Weedlines: A Sargassum Blog

PS-19-05 Daily Log

May 31, 2019 (Day 4)*

*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!

Overnight we steamed from our previous location towards the west to an area roughly 140 nautical miles south-southeast of Pensacola, Florida. As we woke up on Day 4 we found ourselves in an area with quite a bit of scattered Sargassum clumps and mats. The only question was which features to sample, so again, we’ve had great luck in locating Sargassum during this cruise. Seas were very calm, less than 1-foot in wave height, and slight winds. All of this pointed to perfect conditions for sampling. We also knew it was

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A sea turtle with larval jacks in tow (Photo: Sandra Huynh)

going to be another very hot day on the water. While scanning the horizon and choosing potential Sargassum mats to sample, we were greeted by a large loggerhead sea turtle that arrived with its own entourage of juvenile fishes swimming under and behind it. It the open ocean, you get flotsam wherever you can, and these juvenile jacks seemed content to follow the turtle, even in the presence of ample Sargassum. After checking us out for few minutes and finding us relatively uninteresting, the loggerhead swam off with her/his minions trailing behind. Out of an abundance of caution, we turned and idled away in the opposite direction to choose a Sargassum feature to sample and minimize any further potential interactions.

 

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Graduate student, Courtney Stachowiak, collects abiotic data from the ship’s many data acquisition systems. 

After we collected water samples and our CTD profile, we deployed our neuston net and sampled along a line of small-medium Sargassum patches. We successfully collected several juvenile Grey Triggerfishes (yeah!), as well as more Sargassumfish and small jacks. After processing the neuston sample, the small boat team departed to collect reflectance observations and the remaining members of the science team completed a Sabiki rig hook-and-line sampling set. Numerous adult mahi mahi were cruising the weedlines, so we had to reel the fish in quickly to land them. Again, we collected over 30 juvenile amberjacks  (species to be determined), but no other species. We decided to opportunistically sample by continuing to fish our Sabiki rigs, but this time with little bits of squid on the hooks. In doing so, we attracted and collected several Rough Triggerfish that we would not have collected otherwise. We may go back to this technique later, if needed.

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Juvenile Almaco and Lesser Amber Jacks caught with sabiki rigs. (Photo: Sandra Huynh)

After lunch we processed the hook-and-line fishes, and collected more algal reflectance observations on the small boat before we steamed away to locate ‘open’ water, which like yesterday, was just not going to happen. We were really surrounded by Sargassum, so we did the best we could to collect water samples and a neuston net sample while avoiding clumps of Sargassum. All sampling ops went well, although we caught relatively few fish larvae in both the neuston and ‘deuceton’ net samples. There was lots of Trichodesmiumin this area as well, which can really clog nets and decrease filtering efficiency; this may partially explain the low larval numbers. In any event, we hope to find a ‘real’ open water station or two before the cruise ends, in part because we tend to find lots of cool billfish larvae in those areas (so stay tuned for that!).

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A cephalopod paralarvae (Photo: Carla Culpepper)

Having completed all of our scheduled ops for the day, we gathered on deck after dinner to deploy the frame trawl again. And once again we were not disappointed! Among the many cool fish larval stages we collected were barracudina, cardinalfish, snake mackerel, eels, mahi mahi, and remora. And for inverts, a small pelagic octopus was a highlight, as well as several Ceratapsis montrosa, a relatively rare (and purple!) mysis stage of the deep pelagic shrimp Plesiopenaeus armatus. Although the larval stage Ceratapsis are relatively small, they have been found in the diets of large pelagic fishes, such as yellowfin, bluefin, and blackfin tuna!

Tomorrow we will likely continue to the south and west to search for Sargassum (and open water) habitats in the Loop Current.

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A small Barracudina caught in the methot net. (Photo: Sandra Huynh)

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