Scott Inlet – trawling and long lines

This is the forth installment on my field work in Scott Inlet, Baffin Island. Previous installments can be found here, here and here.

17 Sept 2013 – the ship spent the night just outside Scott Inlet starting out out at anchor, but wind and swell caused it to endlessly rub against the anchor chain. The mate, who was on watch, decided to start up the engines, pull the anchor and motor around for the night. All the while, small chunks of ice butted against the hull right beside my bunk which left me with visions of the sinking Titanic. No sleep was to be had, leaving us all looking rough around the breakfast table in the morning.

Over the course of the day we completed 5 trawls – the first time the Nuliajuk had done a bottom trawl. With each trawl, the turn-around time with the equipment sped up as everyone figured out what they were doing. Each trawl was slightly deeper than the last as no one knew exactly how much cable the trawl net had (it turns out around 900m worth). The catch included: Greenland Halibut, Flounder, Arctic Cod, Polar Cod, Alligator Fish, Snail Fish, Northern Shrimp, Striped Shrimp, other assorted shrimp, 2 species of skate, Hookear Skulpin, Eel Pout, and assorted jellies, sponges and stars. I saw none of the animals as I stayed on the bridge taking notes on times, locations and depths while trying not to get sea-sick (I could have popped down to the lab – but didn’t think my stomach could take it).

For the night, we retreated to anchor in Refuse Bay. It was nice not to have to dance around to get my socks off at the end of the day.

18 Sept 2013 – We took the day to circumnavigate Sillum Island, one of two islands that Scott Inlet branches around. The aim was for me to do CTD casts while the long-lines were being set up for sharks. The occasional depth sounding of the chart didn’t even hint at how complex the bottom topography is, multiple deep pools of 700 m and more are separated by shallower sills. Bumps and dips break the flat of the deeper pockets. Mostly, the depth sound returned a hard signal meaning the bottom was probably rock, but occasionally, the signal would return spread out suggesting isolated muddy patches (or something else).

Against the electric blue of the glaciers, the fresh snow looked dirty. In gullies where glaciers reached the water, calved off chunks floated away. These bergy-bits often sported whimsical shapes reminiscent of ancient monsters or partly submerged houses.

I finished the day with 47 CTD casts over a wide area, downloaded and backed up to three places (I’m mildly paranoid about losing data).

Greenland Shark complete with copepod (shark is on its back)

19-20 Sept 2013 – Over the next two days we fished for Greenland Shark deep within Scott Inlet (it was delightfully calm in the sheltered Inlet, I could set a cup of coffee cup down and not have it instantly spill everywhere). We used a long-line bated with squid for the sharks. A long-line is exactly as it sounds, a several hundred metre long line with shorter lines attached every few metres ending in hooks. Anchors weight down both ends keeping it on the bottom, which in our case was around 600 m. Off of the anchors at both ends were buoyant ropes attached to floats so we could recover everything (both ends in case we encountered a snarl and had to cut the line – then we could start again at the other end). Both days, the whole mess of lines, anchors and hooks was left in the water for 24 hours.

While I was there (shark fishing continued after I left), we caught 14 live shark and several more that had been snacked on. Sizes ranged from 1.6 m (baby size) to over 3 m with a good mix of males and females. We didn’t catch anything else, so why were the shark even there? And what were they eating? The sharks were measured, tagged and tissue and blood samples were taken. The question as to why we needed the centrifuge was answered since the blood was spun to separate out the plasma.

Most sharks had a copepod parasite (Ommatokoita elongata) attached to their corneas. Each parasite dangled a finger-length yellowish egg case from the shark’s eye, no doubt impairing the shark’s vision (but, they live so deep, vision is probably not critical for their survival).

We brought on board a couple of shark heads (the assumption was that other sharks had eaten the rest of them). I took the opportunity to get a close up look. The Greenland Shark doesn’t have flashy teeth like a Great White Shark does. Instead, it has tiny teeth reminiscent of a saw blade or razor wire. These shark bite and twist, effectively removing chunks of its prey. Up close, the teeth looked deadly.

Plastic in the ocean – a depressing thought

A myctophids (photo by G. Hanke RBCM)

“No scientist would ever use the state of Texas as a unit of measurement”

       – Captain Charles Moore

My husband and I went to a talk by Captain Charles Moore recently. He wrote ‘Plastic Ocean’, a book I’ll read and write a review of (we have been planning to get the book for some time). He brought up some interesting and depressing points about how much plastic is in our oceans and what it’s doing to the life there.

Only about 10% of the garbage that gets into the oceans washes ashore; the rest is concentrated into the mid-ocean gyres. An unfortunate side effect of our convenience-based consumer lifestyle is that much of the garbage produced is plastics, which float and don’t breakdown. It takes approximately 6 years for the garbage to travel around a gyre and the average life of the garbage in a gyre is 10 revolutions – that is 60 years.

