Sunday, November 7, 2010

Home Again

Gareth here, now back on dry land and writing from the warmth of my home, having slept last night in my own bed (which wasn't rolling back and forth all night!). We returned to port on the flood tide early yesterday morning, having left Georges Bank a day early -- gale force winds and seas of up to 21 feet were in the forecast, so we headed for the calmer waters of Cape Cod Bay to do some last calibrations before heading home. During the 10 hour steam from Georges to the Bay we saw some pretty heavy seas - wind speeds topped 40 knots and the ship made some pretty impressive rolls! Luckily all of our instruments had been tied down thoroughly so although a couple of the scientists and their chairs toppled over on the rolls, none of the equipment did.

The science party for Endeavor cruise 487. Left to right, back row: Cindy Sellers, Nick Woods, Nick Nidzieko, middle row: Gareth Lawson, Phil Alatalo, Kelly Kleister, Kaylyn Becker, Reny Tyson, Tim White, front row: Peter Wiebe, Wu-Jung Lee
All in all, we only ended up having one calm day out of seven days on the Bank, but even in the rough weather we were able to get the work done and the cruise was a success. Like on our first cruise we saw a whole lot of krill with our various instruments, and are looking forward to analyzing all of the data we collected to understand more about the krill's habitat and behavior. Thanks to the Captain and crew of the Endeavor, as well as all of the members of the science party who made the cruise a pleasurable as well as successful one!


Stay tuned for more krill research and blog posts as later in the winter we'll be back out on the water piloting a new broadband echosounder mounted on an autonomous underwater vehicle...

Friday, November 5, 2010

Counting krill by sound

Hi! This is Wu-Jung reporting the acoustic side of our cruise. I am a grad student in the MIT/WHOI Joint Program working on the acoustic scattering from marine organisms. Coming out to Georges Bank in this season is quite exciting for me who came from tropical Taiwan!

So, we've been talking about sampling the water column using many different types of technology such as an optical device (VPR) and a net system (MOCNESS). However, the volume of water that we could look at using these methods is tiny compared to the size of the ocean, and we can only do this sampling at a handful of stations. How can we see the big picture of the distribution of krill as we drive over Georges Bank?

We use acoustics! Sound travels very well underwater compared to light. By transmitting sound into the ocean and analyzing the frequency, amplitude, and timing of the echoes, we can identify animal aggregations and estimate the number and composition of the aggregation. When we ‘ping’ (send short bursts of sound) along the way while doing the VPR and MOCNESS sampling, we can begin to ‘connect the dots (stations)’ between these locations where we have ground-truth photos and net samples of the animals. We can then start to put pieces together to restore the big picture of organism distribution in the entire area.

This time we have two acoustic devices onboard: the Greene Bomber and the Hammerhead. The Greene Bomber is a multi-frequency narrowband system that has 4 transducers (functioning as a combination of speakers and microphones) at 43, 120, 200, and 420 kHz. The Hammerhead is equipped with 5 broadband transducers encompassing a wide frequency band between 35 to 600 kHz.
People busy on the deck preparing to deploy the instruments. In the front, Patrick, Kaylyn, Gareth, and Oscar (left to right) working with the Greene Bomber. Under the A-frame, Dave (left) and Cindy (right) working on the MOCNESS. (Photo by Wu-Jung Lee)
Gareth (left) and Patrick (right) deploying the Hammerhead. (Photo by Wu-Jung Lee)

The narrowband acoustic measurement is a very well established method for studying the distribution of marine organisms. Different marine organisms scatter sound differently in different frequency bands: fish can be observed starting at lower frequency such as 43 kHz, but the zooplanktons most likely only show up at higher frequency bands like 120 kHz and above.
Echograms from the Greene Bomber. The zooplankton is more obvious on the higher frequency channel (120 kHz), while the fish show up on both channels. (Image courtesy of Dr. Gareth Lawson)

However, looking at data from a narrowband echosounder is like watching black-and-white TV. You see things, but it is hard to tell a red apple from a green one. Without sophisticated signal processing techniques that can be applied to broadband echoes, the resolution of the resulting picture (the ‘echogram’) is not very good either. Moving towards broadband echosounders is like upgrading your TV from black-and-white to modern color hi-def TV – not only do you have vivid color of the objects, detail of the objects are enhanced, too.

