Weedlines: A Sargassum Blog

PS-19-05 Daily Log

May 28, 2019 (Day 1)*

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

Welcome back to Weedlines, our daily cruise blog that documents our Sargassum research activities aboard theR/V Point Sur. This will be the last cruise for our NOAA RESTORE Sargassum Project, so we hope to make the best of our time at sea. We’re glad you’re joining us for the ride, and we would like to remind you that we also post updates on the @larvalfishlabTwitter account, so follow us there as well!

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The sargassum collected with the neuston net to be sorted by the science team. (Photo: Sandra Huynh)

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The R/V Point Sur as the sun sets over the Port of Gulfport (Photo: Carla Culpepper)

As a reminder, the overall goals of our project are to understand the nursery role function of Sargassum habitats for the juvenile stages of numerous managed fish species, and use this information along with remote sensing estimates of Sargassum biomass to develop habitat indices for species and ecosystem assessments. Among the many commercially and recreationally important fish species we encounter are Grey Triggerfish, Tripletail, Greater Amberjack, Lesser Amberjack, and Mahi Mahi. In addition, juvenile sea turtles are often associated with floating Sargassum mats, so although sea turtles are beyond the scope of this project, the utility of our habitat indices extends beyond fishes. These are just a few of the reasons why we are so excited about this work!

Now on to today’s news.

We left the Port of Gulfport shortly after midnight. Remote sensing observations and first-hand reports indicated that Sargassum is plentiful in the northern Gulf right now, which is great news. The not so great news is that the sea conditions are not optimal. Forecasts across much of the northern Gulf call for 3-5 or 4-6 foot seas during the early part of this week, along with wind speeds ranging from 10-20 knots. For a vessel the size of the R/V Point Sur, these conditions are not a problem. However it is hard to effectively sample Sargassum habitats in these conditions. First, even moderately rough seas can break apart Sargassum weedlines and mats into smaller, scattered clumps, which are more difficult to collect with our plankton nets. Also, it is hard to visually locate Sargassum on the horizon as weedlines dip into wave troughs. Lastly, sample collection is made more difficult in moderate-to-rough seas; the neuston net comes out of the water in the wave troughs, reflectance measures are hampered by turbulent conditions, and in general it is more difficult for the vessel to maintain a position near weedlines and mats for operations like hook-and-line fishing and CTD casts. So not only do we have to consider where to Sargassum is today, we also needed to determine if we could collect samples in the first place.

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Caitlin Slife gives a thumbs up so she completes her water collection. (Photo: Sandra Huynh)

This sampling compromise sent us to relatively shallow waters (<100 m depth) approximately 60 miles or so south of Dauphin Island, Alabama. After searching all morning in ‘bumpy’ seas (3 feet or so), we located an area with numerous weedlines shortly before lunch. Everyone jumped into action and the sampling began! We made our CTD cast adjacent to the weedline to collect temperature and salinity data, as well as water samples for analyses of nutrients. We then towed our neuston net through a Sargassum mat to collect algae and juvenile fishes. Much of the Sargassum appeared ‘healthy’, but unfortunately we did not collect many fishes. We did net a few amberjack and other carangid juveniles, a tripletail, and an early juvenile mahi mahi. We’re not sure why there were so few fish this time. Maybe it had something to do with the several small sharks that schooled around us all day (?). Or perhaps it was due to the relatively low salinity in this area (around 28 ppt). In any event, it took us a while to rinse and pick our way through the entire sample, and before we knew it we had to move on to our open water sampling station. We repeated our sampling ops here, collecting many larval fishes in the neuston net (including mahi mahi).

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A tripletail collected with the neuston net (Photo: Sandra Huynh)

Given the rough start, the day was an overall success. We did not collect everything we wanted, but we made the best of a less than ideal situation, and got quite a bit done. For tomorrow (Day 2), our plan is to hang around the eastern Gulf, as the seas here have calmed and the forecast looks promising; as does the remote sensing images, which show high Sargassum biomass to the east of our current position.

Kudos to my science team and the crew of the Point Sur for getting this cruise off to a great start!

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The science team washing down the neuston net after an open water tow (Photo: Sandra Huynh)

 

 

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