At first the plastics resemble what they started as – a milk crate, a laundry basket, etc. Since plastic presents a hard substrate, algae eating fishes claim larger chunks as shelter and keep the surface fairly algae free. This clean plastic eventually gets colonized by barnacles and corals creating a new multi-level trashy ecosystem – with algae as the base, then on to herbivores, planktivores, secondary invertebrate consumers, and so on ending at the top predators (large fishes, birds, dolphins and relatives).

As hard-shelled invertebrates grow, their mass overcomes the buoyancy of the plastic. The reef sinks, and over time, the attached organisms decay or dissolve in the cold ocean depths. Buoyant once again, the plastic floats to the surface and the cycle of colonization can begin anew.

In the long run, this plastic garbage will rub up against other debris or be broken by wave action. The plastic pieces get smaller and smaller. A ruby-red bottle cap might be scooped up by an albatross to be fed to its chick or the plastic rings holding a six-pack together might end up around a sea turtle, restricting normal shell growth. Captain Moore mentioned myctophids, an abundant group of lantern fishes which are a vital part of the open ocean food web. Dissections of their stomachs show some of these fish are eating as much plastic as food. Even the tiniest pieces can be ingested by filter feeders.

Plastics are known to absorb pollutants. Species low on the food web eat plastic scraps, creating another way for pollutants to end up in our food. I wonder, what that tuna I ate for lunch ate for its lunch?

So what can we do? I try to use as little as plastic as possible. I have my own metal water bottle and ceramic coffee cup. I keep food in glass containers, and use re-fillable bottles for shampoo and cleaning products. Any other ideas?

as a tangent: thanks to my husband for helping me with this one.

You are what you eat – the colour version

A flamingo from a local butterfly garden

Every kid knows that a flamingo is pink because of what it eats. They filter water through their beak to catch brine shrimp and algae. The beta carotene in their food is converted to the pink pigments in their feathers, without this pigment source the bird would be white. Unfortunately, flamingos aren’t found on my Pacific island except in captivity. But, we do have critters using the same pigment trick.

Recently, I met up with the local Natural History Society (I’m a member) for a beach seine at night because that was when the best low tide was this time of year. Based on the wind storms recently, we were lucky the wind had dropped off and it wasn’t raining. The surf was manageable with the net for people wearing hip-waders and dry-suits – so not me as I don’t own either. Two people took the net out into the surf. The first seine was over sand resulting in hardly any fish. So, the net was taken out and hauled in a second time over eelgrass. All sorts of interesting intertidal creatures were pulled up.

Everyone gathered around to check out the fishes, crabs and shrimps. The fish catch included: walleye pollock, English sole, stary flounder, sharpnose sculpin, sailfin sculpin, sandlance, roselip sculpin, tubesnout, high cockscomb, a type surf perch, Pacific spiny lumpsucker (the cutest fish ever) and a penpoint gunnel. Each type was put into a clear ziplock bag along with plenty of water and passed around. By holding the bags up to my headlamp, I got a good look at each critter.

The penpoint gunnel intrigued me because it was neon green – a tropical water colour in our temperate zone. A picture can be found here, the fish looks like an eel, but isn’t. This guy hangs around in eelgrass or sea lettuce beds waiting to ambush little crustaceans and mollusks. The bright green colour of the one we found would allow it to blend in almost perfectly (they also come in other colours to match other seaweeds). Like the flamingo, the penpoint gunnel gets it’s colour through what it eats. The green comes from the sea lettuce.

Few of the fish and invertebrates were held on to for a local museum’s tide pool, the rest were released. As we packed up our gear, another beach seine group arrived. In the darkness, all we could see of them was dark shapes and headlamps – it was like looking at ourselves a couple hours in the past.
 
As a tangent, my trips to the beach seem to coincide with when my rubber boots are muddy. Once again they are clean.

Arctic Update 3 – Sharks!

The Amunsden sent over a mechanic to fix the hydraulics – so no deploying the CTD by hand (we did seriously consider it). Our day of trawling with the icebreaker resulted in no fish. I don’t know if that means their experiment failed or not. The scientists on board invited us over for dinner, then slept through the meal – so no boat came for us. Eventually, we got hungry and cooked up our own dinner. We were three scientists working together to cook instant rice and we failed. I didn’t realize it is possible to screw up instant rice! We screwed up scallops too.

26 July 11, we went back to pull up the line of hooks we set out two days earlier (we didn’t intend to leave the line in the water so long, but, we couldn’t pull it up without hydraulics). Most the hooks were gone, we assumed fish took the bait, then shark took the fish. We caught a female greenland shark that was 3.5m – big, however, the largest of these sharks reach 7m (or more, according to Pat, a fisherman from Newfoundland who is one of the crew).