The development of broadband echosounder technology is just getting into a stage that it can be applied in the field. Therefore, we tried to deploy both systems simultaneously as much as we could, in order to compare the broadband system which is still in an experimental stage with the more established narrowband system. Now we’re coming back with the first ecological application of the broadband system!

Here’s more info about the recent development of broadband acoustic systems at WHOI:Now in Broadband: Acoustic Imaging of the Ocean

Thursday, November 4, 2010

How to Find Particles in the Sea


One of our biggest challenges in marine biology is measuring populations of organisms, whether they are whales, fish, krill, or bacteria.  We want to know how many, what kind, over what area they occur, and ultimately what controls their distribution….why are they there?  For this cruise, we have the bird and marine mammal team using binoculars, while the zooplankton team uses underwater optics and acoustics to seek out their target organisms.  But each system for detection has its strengths and weaknesses, which is why we use so many instruments to measure the distribution of marine organisms.  Furthermore, like a lawyer trying to win a case, we try to provide numerous lines of evidence that ‘prove’ our estimate of population size.

Recovering the VPR mounted in a CTD rosette on board the R/V Endeavor
I have been using an optical instrument for many years now that Kaylyn described in an earlier blog post: the Video Plankton Recorder.  While plankton nets physically collect plankton, the VPR takes pictures of them.  Instead of samples containing thousands of copepods, we collect tens of thousands of images.  But as Kaylyn has explained, many of these images show no organisms.  We employ computers to scan the video and capture images of particles that are in focus.  Each picture-file is associated with a time, location, depth, temperature, and salinity. The computer can also help us to automatically identify the image, but someone like me will confirm each identification and identify any images that the computer is ‘confused’ about.

Copepod
Diatom chains and marine snow
So what do we see?  Depending on the magnification used, we can view diatoms, dinoflagellates, radiolarians, marine snow, copepods, gelatinous organisms, krill, fish, and other large zooplankton.  We may see layers of the same organisms – for example, we often see krill aggregating at the bottom of our casts in the daytime and spreading out much higher in the water column at night.  Many times and often most times, the particles we see are not living, exactly.  They are called marine snow and can consist of tiny bits of dead plants and animals that stick each other, forming a tear-drop shaped particle.  We can also see larval forms of other animals such as sea anemones and starfish and swimming behavior and natural swimming position of zooplankton which we ordinarily would not be able to see from a specimen caught in a net.  This is particularly true of the gelatinous zooplankton like jellyfish and ctenophores. 
 
Jellyfish
Starfish larva
 Many times it is difficult to identify exactly what we are seeing on the video. That is why it is important to conduct net tows, like the MOCNESS to help us identify planktonic organisms as well as give us estimates of their abundance.  The acoustic instruments like the Greene Bomber and Hammarhead produce plots of back-scattering for larger areas of the water column, further helping us to see ‘the big picture’.  The ADCP gives us information on the currents which control the movements of plankton.  Using all these oceanographer’s tools helps us answer the questions of who, why, how many, and where – and to convince ourselves and others that we are closer to the truth!

