Weedlines: A Sargassum Research Blog

PS-18-07 Daily Log

July 13, 2018 (Day 5)*

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

Happy Friday the 13th from the Gulf of Mexico! More good luck for us during our Sargassum cruise; read below to catch up on all the action.


A majority of our day is spent rinsing through the sargassum at this table to ensure we get all the vertebrates, invertebrates, and any unique items, biological and manmade. (Photo: Carla Culpepper)

Well, we’ve come full circle in our sampling ops so far–literally. We’ve had success locating Sargassum  around the edges of the recently formed eddy that is separated from the Loop Current, and today was no exception. We cruised around a bit this morning looking for Sargassum, and in the process spotted a few whales in the distance (always a treat). Being relatively free of Sargassum for a change, we decided to start the day with an open water station, which went very smoothly (neuston net tow, CTD cast, and water sample collection). We then continued our search for Sargassum, and picked up quite a convoy of (Pantropical Spotted) dolphins along the way, until we arrived at a location with numerous large Sargassum  mats!


A Great Barracuda seen exploring the Sargassum   mats and underneath the boat for a majority of the afternoon (Photo: Carla Culpepper)

Again, our sampling went smoothly. We collected a large amount of Sargassum, which included several small juvenile Tripletails and Sergeant Majors, among other species. The camera rig survey, CTD cast, and water collection proceeded without a hitch. Once again our Sabiki fishing was an adventure; many juvenile Amberjack (Seriola spp.) were collected, as well as a few Bluerunners. No large Mahi Mahi to contend with this time, but there was a very menacing Great Barracuda patrolling the weedlines, as well as several larger tunas/mackerels (we couldn’t see them well enough for an identification).

small boat

Small boat ops discussing with the vessel the best techniques to deploy the plankton purse seine. (Photo: Valeria Nunez)

Afterwards we spent some time with the ROV again and conducted a second video survey using this method. Lastly, we spent the last daylight hour practicing the deployment/retrieval of our plankton purse seine, a gear we’ve yet to use so far during the cruise. We have some kinks to work out here, but we hope to use it before the cruise is over.




Purse seine

The science team and crew watch as small boat ops practices deploying the purse seine. (Photo: Captain Nicholas Allen)

Having circled around the eddy, we’ve decided to head to a new region in the hopes of collecting Sargassum  and associated fishes under different environmental conditions. So we’ve set a course towards the birdsfoot where the Mississippi River enters to the Gulf of Mexico. There are usually strong “tide lines” here, which are density fronts formed where the freshwater from the river meets the sea. So stay tuned to see how it goes!


The top map (from NOAA AOML) shows the geostrophic currents in the Gulf of Mexico for July 13, 2018. The small arrows show current directions, and the background colors denote the dynamic height (in cm). Note the large, clockwise eddy that has recently separated from the Loop Current. This is the feature we’ve been sampling so far during this cruise, as indicted in the bottom map (orange dots are Sargassum  stations; blue dots are open water stations).

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