June 2009 Whale Shark Tagging Expedition
On June 8, 2009, GCRL scientists Dr. Eric Hoffmayer and graduate student Jennifer McKinney headed to Leeville, Louisiana to join professional photographers Andy Murch and Claire Pinata and professional documentary filmmaker Ulf Marquardt. Early the next morning, the expedition team set sail aboard the F/V Norman B with the hopes of encountering an aggregation of whale sharks, Rhincodon typus, in the northern Gulf of Mexico.
Commercial snapper vessel, the F/V Norman B, which took whale shark
They were met at the dock by Captain Russell Underwood, a commercial snapper fisherman, and his crew: David Ingram, Jack Malachon, and Ron Long.
Captain Russell Underwood at the wheel of his vessel the F/V Norman B
Captain Underwood has made a living on the sea and has been fishing these waters for over forty years. In June of 2008, Captain Underwood contacted Dr. Hoffmayer after encountering a group of more than 40 whale sharks while fishing near Ewing Bank. He was so fascinated by his encounter and interested in the presence of these beautiful sharks in our waters that he decided to aid in the scientific research. Captain Underwood graciously donated his time, vessel, and crew to host our group on a seven-day excursion to learn more about the whale shark.
It took the vessel nearly twelve hours to reach Ewing Bank and our anticipation was high. When we arrived at the Bank the following morning we immediately began looking for whale sharks. The first signs of a whale shark are often the tall dorsal fin protruding from the water and the gentle sway of the caudal fin. However, looking for a whale shark in a large body of water is much like looking for a needle in a haystack. We needed "eyes in the sky" to increase our chances of an encounter. A spotter plane had been hired to survey the surrounding area for whale sharks and keep us informed of any sightings. Approximately two hours into our search, the plane spotted a whale shark radioed us the coordinates. The fifteen mile steam at eight knots felt like an eternity, and unfortunately, by the time we reached the location the shark had gone down. This is a common problem with animals that do not stay at the surface. So we again began watching the sea for a telltale sign of a whale shark.
Crewmen David Ingram and Jack Malachon, on the cabin top of the
F/V Norman B looking for whale sharks
After many hours of staring out into the blue, our determined Captain declared it was time to change course. We began to head west to some underwater pillars near the Flower Gardens Bank National Marine Sanctuary, another location where Captain Underwood had encountered whale sharks, and agreed to start our search again in the morning.
The next day was long and dreary. You could tell everyone was a little worried that the trip was going to be a flop, but no one wanted to say it for fear of jinxing the few days left. In the first two days of the trip we had covered many miles with only one brief sign of these massive sharks. The seas were rougher in this new location, so after a few hours of no activity we headed back toward Ewing Bank.
On the third day, June 11, the Norman B was back in the waters over Ewing Bank. Shortly after daybreak, we encountered a weedline of Sargassum, which in a featureless ocean, provides habitat for all sorts of life, including whale sharks.
A weedline of Sargassum, an important habitat for all sorts of life,
in an otherwise featureless ocean
Screams from the roof directed everyone to look straight ahead. Iimmediately ahead was the large dorsal fin of a whale shark. But just as we all made sight of the fin, the dorsal fin sank below the surface as the shark dove. Hoping the shark would resurface soon, a small skiff was launched off the side of the Norman B and we loaded our gear into the boat. The skiff made tracking the shark easier and safer for both people and shark.
By the time we were all in the skiff there was no sign of the shark. We stayed in the skiff and searched perpendicular to the Norman B, hoping that having two vessels searching would increase our chances. After nearly an hour we headed back to the Norman B, disappointed at the second unsuccessful sighting. A few hours later, this scenario was repeated with a third sighting. When the crew headed back to the Norman B after yet another fruitless skiff ride, we were worried that we would return home having had three sightings but no encounters for further data collection or tag deployment. The Captain and deckhands were still confident, but the scientists and film crew were anxious.
