Hello from just off Weymouth! We finally set sail last night after spending the first two days loading equipment & getting it all set up… and enjoying our last beers on land for a month.
So day one…
If anyone thought that scientists were high-tech, think again! Today we spent the day trying to calibrate the echosounder that we use for finding fish. How does this work? The echosounder basically transmits a sound into the sea directly below the boat, this sound reflects off fish, allowing us to ‘see’ where the fish are in the water column. Sounds good so far? Also we use different frequencies to allow us to determine fish species: different fish reflect different frequencies by different amounts. So, for example, a cod has a swimbladder (an organ that inflates or deflates with air to allow it to move up and down the water column), reflects more sound at lower frequencies (your ‘bass’ sounds) than at higher frequencies (your ‘soprano’ sounds). To allow us to compare the echoes at the different frequencies for the different species of fish, and also to allow us to estimate how many fish there are, we have to calibrate the system… hence today’s task… headed by Sophie Fielding from the British Antarctic Survey (aka the acoustician), with lots of help from Viv, Mick (pictured with the trusty calibration ball), & Gareth our trusty fishermen.
So… calibration… hmmm that high-tech business… hmmm. This (believe it or not) involves dangling a ping-pong sized metal ball (tungsten-carbide sphere for those who want to know) on 3 fishing lines (on fishing rods) below the boat, and into the middle of the narrow beam of the echosounder (think of the sound being transmitted vertically through the water in a narrow cone shape). Well, no easy task by any means… imagine a bunch of rather stressed looking scientists & technicians poring over fishing lines and over the side of the boat, peering into the depths, making small adjustments to the fishing reel while muttering into a radio. That was calibration! Well plus a large dose of stress! Let’s put it this way… it’s challenging to try and get the ball to stay in position when you have a large tidal current pushing it against where you want it to be. Plus getting seaweed stuck on the ball doesn’t help get an echo back from it! But finally, after a long day starting at 4:30am and ending at 8:30pm we have 3 calibrated echosounders, & we’re ready for our fish! THANKS SOPHIE!
Now, sleep… and offshore into the windy weather that is coming our way… batten down the hatches!
:o) Sleepy Clare