5 January 2004
We had the greatest New Year gift - almost flat sea, blue sky and the most magnificent view of Big Ben as we sailed so close on our acoustic work in the intensive predator study box. We now have a stunning portrait of the whole ship's complement (well most - somebody had to stay on the bridge driving the ship) in front of Heard Island in the sunshine.
At present we are in what we call the Macaroni Box. This is where the macaroni penguins have been foraging intensively. The rectangular intensive study area (box) just to the southeast of the island includes the foraging area and an area where they haven't been foraging. We are using acoustics to map out the distribution of fish and zooplankton in the box. This is followed by intensive day/night trawling in both the foraging and non-foraging areas to see if the species composition is the same in both areas and whether the vertical distribution and behaviour of the fish, krill and other zooplankton are likely to be the same too.
The acoustic mapping is going really well. Just to fill you in what this does… some of you will be aware of fish finders. The gear we use is an extra large fish finder. It works very "simply". Imagine sitting in a long soundproof hall which is divided by a soundproof wall down the middle, except at one end where there is a large opening from one half of the divided hall to the other. You are sitting on one side at the end away from the opening. Somebody is sitting on the other side of the wall beating a drum. You can hear the drum by how well the sound bounces off the end wall at the opening (the sound reflects around the corner of the wall into your half of the hall). How well you can hear the sound depends on what the wall at the end of the hall near the opening is covered with. If it is solid, say rock, you will hear the drum fairly clearly because the sound will bounce easily off the rock (echoes in a canyon). If the wall was covered in foam you will not hear it so well. If there was no wall at the end of the hall, you would not hear it at all.
That's how we know where the fish are - by sending sound waves through the water from a tiny but powerful drum in the bottom of the ship and listening for the return of the sound waves with a special device. Some fish, those with swim bladders such as icefish, are good at reflecting sound while other fish, those without swim bladders , ie toothfish, don't reflect sound well at all. The ability to translate the sounds we hear, acoustic marks, into abundances of fish is not so simple. It has a lot to do with physics of sound, seawater and the backscatter of sound expected off different types of materials. It also involves mathematical modelling and statistics. I won't go into those here (not only have theses and books been written about them to explain the intricacies of these calculations but equations don't transpose well in emails).
So we now have our first map of the distribution of fish in the macaroni box and have been trawling for the last few days. As you might expect, nature does not follow the carefully laid out experimental plans developed back home. Once we started trawling the penguins decided to change their diet slightly) and moved their main foraging location (also slightly) just to the east of the intensive study area. Bummer!
Disaster? No way. This was great! There was still some overlap with our intensive study area. The whole aim of our approach is to be adaptive and so we are analysing our acoustic and other data as we go. We had noticed in the latest acoustic data from mapping the area that some compensation in our design may be required. As a result we were ready to adjust our protocol to accommodate the change but not to compromise the results. We are talking with the island party daily to ensure we remain well coordinated and on top of how the predators are behaving, as well as being sure that any changes that we wish to make to our plans at sea are consistent with what our predator experts stationed on the island are observing and understand to be the behaviours of the predators. Interestingly, the macaroni penguins had partially shifted from a diet totally of krill and amphipods to include some fish in the diet. This coincides very well with the maps we have showing the distribution of fish and krill in the old and new foraging areas.
Time is a blur, now that the key dates are gone and we are into intensive trawling - non-stop, day and night for 4 days. We have breaks only around sunrise (approximately 4.00 am) and sunset (approximately 9.00 pm) when all the fish and krill move down and up respectively in the water (they can move over 200 m in depth, we can watch it on the acoustics screen). The reminder of the passing of another week is when you runout of clean clothes and have to weave in time in the laundry during the shift.
I had forgotten how much I enjoy fishing - the methodical deployment of gear, retrieval, and then the expectation of what you might find. It's a large team that makes it all happen and they are a great group to work with. When the seas are up, you can understand why commercial fishing is a very dangerous activity with such heavy gear swinging about, slippery decks, many whirring winches with cables and chains being pulled taught by the drag of the ship sometimes in different directions and the occasional wave being sucked up the trawl ramp flooding the deck. Lucky the guys down below (we watch from the safety of a mezzanine floor) all wear harnesses so that those nearest the ramp are attached with safety lines.
At the end of the trawl, the codend (the bag with all the fish) is untied and the fish fall into the bin to be sorted in the wet lab, usually less than a couple of kilos. The day/night cycle is very clear with fish appearing in the surface layers at night but only in deeper water in the day. I like trawling at night best. There is something about the cool (well, cooler) night air, the dark around and the yellow light of the trawl deck.
Those of us in the wet lab sorting are all trying to remember the names of each species. Dick rattles them off - Paradiplospinus, Notolepus, Electrona, Protomyctophum, Bathylagus, Gymnoscopelus, Melanostigma and so on. Tim and Stevie have seen a lot of them before as well. But for somebody like me who can't remember the names of people two seconds after being introduced it means reciting the names like a mantra in order to remember them and even then… Some I remember from a long time ago but it is putting faces to names that is really important. And what faces to remember! If you know what orange roughy look like then you have some idea of the large bony heads with very big eyes, but these fish vary in size from the size of your finger to the length of your forearm. Combine that with very black features and, on some, extraordinary toothy grins and you have the picture. We have even picked up a larval grenadier (rat-tail), the size of a large fingernail, which grows to the size of your arm. And we picked up a large one too.
We are also getting lots of jellyfish. The best so far was one with tentacles that stretched 3-4 metres. The net had picked it up whole. We had been towing into the current which means the long trailing tentacles would have been pointing directly into the sweep of the net. A great catch!
Ian, our communications officer (the third Ian on the boat - Andrews also make three), observed the other day the technology involved in this work. Tracking of the animals requires small transmitters carefully attached for a single foraging trip to the backs of the animals, satellite communication and transmission, receipt of the information from the tracking station via computer networks and satellite phone systems, acoustic information on the spatial and vertical distribution of fish and krill from acoustic and computing equipment, sampling of the animals in the water using trawls equipped with depth and location equipment, deep sea sampling devices (the CTD and benthic grab), underwater video equipment able to be used fully to 1000 m depth with laser guides for estimating distances in the videos and a control unit to help ensure the video unit is where it should be. The mind boggles.
We have been extraordinarily lucky with the weather. Apart from Big Ben having a prolonged burp at 40 knots for 12 hours we have been able to continue our work. The barometer fell precipitously the other day as the winds rose. It was expected to last for two days but instead the winds dropped to less than 10 knots. This afternoon we are expecting to batten down the hatches for 40-50 knots as a number of intense lows bear down on us. Hopefully it will hold off until we finish all our trawling for this area.
The fur seal intensive study area is next.