Calm seas and fair winds,
Phil Alatalo, Research Associate, WHOI

Krill
 

MOCNESS: Not just sampling Krill

MOCNESS MOVIE Movie Credit: Peter Wiebe
Hello, Kaylyn here just to update you on our MOCNESS tows. The MOCNESS stands for Multiple Opening/Closing Net and Environmental Sensing System. The MOCNESS has 9 nets with a 335 ┬Ám mesh size that can sample different regions of the water column because when one net closes the next opens. We use the MOCNESS to sample the water column to identify what animals cause the acoustic scattering we are seeing on our instruments.
Spraying down the MOCNESS making sure all animals reach the codends. (From right to left Wu Jung, Nick, and Kaylyn in the back) photo credit: Nick Nidzieko
Although this cruise's main emphasis is krill, the MOCNESS samples most of the water column, so we get to see more than just krill. Some common animals that we have seen are copepods. Copepods are a type zooplankton that are food for many animals such as krill, fish, and whales. We have generally seen two genera Calanus, and Centropages. This cruise we have also seen Fish Larva which was to be expected because we timed this cruise with the Herring spawning event. Another animal is an Amphipod which is a planktonic crustacean that birds and fish feed on.
A jar packed full of copepods (Calanus finmarchicus) as well as amphipods, and a couple of fish larva. photo credit: Kaylyn Becker
We have also seen Jellies, particularly Ctenophores, Jellyfish, and salps. These animals are translucent filter feeders and feed on phytoplankton and zooplankton.
A sampling jar with a large Ctenophore and several copepods probably Calanus finmarchicus photo credit: Kaylyn Becker
Normally we don't get a sample of benthic animals (animals that live on the bottom of the seafloor) because we don't sendthe MOCNESS all the way to the seafloor. This cruise however we accidentally brought the nets a little too close to the bottom and ended up with an octopus in our nets. We have loosely identified him as a North Atlanic Octopus Bathypolypus articulus, and have dubbed him Phil Jr because Phil found him in the net.
Phil and the Octopus dubbed "Phil Jr" photo credit: Gareth Lawson photo credit Kelly Kleister
One of our other interesting finds was Pteropods. Pteropods look like grains of sand to the naked eye but are beautiful under a microscope. Their name means "winged foot" because they look like they have wings and are flying through the water. They are basically snails that live in the water column. Gareth was particularly excited about the Pteropods because next year he will be studying how Ocean Acidification affects these animals in the Atlantic and Pacific Oceans. Due to increasing anthropogenic CO2 emissions, the ocean's pH is decreasing. Pteropods shells may dissolve in an acidic environment so they are particularly sensitive to this changing chemistry of the ocean.
Photo from : http://www.arcodiv.org

Tuesday, November 2, 2010

Whales have names, too??

Hi, everyone! Let me first begin by introducing myself. My name is Kelly Kleister and I work with the Whale and Dolphin Conservation Society out of Plymouth, MA as a marine mammal observer. I’m also one of the marine mammal observers on the marine predator team aboard the R/V Endeavor, along with Reny Tyson (Duke) and Tim White (CUNY). Despite the earlier technical difficulties and more recent bad weather, we are happy to report that we’ve already had some great sightings! After receiving our final delivery by boat off of Provincetown, we began to get underway and head for Georges Bank. But before we had even completely left the Bay, we saw 5 humpback whales (Megaptera novaeangliae), one of which I was able to identify! Her name is Circuit and she was traveling with her latest calf. Circuit was first sighted in 1999 and previously had a calf in 2008.

Circuit's fluke pattern.

Now, you may be wondering ‘How do you identify a whale’? Well, it’s actually quite simple and it’s what I’ve been doing with WDCS. Each humpback whale has a unique black and white pattern on the underside of their tail, or fluke. It’s kind of like their fingerprint and this is how we can positively identify one humpback from another. The Gulf of Maine population returns to these waters every May to begin feeding on small bait fish and krill. They’ll eat about a ton and half of food every single day until they leave between September and November for their breeding grounds in the Caribbean. WDCS and many other similar organizations have been photographing, documenting, and naming these whales since 1976, when the first humpback whale was ever given a name. We’ve seen many of these whales come back every single year, some since the year they were born. And it’s through this almost 40 year study that we can determine how our local humpback population is doing by seeing who’s coming back every feeding season and, more importantly, who’s bringing new calves to the area.

Yum!! Whale food! Photo credit: Kelly Kleister

Circuit, however, didn’t fluke for me but I was able to ID her by a small white dot that’s on the right side of her dorsal fin. It was great to start off the trip with her and her calf, both of whom we’ve seen a lot of these last few months. And with that we headed off for Georges Bank.

The image on the left is when we saw Circuit before leaving, the one on the right is from a previous sighting. You can see how by matching the markings we can positively ID her just from her dorsal. Photo credit: Kelly Kleister

Unfortunately, our first day out on the Bank was really rough and we were unable to begin our observations. When there are high winds and a lot of whitecaps, it makes it difficult to distinguish a whale from a wave. But Halloween brought some great treats for us. We spotted a single humpback blow at a distance, but soon after we were greeted by a pod of longfinned pilot whales (Globicephala melas) right next to the boat! We had a pod of about 5 or 6 whales, which also included a young calf. They seemed to be feeding off of the red fish that some nearby fishing boats had tossed overboard, along with the numerous seabirds around our vessel that had also taken advantage of the floating buffet. So far, we haven’t seen anything else as sea conditions haven’t been too great. But hopefully the next few days will be much better and we’ll be able to report back with some more amazing sightings!

The little head closest to the camera is a baby!! Photo credit: Reny Tyson

More pilot whales. Photo credit: Reny Tyson

Monday, November 1, 2010

"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