Why We Are Sampling During the Transit on the Southeast Shelf

Some have asked why we are sampling on our transit on the southeast US shelf.  Many species fished in the northeast may spawn or in some other way originate in the southeast.  For example, chub mackerel (Scomber colias) adults are fished in the northeast, but larvae have not been collected in our 40 years of sampling the shelf north of Cape Hatteras.  Also, historically southeastern species, such as blueline tilefish (Caulolatilus microps), are beginning to occur in the northeast so regularly that fisheries are emerging in the northeast. Like the Slope Sea, this region has had relatively little plankton sampling as compared to the northeast US shelf and Gulf of Mexico.

There has been sampling on the southeast shelf; with ichthyoplankton (eggs and larvae of fish) collections going back at least to 1965-1968 from the R/V Dolphin cruises.  There have also been a couple of monitoring and collaborative research programs. The Marine Resources Monitoring, Assessment and Prediction (MARMAP) program sampled portions of the southeast shelf in the 1970s and 1980s.  During the 1990s and early-2000s, sampling was conducted from South Carolina to southern Virginia as part of the South Atlantic Bight Recruitment Experiment (SABRE).  So, the absence of data points in the map below is due to infrequent sampling and also highlights the need to compile historic data to allow us to compare the past to the present.  A new collaborative effort between the Oceans and Climate Branch from the NEFSC and the SEAMAP Plankton group from the Southeast Fisheries Science Center is beginning to compile these data and attempt to fill in gaps and compare historical data with current conditions with cruises like this.

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Map of ichthyoplankton collection locations on the east coast of the US and Gulf of Mexico with the location of bongo tows represented by red dots.  The map is a product of the Fish Larvae Explorer (FLEx) project, which is a collaborative product of the NOAA Fisheries And The Environment (FATE) and Coastal & Oceanic Plankton Ecology, Production & Observation Database (COPEPOD) projects.  FLEx was created to develop the use of ichthyoplankton time series as indicators of ecosystem status and to enhance ecosystem-based fishery management.

We are sampling some cross-shelf transects on our transit south to compare with historical collections.  Our first transect in Onslow Bay, North Carolina,  along a frequently sampled transect from the SABRE project will provide important data on how distributions and oceanographic conditions are changing over time.  We plan to collect as many plankton samples as possible before docking in Cape Canaveral on June 23.

Harvey Walsh
Chief Scientist
NOAA Ship Gordon Gunter  GU 1702

 

 

 

Storms and strong currents end Slope Sea operations

The Slope Sea portion of this cruise ended a little early due to storms and strong currents, but will provide important information on this poorly understood region of the ocean.  We did not complete our entire planned cruise track for the Slope Sea, but we did complete 84 stations in the northeast for a total of 133 bongo and CTD tows and 13 water casts.  The bongos will be used for our plankton analyses, including our hunt for bluefin tuna larvae.

Plankton sampling continued to catch scombrid larvae, including a few more potential bluefin larvae. We never hit a large enough patch to justify releasing drifters. We will save the drifters for another cruise that leaves in two weeks for the Slope Sea.  The water samples from the water casts will be sent off for dissolved inorganic carbon (DIC) and total alkalinity analyses. Both DIC and total alkalinity are used by chemical oceanographers to estimate pH of the water, and examine current ocean acidification conditions of the ecosystem. The basic hydrographic data collected (temperature and salinity by depth) will be used to define ocean features in the Slope Sea and to help ground truth satellite data.

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Picture of a recently caught 8-mm long little tunny (Euthynnus alletteratus) larvae.  Larval scombrids eat other larval fish, as seen by the larvae in the stomach of the little tunny / bonito.  Photo credit: Ciara Willis, Dalhousie University

washing down bongo nets

Ciara (front) and Chris (middle) wash down the bongo nets as ENS Fuller (back) prepares for a water cast.  Photo credit: Harvey Walsh, NOAA/NEFSC.

Weather and sea conditions required an adjustment to our planned cruise track, moving inshore one evening when winds and seas along the Gulf Stream made bongo sampling difficult.  We normally send the bongo down to 200 meters deep ( about 660 feet), and use about 280 to 300-meters of wire, and still could not get the net to that depth.  On the final tow of the evening, we deployed over 400 meters of wire and still could not get the net below a depth of 150 meters ( about 480 feet).

