Weather/Location
Position: N 58.37.239; W 171.05.968
Air Temp: 4.5-6.0 (deg C)
Water Temp: 4.94 (deg C)
Wind Speed: 16 knots
Weather: Overcast and rainy
This is the screen I use to get info about our ship’s location. The little white speck inside the red oval is our ship.
Science and Technology Log
We have been at sea now for almost five days in search of pollock. The fish had not been spotted on the lines we traveled on until today. We had the opportunity for our first pollock trawl around 02:00, and used the Methot net to bring in two zooplankton samples earlier in my shift. This was by far the most action yet. I was eager and ready to see what the fishing process was all about. This log will focus on the zooplankton samples.
The Methot net was put in the water and lowered to the desired depth determined by watching the location of the acoustic return. After twenty minutes the net was brought back up and the catch was unloaded. I was expecting a net full of euphausiids, but the critters were actually collected in a small container on the back end of the net. The catch was brought into the fish lab and dumped into a bucket so we could separate the other organisms caught in the net (9 jellyfish and 23 tiny pollock in this case). Once the other fish had been removed, we took a sample (a ••• cup scoop) to weigh and count the euphausiids in the sample (sample is shown above). The rest of the catch was also weighed.
There were 543 euphausiids in the scoop. The weight and number help estimate the amount of euphausiids in the entire catch. We repeated this process again a few hours later. The second sample had almost twice as many euphausiids, 13 jellyfish and fewer than 5 pollock.
The survey tech and skilled fishermen lower the Methot net into the water.
Personal Log
Until today, the fishing portion of this trip remained a mystery. However, I was feeling a little sea sick, okay very sea sick, so it was probably a good thing. We encountered some VERY rough seas with sustained winds ranging from 30-40 knots and swells averaging 17 ft. Some of the swells were much larger; one was rumored to be almost 35 ft. high. Apparently the rough seas are expected to return tonight and tomorrow. My sea legs are securely fastened, so I am ready to take on whatever the sea has to offer.
When we brought in the first haul of pollock last night, my eyes must have looked like they were going to roll out of my head. I couldn’t believe how many fish were coming across the conveyor belt. This was what I had been waiting for, so I got on my rain gear and started sorting the fish. Each species was placed into separate crates so a count of all fish caught could be taken. Of course, pollock made up the majority of the catch. In the next few weeks, I will become an expert member of the pollock survey team. Everyone on board, both scientists and crew, have been more than willing to answer my
A sample of zooplankton brought up in the Methot net. These are euphausiids, which are also referred to as krill.
Getting used to the 16:00-04:00 (4pm4am) shift has been trying. Today’s shift was the first that didn’t require a nap. Due to the odd shift hours, I’ve been waking up at 14:00 (2 pm) and going to bed around 05:00 (5 am). This makes mealtime tricky. Dinner is served first, then I eat some breakfast in the middle of the night. My body is thoroughly confused. The ship’s cooks are wonderful, and continually provide a stocked mess hall with loads of choices. I swear the dessert bar is continually whispering my name. I couldn’t ask for a more kind, welcoming group of people to work questions. One part of this adventure I’m looking forward to is getting to know the wide range of characters who make this important research possible.
It was certainly a thrill to see the first whale of the trip. The pod was spotted just off the bow of the ship andlater seen in the distance.
Animals Seen
Fin Whale
Jelly Fish
Flathead Sole
Northern Flathead Sole
Arrow tooth Flounder
Pollock
Yellow Irish Lord
Euphausiids
New Vocabulary
Zooplankton– A very small or microscopic animal organisms possessing little or no power of locomotion (can’t move themselves), leaving them to merely drift or float in the water.
Euphausiids (eu·phau·si·id) – A type of zooplankton, also known as krill, are tiny shrimp-like crustaceans that form an important part in the diet of many animals including whales, seals, fishes and birds. These are the main food source for pollock.
Methot Net – Methot is the name of the man who designed the style of plankton net we used to catch the euphausiids.
One of several jellyfish brought up in the nets. This guy is slimy and heavy, but not a stinger
What is this trip all about? Well, NOAA is working to collect a range of pollock fish samples from across the Bering Sea. The samples collected will help set fishing regulations based on the estimated pollock fish population. The fish are looked at to assess the male to female ratio, size and age.
