Weedlines: A Sargassum Blog

PS-19-05 Daily Log

May 30, 2019 (Day 3)*

*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!

We had another very successful day on the water, thanks to the tremendous efforts of the science team and vessel crew. As the song goes, “the heat was hot”– it was a real scorcher on the water today, but everyone persevered. Very fortunate to have such a wonderful team and a tremendous crew on the Point Sur.

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Emily Gipson and Eric Haffey rinsing the Sargassum of any animals and plastics. (Photo: Sandra Huynh)

Today we were once again in the eastern Gulf of Mexico, approximately 90 nautical miles due south of Panama City, Florida. There was quite a bit of Sargassum in the area, however it was not consolidated into large mats as before, but rather long, then and often “patchy” weedlines. After searching around a bit, we decided to sample along one of these weedlines and a moderately sized mat of Sargassum. We were definitely in dark blue water at this site (salinity was approximately 36). This sample yielded numerous Sergeant Majors, Sargassum fish, and small filefishes, but unfortunately none of our target, commercial species of interest. One Sargassumfish from this sample was the smallest we’ve ever collected, about 1 cm in length (and a big
hit on Twitter, so thanks everyone!). After processing this sample and having a quick lunch, the optical oceanography group went out in the small boat to collect reflectance observations, and the remaining scientists on board attempted to hook-and-line sample a relatively sparse aggregation of Sargassum. Three small amberjacks were collected, and few other fishes were observed. Overall the habitat was just too spread out to be sampled effectively via hook-and-line, but we gave it our best effort.

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The science team was very excited about spotting a Manta Ray swimming around the boat! (Photo: Sandra Huynh)

Sampling at today’s Sargassum station attracted several more visitors to the R/V Point Sur. A pair of Atlantic Pantropical Spotted Dolphins were observed swimming along a weedline, and a whale spout was observed in the distance. A pair of cattle egrets, obviously lost, circled the vessel and finally landed for a rest. And then there was the Manta Ray! It swam along the starboard side of the vessel for a few minutes, nearly surface once or twice. We did our best to get pictures but she/he was a bit shy. Still, that was a first for most of us, so we were quite happy about the visit.

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A couple of cattle egrets took a rest on the vessel for a bit in the afternoon. (Photo: Sandra Huynh)

After wrapping up our sampling ops at the Sargassumstation, we moved to an ‘open water’ location, which was really ‘mostly open water’, as there were many small, fragmented clumps of Sargassum scattered about. We did our best to avoid Sargassum, but finding a true open water site was not going to happen today; we were simply surrounded. The standard ops proceeded well, including our CTD cast, water sample collection, and neuston net tow. We also completed two ‘deuston’ net tows as well; all net tows were relatively thick with Trichodesmium (also called ‘sea sawdust’), which is a cyanobacteria common in offshore, oceanic waters in subtropical and tropical areas. So we could see larval fish eyeballs in the samples, but we really won’t know what we have in these samples until they are sorted back in the laboratory.

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The science team recovering the methot net (Photo: Sandra Huynh)

Having wrapped up our primary sampling ops, we decided to deploy the Methot frame trawl after dinner. This is our largest net sampler (5-square meter aluminum frame with a 3.1-mm knotless mesh net) that is towed at a relatively fast speed (4 knots) compared to other larval and juvenile fish samplers. Theoretically, the frame trawl is used to collect the more evasive juvenile fishes in the open water habitats that are too fast to be collected in our smaller plankton nets. For us, however, it has not sampled juvenile fish very well, and tonight was no exception. However, in spite of its relatively large mesh

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The science team determine the identity of the larval fish with the help of a microscope (Photo: Sandra Huynh)

size, the frame trawl often collects the coolest fish larvae and invertebrates. Tonight we collected an incredible assortment of larval fish specimens, including barracudinas, groupers, flounders, eels, and lanternfishes, among others. We also collected several pyrosomes, salps, pteropods, and heteropods. What a way to end a great day on the water.

 

Overnight the plan is to steam towards the west and hopefully reach the northern edge of the Loop Current. So be sure to check out tomorrow’s blog post, and thanks for following.

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Dr. Frank Hernandez and co-investigator, Glenn Zapfe, work together to identify some of the organisms caught in the methot net. (Photo: Sandra Huynh) 

 

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