ROLL WITH THE PUNCHES
August 15, 2018
If you were to consider physical appearances alone, even I would admit that there are a few shark species that could be considered “scary”. These might include the fearsome great white, the speedy mako, or the snaggletoothed sand tiger shark. Basking sharks were also historically considered terrifying sea monsters based on their size and sinuous feeding behavior alone. But, since the latter have yet to make an appearance at Malin Head this summer, I decided to temporarily change tactics and turned my attention to a different species. This was actually fairly easy, because Ireland is home to much more than the animals I came here to study. In fact, over 70 species of sharks and rays reside in Irish waters. Thus last week, I took a break from sea monster searching to chase a species that can only be classified as the opposite: the beautiful and ubiquitous blue shark.
Blue sharks (Prionace glauca) are one of the world’s most widely-ranging species of shark. Like the basking shark, they are highly migratory, but this species is slightly less selective in its choice of habitat. They can be found in offshore and pelagic (i.e. open ocean) environments in both tropical and temperate waters. In these areas, blue sharks are highly abundant, likely because they have a relatively high rate of reproduction. In general, sharks, like humans, exhibit what is known as a “K-selected” reproductive strategy. That means that these animals grow slowly, live a long time, and produce few young compared to other organisms. However, even among shark species there is significant variation in these characteristics. In fact, chondricthyans (sharks, skates, and rays) have the most diverse array of reproductive strategies of any vertebrate group (Mull et al., 2011). Whereas the basking shark might give birth every 3 years, blue sharks are significantly more productive, giving birth to an average of 30 pups after a 9- to 12-month gestation (Nakano and Stevens, 2008). Yet because of their abundance throughout the world’s oceans, blue sharks are currently a major component of bycatch by longline and gill-net fisheries and targeted heavily in the international shark fin trade (Nakano and Stevens, 2008). An estimated 20 million individuals are taken annually, though many catches are unreported (IUCN). Furthermore, due to the “K-selected” life history strategies of these organisms, it can be difficult for overfished populations to recover.
Here in Ireland, blue shark fishing tends to take on a slightly different form. Because they are fairly accessible and easy to catch, these animals have become targeted for sport. Blue sharks will arrive in Irish waters in June and remain until October, when they are taken by recreational anglers on a catch-and-release basis. In many cases, this method of fishing can actually be of great use to researchers who are attempting to examine blue shark abundance and movement patterns using fishing records and different tagging techniques. However, it remains unknown how angling affects the behavior of the sharks immediately following their release. This is the question that drove me across the entire country, from the northernmost point in Ireland to the southernmost region: County Cork.
I had met Dr. Nicholas (Nick) Payne last summer at a research symposium hosted by Dr. Jonathan Houghton’s laboratory at Queen’s University, Belfast, where I am currently a visiting researcher. Now a lecturer at Trinity College in Dublin (TCD), Nick uses biotelemetry and biologging to examine how environmental variation affects the distribution, movement, and behavior of aquatic animals, including multiple shark species. Having heard of the dearth of basking sharks up in Malin Head, Nick generously offered me the opportunity this summer to see a different shark species, one that I had never seen before. As part of a larger blue shark monitoring project down in County Cork, he and Dr. Tom Doyle of University College Cork (UCC) are working to look at the short-term behavioral response of blue sharks to catch-and-release angling. To do so, they’re using a piece of equipment known as an accelerometer. It’s essentially a FitBit for sharks. Simply put, accelerometers measure acceleration (i.e. rate of movement) in three different axes: forward and backward, side to side, and up and down. Combined with sensors that indicate the speed and direction of the animal, accelerometers can be used to distinguish different types of behavior and estimate the cost of these behaviors, energetically-speaking. For example, a shark swimming quickly and erratically throughout the water column likely expends more energy than one slowly cruising along the bottom of the ocean. In humans, this would be analogous to running over hurdles or through obstacles versus slowly walking in a straight line. The accelerometer can then produce a data “signature” of each type of behavior over time, and the speed and acceleration that these behaviors require can be used to indicate energy expenditure. A major challenge to using this equipment, however, is this: accelerometers must be fully recovered from the animal in order to download the data. That means that finding the shark and attaching the tag to its dorsal fin is barely half the battle. Indeed, as we were to find out, finding the accelerometer again is often significantly more difficult.
Fortunately, during the week that this project took place, Cork was everything Malin Head hadn’t been in terms of weather – bright and sunny, with light to moderate winds. This only highlighted the refined beauty of the area and its waters, its colorful buildings and placid harbor a stark contrast to my field site in the raw and wild Inishowen. We set out the first morning on the catamaran that was to serve as our research vessel for the trip. Our goal for the day was to catch and tag two blue sharks. In addition to Nick, Tom, and me, the boat hosted Luke Harman, an experienced fisherman and researcher at UCC, as well as Damien Haberlin and Cian Luck, a post-doctoral researcher and PhD student, respectively, at MaREI (Marine and Renewable Energy Ireland). And of course, no trip could be complete without two members of Ireland’s National Angling team. As we fished several kilometers south of Cork, I spent a large part of the first morning learning the lingo (“rubby dubby” = chum) and watching these professional fishermen with fascination. Though I’d fished a fair bit throughout my childhood, I had never seen anyone use balloons as floats. To be fair, however, I’d also never seen anyone catch a fish so quickly. By late morning, we had landed our first blue shark.
