NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
May 2 – 25, 2004
Mission: Swordfish Assessment Survey
Geographical Area: Hawaiian Islands
Date: May 20, 2004
Lat: 19 15 N
Long: 157 06 W
Sky: Beautiful day; lots of sunshine with scattered cumulus clouds
Air temp: 26.6 C
Wind: 132 degrees at 15 knots
Relative humidity: 62%
Sea temp: 26.7 C
Depth: 3116.6 m
Sea: Swells less than a meter offering up a very smooth and pleasant ride.
Science and Technology Log
Several escolar, 2 snake mackeral, 2 sharks and 2 swordfish on the line today. The sharks were both silky sharks. One was tagged and released. The same treatment was intended for the other but it broke free of the hook before we got it on board. Both swordfish were dead.
The last of the swordfish was the biggest we have seen: 185 cm plus a sword of over 60cm and weighing in at 90kg. A couple skipjack tunas were landed with troll lines.
We are staying in the same area for the longline set tonight. We didn’t even bother to check Cross seamount as things are pretty good here and we would probably have had to turn away from there out of respect for others’ presence.
In reviewing Kylie’s presentation (see personal log), Rich commented that we know what the movements of the animals are, but we don’t know so well why they make various vertical movements nor how they are able to deal with the stresses imposed by those movements. The temperature/cardiac function relationship described yesterday adds a bit to the puzzle as do studies of tolerance to oxygen reduction. I found this quite interesting and hope I can condense the story to something meaningful for you.
At depths reached by bigeye tuna oxygen levels are far lower than levels experienced by skipjack and yellowfin tunas at the depths they are normally found. Tunas characteristically have high metabolic rates which might seem impossible to maintain at low ambient oxygen levels experienced by the bigeye. Fishes tolerant of low oxygen levels are typically very sluggish, have low metabolic rates and have blood with a higher affinity for oxygen than less tolerant species. In exchange for that high oxygen affinity (a benefit at the gills), they sacrifice maximum delivery of that oxygen to their tissues; their blood just doesn’t want to let go of it.
Bigeyes then, as you would expect, have blood that grabs oxygen more readily than blood of skipjacks and yellowfin. So how are bigeyes able to remain so active when their fellow fishes with high oxygen affinities just can’t keep the pace? Recall those heat exchange units we’ve mentioned before??? Bigeyes’ blood loses much of its grasp on the vital gas as it is warmed by those heat exchange units. And remember that at the gills the blood is “cold” again. What a great system — readily grab and hold oxygen at the gills even in low ambient oxygen environments, and readily release it in the muscles. Pretty cool, I think.
To conclude, I quote from the summary section of my source as to the value of these studies. I presume that what is stated here specifically with respect to bigeye applies more broadly. “Understanding the vertical movements and depth distribution of bigeye tuna, as well as the physiological abilities/tolerances and oceanographic conditions controlling them, has been shown to be critical to improve longline catch-per-unit effort analysis and long term population assessments in the Pacific.”
Following the line retrieval, I managed to get some time on the upper deck in my favorite shady spot with my book. Reading, snoozing and enjoying the view passed the afternoon along with an interruption to assist with a troll line catch. This was very nice after such a gloomy yesterday that was topped off with another late night at the movies (Pirates of the Caribbean).
Just before supper Kylie did a rehearsal of a presentation she will be making in Australia about her vision studies. Rich and Kerstin made comments and suggestions to help her polish the presentation. It was interesting to hear them address content and presentation issues much as I do with my own students.
Kerstin asked me today if it is getting tough coming up with material for the log. I suggested that indeed it is becoming more of a challenge. Perhaps out of sympathy, she called me to her lab early this evening to share with me some details related to the eye socket of a swordfish. Thanks, Kerstin, and keep ’em coming!
Many native plants and animals of the Hawaiian Islands have suffered due to the introduction of non-native species to their environment. The green cover of the islands is very different in most places than what Polynesian settlers saw. Mongooses and ginger are two introduced species. See if you can find out how they got here, why they were introduced and specific impacts they have had on native species. (There are others for which you could do the same investigation including many in your home area).