mako shark – Page 4 – NOAA Teacher at Sea Blog

June 28, 2006March 19, 2021

Brenton Burnett, June 28, 2006

NOAA Teacher at Sea
Brenton Burnett
Onboard NOAA Ship David Starr Jordan
June 26 – July 6, 2006

Mission: Shark Abundance Survey
Geographical Area: California Coast
Date: June 28, 2006

Weather Data from Bridge
Visibility: 10 nautical miles (nm)
Wind direction: 300 degrees
Wind speed: 17 kts
Sea wave height: 2-3’
Swell wave height: 3’
Seawater temperature: 19.6 degrees C
Sea level pressure: 1015 mb
Cloud cover: Scattered clouds

A National Marine Fisheries Service (NMFS) tag and insertion tool. — NOAA Fisheries tag and insertion tool

Science and Technology Log

Dr. Kohin, our chief scientist, tapped me to assist on the shark platform this morning! This means I helped remove the hook from sharks’ mouths and helped with the tagging. Note: I didn’t get bit once nor was I lost overboard. And the sharks did well, too. There are many tasks that lead up to shark tagging and hook removal. As the long line is drawn in by electric winch, one member of the science team unclips the gangion (or the buoy) and passes it on to others for stowing. If no catch was made on that hook (which is the case most of the time), the bait has to be removed before stowing. If there is a shark, however, it is walked “on its leash” to the stern (back) of the ship to the shark platform where Russ Vetter and Rand Rasmussen (and often Suzy Kohin though she is also busy coordinating the efforts of everyone) work to collect data and release the animal. Others record data and provide the materials necessary for tagging. As is often the case when conducting scientific research, much of this work can be repetitive. But when something comes in on the line, or when something unexpected happens like when a gangion is twisted on a line, there is lots of activity and excitement.

To be sure, the most excitement is on the shark platform. This 4 foot by 8 foot (approximate) platform is connected along its long side to the shark trough. The shark platform is accessed from the deck by a large chute that is as wide as the platform is long.

The shark trough is lowered just under the water until the shark (still on the line) can be maneuvered into the shark trough by Russ. Once there, Russ and Rand are quick to hold down the shark so that they can safely work on it. Rand uses a small thick blanket to cover the shark’s mouth and sharp teeth. Before releasing the animal, however, he needs to remove the hook. While the two of them hold the shark, another person (which was me this morning) cuts the hook or wire lead. By this time the sex of the shark has been determined. This is easily accomplished by observing the rear underside of the shark— two finger like “claspers” near the pelvic fins are present if the shark is a male. The last step before releasing the shark is to measure its length. A meter stick along the edge of the trough makes this an easy task.

If the shark is a mako or a thresher, however, a number of other tasks are undertaken before hook removal and release of the shark. First, a National Marine Fisheries Service (NMFS)”spaghetti tag” is attached just forward and to the side of the dorsal fin. These are “conventional tags” which give the animal a number and provide an address to send the tag to if the animal were recaught. The spaghetti tag is barely more than a plastic wire attached to a pointed piece of metal. To insert it, a small incision is first made in the shark’s back. Then, using an awl shaped tool, the metallic portion of the tag is wedged through the incision just under the skin. Because these tags may not stay in for life, a backup tag is also used. These are called ROTO tags and they are attached directly to the dorsal fin. Sharks returned with ROTO tags also indicate to researchers that oxytetracycline has been injected into the shark. These tags, like others, contain reward information for the return of specimens or information about them.

For larger and healthier sharks, satellite tags, of which there are two, may be attached to the shark. The SPOT tag (smart position and temperature tag) is a bit thinner and smaller than a computer mouse. Attached to the dorsal fin (in lieu of the ROTO tag), the SPOT tag has two metal washers on its exterior. If the shark rises to the surface, with its dorsal fin out of the water, these washers dry long enough to disrupt the electrical current that normally passes between them through the water. This cues the tag to transmit the shark’s position to a satellite. Using these tags costs more than $2,000 each, so it is important to use them with animals that are large enough to receive them and ones who are in good health.

If a shark receives a SPOT tag, a PAT tag (popoff and archival tag) will also be attached. The PAT tag records water temperature, depth and light levels at one minute intervals. After a few months or some other specified time, the tag is designed to pop off and float to the surface. At that time the tag transmits a summary of its data collection to researchers via satellite. If the PAT tag can actually be recovered, the full set of data at its full resolution can be retrieved.

