Wednesday, August 10, 2011

"She'll be right, Mate" - Shark Tagging with NOAA/NMFS

This summer marked another great shark tagging cruise for NOAA/NMFS’ Large Pelagics Group, with over 200 blue, short fin mako, and common thresher sharks tagged. The Ventura II set out near the Channel Islands for a ten-day trip under blue skies with a great crew, in hopes of catching  as many juvenile sharks as possible. As a bio undergrad with hopes of doing research, it was an awesome experience to be able to handle and tag some of these shark and all three of the interns- Mackenzie Merkel, Nathan Mertz and I- saw firsthand the importance of planning and execution for research. I feel extremely fortunate to be have been under the wing of John Hyde and Natalie Spear from NOAA/NMFS, and Paul Rogers from Flinders University in Australia- all three very motivated scientists and good people. This high tagging tally forms the basis for a large pool of information and samples that can be obtained from these annual juvenile surveys- DNA samples, muscle biopsies, length, condition and sex of sharks, as well as stomach contents and a few organs from dead specimens. Also collected this trip were parasitic copepods for  Paul Roger’s continuing study of mako sharks. These copepods found on the skin and fins of both mako and blue sharks are being studied as possible biological markers to indicate interactions of different shark subpopulations or species.

For a student who doesn’t quiet have her sea-legs yet, what would seem mundane for seasoned scientists was more than new for me, from baiting 200 hooks with sleepy eyes to the actual tagging of sharks. I had also never participated in long lining before and with all the negative perceptions surrounding this industry, it was surprisingly less invasive in terms of by-catch than I had expected. With two sets a day for ten days, the total tally of 202 animals included 1 opah, 1 pelagic ray and 1 Mola mola, the latter two of which were thankfully unhooked at the rail and swam away. This personal realization about long lining, which although based on a very small sample-size using only a fraction of the industrial hooks, could be testament to the gap between an assumption and the actual experience. I would like to avoid sounding cliché, but it’s amazing how much more you learn from hands-on experience than from just reading about it. No book has or can describe the smell of blue shark under the fingernails at the end of the day, or the pure muscle that makes up the body of even the smallest sharks we tagged. I really loved the actual handling of the sharks, which on our busiest set, was up to 43 blues in a row! It was the mako’s however, that were my favorite, their black eyes and the way they thrash violently from side to side was plenty more aggressive than the characteristic wriggling of the blue sharks.

One set in particular stood out not only because of the low count of two sharks, but for the healthy dose of adrenaline it gave us. The first, a small mako, appeared to be dead as we pulled it on deck and the water running over its gills thankfully paid off. With time and attention, what seemed to be a lifeless little mako turned into a lively one. The next shark was memorable for its 202 cm length paired with how feisty it was. Once on the cradle, it demonstrated its teenage angst by biting through one of the four supporting ropes of the cradle. The rope broke completely off the hydraulic pulley and all of us just looked at each other with wide eyes, surprised.  We sprang into a chaotic impromptu rearrangement of shark, personnel, and ropes, and the cradle was  fixed onboard to bring up the shark. The shark had tired out enough for everyone to hold it down, but as the first big fish of the trip, it definitely made its debut one to remember. I was quickly reminded of the awesome power and agility of these sharks that had been somewhat diluted by handling so many docile juveniles up to that point- a much needed paradigm shift to say the least.  
All but one of the sharks was given a conventional tag- a metal arrow-shaped anchor about a centimeter long attached to a six-inch flexible plastic flag label. These metal anchors are placed in the muscle next to the dorsal fin, from which a small fin clip was taken. The largest mako was given a GTOPP-funded SPOT tag (Smart Position and Temperature Tag), which unlike the conventional plastic tags, can transmit to the satellites which calculate a position. Because of its large size, this mako was given the tag in the assumption that it would  move through different territories more so than juveniles might. The team affixed the plastic tag onto the dorsal fin to keep the oval, battery-operated device from falling off, yet to not be invasive in the shark’s daily behaviors. Hopefully in the near future, the shark we brought onboard on that very day can indicate to the team its movement patterns and where it spends most of its time.

The shark deterrents we picked up in Avalon, Catalina, were tested in our lone night set, with an  outcome differing from our expectations. We clipped a deterrent- a plastic cylinder wrapped in foam, containing a battery-induced electrical field- on almost every other lead going out on the mainline. Unfortunately, the ratio of sharks on deterrent hooks to total number of deterrents used was about 16:21. This high ratio could indicate that improvements are needed for these to effectively repel shark, however, the sample sizing was also very small. Regardless, the possibility of using shark deterrents on future surveys and in commercial fishies could help reduce shark bycatch.

The waters of the Southern California Bight have not only been my personal playground since childhood, but also for sailors, divers, and commercial fishermen, due in part to the biological diversity of pelagic predators. The Ventura II was flanked by a pod of dolphins almost every day, not to mention the pod of white scarred Risso’s dolphins, giving us false hope of nearby swordfish. About three whale spouts were seen returning into coastal waters, almost greeting us before diving down deep. Every night and day, we saw salps forming large stringy colonies that feed on phytoplankton blooms. These salps were joined by a transluscent pink pyrosoma we found during the night set, a column-shaped and hard tunicate that are closely related to salps. It was refreshing to see this kind of life throughout the cruise, especially with the amount of juvenile sharks tagged, because all members of this pelagic environment play a role in the health of the environment. On two occasions, we saw evidence of the predatory instinct of the sharks in the area. We pulled up a mako hooked in the mouth but missing its body from the gills down; the bite marks were testament to an attack from a larger shark. Another live shark was pulled on deck with a large bite mark on its back, while the opah also had a cookie cutter shark bite. All these were seen above water, however we were itching to see some underwater action. Paul and I rigged up a classy little contraption we called the “Ghetto-Pro”, a makeshift version of the professional “Go-Pro” cameras, by duct taping and zip-tying my digital underwater camera to a gaff. Running video over the rail, we were able to see some footage of hooked sharks- a small mako and a large blue- along with a pretty cool sequence of a mola mola being unhooked and swimming away in their odd manner.

Needless to say, the cruise was a blast, I’m still grinning about the experience. With the information gathered not only on this cruise, but from years past and years to come, the abundance and distribution of juveniles sharks in the Southern California Bight might be better understood for scientists and the general public alike.

-Liana Heberer

1 comment:

  1. that was a great post, have been out to sea, not tagging sharks, but whale monitoring....good read up for easterners off the coast of Chatham, with everyone barking great whites