PS-19-05 Daily Log
June 1, 2019 (Day 5)*
*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.
We hope you enjoyed yesterday’s blog entry. Remember we also post throughout the day on the @larvalfishlabTwitter account, so follow us there as well!
Wow, today we found the Mother of all Sargassum mats approximately 240 nautical miles south-southeast of Pensacola, Florida. Unfortunately we did not have a small drone or other means of accurately estimating its size, but it was the largest we’ve seen to date in our project. It was located in a region where the Loop Current is essentially running in to itself, and perhaps on the verge of pinching off an eddy (though the Loop Current is notoriously unpredictable). Here there are currents converging in this particular region, which makes for a high probability of Sargassum aggregation, and we were fortunate to find lots of it today.
The size of the mat was pretty daunting, and we were not sure where to start at first. We decided to drop off a camera rig along one edge of the mat to get a feel for what types of fishes were present. While the camera was recording, we motored to the other end of the mat and collected our CTD profile and water samples. Afterwards a quick scan of the
video revealed that the Sargassumwas very ‘thick’, nearly a meter deep. This reduced the visibility under the mat, creating a dark blue/black shaded environment under the canopy. High abundances of fishes were observed, but unfortunately we could not identify them due to the poor visibility. We then collected a neuston sample by towing across one of the mat edges, and collected a number of fishes, including Tripletail, filefishes, and small jacks, among others. This was one of our largest fish collections in the neuston net so far this cruise. Given the many fish we were seeing, we were excited about our hook-and-line Sabiki fishing set. And there was certainly a lot of action there, as we reeled in the amberjacks, sometimes four or five at a time! There were other fish there, including triggerfishes, but they could not beat the “AJs” to the hooks, so we did not sample them well. But overall, we had quite a successful sampling set here.
Once again finding open water was a challenge, though we managed to find gaps in the Sargassum to collect our CTD profile, water samples, and our neuston net sample. Unfortunately we did not collect many fish in the neuston net. However, the ‘deuceton’ came through with lots of larvae tonight. In fact, two deuceton tows collected over 40 billfish larvae! With the adjoining smaller net we collected common prey for billfish, including copepods and cladocerans, so we’re excited about studying their trophic ecology in this region of the Gulf.
As we’ve done the past few nights, we decided to tow the frame trawl to end our evening. Now that we were in >3,000 m water depth, we decided to send the net a bit deeper than usual, and wow, did we collect some wonderful specimens! We’ll tweet some images of these in the coming days as we sort through them, but among the highlights was a beautiful, deep ocean cusk-eel larva with a long, trailing gut (which is thought to mimic siphonophores, and therefore offer a measure of protection from predators–though that’s only a guess as to its function). We caught several very long (>150 mm) eel leptocephali, as well as lanternfishes, larval surgeonfishes, and many other species we’ve yet to identify. So stay tuned for more cool pics!
We’ve passed the midway point of our cruise, which has already been a great success by most measures. Tomorrow we will likely sample in the ‘lower’ Loop Current region again, but perhaps to the west of our current location where the Loop Current is running towards the north. Afterwards we can ride this conveyor belt towards home. But we have a few days yet, so more Sargassum collections are ahead. Thanks for following along!