not today. In the quiet following the period of intense longline activity, I began the process of securing the jaws of the blue shark for display. This was a female of good size (165cm, 45kg) and with a nice set of choppers. I was being pelted with rain as I worked through lunch and beyond. I thought if I stopped I wouldn’t go back out to deal with it any more so I just kept peeling away the flesh to expose the teeth and reduce future odor issues. Had it pretty well done as chill started to get to me. I headed for the warmth of a stairwell over the engine room pausing momentarily to enjoy the (usually) stifling heat before finishing my route to room and warm shower. I did return to inspect my work. In comparing it to Eva’s similar effort I felt more had to be done to match her high standard. But now it’s done and jaws are held wide apart with crossed chopsticks as nature tends to the final phase.
No longline duties at the start of tonight’s set which I think is in last night’s neighborhood. Perhaps I will be in there as a reliever a bit later.
For something completely different and to address the history buffs among you:
How long ago is it estimated that Polynesians discovered and settled in the Hawaiian Islands? When were the islands discovered by European explorers? Why was captain Cook first welcomed by the native people, but not received so well (and eventually killed) when he returned shortly after his departure?
Any subject areas I’ve not touched on yet?