Plankton Ops

The plankton sampling team for this cruise is made up of six researchers from NOAA Fisheries and regional universities.  Each 12-hour watch has a team of three people, so that we can sample day and night.  Betsy Broughton (NOAA Fisheries/NEFSC), Christine Hernandez (Woods Hole Oceanographic Institution [WHOI]), and Quentin Nichols (NOAA Fisheries/NEFSC summer intern, UMass Amherst) staff the night watch, 3-pm to 3-am.  Ciara Willis (WHOI summer intern, Dalhousie University), Chris Gingrich (NOAA Fisheries/NEFSC summer intern, Washington College) and I stand the morning watch, 3-am to 3-pm.

There are still a lot of questions about this area as a spawning ground for Atlantic Bluefin tuna.  One of the research questions being addressed on this cruise is how the currents of the Slope Sea affect the planktonic larval stage of bluefin tuna.  Plankton are organisms that rely on the wind and ocean currents to move through the ocean (from the tiny algae and small amphipods to larval fish and crustaceans to jellyfish). We are hoping to find patches of larval bluefin tuna where we can release drifters that will track the movements of the water surrounding the larvae as they grow.

sorting samples.jpg

Christine Hernandez (front) and Ciara Willis (back) sort samples in the lab as the samples are brought on board.  They also take pictures of larvae for us to post (see images below).

At each station, we sort a small portion of the sample we just collected for any fish larvae we can find.  The larvae we’re looking for are tiny, 2-10mm (about 1/16 – 3/8 of an inch) long, so we need to use microscopes. We also have to work fast, so we don’t drift too far from where the larvae were caught. We have found one potential Bluefin larvae already, which we will verify with DNA analysis.  We are hoping to find a larger patch to justify releasing the drifters.  We’ve also seen plenty of cousins of Bluefin including bullet or frigate mackerel (Auxis spp.).

larval bullet-frigate mackerel.jpg

Picture of a fresh caught larval bullet / frigate mackerel.  These are small cousins of the bluefin that are found in surface waters of the open ocean.

The influence of the warm Gulf Stream waters can be seen in the diversity of the fish community caught in the bongo nets.  In addition to the tuna and mackerels, we are catching more tropical and subtropical species like driftfishes (family Nomeidae) and eyed flounder (Bothus spp.).

larval driftfish

juvenile driftfish

Larval (top) and juvenile (bottom) driftfish caught in the bongo nets.  Driftfishes are open ocean (pelagic) species, often associated with drifting algae like sargassum or jellyfish, particularly as juveniles. Photos of fishes by Christine Hernandez and Ciara Willis.

Harvey Walsh
Chief Scientist
NOAA Ship Gordon Gunter, GU1702

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