These aren’t scary sharks, in fact they are the slowest swimming fish out there. They range from here, Baffin Island, to off the coast of Norway and quite a distance south, off the coast of Georgia at over 2000m in depth. We don’t know if they go further, in fact, there is a lot we don’t know about these sharks. Greenland sharks aren’t as sleek as tropical ones. Their skin is blotchy gray – smooth in one direction and rough the other way (true of all sharks). Their fins are quite rounded. They have a thick layer to protect them from the cold It’s not fat – something else like a collagen layer, whale sharks also have this. Most of them have a parasite hanging off their eyes rendering them essentially blind. Since, they hang out so deep, being blind is probably not a hindrance.

In the morning of 27 July 11, we brought up another shark line, this time there was 13 sharks. Four had been munched on and were dead, as we brought them up to the surface to cut them free, northern fulmars (a sea bird with a head like a pigeon’s) darted in for whatever scraps they could get. The ship was soon surrounded by these birds as they squabbled for the best spot. It took all day to tag the nine healthy sharks, all of them 2.5m and bigger. As soon as the fishing lines were in, I got my fourth CTD cast done.

Late last night we arrived back in Pangurtung to refuel. The wind is expected to pickup, so, we may not be able to get back to work for a few days.

Buckets of water

I was asked why a bucket full of water looks shallower than an empty one, so I pulled out an old physics book to find the answer. It’s been many years since I’ve taken optics, although recently I’ve developed a new interest for it.

Refraction occurs because the speed of light changes based on the density – something I discussed here. The refractive index is the ratio of the speed of light in a vacuum to the speed in the medium. If we think about water with its refractive index of 1.33, we find that light travels 1.33 times faster in a vacuum than the water. The denser the medium, the greater the difference in speed of light and the bigger the refractive index.

Not only does light slow down, it also bends. When a ray of light hits a surface at an angle (angle of incidence) it gets bent to a new angle (angle of refraction) inside the surface. With a little trigonometry applied to these angles, we find that their ratio is also the refractive index, a trick discovered by Willebrod Snellius (of Snell’s law fame) in 1621 – although an Arab scientist figured this out almost 500 years earlier.

So, what fun can we have with the refractive index? Ever looked into a still pool of water? Due to light rays bending in the water, the pool will look ¾ the depth it actually is. If a post sticks up through the water, it will look oddly disjointed at the surface – appearing to extend at one angle above the water and another below the surface even through the pole is straight.

From another point of view, what does a fish see when it looks up? A fish sees a lot more than expected. By looking up in a cone of 98 degrees, a fish gets a 180 degree view above the water due to refraction. The view above the water would be strange – someone fishing on the shore would look excessively squat, standing at an odd angle and probably distorted due to ripples on the surface. But, the fish would see the fisherman, making it much more difficult to be successful at fishing (spear fishing is even more complex due to refraction). By the way, if you put on your goggles and hopped into the local swimming pool, you would see what the fish sees.

Origami Shrimp

In my aquarium I have a number of Amano Shrimp who keep the place clean. Amano Shrimp originate from South Eastern Asia and have clear bodies about a knuckle long with wine-red spots. They have an interesting life cycle in that they are a fresh water shrimp whose larvae require salt water to live. In the wild they must migrate up and down rivers throughout their lives. When I give my fish flake food, these shrimp always dart forward and snatch the largest flakes. They then fold up the flakes into what looks like origami shapes before munching on them. I assume they fold their food this way to make a large flake less cumbersome to move with – or perhaps they just like origami.

Origami is a Japanese art of folding paper. According to wikipedia: The goal of this art is to transform a flat sheet of material into a finished sculpture through folding and sculpting techniques, and as such the use of cuts or glue are not considered to be origami. I have a number of origami how-to books from which I could make creatures from sea stars to giraffes – I don’t do a lot of folding, I just have some books.

Origami is an applied geometry that has practical applications beyond making pretty cranes. Origami folds can be planned mathematically as there are a limited number of ways a piece of paper can be folded. Computational origami extends the math to optimize folds for practical like folding an airbag for car or finding an efficient way to fold solar panels to make the journey to space.

Interesting links here and here.

Tippy fish

I had a little aquarium on my desk before we moved. Now that we have space I’m setting up a much larger tank but I haven’t transfered over my fish yet. So right now my little aquarium is sitting on a dresser in front of a window. It’s a west-facing window, so in the evening the sunlight comes pouring in the side of the tank. I looked in my little aquarium a couple of evenings ago and my cardinal tetras were swimming on their sides. Something had to be wrong! A terrible tetra plague? Inner ear infections for all? I immediately called in my fish biologist spouse. He took one look at the tank and laughed. It turns out my fish were just confused.