Pollock, a member of the cod family, are mainly found in the Bering Sea. They are typically found between 328 to 984 feet depths. Pollock lives up to 17 years, and reach maturity around age 4. The maximum size of the pollock is slightly larger then 3 feet long.
The colors in the picture at right indicate the amount of return from the 3 spheres seen towards the top. The other mass of colors at the bottom and surrounding the lines are fish, which are interfering with the read.
We are currently preparing to set sail. Departure time is set for 15:00 (3:00 pm). Our first anchoring will take place just a few hundred feet from where we are docked in Dutch Harbor. At that time, the Chief Scientist and other members of the science team will calibrate (check the accuracy) the echo sound system used during the course of the survey. Once the calibration is complete and the data is collected, we will continue to sail in search of pollock fish.
The echo sound system is used to measure the amount of return or “back scatter” from a ping (term to describe the sound sent down into the ocean). Depending on the size of the return, the scientists are able to determine if they are detecting fish. Pollock are known to give a return within a specific range, which provides the scientists with one of the clues that help them make an educated guess about the type of fish being detected.
In order to calibrate the echo sound system, three metal spheres that have an expected return level are lowered into the sea. A ping is sent into the open sea, and the scientists are able to watch the amount of return from the spheres through their computer. The amount of return can be seen using a color-coded scale. Red shows the highest level of return, and gray is the color indicating very little return. The scientists can then see if each sphere is giving the expected return. If a sphere is giving off more or less than the expected return, the scientists then know how to adjust the level of return they are getting from fish throughout the project.
Eagle or seagull? This guy sits and waits for a food meal on top of the hotel dumpster.
Personal Log
After a day and a half in Dutch Harbor, I’m glad to finally be getting under way. Dutch Harbor is a small, small town. There are a few restaurants, one hotel and a Safeway. All of the other businesses are linked to the fishing industry in one-way or another. Flying into the island was an incredible experience. The plane hummed through the air between multiple tiny landforms. The airport runway stretches out to the edge of the sea, allowing the passengers to think, for just one moment, they are making a water landing. The plane touched down just beyond the shore.
Since my arrival, I have been welcomed with warmth from all of the NOAA scientists and deck crew. Everyone has been more than wiling to answer even the most ridiculous of questions I’ve had. My time the past two evenings were spent getting to know several of the Oscar Dyson officers and crew members.
A good chunk of Monday was spent hiking Ballyhoo with two of the officers from the ship. Ballyhoo is a steep hill behind the airport (approx 1400 ft. elevation). The hill was littered with WWII shelters. As we tromped up the hill, the wind began to pick up. By the time we were nearing the top, the wind was practically knocking me sideways. The gusts were sustained and powerful. Certainly some of the windiest conditions I’ve encountered. The wildflowers growing on the hillside were reminiscent of the summer blooms found on Mount Rainier. The views from the top were breathtaking. Several bald eagles swooped past the emerald hills, and the sun started to peak out as we made our way back to sea level.
Animals Seen in Dutch Harbor
Ground Squirrel
Jelly Fish
Bald Eagles
Variety of Seabirds
Arctic Fox
Guard dog
This little ground squirrel wasn’t bothered as we walked by.
New Vocabulary
Echo Sound System – A tool used to measure the return or “back scatter” from a ping. The amount of return helps determine what is hiding under the sea.
Ping – The name of the sound that is sent into the water to create an echo/return for the scientists to read. The ping is a constant, repeated sound wave. Several different frequencies are used to detect objects.
Return – AKA back scatter, is the amount of acoustic sound waves/echo bouncing back off an object beneath the water.
Trawl – The phrase used when talking about catching fish using a large net
The Echo Integration-Trawl Survey of Walleye Pollock closed the season with a total of 74 Aleutian wing trawls (AWT mid-water trawls), 19 bottom trawls, 27 Methot trawls (plankton) and 81 ConductivityTemperature-Depth Sensor Package deployments (CTD water quality checks) collecting a wealth of biological and physical oceanographic data. The crew and scientists are excited to be headed back to shore but also there is a good feeling regarding the mission of the trip and the validity of the data collection. Of the 50,840 Kg of fish netted more then half was caught in the 44 AWT mid-water trawls executed this third leg of the survey. During this time we took the length of 16,761 individual pollock and identified 19 other species of fish.I spent some time looking at graphs of preliminary data to try and make sense of what was accomplished from the work done during the sail. This past winter had a higher incidence of sea ice relative to the previous years. Generally the colder and saltier the water, the greater the density and the deeper it sinks. Although this concept was illustrated in salinity measurements at different depths (deeper being saltier) we found this not to be true when looking at temperature profiles.
