PS-19-05 Daily Log
June 4, 2019 (Day 8)*
*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!
Well here we are, Day 8, the last day of sampling of our last cruise for this project. Tomorrow will be steaming home, packing and unloading samples, gear, and supplies (probably in the rain) –you know, boring stuff. So this will be the last installment of our cruise blog.
Through the magic of remote sensing, and the keen eyes of the guys on the bridge, we woke this morning to a series of pretty large Sargassummats located approximately 30 nautical miles south-southwest of the birdsfoot delta. Okay, there’s a lot of science that goes into these satellite images, but they seem pretty magical to us. The mats were teeming with fishes. Large Mahi Mahi were schooling between mats, and we could see many juvenile jacks, filefishes and triggerfishes under the Sargassumcanopy as we cruised closely by to inspect potential sampling targets. All indications were that this was going to be another great day.
We began as usual by collecting CTD profile data and water samples, followed by a near perfect neuston net tow along the long edge of a large Sargassum mat. This tow yielded numerous chubs, jacks, filefishes, and other species we’ve grown accustomed to in the weedlines. We scooped up a pretty good chunk of the mat, so it took several hours to rinse through the algae and collect the fishes and invertebrates. Sargassum mats drifted by the vessel as we worked, and one of these mats had a young green sea turtle rafting on top. It’s flippers spread out, it looked like it was asleep, or at least oblivious to our presence. We tweeted a picture of the carefree turtle, and friend-of-the-lab and turtle expert Dr. Kate Mansfield (@UCFTurtleLab) replied that they commonly see this behavior. Floating on top of the Sargassum hides them from predators lurking in the waters below, and the warmth provides a perfect and cozy nap environment. So fair winds and following seas, little turtle!
We worked in a Sabiki hook-and-line sampling set before lunch, and caught quite a few juvenile amberjacks and Blue Runners (Hardtails). Having still not collected many triggerfishes, in spite of our best efforts, we pulled out the (sometimes loved, sometimes dreaded) plankton purse seine! Conceptually, the idea is simple. Our seine is a 10-m long by 3-m deep curtain of 1-mm mesh that can be used to encircle a small patch of Sargassum and “pursed” to collect larger fishes that easily evade the neuston net. Deploying the purse seine off the small boat, however, does take some practice and we were admittedly rusty. The first attempt actually went very well, and collected a few smaller juvenile amberjacks as well as a Grey Triggerfish (yes!). The next several attempts, however, were not so great. Finding the right size mat is important, and many little things have to go right for it to work, and we just didn’t have the best of luck today. But it was a valiant effort by the small boat team on yet another very hot day, and their efforts are greatly appreciated.
By mid-afternoon we were faced with a decision as to what to sample next. Based on the remote sensing imagery, we appeared to be very close to the “tide line”, where the green coastal waters abut the dark blue offshore waters, and there appeared to be high Sargassum biomass. We steamed north in search of Sargassum along this feature, but could not find any significant weedlines. After searching for a couple of hours, we turned back south to find open, blue waters again just before sunset and completed two deuceton net tows, the last field collections for our project.
It was a bittersweet feeling, leaving that last station. There’s a lot left to do on this project now that the field collections are completed, and we will be working on our data analyses over the next year. But there’s just nothing like the thrill of being on the water, searching for Sargassum, and wondering what will come up in the net next time. Of the four cruises, this has been one of the most successful, as we’ve sampled everyday we’ve been out. Just a tremendous job by the science team and by the vessel crew.
We hope you enjoyed our blog. Should you have any questions, please feel free to get in touch. And while this is the end of our cruise blog, it’s not the end of the project; we will do our best to provide additional project updates on our website and twitter page, so please stay in touch.
Thanks again, it’s been great sharing our work with a wide audience.