NOAA Teacher at Sea
Onboard NOAA Ship Oscar Elton Sette
May 2 – 25, 2004
Mission: Swordfish Assessment Survey
Geographical Area: Hawaiian Islands
Date: May 17, 2004
Lat: 18 24 N
Long: 157 47 W
Sky: Stratus cloud layer shielded us from the sun until longline was in then it started to break up by 1030. Sun for awhile then clouded over again by midafternoon. Thinning by evening but still a good blanket on us.
Air temp: 27.3 C
Wind: 35 degrees at 7 knots
Relative humidity: 54.5%
Sea temp: 26.8 C
Depth: 4489.2 m
Sea: 2-3 foot swells; no problems
Science and Technical Log
Yesterday after picking up the line we began a westward passage toward Swordfish Seamount. It was a long way off and there was no hope of getting there last night. The line was set along our course at 18 34 N and 156 47 W at no particular oceanographic feature that I am aware of. Perhaps that is why out haul today was none too exciting — a couple escolar, a snake mackeral and two blue sharks. Only one of the blues was brought on board. We will be at Swordfish to set tonight and look forward to a more interesting catch tomorrow.
I have covered each of the areas of research going on by the science teams aboard for this cruise. Today, my focus will be on sharks. We have caught 4 species so far and that has aroused my interest in these animals. I’ll provide some general info as well as some specifics for the species we have caught. For those of you interested in more, my information comes from two sources: Smiths’ Sea Fishes by Margaret Smith and Phillip Heemstra, and Diversity of Life by E.O. Wilson.
Sharks along with skates and rays are among 700-800 species in the subclass Elasmobranchii of the Class Chondrichthyes. Like all members of the class, their skeletons are entirely cartilaginous, but Elasmobranchs are distinguished by an upper jaw that is not fused to the skull and 5-7 pairs of gill slits.
There are about 350 species of sharks ranging in adult size from the 23 cm green lanternshark to whale sharks, the largest of all fishes, which reach 13 meters. Sharks lack a swim bladder, but produce large amounts of lipids which are stored as oils in the liver for buoyancy. The liver can account for up to 25% of the animal’s total weight. Sharks maintain osmotic (water) balance by maintaining a high concentration of urea (so high as to be deadly to most fishes) in their blood and tissues thereby reducing water loss to their salty environment.
All sharks we have caught (except the bigeye thresher, Order Lamniform) belong to the Order Carchariniform. This is the largest group of sharks; it includes about 200 species. These two orders are distinguished from one another in the following ways:
Carchariniforms: purse-like egg cases or live bearing; a movable nictitating membrane (eye covering).
Lamniforms: bear live young with uterine cannibalism (now there’s an interesting bit) evident in some; no movable nictitating membrane. There are also differences between the orders in the internal structure of their intestines — very interesting but I won’t go into description.
Specifics about each species of shark we have taken follow.
Blue sharks: the most fecund of all sharks; viviparous and bear 35-135 pups per litter; 50 cm at birth; attain 3.5 m; widespread in all oceans; favor water 12-16 C.
Oceanic white tip: in all oceans; away from continental shelves; viviparous bearing 6-8 pups usually; 60-65 cm at birth; up to 3 m; abundant in tropical seas.
Silky: widespread, prefer warm water; feeds inshore and in deep water; viviparous bearing 9-14 pups; 80-85 cm at birth; up to 3 m.
Bigeye thresher: widespread in warm ocean waters; ovoviviporous (provides embyo with no nourishment beyond the original yolk); 2 pups per litter; 100-130 cm at birth; attain 4.5 meters.
Well, I guess you can tell what I did today, and I might have a few more tidbits about sharks to add tomorrow. I am completing the log before the line set tonight so as to take in a movie afterwards. Don’t know what’s playing tonight, but it will be free and relaxing.
Tomorrow begins our last week at sea. Little time remains for you to file your questions with me. I’m looking too for suggestions for topics to try to address so if you have ideas, please suggest. I have asked for a tour of the engine room which is a possibility for Tuesday if tickets aren’t sold out. That might give me some interesting goodies to pass along.
We have seen fish that are rather uniformly dark in color and some that are brightly colored. What are some of the roles of coloration in fishes (as well as other animals)? Describe countershading and how it serves an animal like the blue shark.