To wrap up Shark week, we will continue the story of our Pacific sleeper shark research project. Now where did we leave off…?
“It’s a shark!”
Everyone clambered to the side of the boat to lean over and get a look. Sure enough, on our last hook of the day was a huge shark! Days of fishing had finally paid off!
After a round of high-fives, we settled down and got to work—there was science to be done! The first thing we needed to determine was if this shark was a good candidate for our primary study. Jared carefully maneuvered the animal to the side of the boat and opened the side doors so we could get a closer look and an estimate of total length.
The plan for the Pacific sleeper shark project is to bring up to five young sharks into the ASLC for short periods (one at a time) for select studies on their metabolic rates and on thermal-, feeding- and functional biology. We will then release them again with telemetry tags to monitor their movements back in the Bay. The Alaska SeaLife Center has previously led similar projects that aimed to keep wild animals in temporary captivity—under our expert husbandry and veterinary care—while controlled studies are conducted. From our work on juvenile Steller sea lions, there was no evidence that this period of temporary captivity reduced survival and animals exhibited normal diving behaviors after release—suggesting this can be a great way to answer questions that would be nearly impossible to study in the wild without controlled access.
In our case, the ‘young sharks’ we were looking to bring back to the center would be in the 1.6 to 2m range (or approximately 4 to 6ft).
Holding up the measuring tape, Dr. Horning called out: “Nose to tip of the tail is about 2.8m—just over 9ft long!”
This meant that our shark—an immature female—was too big to bring back to the ASLC, but there was still a lot we could learn from her! We knew there was a good chance we’d catch sharks that were too big or too small for our primary study, so we’d set up a protocol for what information we’d gather in these “catch and release” cases.
Since this was the first Pacific sleeper shark anyone on our team had seen alive, we all took a moment to make some general observations. The shark in general was not thrashing around like some species do at the surface, but instead was just slowly rolling. This meant we could handle the animal with minimal maneuvering—which improved the safety of the shark as well as our research team. As it moved its head, we noticed that one of its eyes had a parasite growing out of it. This parasite—a copepod called “Ommatokoita elongata”—is common on both Greenland and Pacific sleeper sharks.
Typically only one copepod is found per eye. This image is from a Greenland shark–we didn’t get a great picture from our shark due to the rocking and rolling. Credit: Louise Murray
We also noticed that there were rows of circular ‘scars’ along the animals’ head. Upon further inspection, it looked like sucker-marks from the arms of an octopus or squid! Perhaps our shark had recently had a cephalopod snack?
Measurements—life in the slow grow lane
One of the most fascinating things about sleeper sharks is that evidence from their close relatives, the Greenland shark, suggests these animals grow very, very slowly—at a rate of only 1cm per year—and may in fact be the longest lived vertebrates on our planet! By testing the radiocarbon in the eye lens of sharks, the Greenland shark team found that the oldest animal they tested, measuring in at just over 5m long, was most likely somewhere between 270 and 512 years old! In fact, their samples suggested that these sharks weren’t even sexually mature until the age of around 150 years!
To help scientists with NOAA Fisheries better understand how the Pacific sleeper shark grows and matures, we took measurements of the sharks’ length, girth, fin size, and various other measurements like distance from eye to snout and mouth width. These measurements will contribute to a data set to eventually estimate age of Pacific sleeper sharks without requiring invasive samples or dead specimens.
There is also much we don’t know about the general health of these animals. Their health is important to understand so we can properly maintain these animals in captivity, and begin to assess and mitigate the possible effects of manipulations, transport, and temporary captivity. If we are hoping to utilize these very animals to study their behavior and ecology back in the wild after their release, then we need to consider whether we may be affecting the very data we want to collect through our interactions.
So, just like you might have your blood drawn at the doctor’s office to see how your overall health is doing, we also took a blood sample to look at some basic veterinary parameters for Pacific sleeper sharks. We are lucky to have Sarah on our team, a veterinarian technician who has previous experience working with sharks at Shedd Aquarium in Chicago. Even with the boat moving up and down in the swell, and her fingers immersed in the icy waters of Resurrection Bay, Sarah managed to get a blood sample quickly and safely from the animal.
The last step of our process was to attach a satellite tag to the shark. This step is important for a number of reasons. As part of our effort to assess whether our handling and research has any negative impact on the animals we are working with, we want to compare any data on movement and behavior immediately after release, to subsequent periods. In the future, we will also be able to compare animals that were only caught and released, to those that spent some time in residence at the ‘ASLC shark hotel’. If we caught the shark, brought her to the surface, did all our measurements and then just let her go, we would have no way of determining if she was okay. The satellite tag gives us the ability to monitor her behavior and survival post-release.
In addition to monitoring for any effects of our research, satellite tags like the one we used provide amazing information about what these animals are up to living 400-1,000ft below the surface. The miniPAT tag we selected was made by Wildlife Computers Inc. in Redmond, WA. miniPATs have sensors that tell us the diving patterns of the shark, the light levels it encounters, and the temperatures of the water around it. From the surface of the ocean, these tags transmit their data to orbiting satellite using the Argos system that is the mainstay of global wildlife telemetry, especially in marine environments.
Sleeper sharks rarely come to the surface, if at all. Thus, unlike the tags we use on seals and sea lions, these tags can’t transmit their data while attached to the animal. Instead, we can program the tag to detach itself after a set amount of time (in this case we programmed it for 180 days) at which time it floats to the surface and will transmit its data to the satellites. The tags also are programmed to detach early if the animal dies, or if the animal dives deeper than the tag can safely go without being compromised by pressure.
Farewell for now!
So with her tag in place and the datasheet filled out, we slipped the hook out of the shark’s jaw and let her go. Having worked primarily with pinnipeds, I expected her to high-tail it out of there. But like everything with Pacific sleeper sharks, she was in no hurry–slowly rolling away from the boat and disappearing down out of sight with a few lazy flicks of her tail. Buzzing with the excitement of the day we headed home, not expecting to hear back from this shark for another 180 days…
Written By: Amy Bishop and Markus Horning