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Salty days, windy nights

Field season in the Keys officially started this year on June 11th. This year I brought with me two interns who are part of the Certificate Program in Marine Biology at FSU. They will be helping me with my research and will also do a research project of their own.

The first day in the field I like to go out to the reef and do a training dive at Sombrero Key. This way we can all get familiar with the boat, the gear, and diving without worrying about data just yet. This year the visibility was fantastic and the interns passed their check-outs with flying colors!

After the reef intro dive, it’s time to go check out grouper holes in the bay. To date I have information on 60 different solution holes that have at some point been home to a juvenile red grouper. Not all of these holes are occupied in a given year, but one thing I’m interested in is tracking these holes over time to see, in a given year, which holes are occupied?

So far this year occupancy by red grouper is right about 50%, which is right about what it has been the past two summers. The next step for my research is to randomly select a subset of occupied holes from which I will remove the red grouper. Removals are done using hook and line, and once caught the fish will be relocated to an empty hole miles away. After removal I return to the hole every few days to make sure no new grouper has moved in and also to record any changes in the number and identity of the fishes and invertebrates that also live in the holes.

However, I can’t get out and work unless it is relatively calm out. When it is calm, as in the picture above, the bay is beautiful! Too bad it hasn’t looked like this for a while now, thanks to Tropical Storm Debby now churning up the northern Gulf of Mexico. But the forecast starts to look good in a couple of days, so stay tuned for more updates on red grouper, solution holes, and doing research in the Florida Keys!

How to sample very large fish

I spent most of the month of May traveling around Florida training  fishing charter captains how to collect biological samples of goliath grouper (formerly known as jewfish). These trips were phase one of a 3-year grant that our lab was awarded to collect age structure information about the goliath grouper population in Florida. Since 1990 when a moratorium was placed on all goliath grouper landings, the population has since increased and goliath grouper are now a common sight at reefs and wrecks along the Florida coastline. Just how much the population has rebounded remains in question and information about the age-structure of the population (How many young fish are there? How many adults?) is critical to determining just how much the population has increased and what kinds of management decisions must be made to prevent another near extinction.

The typical way to age a fish is to use the otolith, or ear bone, that most fish grow inside their heads. Used for maintaining balance when the fish is alive, once removed the otolith can be used to determine how old the fish was. Otoliths grow in spurts, just like fish do, that roughly correspond to the seasons, and so the otolith grows ring by ring, much like a tree. Obviously, counting otolith rings requires killing the animal, something we would like to avoid doing to an endangered species. Instead we use the rays of the dorsal fin which also grow rings like a tree. The rays are embedded in resin, cut into thin sections, and then the rings are counted under a microscope.

In the past few years our lab has caught and sampled about 250 fish, but at least 1000 are needed to reliably estimate the population. This is where the charter captains come in. Once trained by us, they will be able to land and sample goliath grouper if they happen to catch one during a charter. We get the samples and the customers get a rare, up-close experience with a huge fish!

Check out the lab’s website for more info. And here is a video detailing the complete sampling protocol. Spoiler alert: big fish and biologists below!