Field Update #2: Progress
It has been about three weeks since my last update and we've made a lot of progress. The cage is working beautifully and we are continually making adjustments so that field work goes smoothly and safely. It is really amazing how the tiniest things can make a huge difference... My watch, for example, has a tendency to stray from my computer time, which the lights are synced to each day. Keep in mind that even a second off between the video camera and lights will set their cycles on different paths that drift further and further apart over time. I noticed them doing just that with each drop and thankfully caught the problem a few days ago. Each time we leave the dock, we solve little problems like this and get one step closer to our goal.
So far, most of our animals have been either dead at the boat or dead once the cage reaches the bottom. All of these individuals have been small Cuban dogfish, making us think that size could be a factor in the post-release mortality and/or post-release behavior of these sharks.
On the right, you can see a Cuban dogfish being scavenged by deep sea isopods. On the left, another shark can be seen swimming around... the strange thing is that we didn't put that shark in the cage. For a size comparison, the one on the right is about 50 cm, making the second one around 20 cm. We think that it swam in through the mesh and got a bit disoriented before swimming right back out.
Support for our idea that size influences mortality came just two days ago when we hooked a 69 cm female, the largest individual to date, and lowered it to the sea floor for around 1.5 hours. Unfortunately, shortly after dropping the cage, we received word that boats would likely be grounded the following day due to rough weather. To be on the safe side, we turned around at the dock and ran out to Exuma Sound to pick up the gear in advance. The shark was still alive when we opened the cage door, leading me to believe that it had a good chance of recovering from capture had we left it on the bottom for the target 24 hours. Instead, we released it early and it sank back into the depths in good condition. This valuable bit of data, while still incomplete, is a promising step forward. I am hoping that this week will yield video of a live shark swimming around the cage and, ultimately, out the door.
On top of the Cuban dogfish, we recently caught an immature male bluntnose sixgill (Hexanchus griseus) - a great introduction for the new team of shark interns on their first day out. Here is a screenshot courtesy of Cam Raguse (aka Crab Rangoon), who hopped in for the release. You'll notice that this one was a little too big for the cage...
Hope you are all doing well, and please shoot me an email if you have any questions or ideas!