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Shark Info 4 / 02   (12-20-2002)

Author

  Intro:

Remote detection sonar threatens the oceans

Shark Info

  Main article:

Remote detection sonar threatens the oceans

Dr. A. J. Godknecht

  Article 1:

CITES Appendix II to finally include whale sharks and basking sharks

Shark Info

  Article 2:

Shark Research Trip to the Gulf of Mexico (Part II)

Dr. A. J. Godknecht, Dr. G. D. Guex

  Fact Sheet:

Cuban dogfish

Shark Info


Shark Research Trip to the Gulf of Mexico (Part II)

By Dr. A. J. Godknecht, Dr. G. D. Guex

This is a continuation of the report we began in Shark Info 3/2002 on our shark research trip to the Gulf of Mexico. Due to current events (see report on LFA sonar in this Shark Info) we decided to bring this report on the Oregon II mission in three instead of only two parts. The last part of this report is thus scheduled to appear in Shark Info 1/2003.

Day 5

Melissa and Jill appear and we begin by counting off 100 round hooks. We then attach the fairly slippery chunks of mackerel to the hooks, laying the bait lines as parallel as possible on a wooden table to ensure quick handling when attaching them to the longline.

CTD

The CTD device is lowered into the water after the longline is set.

© G. D. Guex

Tonight it’s Todd’s turn to help us set up the longline. Mark explains the job-sharing functions between the crew and scientists. The crew operates the equipment and the scientists do the rest. After the first buoys and the starting weight are overboard, Todd clinks the bait lines in ten-meter intervals to the slowly unreeling longline. We then move to the bow of the ship to lower the CTD equipment which must measure water data. As soon as the CTD is returned on board and cleaned with fresh water we must wait.

Half an hour later our first longline is ready to be pulled in. This time we bring in a series of Atlantic sharp-nosed sharks and two even larger female spinner sharks. Rather than being marked, the spinner sharks are killed in order to undergo more precise analysis. On each trip Mark is called upon to comply with a series of requests for sample material from various laboratories. Some labs request samples of flesh from food fish in order to examine them for mercury and other heavy metals. Others need reproductive organs for development biological studies, and still others would like otoliths from groupers in order to gain information on their age and growth, etc. So there is always much more to do than simply mark and release the catch.
Atlantic sharpnose shark

An Atlantic sharp-nosed shark (Rhizoprionodon terranovae) is pulled aboard at almost brutal speed.

© G. D. Guex

Next station: The only animals found on the longline are several dead Atlantic sharp-noses – a very sad scene, indeed. In attempting to determine why the entire catch died, CTD data revealed that only 0.6 ppm (parts per million) of oxygen were found on the seafloor – much too little to guarantee survival of the sharp-noses on the hook for longer than several minutes.

Two longlines to go, and then towards six a.m., breakfast time. Each morning Paul prepares a breakfast which would undoubtedly be considered an extensive lunch in Switzerland. For snacks he makes sure we have fresh fruit, Gatorade, ice tea and, of course, liters of coffee. After all, in these temperatures one has to pay attention to replenishing the body fluid household.

Up until the day shift starts, we lower a total of four longlines with mediocre results, although at least we found no more dead animals. We finish around 12 noon, quite exhausted but ready to again spend our free time looking over the shoulders of John Carlson and his girl group as the day shift begins their work.

Day 6

After a second day of barely three hours sleep we can hardly get out of bed. But after all, we don’t find ourselves on a shark research trip every day. So we take over the longline which the day shift had set. The composition of species caught at the last three stations clearly reflects our proximity to the Mississippi delta where the seafloor is flat. On the longline we find about 20 catfish and two eels. But we’re lucky. Between the catfish we pull two bull sharks (Carcharhinus leucas) towards the ship. Barely measuring 1.30 meters in length, these medium-sized sharks are already so heavy that we cannot haul them aboard. We must thus be satisfied with estimating their length, determining their sex and marking them below the dorsal fins. Finally we give them their freedom by cutting off the bait line.

The next station is a three-hour sail away. Time to relax a bit and enjoy some biology. With great interest we observe some flying fish appearing in the cone of light stemming from the floodlight on deck, or try to determine the species of jellyfish which we see passing in the water. Our two girl colleagues disappear and spend time looking at some TV series or DVDs in the TV room. As we learned during our trip, this was apparently their main activity when not working or sleeping.

The next station is also located near the Mississippi delta region. After setting the lines and receiving initial data from the CTD we fear the worst for our catch because only 0.6 ppm of oxygen is registered on the seafloor. All of the sharks pulled on board, including two spinner sharks, are dead.

Dasselbe bei der nächsten Station, doch hier haben wir – besser We find the same situation at the next station, although here we – better said one shark – has some luck. Of the four sharks we pull aboard, three are dead and one 1.35 meter long finetooth shark (Carcharhinus isodon) is more dead than alive. Time is vital if we want to save him. We measure him, decide to forget about the marking and return him to the water as quickly as possible. Our last glimpse showed him swimming slowly, rather than just drifting down into the water – a good sign. We wish him luck.

Day 7

After 10 hours of sleep the world looks considerably clearer again. Still, it’s a strange feeling when in a barely conscious state, the first thing you see in the morning is a lady holding a shark head.

In the meantime we arrived at station 14. According to the day shift, barely any more sharks have been caught since leaving the Mississippi Delta. As we move towards the open sea we notice the difference in both the water’s color and the new species on the line. The Gulf is considerably deeper here than in the coastal region. We catch two red snappers and a yellow-banded grouper. Melissa is quite excited because she works with these groupers. After taking some otoliths and tissue samples, the fish winds up in the kitchen. Somehow Paul’s kitchen aid has a sixth sense because he always manages to appear precisely then when something of culinary interest is pulled on board.

Cuban dogfish

The Cuban dogfish has very large eyes which appear to shine green.

© G. D. Guex

Although we catch and mark a total of only six sharks during the entire shift, we have special forms that include a scalloped hammerhead female (Sphyrna lewini) and, at a particularly deep area at a depth of 150 meters two small Cuban dogfish (Squalus cubensis) with huge eyes which glow green under certain light conditions. This coloring is caused by the light amplifier (Zona pellucida) found behind the retinal cells. This so-called silver coating reflects the light, similar to cats’ eyes, and thus lands with almost double the intensity on the retinal cells.

The seventh day, the fourth at sea, turned out to be extremely exciting and, being well rested, we also managed to enjoy the beautiful weather and the calm sea.

To be continued in the next issue of Shark Info

* Alexander J. Godknecht and Gaston D. Guex are biologists and members of the Shark Foundation Board of Trustees and the Shark Info editorial staf.

May be published only by indicating the source: Shark Info / Dr. A. J. Godknecht, Dr. G. D. Guex



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