It was stunning. The colors that I had seen in photographs were somehow more brilliant in reality. These sharks are colored a deep navy on their dorsal side, which fades to stripes of turquoise and then silver above the stark white of their underside. They are also astonishingly slender, almost delicate, with massive round eyes. By late afternoon, we had captured and released five of these animals, all between 1.5-2.3 meters long (or approximately 5-8 feet). Of these, two received accelerometer packages. With such an experienced crew, the whole procedure, from first bite to release, took very little time - under 20 minutes, in some cases. Once the shark was landed on the boat, we collected genetics samples and took photographs while attaching the accelerometer firmly to the fin. For the remaining three sharks, we attached an ID tag instead. These would be useful if the shark were to be re-captured or re-sighted in the area or elsewhere within its range.
Even after the success of the first day, we knew better than to fall into complacency. The next two days would pose the bigger challenge: finding the packages floating somewhere in the middle of the ocean. They were programmed to release from the sharks at around 07:00 the morning following the initial tagging. In addition to the accelerometer, the packages were outfitted with satellite and VHF tags that would be used to relocate them. Once at the surface, the satellite tag would transmit a signal to Argo satellites orbiting overhead, which would send Nick information about the general location of the package. We would then take the boat to that location, and hone in on the package using a VHF receiver on the boat to detect the shorter-range signal of the VHF tag. Researchers often use this method to relocate different kinds of equipment at sea, and it all sounded very simple in theory. Putting theory into practice, however, was a different story.
Telemetry technology can be finicky for a variety of reasons. Most of the time, tags will function as planned. To ensure the user understands the equipment, companies will produce easy-to-read manuals and can be accessible via phone or internet for other questions. When the technology fails to work, however, deducing the exact cause can be challenging – particularly if the equipment is already on the shark. At that point, it doesn’t matter if the issue is user-related or the transmitter itself isn’t functioning properly. What does matter is that there is a back-up plan. Fortunately for me, I was with two experienced and good-humored researchers. Thus on day two, when the satellite tag had failed to produce any sort of location for us to reference and our VHF receiver decided to malfunction, Tom and Nick cheerfully led us out on the catamaran for essentially a well-informed wild goose chase. From their previous tagging experience, we knew the general direction that blue sharks tended to travel once caught, and we used information on tides and wind to establish transects that we would conduct with the boat while attempting to listen for the VHF signal on the package. It was a sound idea, but as the day wore on, the ocean seemed to expand in size. The package was no bigger than a small jewelry box, and though it was painted bright red, it became hard to imagine sighting something so small amidst even the slightest of swells. By late afternoon, we decided to turn back and hope that the satellites would soon have better luck. Just then, Nick’s phone pinged. According to Argos, the package was located 30 km south of us. It was too far to reach that evening, but weather looked promising for the next day. Of course, we were all too aware that for every hour that it wasn’t retrieved, the package could potentially float further and further away.
Our third day at sea began as the pink sun rose over the harbor. We had received no additional information about the whereabouts of the first package since the previous afternoon, and had heard nothing at all from the satellites regarding the second. But again, the crew was nothing if not resourceful and knowledgeable about the study system. Upon arrival at the first package’s last (only) known location, Luke, Tom, and Nick pointed us in the direction of the prevailing tidal flow of the previous night. As before, we would stop every few miles and listen for the VHF transmitter using an onboard receiver. Within an hour, it seemed their intuition had paid off. It’s almost humorous how much joy a faint ping can bring to an entire boatload of seasoned researchers. Still, it took nearly three hours of maneuvering the vessel toward the ever-strengthening signal to finally reach our desired destination. Just before noon, as we all stood at the bow straining our eyes against the reflection of the sun, we heard an excited shout from Tom: “There it is! There! There!” Sure enough, the package was floating by, reminiscent of a water beetle with its two antennae projecting high in the air. Without the signal, we surely would have missed it.
Just two days later, we would finally receive a satellite transmission from the second accelerometer package. It was located roughly 90 km south of Cork – three times the distance of the first tag. Interestingly, this package happened to be attached to one of the largest specimens the researchers had seen, a 2.3-meter female. Both sharks seemed to have traveled in exactly the same direction following release, a trend consistent with previous tagging efforts by Tom and Nick. Unfortunately, by this point I had returned to Buncrana, as I had planned to spend the following weekend “ringing” (or banding) storm petrels on the island of Inishtrahull. But ultimately, it seems as if everything has worked out as planned, albeit not necessarily on our allotted timeline. And, at the very least, if the basking sharks don’t show up this field season, I will have at least been fully exposed to the many types of wildlife that Ireland has to offer. Yet my week with the blue sharks had opened my eyes to more than just that. Fieldwork is challenging, as I’ve learned the hard way these past few summers. However, too few early career researchers realize that fieldwork can be challenging for anybody, regardless of whether you're an established scientist or just beginning your PhD. While it is certainly necessary to feel tremendous responsibility when dealing with telemetry equipment that costs thousands of dollars, it is also critical to recognize that there are so many parts of wildlife research that are out of our control. Study organisms do not play by any rulebook, but that is fundamentally why we study them. And while current telemetry techniques are far from perfect, they also have the potential to yield tremendous insight into entire hidden ecosystems. If we want to continue to love what we do, to reach the top of our field as researchers, and to generate ground-breaking science, there is really only one thing to do: stay positive and roll with the punches.
Special thanks to Dr. Nick Payne and Dr. Tom Doyle for providing me with this opportunity. I look forward to seeing the results!
Mull, C. G., Yopak, K. E., & Dulvy, N. K. (2011). Does more maternal investment mean a larger brain? Evolutionary relationships between reproductive mode and brain size in chondrichthyans. Marine and Freshwater Research, 62(6), 567-575.
Nakano, H., & Stevens, J. D. (2008). The biology and ecology of the blue shark, Prionace glauca. Sharks of the open ocean: Biology, fisheries and conservation, 1, 140-151.