Basket star
In the sea, deeper does not always mean colder. The Bering shelf is influenced by more than one current system and we found the data taken from the northern parts of the transect along the shelf had colder water than the southern areas as expected but along the slope near the edge of the deep basin the water remained consistently warmer relative to the shelf water despite the latitude change, rarely dipping below 1°C. Generally, we found colder water near the bottom of the shelf between 50 and 100 meters then we did near the bottom of the deeper slope at 200 meters or more. This is mainly due to ice melt in the northern latitudes slowly moving cold water along the bottom of the shelf, where as the deep basin and slope are influenced by slightly warmer currents moving northwest from the Aleutian chain. As a teacher working on the water in the east I came out here assuming the deep areas would be colder but instead I was schooled on currents and their influence on water temperatures.
Leg 3 Transects of Pollock Survey Area: Fish symbols indicate trawl locations. Circles represent CTD readings and diamonds represent the line between Russian and US fishing grounds.
Through much of the cruise the lead scientists on shift spend enormous amounts of time monitoring the acoustic signal (echograms) from sounds waves beamed below the ship. When they find a significant mass of pollock they often would take a sample – go fishing. Using patterns on computer monitors scientists are able to hypothesize which signals indicate pollock. Both the length data taken from measuring fish and the acoustic estimates are used to come up with biomass numbers. In the echogram in figure 3 there is what appears to be a signal indicating mixed size pollock. We know that pollock schools tend to be homogeneous with respect to age and size. The strong blue layer at the top of the echogram represents plankton near the surface and in this instance the fish are mostly near the bottom with larger fish indicated in blue and more evenly dispersed, while dense schools of small fish show up as odd shaped clumps with lighter colors. When we sampled this water we found this to be true; we observed two groups of pollock, large adults and small two year old juveniles. The data in Figure 4 (histogram lengths) shows the two size groups. Cannibalism may be part of the reason the smaller fish stick together in separate densely packed schools.
Temperature Profile from CTD readingsConductivity (salinity) Profile from CTD readingsEchogram of trawl haulTrawl histogram
In the echogram, we see more evenly dispersed adult pollock. This is verified by the haul 92 histogram in figure 6 that shows that most of the pollock sampled where between 40 and 55 centimeters long. Looking at the distribution of pollock in our study area (Figure 7) shows a consistent band of greater incidence of fish near the slope particularly to the western parts of the study area. As the fishery scientists fine tune hydro-acoustic technology they hope to get a better understanding in zooplankton (Figure 8) trends that influence survivorship of young Pollock. A Krill Survey would be ambitious but by looking at the higher frequency acoustic waves, verified with Methot Trawls, one can estimate krill biomass in pollock regions. Environmental monitoring of chlorophyll concentration (phytoplankton measured from CTD water samples analyzed back on shore) and krill biomass (zooplankton) relative amounts from year to year can help create a better understanding of the resources necessary to support fish stocks.
FIGURE 7: Preliminary data of pollock distribution throughout the survey areaFIGURE 8: Preliminary zooplankton estimates throughout the pollock survey area
I would like to thank Chief Scientist, Paul Walline and B-Watch Chief ,Patrick Ressler for taking the time to explain to me the science of hydroacoustic survey analysis and sharing with me their preliminary data.
Chief Scientist, Paul Walline, monitoring the echogram from the bridge of OSCAR DYSON.
Bird of the Day:
The bird survey folks identified over 35 species on our trip. I became familiar at least 6 species of birds that I felt comfortable identifying on the fly. When there were hundreds of birds circling the boat there was sometimes one type of bird that stood out making identification a snap. The Auks are related to penguins and have rounder body shapes and unique flight patterns. Like penguins of the southern hemisphere, the denser body composition makes them excellent at swimming under water, but they less nimble taking off and flying in the air compared to sleeker less dense seabirds like the gulls. Unlike penguins all 13 species of auks in the northern hemisphere can fly. The two most abundant types observed onboard are the Murres and the Puffins. I was fortunate to see two species of puffin this trip, the Horned and Tufted Puffin, seemingly too exotic for the Bering Sea. Both have specialized large colorful beaks for carrying multiple prey items and attracting mates. As we sail southeast we are fortunate to be seeing more of them.
