Thursday, 28 August 2008

First Trawl

We just did our first trawl of the cruise. I was briefly worried we'd be swamped with fish, but my previous experiences with tropical trawling should have told me what to expect - not much of a catch! 15 odd kilos, in fact, after a half hour of trawling with a massive net. A lot (about 13 kg) of that was jellyfish, 3 big ones that weighed in at over 7 kgs, and over 400 little ones that were over 6 kgs!

On the left, you'll see Arrie proudly holding up a Selar crumenophthalmus. Sneakily mixed in with 15 of those was a Decapterus russelli, which looks quite similar lying around in a bucket! This is the thing with biology and particularly sorting collections of biological materials; it pays to really pay attention to very small details.

Jéssica and I spent a while keying out some small juvenile barracuda. Eventually we got kind of stuck after they started asking about colour patterns and other characters only present in adults. Apparently, one catches a lot of small barracuda, according to Sean, so it would help to have keys that work with babies too. We went off down the wrong track for quite some time because I didn't look carefully enough at the angle of the gill arch for gill rakers - there was one there, but it was hard to see without a microscope. What was I just saying about paying attention to small details...? We eventually decided they were either Sphyraena acutipinnis or africana, but couldn't be certain either way (some people consider these species synonymous).

Arrie and Jéssica are now busy taking samples of the catch for FishBol, part of the Barcode of Life project, the ultimate aim of which is to make accurate identifications of species much easier for non-taxonomic experts, but it requires being able to sample a region of the genetic code of the specimen called Cytochrome Oxidase I. The idea is that eventually, when technology moves forward, you'll be able to buy genetic "barcode scanners" and with a small piece of tissue, get a readout of what you're dealing with in a few moments without recourse to keys or even taxonomic experts for particularly difficult groups. Of course, until such magic arrives, you're stuck with taking along expert taxonomists, which is one of the fields I've been involved in during the past few years! Arrie's main involvement on board is to do genetic sampling; he does fish genetics work at the University of Pretoria. The photo on the left shows Jens, Jéssica and Magne sorting the catch.

Some of the catch:










A flying fish? In a trawl? It is! (On the left). We think this is Parexocoetus mento.










Some Sardinella.

In other news, we started trying to do some Bongo net plankton sampling, but the place where it was first deployed from was threatening to take out one of the pulleys for the CTD, which was obviously a bad thing! The Bongo was then moved aft; on the next time it was deployed, one of the cod-ends (the bit where all the samples ends up) fell clean off, and one of the nets developed a tear in - we have to fix that but just haven't had a chance yet, unfortunately.

We are currently running a series of acoustic survey lines, where we use the advanced echosounders aboard the ship to detect fish swimming in the water column. Any particularly interesting-looking aggregations are targetting with a net and collected to see what they actually are.

Before I go to bed (I should have hopped into bed at 6 and it's now nearly 10:30 - and I'm due to be back on shift at midnight until 6am!), I have an updated position for those of you following us on the map. A friend of mine has coded a neat little PHP application that reads all the google map URLs in this blog and plots a "cruise track" - I'll try and implement that tomorrow if he sends me the code and I get some time. It's really nifty! We're currently cruising along here.

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