Brendan Talwar

A crowdfunded ecology project byBrendan Talwar

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Field Update #3: Survivors

Lab Note #10
Sep 21, 2014

Hey everyone,

We've had a great few weeks. Some Cuban dogfish have survived in the cage, and show signs of recovery within the first few hours post-capture. Most of these are large females and we're hopeful that we can continue catching individuals in high numbers over the coming weeks to boost our sample size across a range of capture depths and temperatures. While only a few have swum out on their own, we've been able to release the rest at the surface in good condition. We're hopeful that those animals make it back to the bottom safely. 

We've actually seen some interesting behavior from predators outside the cage at depth. Most recently, a large grouper (not sure on the species quite yet) patrolled around the cage for around 6 hours, even going nose to nose with one of our caged animals. If the cage wasn't there, chances are pretty good the dogfish would've made a quick meal for the ~1.5m long grouper. This raises one of the primary criticisms of using caging to assess post-release survivorship, as we are effectively eliminating predation from the equation. Over the 30+ minutes it takes to swim back to the bottom, these dogfish are potentially easy targets for large tiger sharks and bluntnose sixgill sharks cruising around below 200m. We're brainstorming about ways to look at survival rates during the first 30 minutes or so post-release in the absence of a cage to get a handle on how many make it back to the bottom without getting eaten. Hopefully we can start quantifying this side of things in the next few weeks. 

For now, we're in the middle of field work and just need more data points. Now that Island School research class has started, we should be getting in 2-3 longline sets a week, with students contributing to field work on two of those trips. Our team has been having a great time and the kids are all really excited about the work, especially as they read and learn more about fisheries bycatch and deep sea sharks. 

As always, please let me know if you have any questions or are interested in hearing more! Have a great week. 

Cheers,

Brendan

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