Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 3, 2018 (Day 5)*

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

After cruising north overnight we arrived at a location southwest of the birdsfoot  where we found Sargassum and environmental conditions to be very different from the Loop Current region. Here is a short synopsis of some of the day’s activities.

blue green.jpg

Sargassum is often found in the convergence zone, or tideline, of “blue” and “green” water. (Photo: Carla Culpepper) 

Overnight we steamed towards the north from our previous location within the Loop Current, and by morning, we quickly located a “tide line” (at approximately 26° 24′, 87° 50′) that extended for miles in a roughly east-west direction. Visually, we could easily distinguish the convergence of two water masses, with “green” water to the north of the weedline, and “blue” water to the south. This was further verified with the vessel’s flow-through system and thermosalinograph; we measured higher salinity and cooler temperature on the blue side, and lower salinity and warmer temperature on the green side. These conditions were similar to what we experienced last year in roughly the same area, but notably different than the past few days in the very “blue” Loop Current waters.

It was windy this morning, sea conditions were a bit rougher, and the currents associated with the convergence line made it difficult to navigate near the weedline without running it over. As such, the neuston net tow was less than ideal, as only half of the net was towed through the Sargassum line. Whereas the Sargassum collected in the Loop Current was more golden in color, “fresh” and free of biofouling, today’s Sargassum seemed “older”, with some senescence observed, as well as considerably more biofouling. Still, we got fish today, including a few Bermuda Chubs, Sergeant Majors, and Sargassumfish, as well as many Sargassum shrimps and crabs.

Lesser amber jack

A Lesser Amberjack collected during the small-hook Sabiki rig sampling effort. (Photo: Brian Jones) 

We collected water samples and reflectance data from both the green and blue sides of the convergence, then positioned ourselves for hook-and-line fishing with the small-hook Sabiki rigs. Within a few minutes, a small sea turtle (carapace length approximately 8-10 inches) appeared on the outskirts of the weedline. In an abundance of caution, we immediately reeled in all lines and allowed the vessel to drift away from the Sargassum. Once we were a safe distance away, we cruised further down the weedline and started a new fishing set there. Here we caught numerous juvenile Blue Runners (Hardtails), Greater Amberjacks and Lesser Amberjacks.

turtle

A juvenile Green sea turtle spotted near a Sargassum feature. (Photo: Brian Jones) 

A second juvenile sea turtle, roughly the same size, was spotted several hours later while the vessel drifted along the Sargassum while we were collecting additional reflectance measurements. As no gear were over the side, we maintained our drift for a few moments as the turtle continued to swim down the weedline.

After working the weedline, we cruised south to find “open” water, i.e., water free of Sargassum–which is turning out to be a very difficult thing! We moved 1-2 miles away from the weedline and still collected a few handfuls of Sargassum in the cod end of the neuston net. Similarly our frame trawl sample contained a small amount of Sargassum. It is likely that the windy conditions in the morning broke down some of the larger Sargassum patches, resulting in a “halo” of scattered Sargassum bits covering a wide area around the weedline.

processing.jpg

Glenn Zapfe, Eric Haffey, Olivia Lestrade, and Valeria Nunez enjoy a few laughs while rinsing Sargassum. (Photo: Carla Culpepper)

All in all, a relatively successful day with Sargassum samples from a very different local environment. We will likely stay in this general vicinity tomorrow to continue sampling along blue-green tidelines, if possible.

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