Weedlines: A Sargassum Research Blog

PS-18-07 Daily Log

July 10, 2018 (Day 2)*

*Note:these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

After a great first day at sea, we were excited to do it all over again. We drifted overnight along with the Sargassum, and after breakfast (waffles!) and cup (or two or three) of coffee, we got to it!

Sabiki

The science team and the vessel crew enjoy watching as the designated anglers use sabiki rigs to catch juvenile Sargassum associated fish. (Photo: Carla Culpepper)

Our intent today was to collect 2-3 small-volume neuston tows, in order to examine sampling variability within a single Sargassumfeature. However, we were a little overzealous and grabbed quite a bit of Sargassumon the first tow (oops). So we spent much of the morning processing that first sample. Again, relatively few fish, especially compared to last summer. The scientist in us always wants more fish, but understanding variability in Sargassum biomass, distribution and fish associations is a big part of this project, so these data will be very helpful in our assessment of these parameters.

After lunch, we set out the camera rigs to record under the Sargassumcanopy, and conducted hook-and-line sampling, which yielded a few juvenile Hardtails (Bluerunners) and Amberjack (Seriola sp.). One of the Amberjacks was host to a pair of parasitic isopods which were attached to its tongue (!), which is very cool or very gross, depending on your point of view. We’re not sure which species of isopod these were, but we know that some isopods actually feed on the tongue until it falls off (by depriving it of blood flow), then functionally replace the tongue by attaching itself to the bottom of the fish’s mouth. Again, very cool!

IMG_7719-2

Pair of parasitic isopods in the mouth of an Amberjack caught with the sabiki hook and line rigs. (Photo: Angie Hoover) 

We had enough time to conducted a second neuston tow, after which we steamed a kilometer or so away from this area to an ‘open water’ (free of Sargassum) station for a CTD cast, water collection, and more net tows. Our large open water net sampler (Methot Frame Trawl) unfortunately did not collect the desired juvenile fishes, but did collect a number of larval fishes, including eel leptocephali, tunas, and barracudas. The ‘open water’ neuston followed, but during the tow we encountered stray clumps of Sargassum, so the sample was a bit of a mixed bag.

Our plan was to then head back to the large Sargassummats for a last round of sampling with the light-traps after dinner. But, we were not able to locate them again (?!). Finding ourselves in relatively open water again, we decided to do a night tow with the large frame trawl. Again, we encountered stray clumps of Sargassum, quite a few large jellyfish (Aurelia), and lots of cool larval fishes and invertebrates, including many eel leptocephali, an Angelfish (Pomacanthidae), a Pearlfish (Carapidae), and many more.

Barracuda.jpg

Barracuda larvae caught in open water neuston net (Photo: Frank Hernandez) 

After processing this last sample, we set a course further south for the edge of the Loop Current, where our remote sensing team has identified likely areas of high Sargassumbiomass. We hope for another successful day!

Tuna

Pair of tuna larvae caught in the open water neuston net (Photo: Frank Hernandez)

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