"Current" events on Georges Bank

Out here on Georges Bank, we are busily mapping krill patches, but we also want to understand the physical environment in which we find the patches. The ocean currents on Georges Bank are constantly changing, and this movement may play an important role in determining the size and location of krill patches. To understand what role the ocean currents play, we have been measuring them as we go.

The tool we use to measure the currents is an Acoustic Doppler Current Profiler, or ADCP. The ADCP measures ocean currents at different depths using the Doppler effect. You hear this effect every time a train goes by blowing its whistle. When the source of a sound is moving toward you, you hear the sound as a higher pitch. When the source is moving away from you, you hear a lower pitch. The change in pitch is known as the Doppler effect.

Using this idea, ADCPs can measure ocean currents. The ADCP sends out a pulse of sound, which bounces off particles moving with the water and back to the instrument. Just like a train, if the particles are moving away from the instrument, we will hear a lower pitch on the returning sound. If the particles are moving toward the instrument, we hear a higher pitch. The change in the pitch of the returning sound tells us how fast the water is moving, and in what direction.

We have three different ADCPs on the ship: Two mounted on the bottom of the ship, and one mounted on the HammarHead towfish. We will use the data from these instruments to see how the currents flow, and then determine how these currents may be affecting the distribution of krill.

An example of data collected using the 75kHz ADCP mounted on the bottom of R/V Endeavor

Gareth preparing to deploy the HammarHead towfish with ADCP mounted on top to measure ocean currents

Seabird Observations

It's been an exciting and blustery week studying seabirds from the Endeavor’s flying bridge. The sea state has rarely been below Beaufort 4, and spotting some of the smallest seabirds, e.g., dovekies, has been a challenge. I use 10 x 42 binoculars to help with identification, and observations are recorded using GPS software specifically designed for top predator surveys. Age, sex, and behavior of seabirds are logged when possible, as well and association type, e.g., whale, tuna, other seabirds. The spatial aspect of the data helps us link the prey field, as determined by acoustics and net, with the distribution of predators (seabirds & marine mammals).

Greater shearwaters breed in the south Atlantic on Tristan da Cuhna, Nightingale Island, Inaccessible Island & Gough Island. Greater shearwaters found on Georges Bank this time of year are likely nonbreeders (photo: T. White)

I enjoy surveying Georges Bank this time of year because arctic breeding seabirds begin to make an appearance. Species such as: northern fulmar (Fulmarus glacialis) black-legged kittiwake (Rissa tridactyla), great skua (Stercorarius skua), northern gannet (Morus bassanus), and the alcids: razorbill (Alca torda), Atlantic puffin (Fratercula arctica), common murre (Uria aalge), thick-billed murre (Uria lomvia), and dovekie (Alle alle). Some alcid species can reach depths greater than 100 meters in search of prey. Dovekies are interesting alcids to find on Georges Bank because they breed very far away, in places like Greenland and Spitsbergen. The winter population of dovekies on Georges Bank has recently been increasing, and arriving earlier in the season. It is possible that dovekies are shifting their winter distribution farther south in search for food such as krill.

Black-legged kittiwakes breed in northern Canada & winter on Georges Bank (left 1st winter; right adult). photo: T White

Migrating non-seabird species have been spotted over Georges Bank the last few days. Groups of common eiders (Santeria mollissima), white-winged scoters (Melanitta fusca), and single common loons (Gavia immer) were observed streaming by the ship. A single snow bunting (Plectrophenax nivalis), 6 dark-eyed juncos (Junco hyemalis), 1 female red-winged blackbird (Agelaius phoeniceus), a mourning dove (Zenaida macroura), and a female purple finch (Carpodacus purpureus) have all stopped to rest on the Endeavor.

Tim on the flying bridge logging observations. photo: Peter Wiebe

Rough Seas on Georges Bank

Peter Wiebe captured a wave coming over the rail soaking the deck!

Kaylyn here, reporting some bad weather out here on Georges Bank! We finally received our fixed HTI Green Bomber system working and we steamed out to Georges Bank. When we arrived we were faced with some pretty big seas. We were able to deploy the Greene Bomber so we can start collecting acoustic data! Unlike the Bomber the Hammerhead (the broadband acoustic system) is more fragile and can't be deployed in really bad weather. Choppy seas also means the whale observers Reny and Kelly couldn't survey today because the swells are high and full of whitecaps. Tim our bird observer stood out in the strong wind and the cold all day, and saw many species of birds. The zooplankton team braved the rolling wet deck to deploy the VPR at two stations, before the weather got even worse. The good news is the Greene Bomber is going strong and allowing us to collect acoustic data and plan locations for a MOCNESS tow in the future. We are seeing krill-like returns on the instruments!

Deploying the Greene Bomber photo credit: Peter Wiebe

VPR Cast in High Seas (from left to right Gareth, Kaylyn, Nick, Dave, Patrick, Wu Jung, and Phil) photo credit: Peter Wiebe

Wave Came up over the Stern (from left to right Kaylyn, Nick, Patrick, and Wu Jung) photo credit: Peter Wiebe

Nick trying not to stumble walking on a rolling ship!