It is interesting to note that light levels act as a proxy for time of day given that noon and midnight can easily be determined from them. And, in turn, this information can be translated into a longitudinal position as one notes the shift of day time from the location of tagging. Light level can also be used to determine latitude as on all days except those nearest the equinoxes, the length of day is dependent upon how far one is north or south.

Between the SPOT and PAT tags, the horizontal as well as vertical movement of the animal can be tracked over a period of time. Using only conventional tags, only one additional location can be mapped, and that only with a recatching of the animal. With these methods, it is hoped that the travels of these young makos and threshers, will be better understood as they feed and breed.

Personal Log

Every day has been exciting, but today helping on the shark platform has topped it all. I was lucky, too, as that set was the most productive, so far. We caught 57 sharks on 202 hooks—a pretty good batting average. And five of these were makos. We also caught a larger thresher shark, rare out this far. I was thrilled to think I’d get to see this guy up close, but alas it was not to be. The thresher threw the hook and escaped—the big one got away! Fortunately, later in the trip we’ll likely be more in thresher waters!

June 27, 2006March 19, 2021

Brenton Burnett, June 27, 2006

NOAA Teacher at Sea
Brenton Burnett
Onboard NOAA Ship David Starr Jordan
June 26 – July 6, 2006

Mission: Shark Abundance Survey
Geographical Area: California Coast
Date: June 27, 2006

Weather Data from Bridge
Visibility: 10 nautical miles (nm)
Wind direction: 350 degrees
Wind speed: 9 kts
Sea wave height: 1’
Swell wave height: 2-3’
Seawater temperature: 20.0 degrees C
Sea level pressure: 1012.7 mb
Cloud cover: Cloudy

The mako sharks we catch are one to two years old and are between 70 cm and 140 cm (around 3 feet) long.

Science and Technology Log

Our first full day of setting and hauling netted 68 sharks. In the morning we caught 21 blues and 5 makos, and in the afternoon 39 blues and 3 makos. Unfortunately, one mako and one blue did not survive and were brought aboard for sample collections. Though everyone involved understands that the work being done here is ultimately about helping these sharks survive and thrive in the wild even when an animal dies, there is, among everyone, a definite sense of loss and regret when an animal is lost. The data collection process involves a great deal of care for that reason.

Studies have been done to look at the stress related hormone levels of sharks caught on long lines, and the length of “soak times” used in this project follow those recommended guidelines—three to four hours from the start time of setting the line to the start of hauling it in. The design of long line helps to maximize survival, too. The gangions, which are the lead and hook assembly that attach to the long line, are about three meters long which gives these sharks room to swim while hooked. This is important for blues and makos as they, like many other sharks, need to keep in constant motion so fresh, oxygen-rich water is always moving through their gills.

Another challenge is that, on occasion, a shark will swallow the hook, so whenever possible a “circle hook” is used that will not hook in the stomach or esophagus, but only on a “corner” of some kind. If a circle hook is swallowed it will get pulled out by the shark’s movement away from the line but when the animal turns away, the circle hook will catch in its mouth. Even if a hook, like a J-hook, cannot be removed from an animal because it was swallowed, this does not necessarily mean it will die. Sharks with hooks in them have been released and recaught years later. When a shark does die, its body is utilized to understand sharks better. This is especially true for the mako sharks. Dr. Jeff Graham and two of his students, Dovi Kacev and Noah Ben-Aderet, as well as Miguel Olvera, another graduate student, are collecting a number of tissue samples for themselves and others at their home universities.

The gills of the mako sharks are of interest because makos are a high-performance, speedy, shark. A comparative anatomy study is being done to compare the design of their gills to that of tunas, another high-performance fish, though tunas are in the class of bony fishes, Osteichthyes, and sharks are cartilaginous being members of Class Chondrichthyes. For this reason, the gills of available specimens are being collected.

Shortfin makos (and, incidentally, common thresher sharks which also might be seen on this trip) are among the very few warm-blooded species of shark. Higher temperatures facilitate their higher energy usage as the fastest sharks in the ocean. Makos achieve higher body temperatures, in part, because their “red muscle” tissue is located close to the spinal column and not, as in most other sharks, close to the skin. This red muscle is responsible for maintaining prolonged periods of powerful movement. This muscle works in tandem with the circulatory system to create a heat exchange system called countercurrent circulation. The internal location of the red muscle and the countercurrent circulation work to preserve heat and even warm the blood before it reaches the heart. For these reasons, studies are being conducted on the red muscle versus white muscle are being sampled for later examination.

Because of the mako’s high performance, and the relation of that performance to the circulatory system, heart tissue is also being collected. The vertebrae of the makos is being collected, too, for the purposes of trying to determine the ages of the animals. This was discussed some yesterday in the discussion of oxytetracycline injections.