Personal Log:
Patrick, always with a smile, takes a break from the computer screens to look at the catch.
These last few days, despite the lack of fishing, have not been without excitement. The bottom-study video sled captured Dall’s Porpoises swimming under water as it was deployed off the stern. As we head southeast there seems to be more whales and clearer skies. This evening we saw dozens of fin whales and one pod was feeding so close that I was able to see baleen. The whales’ baleen is used to screen their plankton food. I learned the Right Whale has asymmetrical coloring on its baleen and the right side has a lighter off-white color, which we were able to see from the port side of the ship. I would like to take this opportunity to express my gratitude to the crew of the OSCAR DYSON for their help in getting acclimated to the Bering and to NOAA’s Teacher at Sea program for providing this amazing experience.
Question of the Day
Today’s question: What is next for the OSCAR DYSON? She is headed back out to the Bering to find rare Right Whales. Check out ship tracker at NOAA’s website or the OSCAR DYSON Web site for more info.
Previous Question: How much fish did we catch? 26,575 kilograms (summer extra credit – convert this number to pounds and metric tons)
Roy works with the deck crew to remove the “pea pod” from the trawl net.
Science and Technology Log: Special Operations
When a fully equipped research ship goes to sea everybody wants in. Any scientist doing work in a particular region needs access to that region to conduct their fieldwork. Fishery scientists often catch a ride with commercial vessels to do work at sea. A research vessel can be more desirable for certain projects and NOAA has a system for organizing request proposals and prioritizing work. Unfortunately, a boat is limited in the number of passengers, equipment, food and other resources it can carry. For example one scientist, who is not with us, has sent light meters onboard and requested we collect the data for him. The light meter mounts to our trawl net to study if light penetration affects the vertical distribution of walleye pollock. The pollock survey, the main project of the season, has a science team of 8 not including the birders, ship’s staff and Teacher at Sea. With this many scientists onboard the ship becomes a platform for an interesting mix of experimentation.
Measuring the fish
We finished the transects of the Pollock Survey and are now transiting southeast back towards Dutch Harbor. Tomorrow we launch “the sled”, a large metal-framed instrument equipped with an underwater video camera to record the sea bottom of a special study site. The purpose of the study is to assess the effect of bottom trawling on benthic habitats and measure recovery progress over time. The study site is an area that was bottom trawled back and forth around a month ago. The camera will be pulled in lines perpendicular to the tracks created by the trawling. I got a sneak peak at some of the video footage and the benthic habitat is flat and muddy with strange white sea pens poking upward around 5 feet. Crabs and flat fish scurry around while giant basket stars and sea anemones ornament the bottom. We will use some of our transit time to reflect on some of other side projects that occurred this trip, most of which were designed to refine and validate the survey methodology.
A late night course in net sewing
When the trawl catch is unloaded into the lab the sex, weight and length of individual fishes are recorded. To make the work more efficient, a new measuring board has been designed to length fish. This is the first time it was tested and it performed smartly. The board allows scientists to input digital length data by touching the sensor to the board at the end of the fishtail fork. NOAA Scientists, Rick Towler and Kresimir Williams, designed the instrument using magnetic sensors from scratch, and shared with me the details of their first project and how the length board evolved from an acoustic instrument through trial and error to the prototype we tested this year. When processing data from trawling, there is always a concern as to how to best represent biomass estimates. You should not count a fish that is 10 centimeters the same as you would a fish that is 40 centimeters. Although they would both qualify as one fish they have a different size and thus a different biomass. We know we cannot count every fish so we have different methods of estimating biomass.
Deck crew works to get fish out of the pocket nets
Not all fish are caught with the same efficiency; the retention of fish in a net must be taken into consideration. To compensate for this, an estimate as to fish escapement is often factored into the calculations for fish density. Fisheries Scientist, Kresimir Williams, wants to quantify fish escapement. He is using handmade “pocket nets” to study selectivity and sample escaped fish. In the evening we conducted experimental trawls to monitor escapement from our main trawl nets. We did this by attaching pocket nets to the outside of the trawl net in random placement and analyzing pollock caught in the smaller nets relative to the catch in the cod end. We have found that smaller fish (one year-old juveniles) more often escape the net from near the cod end as opposed to forward, where there is a larger mesh size. Although the data will not be analyzed until later, observations indicate this could be important in interpreting pollock survey results.
