As scientists, anglers and passionate fans of Pacific bluefin tuna we live for day like we have had here on Shogun in the past 24 h. Our mission- to collect tunas for studies back at our home laboratory- the Tuna Research and Conservation Center (TRCC). We arrived in the area where fishing reports had been excellent and proceeded from dawn to dusk to have a wide open bluefin bite. And this time, for the first time in years, we were more than prepared. The Stanford University team had programmed over 100 tags prior to coming out on the trip and anticipation was high.
This year we had some older TAG team members from our lab, including Tag-A-Giant and TRCC technicians Robbie Schallert and Alex Norton, Stanford technician for our Gulf oil spill team Ben Machado. Also on board were Stanford graduate students Dane Klinger and Dan Madigan, and undergraduates who had interned with the TRCC this summer including undergraduates Natalie, Ethan, Sarah, Andrew and James.
Captain and Professor Norm put us in a great spot to drift and before sun up Dan Madigan hooked up. This year to prepare with our younger team, we had held a “tagging class," and went over the cradling of fish on the swim step. Sure enough chaos occurred during the first fast bite when the team barely had their feet wet. We put the fish that first appeared as yellowfin into the side wells and quickly filled to capacity.
We then heard the first call from the crew of, "Bluefin!" The tagging team (Barb, Robbie, Dr. Joe Bonaventura) went into the action- tagging 7 yellowfin. The bite slowed down and we moved on. Within an hour, Norm glanced and viewed a sonar hit that was extremely interesting- the fish were down on the thermocline- in the “feed layer” or deep scattering layer the area I call the "peanut butter of the ocean," filled with small crustaceans and squid. From the moment we stopped on the sonar school until 6 PM we had steady bluefin action that led to what I think may be the highest single electronic tagging stop for bluefin tuna-96 archival tagged bluefin (all with one tagging station!). In addition, we filled up the slammer with bluefin. Scientific samples were taken by Dan and Ben from a handful of bluefin to discern isotopic signatures (think "You are what you eat!") and to also determine from where the fish had come (signatures from the open sea are lower in numerical value than in the productive California Current).
I was a bit surprised to see Captain Bruce, Randy and Tommy admiring an albacore as if they had not seen one in a while. This was the first albacore of the season – remarkable given it happened the third week in August. I thought the albacore were quite skinny - suggesting they had come from offshore. History was made here today aboard the Shogun-by the end of the day, we had collected all the bluefin required for the TRCC this year, tagged 103 tunas and released another 50 more. All in all, we could have tagged 200 bluefin today! Too bad we did not have more conventional and electronic tags! The fish were very young, potentially new arriving fish on the west coast. From prior tagging we know that this year class will be retentive to the California current and provide super fishing on a 30lb 3rd year fish next season so let’s hope their survival will lead to more knowledge and great fishing!
-Dr. Barbara Block
Wednesday, August 10, 2011
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.