11th November 2001
I’m still trying to work out the best way to get an accurate estimate of the catch size and composition. On the face of it you might think that you could weigh a box of fish, and multiply that weight by the number of boxes to know how much the total catch was. But of course there’s more to it than that.
I’ve been carefully watching how the factory operates so I can better understand where all the various components of the catch go, and therefore how best I can accurately measure them. I’ve described before, that the cod end (the end of the net) is emptied into a holding tank in the factory through a trapdoor in the deck. This tank or fish bin is where the journey through the factory starts. From the fish bin, fish pour out onto a conveyor belt where the crew pick off the commercial species into different bins ready for processing. All the ‘rubbish’ as the crew call it, remains on the belt which then empties into a discard chute and goes overboard. The ‘rubbish’ consists of mud, stones, broken corals, shells, starfish, crabs, shellfish, undersized fish etc. Basically everything that is non-commercial.
The commercial species are processed depending on their size and species. Some are just gutted, some have their heads and tails removed, some have their skin & scales removed, ray shaped species are ‘winged’, and a few are frozen whole. The processed fish are washed and put into trays to blast freeze before going into boxes and into the ship’s hold for storage. At the end of each trawl the bosun counts up the number of boxes of each type of fish and gives this information to the Captain.
In calculating the catch composition, firstly you have to consider the bycatch and discard (or the ‘rubbish’). These are all of the things that are caught but have little or no commercial value. Nobody bothers to weigh this stuff – it just goes overboard. As far as I’m concerned this is all the interesting stuff – all the benthic creatures, the ‘weird and wonderfuls’ and among it is the potential to spot something yet undescribed by science. But that’s another story. For now it’s important to consider that not everything in the net is wanted, so I have to estimate how much is being thrown back.
Then there is green weight or live weight and processed or product weight. Green weight is the the weight of the fish as it comes out of the sea ‘live’ including it’s head, tail and guts. Green weight is the figure that is needed to plug into the the calculations when calculating fish stocks, to issue fishing quota etc. Green weight is of concern to the biologist, but green weight is of little interest to the vessel. The vessel is interested in processed weight – that’s the weight of the fish they can sell. They can’t sell guts and starfish. The trouble is nothing is actually weighed until it has already been gutted and processed, so how can we work out what the live fish weighed when all we have is a headed and gutted trunk?
Conversion factors. You can use conversion factors to move from processed weight to green weight and vice versa. Approved conversion factors have been worked out for each species and for each type of processing. For example the conversion factor for headed gutted and tailed hake might be 1.4 so the green weight will be 1.4 times the processed weight. The accuracy of conversion factors is important, because any difference with reality may result in under or over reporting of catches.
Dinner was good, We had chips and ribs with a cake for afters. Not the healthiest dinner but one of the most enjoyable so far for it’s simple goodness and lack of gut churning ingredients like pig’s trotters or tripe!
I spent this evening updating the data further and making a new spreadsheet for the running totals. I’m happy and relieved to finally be getting my head around the figures and processes, and I’m enjoying learning all of it for myself however, I’m also keenly aware that I’m fresh out of university, new to all of this and I’m trying to not only learn the ropes, but to be able to do it with enough confidence to point the finger if need be, and potentially my data could be scrutinised in court. I really hope that Simon was wrong about the vessel mis-reporting, so far I can’t see any signs of them doing anything illegal. Fingers crossed.