The “peas” are equipped with digital cameras
The most exciting project for me is the “Optical Pea Pod”, another Kresimir/Rick design. The pod houses 2 digital cameras, a timed circuit board and a strobe light that is lowered in the net to photograph fish at regular intervals. The setup is designed to produce calibrated stereo images of fish making it possible to measure fish length in deep water. Perhaps, in the future, the cod end can be left open allowing the fish to swim out safely as they are documented. The imaging data can possibly be used to verify the acoustic data that is currently used to estimate the population, reducing the need to handle fish on deck. I would like to thank my technical advisors, Kresimir and Rick, for involving me in their projects and for their support in my work as Teacher at Sea.
Bird of the Day
Adrienne and Travis test the peacameras for pressure down to 80 meters
The Albatross is a seabird steeped in maritime folklore. Mariners of yore would tell stories of the souls of dead sailors rising when they saw the white bird. Famous for being one of the largest seabirds they are a magnificent sight. The Wandering Albatross is capable of extremely long migrations, circumnavigating the globe for years before settling down to breed. Albatrosses, of the biological family Diomedeidae, have recently been reclassified (based on recent DNA evidence) and the number of genii and species is widely disputed. What is clear is that many species are in danger of extinction. The greatest impact to their populations is long line fishing although many were slaughtered for their feathers before being protected after the turn of the last century. Swordfish, monkfish and cod are fished with long-lines involving miles of baited hooks that can attract the birds and lead to their entanglement and subsequent drowning. We have seen two species on this cruise, the Laysan and the Short-tailed Albatross. It is estimated that there are only between 1500 and 2000 Short-tailed Albatrosses remaining the world. Many were harvested for feathers and a volcano eruption at their Japanese breeding grounds decimated the remaining adults. Fortunately juveniles at sea have returned to breed and hopefully with protection, the numbers will continue to rebound. We were lucky to have one spend a fair amount of time of our stern in calm waters the other day as we were stopped for water quality testing.
Rick spends most of the sail tweaking the electronics and the software for things to work. In an attempt to upgrade the failing batteries of the strobe light he designs a super-battery housed in a milk carton.
Personal Log
The Bering is a surprisingly lovely color of blue and if the sun would ever come out I am sure it would accent the aesthetic of the water’s color. When we stop to check the water quality the CTD instrument makes for a decent secchi disk and I have observed anecdotally that the visibility seems to be around 13 meters or 40 feet.On an unrelated topic, the other day Executive Officer LT Bill Mowitt let me in on his “lesson plan” for the weekly drill. We went into a fan room and created an electrical fire scenario. We also left clues around the area for the crew and fire fighter team to assess and react to. When it came time for the actual drill I had front row seats to watch the drill unveil and was then permitted to test the fire house of the leeward side the ship. All went well.
Question of the Day Today’s question: How much fish did we catch? Previous Question: How does one become a Golden Dragon?
The short answer is one sails across the 180-degree line separating the eastern and western hemisphere. We did this going steaming to Russian waters continuing our survey work in the Northwest Bering.
Kresimir and Rick send the final prototype of the pea pod down in the trawl netPollock in the net down below 80 meters – caught and measured on cameraAnother amazing in-flight shot by Tamara K. MillsAn Immature Short-tailed Albatross off the stern of the OSCAR DYSON (image by Mark Rauzon).Executive Officer Bill Mowitt sets up a Fire DrillFire team reacts
NOAA Teacher at Sea
Roy Arezzo
Onboard NOAA Ship Oscar Dyson July 11 – 29, 2007
Mission: Summer Pollock Survey Geographical Area: North Pacific, Alaska Date: July 23, 2007
Weather Data from Bridge
Visibility: <1 nm (nautical miles)
Wind direction: 220° (SW)
Wind speed: 8 knots
Sea wave height: <1 foot
Swell wave height: 0 feet
Seawater temperature: 9.8 °C
Sea level pressure: 1006.7 mb (millibars)
Air Temperature: 10°C
Cloud cover: 8/8, fog
Roy and Tamara get excited about birding on the bridge of the OSCAR DYSON
Science and Technology Log
Consumers became very aware of the issue of by-catch when the media reported the canned-tuna industry was killing dolphins in their nets nearly a decade ago. The industry responded by changing some of their fishing methods and marketing “dolphin-safe tuna”. NOAA monitors and sets catch limits for commercial fishing, regulating by-catch, among other things. The Coast Guard assists by also enforcing these fishing regulations. Some of the scientists working here on the pollock survey have worked as fishery observers on commercial vessels, monitoring by-catch in the Alaska fleets. The by-catch regulations vary based on the region, species and season. For example, on the Bering Sea none of the finfish outfits are allowed to keep any crab, they need a special permit to keep halibut and they need to keep cod if they are fishing for pollock. Commercial trawling for pollock results in typically low by-catch. Some environmental groups have listed pollock as a sustainable fish food compared to other seafood in that the harvest does not seem to significantly harm the environment or severely deplete fish stocks. The Marine Stewardship Council, an independent global nonprofit organization, has certified Alaskan pollock as a sustainable fishery.