Like flying a kite on a breezy day, the current was pushing the net up with too much force or lift to overcome with our standard weight.  The ship’s bridge and crew were safely able to deploy and tow the gear, but the sea conditions wouldn’t allow for us to collect samples that we could compare to all the others we had collected. After we moved inshore to escape the strong current, we continued to see a highly diverse plankton community in the waters just offshore of our standard sampling locations during EcoMon.

plankton in bogo sample

Plankton collected in a bongo sample about 30 miles north of Cape Hatteras, North Carolina.  The sample had squid paralarvae and fish larvae including: common dolphinfish (Coryphaena hippurus), shoal / dusky flounder (Syacium spp.), and unidentified gobies (Gobiidae).  Photo credit: Ciara Willis, Dalhousie University

Even though we moved inshore, we could not escape the thunderstorms that were moving through the area. We had suspended operations at a station just north of Cape Hatteras due to lightning in the area. Have you ever wondered if lightning strikes the ocean? A few minutes after we arrived at the inshore station there was a very close strike, or the ship was struck by lightning ( it depends on who you ask).  Everyone on board was safe, but we lost gyros and some other electronics.  We steamed on to the next station, the second to last scheduled for the northeast part of the cruise, as the ship’s Electronics Technician (ET) began repairing systems.  We discovered that the CTD would not talk to the computer when we resumed operations at the next station. Wherever the lightning hit, our science gear did not escape the damage.

We decided to move down to the southeast shelf, south of Cape Hatteras, North Carolina, to escape the marginal weather, and the unknown amount of time it would take to diagnose and fix the CTD problem.  Thankfully, the CTD was repaired on the transit south thanks to the persistence and skill of Betsy Broughton (NEFSC scientist) and Kirk Andreopoulos (ET on the Gordon Gunter).  We will continue to explore poorly understood parts of the western Atlantic during the second half of this cruise, this time in the waters off the southeast United States coast.

Check back on to read about what and why we are studying the ocean south of Cape Hatteras, North Carolina.

Harvey Walsh
Chief Scientist
NOAA Ship Gordon Gunter  GU 1702

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.

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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.).

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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

Seeing some interesting seabirds, marine mammals and sea turtles

Over the past six days, observers Timothy White and Glen Davis have been working together from sunrise to sunset to collect abundance and distribution data of seabirds, marine mammals and sea turtles from the Gunter’s flying bridge. This project is an extension of the Atlantic Marine Assessment Program for Protected Species (AMAPPS), which is an ongoing partnership between BOEM and NOAA. Timothy and Glen report high diversity and abundance in transitional waters and zones characterized by steep temperature and salinity gradients.

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Observers Timothy White (right) and Glen Davis (left) at work on the flying bridge.

The following species list is rapidly growing and includes unique seabirds not often observed on the shelf:  Trinidade Petrel, White-tailed Tropicbird, Black-capped Petrel, Brown Booby, South Polar Skua, Manx Shearwater, Arctic and Common Terns, Pomarine Jaeger, Band-rumped Storm-Petrel, Audubon’s Shearwater, Leach’s and Wilson’s Storm-Petrel, and Cory’s and Great Shearwaters — the last four are notably migrating to the north widely through the area.

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Numerous Great (left) and Cory’s Shearwaters (right) have been observed migrating north over Gulf Stream waters.  Great Shearwaters breed on sub-Antarctic islands. Cory’s Shearwaters breed in warmer waters on islands in the eastern Atlantic.  Both species are abundant on Georges Bank in summer where they feed on fish. Photo by Glen Davis.

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Endangered black-capped petrels (white-faced morph pictured) were observed on multiple days over well-mixed waters. Photo by Glen Davis.

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A 1st year Brown Booby from the Caribbean. Photo by Glen Davis.

storm petrels

Band-rumped storm petrels originate on islands in the eastern Atlantic and are abundant in the Gulf Stream. Photo by Glen Davis.

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A 1st year Pomarine Jaeger molting feathers.  This bird was born in the Arctic. At sea, Pomarine Jaegers are kleptoparasitic, which means they pirate food from other seabirds.Photo by Glen Davis.