Finally, a cutting from a fin is also being collected to later extract DNA. Relatively little is known about the movement of makos (hence our tagging of them). By examining the genetic relationship of makos sampled, researchers will be able to determine if makos off the California coast are related to makos in other parts of the Pacific, including the southern hemisphere.

Personal Log

Aside from the critters at hand, there have been lots of other activity to feed our curiosities. We’ve been seeing whale spouts, probably fin or blue whales, and Risso dolphins. Ann Coleman, an aquarist with Monterey Bay Aquarium and another member of the science team, suggested we might even see some molas! Molas are the largest bony fish in the world reaching 1500 pounds and a record of 14 feet in total length! We can hope!

Thankfully, I’ve had zero issues with seasickness. In fact, I’ve rather enjoyed being rocked to sleep at night. And, thankfully, the food has been plentiful and quite yummy! That’s all for now…

Brenton

June 26, 2006March 19, 2021

Brenton Burnett, June 26, 2006

NOAA Teacher at Sea
Brenton Burnett
Onboard NOAA Ship David Starr Jordan
June 26 – July 6, 2006

Mission: Shark Abundance Survey
Geographical Area: California Coast
Date: June 26, 2006

The DAVID STARR JORDAN awaits final fueling and preparation for our cruise.

Science and Technology Log

The DAVID STARR JORDAN was first commissioned by the U.S. Bureau of Fisheries, which later became part of the National Oceanic and Atmospheric Administration. Since its commission, it has logged over a million miles studying the biological and physical oceanography of the southwestern U.S. coast and eastern tropical Pacific. While it has a range of 7500 nautical miles (nm) and can be out to sea for 30 days, our cruise will last for 10 days and cover only a few hundred nm. It can berth up to 33 people, but on board this cruise are 12 officers, engineers and crew, and 12 scientists including myself. In ideal conditions, the top cruising speed of the DAVID STARR JORDAN is 10 knots (about 12 mi/hr).

This mission’s goals are to assess shark abundance in the Pacific off the coast of California. This is done through long line fishing. At 1800 hours and approximately 20 nm out from San Diego, we made our first “set”. Making a set is truly a team effort involving no fewer than five of the ship’s crew and eight scientists. The crew run the winches and navigate the ship, while the science team baits and sets the line. Two people ready the “gangions”—a gangion consists of a 4” J-hook, an 8’ wire lead and a “tuna clip”. These two pass the gangions on to two others who bait each hook with a whole mackerel, which is about a 10” fish. The baited gangions are then given to the “hooker” who clips them to the line that is running along the side of the ship and then back beyond the stern. Two others are readying balloon buoys that are attached between every five hooks. The length of the lead on the buoys, which is about 7 meters, plus the length of the gangions, about 3 meters, determines the depth of the baited hooks.

We baited 113 hooks along about 1.5 nm of line and let it soak for one hour. At dusk we began to “haul” the line in. This, too, requires a team effort. Tasks include removing the gangion from the line, “de-baiting” the hook, and stowing the gangion. Of course, if there’s a catch, then it’s really exciting. The shark, still in the water on a hook, is walked to the stern to the shark platform. There, senior scientists, Russ Vetter and Rand Rasmussen, and chief scientist Suzanne Kohin slide the shark into the shark trough, which is then quickly raised just above the water. While two of them hold the shark, they remove the hook, measure and determine the sex of the shark. All mako shark and thresher sharks will get a tag of one variety or another. Though, most of our catches will be blue sharks, other researchers, specifically those at the Pacific Island Fisheries Science Center (PIFSC), are tagging blue sharks.

Oxytetracycline is injected to some specimens, too. OTC dyes the vertebra of the sharks. The vertebra, like the rings of a tree grow layers over time. It is not certain how often these layers form, one study suggests two in a year. Injected sharks that are recaught later will help to answer this question, and ultimately help scientists understand how quickly sharks age and reach maturity. Incidentally, recatches of this sort are typically done by fisherman who are given $100 for recording the shark’s length, the date it was caught, and for returning four to five vertebrae.

Our first set of the trip was a practice run of about 1.5 nm and 113 hooks. The haul brought in four blue sharks and one mako. From here on out, we’ll be making 2 two mile long sets a day with 200 or so hooks.

Personal Log

Though we had a delayed start to our cruise—the two diesel trucks to fuel up the ship were late—there has been very little down time! Now that I’ve been able to check email, I’ll get to questions next time! Until then… Brenton