NOAA Scientist Abby separates out a Chrysaora melanaster jellyfish.
Although we are not dealing with by-catch directly, I find the connection between by-catch, sustainability and fish stocks very interesting. The Echo Integration Trawl Survey uses acoustic data to estimate pollock populations. When we put out our nets we do so to obtain a sample of fish, detected by our acoustic instruments. Since we are conducting mid-water trawls we bring up mostly pollock. The non-pollock species that occasionally get caught in the net are important in verifying the acoustic data and to know what is in the water column with the target species. As a science teacher, the diversity makes for interesting fishing and I have been able to observe a few organisms that spend most of their time in deep water. I have shared some of my images of the unusual species below, all of which I had never seen before this trip. Many of the organisms we bring up go back into the water after we record the data but some of our catch makes it to the galley to be served up for meals.
More Invertebrates
Some type of sea penSmall squidFlathead Sole (Hippoglossoides elassodon). Flatfish tend to swim higher in the water column in the evening following the planktonGreenland Turbot (aka Greenland Halibut)Pacific cod (Gadus macrocephalus)Pacific Herring (Clupea pallasi)Great Sculpin (Myoxocephalus polyacanthocephalus)Smooth lumpsucker (Aptocyclus ventricosus)Shrimp from a night trawlKier, Chef and Assistant to the Chief Steward, makes a serious shrimp bisque.Catch of the day: Chief Steward Rick cooks up Pollock Fish and Chips
Bird of the Day: Turns out, there is no such thing as a seagull. This was passionately explained to me by birder who will remain nameless. You ask, why no seagulls? Simply the term is not used in the scientific community. There are seabirds and of this general group there are well over 100 species of gulls. Some gulls are found well inland. Some species of land-based gulls have become popularized due to their opportunistic feeding around humans. Many of the pelagic gulls I have seen this trip are not as well trained as the ones in NYC and stick to wild foods, not even accepting the occasional fish scraps I have tempted them with off the back deck. I had reported in a previous log seeing Kittiwake’s and some immature Herring Gulls. Today we saw a Slaty-back Gull. It is a handsome gull with striking contrasts of black, dark grey and white. They seem to turn up more each time we reach the northern end of a transect line (above 60° latitude). I also learned that the red spot on the beak is a sign of maturity in many adult gulls. I have a renewed appreciation for gulls and look forward to identifying the species back home.
Bottom trawls, conducted on the previous leg of this study, tend to have more diversity in the sample
Personal Log
We are approaching the northwestern edge of our transect field and the water is deeper and colder and we are finding less fish. I am lucky to find more time to spend on the bridge and witness the communication with Russian fishing vessels, jumping salmon and occasional marine mammal sightings. I have a little camera envy. Some of the folks aboard have the right lens and the right camera to catch the action out at sea. My little 4X zoom digital is looking mighty bleak on the deck and thus I need to rely on the serious photographers for images of some of these exciting finds; their generosity in sharing their images is most appreciated.
Slaty-Back Gull
Question of the Day
Today’s question: How does one become a Golden Dragon?
Previous Question: Why do pollock rise in the water column at night?
Much of the food eaten by pollock fluctuates in their vertical migration depending on light penetration. During the daylight hours many of the euphausiids (krill) can be found lower in the water column. It seems that by staying lower in the darker portions of the water column during the day, zooplankton may be more protected from their major predators. Near the surface, the phytoplankton (algae) uses the sun’s energy to produce food all day. As the light fades the zooplankton rise, feeding on algae, and the pollock follow their food source.
Krill from one of our nighttime raids with the Methot TrawlKrill (pollock food): Partially digested from inside the stomach of a pollockPollock gill rakers screen food from leaving the oral cavity as the water passes out of the gill slits, oxygenating the gills