Luckily Captain Underwood and his hard-working crew were justified in their confidence and another whale shark was spotted. This time we decided that someone needed to get into the water immediately to stay with the shark while the rest of the crew loaded onto the skiff. Claire jumped into the water and snorkeled with whale shark, keeping an eye on its movements. When the skiff finally approached, Andy was able to get in the water and photograph the left side of the shark between the gills and the pectoral fins. Photos of this region of the shark are important because the shark's spot pattern here can be used in a global database for photo-identification. After Andy got the photographs, Dr. Hoffmayer entered the water with a satellite tag.
The spot pattern behind the gills on the left-side can be used for
photo-identification Photo Credit: Andy Murch
The satellite tag is tethered by a stainless steel wire to a titanium dart. The dart is meant to be inserted into the muscle of the shark at the base of the dorsal fin.
Archival satellite tag used to record temperature, depth, and location of
the whale shark for up to a year
Since whale shark skin can be up to six inches thick, a tagging pole is required to get enough force on the dart to pierce the skin.
Dr. Eric Hoffmayer deploying satellite tag on a whale shark in the northern
Gulf of Mexico 6-11-09 Photo Credit: Andy Murch
Dr. Hoffmayer successfully inserted the tag and returned to the boat for a different pole equipped with a sharp, hollow tip designed to take a small skin sample from the shark for DNA analysis. This was when we noticed that there was more than one shark present.
We quickly looked around and realized that we were in the middle of a feeding aggregation. We were amazed by the large numbers of sharks and by how fast they were swimming despite their seemingly slow and graceful movement. In order to systematically collect data on as many sharks as possible, we decided that it was best to follow one shark until all data was collected on it before moving on to the next animal. This required one or two people to swim with the shark and report their findings to someone in the skiff.
The data collected from each shark included an identification photograph, determination of the sex, satellite tag attachment, DNA sample acquisition, and an estimate of the shark's total length.
Claspers identify this shark as a male. Photo Credit: Andy Murch
Since the sharks were swimming quickly, the researchers would re-enter the skiff to move to a new shark. This required a tremendous amount of teamwork. Since the work is so physically taxing we took turns in the water. During the event, 15 animals were encountered, three satellite tags were deployed, and photographs and other data was collected on seven sharks.
After a solid three hours of shark chasing, dusk was approaching and we still needed to conduct plankton tows to determine what was in the water that attracted so many feeding whale sharks. Tows were conducted at the shark site as well as at sites two miles away from the aggregation in all directions (east, west, north, and south). It was obvious as soon as the plankton net was retrieved that the whale sharks were feeding on a high density of fish eggs. Weeks later, back at the GCRL, geneticist Dr. Eric Saillant, determined the eggs were from the fish little tunny, (Euthynnusalletteratus), which is a multiple batch spawner, meaning they spawn several times throughout their spawning season.
Samples were collected at the aggregation location and at control stations
to compare the differences in plankton densities where whale sharks feed
to that of the surrounding area
At the end of the day we were all excited and exhausted, but we were celebrating our success. We sat around over dinner, reliving the afternoon and going over the play-by-play for each shark like a postgame wrap-up.
Over the next few days we continued to search for sharks even though there were no more satellite tags to deploy. We encountered a school of silky sharks, Carcharhinus falciformis, which allowed shark photographers, Andy and Claire, to get some more footage. Back in port at Leeville, we were met by Nicondra Norwood, a New Orleans FOX News 8 journalist. Her report on our success highlighted the collaboration between of fishermen and scientists.
The three tags that were deployed on Ewing Bank were scheduled to record data for eight months. One of the tags came off a shark early, and showed that the shark was heading east towards waters south of the Florida panhandle. We believe the satellite tag came off early because the shark dove to a depth greater than a mile (~1,700 m), which caused the safety system to activate and detach the tag so that it would not be damaged from the pressure. Interestingly enough, the tagged popped up just offshore of a region where nearly 60 sightings were reported during the month of August. After the satellite tags detach from the shark, they float to the surface and the data is transmitted via satellite back to the researchers. The geolocation data that we receive is still pretty raw and needs to be filtered and corrected in the laboratory. By looking at the movement data from these tags, we have a better understanding of how these sharks are using the waters of northern Gulf of Mexico.
Many thanks to the Captain and crew of the Norman B for their generosity, hard work, and determination! We could not have done this without you!