As of June 15, marine mammals sightings include: Sperm Whales, Killer Whales, Striped, Atlantic Spotted, and Bottlenose Dolphins. Loggerhead Sea Turtles have also been observed.

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These striped dolphins were members of a large pod that consisted of ~ 200 individuals. Photo by Glen Davis.

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A loggerhead sea turtle in warm, blue Gulf Stream water. Photo by Glen Davis.

Tim White
Aboard the NOAA Ship Gordon Gunter, GU1702

Searching for Atlantic bluefin tuna larvae and more in the Slope Sea

The NOAA Vessel Gordon Gunter departed on June 10 from Newport, Rhode Island, and immediately headed off the continental shelf to water deeper than 1,000 meters (about 3,300 feet) known as the Slope Sea.  The Slope Sea is an area of the ocean that is bounded to the north and west by the northeast United States Continental Shelf and to the south by the Gulf Stream, whose dynamic currents provide a strong influence over the area.  The Gulf Stream is constantly shifting position and pathways, like a giant water snake slithering through the ocean, and will frequently shed pockets of warm water, called Warm Core Rings, into the Slope Sea.  The dynamic nature of the Gulf Stream creates a mosaic of habitats that are used by a wide range of species.  However, very little of the Slope Sea has been explored, and little is known about who calls it home.

GU1702_10June2017_NE slope sea graphic

Sea surface temperature image from NOAA-19 satellite for the Slope Sea blue fin tuna cruise the day of departure.  The water temperature is shown in the colors, with blue cold temperatures and red warm.  The Gulf Stream shows up as the darkest red.  The black line represents the proposed cruise track for the northeast portion of the cruise.

The cruise now underway is targeting a different set of objectives from the standard Ecosystem Monitoring (EcoMon) cruises run by the Northeast Fisheries Science Center (NEFSC)’s Oceans and Climate Branch.  As described in a previous post, the EcoMon cruises are designed to monitor lower trophic levels, oceanographic conditions, and the distribution of fish larvae and eggs across a wide area of the continental shelf.  While some changes have been made over time, this area has been sampled with the same general sampling approach since the 1970s.

The current cruise stands in sharp contrast to the EcoMon program in that it is focused on a rarely sampled area, the Slope Sea, and much more prominently on a single species, Atlantic bluefin tuna.

Atlantic bluefin tuna are one of the iconic marine fish species.  Over the course of their seasonal migrations, individual bluefin tuna can occupy both nearshore and oceanic waters, swim across the ocean, and cross through international waters and the exclusive economic zones of multiple nations.  These migrations expose bluefin tuna to a wide variety of fisheries, a factor that presents a notable challenge to managing this species.

In recent decades, the common view of Atlantic bluefin tuna was that they spawned only in two places, the Mediterranean Sea in the Eastern Atlantic and the Gulf of Mexico in the western Atlantic.  However, in the summer of 2013 two cruises sampled the Slope Sea, both of them achieving noteworthy catch rates of early-stage bluefin tuna larvae.  These collections were consistent with a hypothesis first put forward in the 1950s that the Slope Sea was a third spawning ground for this species.  Follow up sampling in 2016 again achieved notable catch rates of bluefin tuna larvae.

Researchers aboard the NOAA Ship Gunter are evaluating the distribution and abundance of bluefin tuna larvae in the Slope Sea spawning ground.  This cruise is sampling earlier in the season than previous Slope Sea cruises to provide us information on the regional start of the spawning season for this species.

The scientists aboard also include two sea bird observers who will be conducting visual observations during the daytime transits between stations.  In addition to sea birds, they will be looking for whales and dolphins, sea turtles, large fish, and jellyfish.

While the focus of this cruise is on Atlantic bluefin tuna, one other exciting aspect of the project is that we are not certain of the full suite of other species we might collect or observe during visual surveys.  The Slope Sea has long been hypothesized to be important in the life history of other species, besides Atlantic bluefin tuna, that support economically valuable fisheries off the northeast United States.  Given the limited sampling that has been done in this region, it is quite possible that a new discovery will result from this cruise.  Follow along  for the next 2 weeks, as we travel through the Slope Sea and down the United States Atlantic coast to Cape Canaveral, Florida, as we further describe our mission and our initial discoveries.

Scientists and Crew of the NOAA Ship Gordon Gunter, GU1702
Harvey Walsh, Chief Scientist