Has Krill Biomass in the Gulf of Maine been underestimated?

Although Krill are small, they are very good swimmers and are known to be good net avoiders. The MOCNESS system we are using has two LED strobe lights which are thought to disorient the krill from avoiding the nets. Last night we wanted to test if the strobe light actually allows us to catch more krill or if it’s just a coincidence. In order to do this we towed the MOCNESS in the same area of a krill patch and randomly turned off the strobe light on half of the nets. Our hypothesis was that the nets that had the strobe light on would contain more krill than the nets without the strobe light. Below is a picture of our catches from each of the 8 nets. Which nets do you think had the strobe light on? Feel free to post your answer in the comments.

(From left to right nets 8 7 6 5 4 3 2 1)

Our results seem to be significant! This could mean that previous krill surveys without strobe lights could have been underestimating the amount of Krill in the Gulf of Maine!

Where are the whales!?

Well, we know that we've got krill on Georges Bank, and that's been keeping the 'zooplankton' team busy. The large marine predator observing team members, including bird researcher Tim White (CUNY) and marine mammologists Reny Tyson (Duke) and myself Julie van der Hoop (WHOI), were fairly excited on the first days of surveying. We had some great sightings of humpback whales, pilot whales, common dolphins, and even some leatherback turtles. Then, things took a turn.

Reny Tyson of Duke Marine Lab sets up the marine mammal observing system, with curious onlookers.

High seas kept us off the observing bridge, as every wave looks like a whale and any whale looks like a wave. We had a beautiful sunrise the next day, but after 45 minutes of surveying, the fog socked in. And today? 5 hours of effort... and only one tuna sighting. Our most common sighting this trip? Marine debris, mostly in the form of balloons.

So, let's pray for calm seas, sunshine, and the return of large marine predators. At least we've got a good sound system, and some good company up on the bridge.

We Found Krill!!

One of the Krill from our nets!

Yesterday, we carried out a MOCNESS tow and found some krill! What is a MOCNESS you ask? MOCNESS stands for Multiple Open and Closing Net with an Environmental Sensing System. The MOCNESS is designed to easily sample the entire water column. When one net closes the next one opens so when we bring the MOCNESS to the surface we have 9 different nets that represent different areas of the water column. For acoustic data it is important to ground truth, or show that the backscatter that you

see on the computer actually represents your target organism. The MOCNESS allows us to do this quite accurately. Our MOCNESS tow went well with very little setbacks. We caught a lot of krill of all sizes. The biggest krill seemed to be at the bottom of the water column, and they got smaller as we got closer to the surface which matches what our acoustic data suggested. We didn’t only catch Krill, we also got a lot of Salps at the surface, and some Ctenophores and Amphipods. We even got a couple of small fish! After we bring the nets on board we empty our nets into buckets and then put the contents in jars and preserve them for later sizing and counting. All in all it was great to be able to see krill in person and confirm that the scattering we are seeing are patches of krill.Yesterday, we carried out a MOCNESS tow and found some krill! What is a MOCNESS you ask? MOCNESS stands for Multiple Open and Closing Net with an Environmental Sensing System. The MOCNESS is designed to easily sample the entire water column. When one net closes the next one opens so when we bring the MOCNESS to the surface we have 9 different nets that represent different areas of the water column. For Acoustic data it is important to ground truth, or show that the backscatter that you see on the computer actually represents your target organism. The MOCNESS allows us to do this quite accurately. Our MOCNESS tow went well with very little setbacks. We caught a lot of krill of all sizes. The biggest krill seemed to be at the bottom of the water column, and they got smaller as we got closer to the surface which matches what our acoustic data suggested. We didn’t only catch Krill, we also got a lot of Salps at the surface, and some Ctenophores and Amphipods. We even got a couple of small fish! After we bring the nets on board we empty our nets into buckets and then put the contents in jars and preserve them for later sizing and counting. All in all it was great to be able to see krill in person and confirm that the scattering we are seeing are patches of krill.