Ptown Pick-up

This is Nancy, land support for the krill cruises. I drove up to Provincetown at the tip of Cape Cod first thing this morning to meet the truck (van as it turned out) that was delivering the repaired HTI acoustics deck unit. I wanted to make sure that both crates arrived and were transferred to the Harbor Master's launch as if they were full of eggs. To their credit the guys were all very careful and a great help. The boat puttered gently toward the awaiting Endeavor further out in Ptown Harbor (image). By the time I was back in Woods Hole, about 2 hours later, I got news that the unit was working. Yay!

Problems with Equipment at Sea

Gareth trying to diagnose the problem with the deck unit

Kaylyn here, unfortunately reporting some technical difficulties. Yesterday before our planned departure at 9am, we noticed that out HTI deck unit wasn’t working. The HTI deck unit is the brains of our Greene Bomber which is our multi-frequency acoustic system. Unlike our Hammerhead broadband acoustic system, the Greene bomber can sample the entire water column. In other words this is a crucial part of our acoustic sampling. Gareth decided to delay the cruise 24 hours to try to fix it. We tried all different tests including taking apart the deck unit and adding spare parts from another system but all attempts failed. We decided to ship it to the HTI company so they can properly diagnose and fix the problem. This means we have to depart without a crucial piece of acoustic equipment. You’re probably wondering how we’re going to sample without this system right? Well we contacted people at WHOI and arranged for another similar acoustic system made by BioSonics to be brought out to us via a small vessel the Mytilus. The exchange was quite simple and very quick! We met the Mytilus at a location in Buzzards Bay and they pulled up next to The Endeavor and handed off the acoustic system. Just like that our problems were solved! If HTI can fix the deck unit in time then we will attempt to get it brought out to us as well! We’ll keep you posted!

Mytilus arriving to the Endeavor with awaiting crew photo credit: Peter Wiebe

BioSonics equipment handed off to Gareth photo credit: Peter Wiebe

Georges Bank Krill - Take 2

Gareth here. Today we sail on our second of two cruises to Georges Bank, where we will again be studying the large aggregations of krill that we saw on our last trip out there, and the interaction of these aggregations with higher predators. The reason for having two cruises is that the first one was timed so that it would fall immediately before the herring started to spawn. In early fall the herring mill around in these deep waters just off Georges where we saw so much krill last cruise. Herring are a dominant krill predator, but at that time of year their minds aren't on food as they're getting set to spawn in the shallower waters of Georges Bank. This means that in our first cruise we could study the krill in low predation conditions.

Dissecting a herring caught during our first Georges Bank cruise to see what was in its stomach (Photo: Peter Wiebe)

Our second cruise is timed to occur after the herring have mostly finished spawning (hopefully!). Once they spawn, the herring start to feed, munching down on all the krill found in this region. So during this next cruise we'll be studying the krill's behavior in high predation conditions. This is what we refer to as a 'natural experiment.' In a laboratory setting, it's easy to conduct experiments where conditions (tank temperature, for instance) are manipulated to produce different experimental treatments. In ocean-going fieldwork it's hard to do proper experiments (e.g., it's hard to manipulate the temperature of Georges Bank) and so we look for these natural experiments where conditions vary in a way that we can capitalize upon.

Map of Georges Bank and the Gulf of Maine (NOAA-USGS). The red rectangle shows the area where we worked on our last cruise, and where we'll be starting out again this time.

During this cruise we'll again be heading out to the northwestern flank of Georges Bank, where we'll again be deploying a number of different instruments to map the krill's distribution, including two kinds of echosounders (multi-frequency and broadband), a video system, and a plankton net, as well as observers to keep track of higher predators. Our science party is made up of an 8-person zooplankton team (Gareth Lawson, Peter Wiebe, Cindy Sellers, Phil Alatalo, Wu-Jung Lee, Nick Woods, and Nick Nidzieko from WHOI, Kaylyn Becker, recently of the Gulf of Maine Research Institute) and a 3-person top predator observing team (Reny Tyson from Duke, Kelly Kleister from the Whale and Dolphin Conservation Society, and Tim White from the City University of New York).

Stay tuned for more updates from the fogs of Georges Bank!

Getting Ready for the Next One!

Gareth here. The past couple of weeks have been a flurry of activity as we have worked to get all of our gear ready for our next cruise, which sails this coming Wednesday. Even though we left some of the equipment at the ship's home port of Narragansett RI, we still have a full truckload with some big items being sent down on Monday, along with a vanload of electronic gear.

A truckload of gear being sent to the cruise departure port in Rhode Island (Photo: Gareth Lawson)

Nancy Copley organizing and packing gear in the lab (Photo: Gareth Lawson)

Organizing all of the equipment and supplies for a cruise is a tricky job -- when you're a day's steam offshore you want to make sure you don't forget anything behind! Plus when you're putting complicated electronic devices into the ocean there are always things that go wrong, and anticipating all of the possible problems that might come up and putting together a 'spare parts' kit for each instrument takes a lot of forethought. At this point our packing list has reached 26 pages in length, and we're certainly hoping that we have everything!