Geoff Goodenow, May 20, 2004

NOAA Teacher at Sea
Geoff Goodenow
Onboard NOAA Ship Oscar Elton Sette

May 2 – 25, 2004

Mission: Swordfish Assessment Survey
Geographical Area:
Hawaiian Islands
Date:
May 20, 2004

Time: 1600

Lat: 19 15 N
Long: 157 06 W
Sky: Beautiful day; lots of sunshine with scattered cumulus clouds
Air temp: 26.6 C
Barometer: 1015.2
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.”

Goodenow 5-20-04 oceanic white tip

Geoff with a small oceanic white tip shark

Personal Log

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!

Questions:

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).

Geoff

Geoff Goodenow, May 19, 2004

NOAA Teacher at Sea
Geoff Goodenow
Onboard NOAA Ship Oscar Elton Sette

May 2 – 25, 2004

Mission: Swordfish Assessment Survey
Geographical Area:
Hawaiian Islands
Date:
May 19, 2004

Time: 1615

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
Barometer: 1012.5
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.

Goodenow 5-19-04 bite marks

This was taken to show countershading and nuptial bites. The large bite is obvious but also note the smaller teeth marks below. The bites are made by the males on the females.

Personal Log

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.

Question:

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?

Geoff