As I’ve mentioned in one of my other blog posts, cardinal tetras are small fish with vivid iridescent blue and deep scarlet stripes. Cardinal tetras come from shallow tributaries of the Negro and Orinoco Rivers in South America. Their habitat changes as wet and dry seasons cycle each year, and they move from flooded forest areas to crowded streams when the water is low. The middle Negro is the primary fishing area for these fish, where about 20 million of them are captured annually. About 90 % of fresh water aquarium fish are bred in captivity, but some, like cardinal tetras, don’t cooperate and breed easily in captivity and so are caught in the wild. It has been demonstrated that well-managed fisheries for some aquarium fish (like the quick-to-mature, and naturally prolific cardinal tetra) can actually provide a good living for folks living in rural tropical areas – in fact it can pay better than farming and fishing for food, is way safer than mining for gold, and better is for the environment than cutting down the trees. The tough part is determining if a specific fish came from a well-managed fishery – which I don’t have an answer for.

So why are my fish tipping? It turns out to be a phenomenon called phototaxis: cardinal tetras orient themselves based on the direction light is hitting them. In their wild jungle habitat, the sunlight is always coming from above and provides a frame of reference that the fish use to align their own, internal, up/down direction. In my tank, the afternoon sun is coming through the side so they line themselves up as if the sun was coming straight down.

I would include a picture but the algae really likes the light and has grown on everything

Iridescence part I – little shiny fish

209f3-cardinal_tetraI keep an aquarium on my desk – just a little community tank with an ordinary grouping of fish: angelfish, corys, guppies and cardinal tetras. All have fascinating aspect that I enjoy watching but, from across the room the cardinal tetras, always catch my eye. Cardinal tetras are little, peaceful, schooling fish about 3 cm long, with colourless fins and two stripes running the length of their bodies; the top stripe is an iridescent blue and the bottom one is a vivid red. It’s the iridescent blue stripe that grabs my attention. Like the deep greens in a rooster’s tail or the rainbow colours in an oily puddle, the shimmering blue in my cardinal tetras originates from the optical phenomenon of iridescence.

Iridescence is the result of light striking a thin layer similar in width to the incoming light’s wavelength, also referred to as the distance from crest to trough. Because the layer depth is close to the light’s wavelength, light is reflected off both the top and bottom of the layer. As light bounces around, it interferes with itself. Interference is when two or more waves, alternately a wave and its reflected self, encounter each other and their amplitudes combine. Colour is simply light of a specific wavelength, so to amplify one colour, the two waves meet ‘in phase’ (aligned trough to trough and crest to crest). To negate or reduce another colour, the two waves meet ‘out of phase’ (aligned trough to crest). Because the wave alignment changes based on your viewpoint and/or changes to the layer itself, when you change your angle of view the colours change as well. An observer would see a colour of a certain hue – however if the angle of view to the layer is changed, by moving ones head or moving the layer as examples, the colour can appear different. This explains why patterns within the surface of an oil slick appear to swirl and shift as wind and water move the surface. Sometimes, interference can be the result of many layers of semi-transparent surfaces, where phase shifts may also occur in conjunction with many reflections and interference opportunities, creating multiple layers of iridescence.

If I took a picture of my fish, assuming they would stay still long enough for me to do so, the iridescence would not be reproduced – ordinary pigments and computer screens can’t do it. Instead I would need to make a hologram to capture the effect. A hologram also works through tricks with light, this time by interference and diffraction.

Back to my iridescent fish. The pearly blue stripe results from the presence of Guanine crystals in the cardinal tetra’s skin. These tiny multi-layered crystals are grown in the shape of a dinner plate within individual, almost dry chambers in the fish’s skin. Somehow the fish can control the shape of the growing crystals, because when these crystals are grown in a lab, they form a much more three dimensional shape. The fish’s crystals form a layer compatible with the wavelength for the colour blue, giving the fish a shiny blue stripe. So why do fish need this iridescent shininess? For some fish, the iridescence provides camouflage against the shimmering water surface when a predator is looking up from below or as a large school, little fish could produce a display so visually stunning that their predator gets confused. For my cardinal tetras, since they originate from tannin-stained, blackwater rivers in South America, most likely the iridescent strip allows them to find each other in the murky water and stick together in a school.

Someone, not me, could isolate these crystals and use them to add iridescence into lipstick, nail polishes and other cosmetic items (which is done). It takes about a ton of fish to make only 250 g of Guanine crystals. As I only have four cardinal tetras and no need of fancy lipstick or nail polish, I’ll continue to enjoy just watching my fish swim.

thanks to G. Hanke for the photo as I didn’t have the patience to wait long enough to get one.