Deploying the MOCNESS (from left to right)

Dr. Gareth Lawson, Nick Woods, Wu-Jung Lee, and Dave Nelson

Photo Credit: Peter Wiebe

Recovering the MOCNESS : spraying down the nets

and putting the organisms in buckets

(from left to right)

Wu-Jung Lee, Nick Woods, and me!

Photo credit: Peter Wiebe

Video Plankton Recorder

Kaylyn here adding to our sparse blog! We have been very busy working out all the kinks of our equipment to make sure everything is running smoothly. One of the really cool instruments that we are deploying is our Video Plankton Recorder (VPR) manufactured by Seascan Inc. The VPR is an underwater video microscope system designed to capture the various plankton present in the water column. We deploy the VPR at different stations along our trip and send it down to about 10 meters above the seafloor and then bring it back up. The VPR takes 20 images per second, so when we download the pictures we usually have tens of thousands of images. Since many of the images don’t have an organism in them, we use software to scan the images, and it picks out pictures that may be of importance. The VPR allows us to quickly ground truth our acoustic data and to pick out areas that contain patches of krill. We then can go back to these areas and use a net system to bring krill to the surface. Below I have included a couple if pictures of the deployment of the VPR and really good VPR images that were taken over the past couple of days.

Dr. Peter Wiebe Observing the VPR Deployment

Photo Credit: Nick Woods

The VPR going into the water at Sunset

Photo credit: Nick Woods

Various Planktonic Organisms Photographed by the VPR

Georges Bank Krill

Gareth here, writing from Georges Bank, where we're at sea on a 10-day cruise on the R/V Endeavor, a 185-foot research vessel operated by the University of Rhode Island. We have reason to believe from observations made by our colleagues at National Marine Fisheries Service that there are large aggregations of krill that form on the northwestern slope of Georges Bank and in the southern Gulf of Maine during this time of year. The goal of our work out here is to understand the interplay of physical and biological factors that lead to the formation of these krill aggregations, and to understand how they interact with higher predators, including fish, marine mammals, and seabirds.

R/V Endeavor tied up in Narragansett, Rhode Island

To address these questions, we are doing survey work to map out the distribution of the krill and their predators. For the krill, we have a number of different instruments to map them, including two kinds of echosounders (multi-frequency and broadband), a video system, as well as a plankton net. Then to understand the krill's physical environment, we have a Conductivity-Temperature-Depth (CTD) instrument to measure the salinity and temperature of the water, as well as an Acoustic Doppler Current Profiler (ADCP) to measure currents. And finally for the higher predators, we have two marine mammal observers and one bird observer. All told we have a lot of gear -- just getting the instruments to the ship required a 20 foot truck!

Over the next few days, myself and others in our team will be posting about what we're learning and life at sea. Stay tuned!

Welcome!

Gareth here. I'm very excited to be writing the first post to our new blog! I'm part of a research group at the Woods Hole Oceanographic Institution focused on the role of zooplankton in the ecosystems of the northwest Atlantic Ocean. Right now we're especially interested in krill. A lot is known about krill in the Antarctic, where they're the main food item for all of the cute predators we associate with that region, like penguins, seals, and whales. In our local waters off the northeast coast of North America though, much less is known about krill -- but we know they're out there, we suspect they're an important player in the ecosystem, and so we're going to try to learn more about them!

In the next few years we have a number of field projects examining the ecology of krill and other zooplankton in our part of the ocean. Like swarms of insects, zooplankton are often distributed in 'patches' in the water column, and we'll be trying to understand the processes that lead to the formation, maintenance, and dispersion of these patches. We'll also be looking at how these zooplankton patches interact with and support higher predators, including commercial fishes, marine mammals, and seabirds.

In this blog we'll be providing ongoing updates from the field, so stay tuned to see and read more about oceanographic research (as it happens!), life on oceanographic research vessels, and everyone's favorite zooplankton -- krill!

View through the microscope of Euphausia krohni, a common krill species in the northwest Atlantic. (Photo: N Fitzharris)