Last week, I wrote about National Geographic’s Expedition Great White. In that post, I mentioned that the practice of removing great white sharks from the water for research was controversial, and that I would ask the lead scientist in the show about it. Here are answers to my questions from Dr. Michael Domeier and his colleague Nicole Lucas. They also wanted me to point out that their website has an FAQ page about this technique, which can be found here.
WhySharksMatter (WSM): Many people are concerned that pulling such a large animal out of the water can be dangerous for that animal. Should we be concerned?
Michael Domeier/Nicole Lucas (MD/NL): We know that whales can sometimes incur internal injury when they get stranded on the beach, so this issue was a concern. Fortunately sharks are much smaller than whales, and we started out by testing our methods on relatively small sharks. Our early success allowed us to slowly start working on larger and larger sharks and likewise found that they go through the tagging process without serious injury. We could run into problems if we captured a female with a late-term pregnancy, but we target females at sites and times when they are not pregnant.
WSM: Is it possible to get the data you obtained via pulling the shark out of the water using different methods?
MD/NL: Unfortunately no. We have been using pop-up tags for over 10 years and have exhausted what we can learn from these methods. The location data is not precise and they only give 9 months of data. Using acoustic tagging only gives you information where you have a receiver so that can’t give us the answers to the questions we are asking either. We are looking at large scale long term movement patterns so this technology is ideal. This is especially important for tracking the mating and birthing areas for the females which have a 2-3 year migration cycle.
WSM: Is that data important?
MD/NL: The more we know about these sharks that more we can protect them, and there is still much that we don’t know. This is especially important since they cross international boundaries and we are dealing with mating areas, pupping areas and nursery grounds. These are particularly sensitive areas that need to be protected.
WSM: Have any great white sharks been harmed using this method?
MD/NL: We had an incident in the Farallon Islands where a hook was lodged in the back of the mouth and was difficult to extract. For obvious reasons, you can’t simply reach down into the mouth of an adult white shark and work the hook out. In this case we had to go in through a gill slit and cut the hook in half with bolt cutters. We couldn’t reach the rest of the hook, but after cutting it, it should have easily fallen out so that it could be expelled from the mouth. This particular shark made its normal migration pattern to the middle of the Pacific Ocean, to the SOFA, and 8 months later we are still getting regular messages from this shark, so we know for a fact that it is alive and well. We have now modified our fishing methods for water with very poor visibility so that this can’t happen again. In short, we fish the bait right at the surface so the shark must turn away as soon as it takes the bait, immediately setting the hook in the mouth or pulling it free.
WSM: Even if the animals swim away safely, sublethal effects are a possibility. Since we know so little about these animal’s behavior, is there any way that we could detect those sublethal effects if they were occurring?
MD/NL: As with any tagging study there will be short term sublethal effects. The shark will have undergone stress from which it must recover. Our tags do not allow us to determine the length of the recovery period, but it is likely a matter of hours, a few days at the most. From our popup tagging studies we know for a fact that all of our SPOT tagged sharks are following there normal, seasonal migratory patterns. One interesting anecdote, we once caught the same shark twice in a matter of hours; that should provide some indication of the minimal effect we are having on the shark.
WSM: The show continually mentions that as long as the sharks are back in the water within 20 minutes, they’ll be fine. Where did that number come from?
MD/NL: We don’t write the script for the program and I’m not sure how or why that number is do deeply ingrained in the story telling. I think, perhaps, it is because I had known that white sharks had been restrained for that long previous to our work and the animal survived. Twenty minutes is an arbitrary number; our goal is to get the shark back in the water ASAP, and that is usually in much less time than 20 minutes.