Besides acoustics, we check out a few other things while we are in the area. As I mentioned before, our cruise follows at specific predetermined track. At various intervals along this track we stop for a ‘hydrographic station’ as part of our objective to monitor the physiochemical and plankton conditions. These stations are located about every 60 nautical miles or so, about 6 hours apart, and consist of two parts: the Seabird CTD and two WP2 samples.
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| Recording A Hydrographic Profile |
The CTD (Conductivity/Temperature/Depth) measures various things in the water column, such as temperature, salinity, conductivity, oxygen etc. Certain fish species can be very sensitive to these parameters and their geographical distribution can often be determined by this. Therefore this data can help us explain how their distribution may change from year to year. The CTD gives us a physiochemical profile of what is happening in the water column from the surface down to whatever depth we send it. We usually send it down to a maximum of 1000m below the surface or to just within 20m of the bottom on the eastern side near the shallower Barents Sea (which could be a shallow as 250m or so). Still pretty deep I guess. Sending it to 1000m and back takes the best part of an hour. I am usually in the sauna during these times, as there is not much else to do except watch a wire. The CTD can also take water samples at specific depths, and we do this once a day to make sure the machine is still well calibrated.
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| Straining The Ocean With A WP2 |
The next step is to take two separate samples of phytoplankton (little ‘plants’) and zooplankton (little ‘animals’). The amount (and type) of phytoplankton can give us an idea of the productivity of the area and zooplankton are often an important source of food for many fish. At each station we do a vertical haul from 200m depth using a WP2 net (I don’t know what that stands for). This is an extremely fine net (200µm mesh), which is necessary to filter out these micro-organisms from the sea water. Unfortunately that also means that in particularly rough conditions it is not possible to take a sample as the net could simply be destroyed. Once at the surface it needs to be hosed down with seawater to get all the plankton into the little jar at the bottom.
At random times during the cruise we decide to go fishing, usually once something shows up on the acoustics screen and we want to check what it was. This is done using a midwater trawl, a net towed behind the ship. Two massive, solid steel plates are attached by ropes on either side and these pull the net wide open (about 30m) as the ship moves. The mesh of the net gets progressively smaller towards the end, guiding the fish in from a broad area and then keeping them in the back of the net, the cod end.
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| The Trawl Net, Wound and Shot |
The whole operation is monitored from the fishing room, next door to the acoustics room. On some ships this is done from the bridge, but on the Dana the bridge is on the fore side and the fishing room, like a little mini-bridge, is aft. The captain or the first mate takes charge of things from here. The captain is an ex-fisherman and you can see the thrill of the hunt getting into his eyes when we set him out to fish.
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| The Fishing Room |
Down below, at the business end of the trawl operation, a team of four crew do the work. Three make sure the net is shot correctly (put out) and one controls the various winches to unwind the net. The crew wears cool Reebok ice hockey helmets instead of traditional hard hats. This old dude is the very definition of ‘sea dog’, and I never saw him at work without his pipe in his mouth. Even when he was off shift he would come out to check on things, coffee in hand, blowing smoke.
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| Ol’ Sea Dog |
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| Monitoring The Trawl |
Because this is just a scientific cruise and not a fishing operation, we rarely trawl for more than an hour. The best part of the fishing is when the haul comes in. I get excited at what we may bring in, dreaming of the great loads of herring and other pelagic wonders. It takes a painfully long time, 30min to 40min from once the hauling begins, to bring it in.
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| Hauling In The Net |
As the net starts to come on board it seems impossibly long, but eventually the cod end arrives.
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| The Cod End |
The cod end is where the fish are. Or, to be more specific, should be. But unfortunately far too often this survey we have be trawling mainly on vague acoustic markings, with few solid schools presenting themselves. In these pathetic cases the cod end is just emptied out into a bucket.
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| A Disappointing Haul |
If it is a decent size haul it gets raised up and released into this large funnel:
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| Emptying The Cod End |
From there it goes down this shoot:
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| Off To The Lab With you |
Into the fish lab, where it is weighed, measured, and samples taken for further analysis. Maturity stages are noted (immature, ripe, spent), parasites checked for, otoliths (ear bones) and scales taken for aging etc.
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| The Fish Lab |
Scrutinising the catch is much more fun than scrutinising acoustics. I roam around the lab in the time before the ship gets back on track while the fish people do their thing. As you can see it is not a very formal thing, no white coats and clean surfaces, though there are clipboards. Sometimes they are even casually sipping coffee.
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| Scrutinising The Catch |
Different surveys will have different protocols for particular species. On this survey the Germans were after information on redfish, a deep water pelagic species (usually found 300-1000m depth) that, due to a reasonable sparse scientific record, has fairly unknown population dynamics. Though herring have been very scarce this trip, by chance we have netted more redfish than ever before, and in the surface layers (<30m depth) which is slightly strange. We even caught a couple that were busy spawning. Redfish are ovoviviparous (try saying that when you’re drunk), which means they give birth to live larvae. We put a few in some water and could see them swimming around. Unfortunately these larvae are doomed to failure…
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| Redfish Larvae: Doomed |
The guy on the top left is a small squid, not a freak larvae.
Once the samples are taken and measurements made, the more tasty fish are filleted for out enjoyment. The rest goes out the poop hole and the seabirds and dolphins have their way with it. ‘Poop hole’ is not the technically correct term, but I’m not sure what it is called (if indeed it has a proper name a all) and this seems appropriately nautical and suitable for a large metal whale.
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| The Ship’s Poop Hole |
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