Article by Capt. Mark Sampson
While shark fishing last week we had a blue shark swim up close to our boat. Obviously attracted by the scent that was leaching from our chum bucket and the fish carcasses hanging off the side of the boat, we thought the shark was destined to provide a certain catch and release for one of our clients, but despite the numerous times it swam up to and investigated each of our three hooked baits it never committed to making a meal of one. Wondering whether the shark was just curious, but not hungry, or it didn't like the way our baits were presented, I threw a hookless bait into the water to see what would happen. The shark ate it right away! When another free bait met with similar results my suspicions were confirmed that the shark was hungry, but not so much that it would eat a piece of fish that had a metal hook and wire leader attached to it.
Obviously, sharks don't always refuse to eat something with a hook attached, otherwise they would never be caught, but this one wasn't about to oblige us so I came up with a plan to outsmart the critter. Knowing that sharks use the electro-sensors located on the front of their heads to pick-up on the weak electrical current generated by their prey, and that this shark was probably using those sensors to detect the unfamiliar electrical signature of the metal hook and leader, I grabbed the leader, pulled the bait up to the surface with the hook and leader out of the water and watched as the shark immediately swam up and grabbed the bait right beside the boat.
That little episode was a classic example of not only how sharks use their senses to locate prey, but also how they might use them to detect and avoid danger. I'm not sure who first coined the phrase "ignorance is bliss", but I'm pretty sure it wasn't a fisherman, because as most anglers will probably agree, the more we know about the fish we're trying to catch - the better we'll be at doing so.
It was for that reason, about six years ago, I agreed to help a team of scientists who wanted to learn more about the movements and habits of shortfin mako sharks. Their goal was to put satellite transmitters or SPOT tags on makos and track their movements for months or even years after their release. The researchers were from NOVA Southeastern University and the University of Rhode Island. When we started in 2013, few (if any) makos had ever been tracked this way and everyone was curious to see whether or not makos would even be good candidates for the $1,800 transmitters that require the shark to come to the surface with it's fin out of the water for more than just a couple seconds in order for the satellite to receive precise location information.
In early June of 2013 we tagged the first mako with a SPOT tag and the very next morning when the scientists returned to the boat for another day of fishing they happily reported that the shark from yesterday had already reported in by "pinging" the satellite with it's location information. We were elated by the success of that first shark because it demonstrated that not only were makos good candidates for SPOT tags (by transmitting at the surface every day or two), but also that the boating and handling techniques we've developed are successful in allowing the sharks we release to survive the encounter. Since 2013 we've tagged a total of 42 makos, 6 smooth hammerheads and one common thresher shark with spot tags and have had 100% survival rate - we're pretty proud of that!
Of course, much of what has been learned from each shark has revolved around it’s travels. Whether it was north or south, inshore or offshore, where it was at different times of the year and if it returned to the same area the following year - all good stuff to know if you're trying to learn a thing or two about movements or migrations. But along with location data, the scientists have also been able to derive other valuable information from the tagged sharks that has filled some blanks in the knowledge about what goes on in their daily lives. In the months and years ahead, data from these tagged sharks will be used for various reasons, from fishery management decisions to a better understanding of the life history of the sharks, as well as the health and ecosystem of the ocean.
As a simple fisherman and not a scientist, I'm happy to give a few simple insights of what I've learned from the sharks we've tagged. First, the mako tracks are amazing! Unlike a lot of fish that travel somewhat predictable paths (north in the spring, south in the fall), makos just seem to wander around the ocean. They can be up on the Continental Shelf today and way out over the edge tomorrow. Of the first four we tagged this past May, two left our boat and headed south, one went north and one went way out to the east and then northeast. Overall, we've seen that makos spend a lot of time right along the edge of the shelf, but they never seem to stay in one area for long. We've had them cross the equator and one traveled more than halfway across the ocean.
Our smooth hammerheads, however, stayed mostly on the shelf, spending much of summer off the Delmarva and New Jersey coasts and in the cold weather months in the waters off the Carolinas. What surprised me the most was how much time they spend at the surface, so much in fact that the first ones we tagged burned out their batteries early from transmitting so much!
The thresher we tagged a few years ago in late May wasn't heard from until about 7-weeks later when it pinged twice up in the Bay Of Fundy off Nova Scotia. But that was the only time we heard from it, so it was pretty much decided that they don't swim at the surface enough to be good candidates for the expensive tags.
One somewhat sobering fact we learned from this study is that our makos were being recaptured more frequently than expected. Of those we released, over 30% were recaptured and killed by either commercial or recreational anglers. Since the transmitters continue to send a signal even when removed from the shark, it was obvious when a shark was caught because the tag would make a beeline for the coast and then transmit from land. We had them caught by commercial long-liners out of Spain, Newfoundland and Nova Scotia, and taken by recreational anglers out of Chincoteague Va. and Long Island NY. One of our makos only made it a month before being brought back to the dock by a recreational angler!
Considering the time, effort and expense of getting transmitters on these fish, it was always a heartbreaker to have a data-set cut short by a recapture. The only good thing that came from the recaptures was that they provided researchers with an increased and more accurate understanding of the kind of fishing pressure makos and other sharks face in the Atlantic, and if there is any silver lining to the new 83-inch minimum size on mako sharks, it's that there's now less of a chance that our tagged sharks will be caught and killed before providing long-term tracking data.
We started this season with seven tags programmed for makos and were blessed to be able to get all of them on sharks during our first couple weeks of fishing. As we look forward to following their movements over the next year or two, and perhaps learning new things about these incredible predators, we're also preparing to "Part II" of this year's satellite tagging which will have us attempting to put transmitters on a number of smooth hammerheads for a study on that species.
We have only played a small part in these projects, the scientists are the ones who actually design and orchestrate the studies that are providing new insights about shark biology, habits and life history. But for us, being able to assist them with some of the necessary fieldwork continues to be rewarding, educational and always exciting!
Capt. Mark Sampson is an outdoor writer and captain of the charter boat, “Fish Finder”, docked at the Ocean City Fishing Center.