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An adult and a pre-recruit toothfish.
The adults can
reach over 2 metres in length
and weigh in excess of 150 kg.
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So, why are we way down here by the Ross Ice Shelf as far
south as one can possibly fish? We are now half-way through carrying out
a research programme for CCAMLR. This is a ‘pre-recruit survey’
(scientist-speak for measuring those fish that are too young to spawn) – the
pre-teens of the Antarctic toothfish world if you like. Now just to be
clear there are two species of toothfish; Antarctic toothfish, which is what we
mainly catch in the Ross Sea region, and Patagonian toothfish, which are
largely caught in other fishing areas. Antarctic toothfish live further south
and generally grow larger and Patagonian toothfish have a more northern
distribution. Most media coverage on Ross Sea fishing issues incorrectly
report the catch as Patagonian toothfish.
Why are we doing this? The most important reason is to get a handle on what the fishery might be like in a few years’ time. The Ross Sea fishery is mainly based on adult fish and although we have a really good idea of the sizes (and thus the ages) of these, we know less about the population structure of the smaller fish which will replace them in the years to come. We know from previous work that the younger and smaller fish hang out here in the shallower water in the southern Ross Sea (the shelf). So we are fishing 65 different locations in order to collect these younger fish. We catch them, and then measure many of their characteristics such as their length, weight, sex, and some organ weights - we remove and store their otoliths (to get their ages), and then take tissue samples for a raft of other projects ashore.
Why are we doing this? The most important reason is to get a handle on what the fishery might be like in a few years’ time. The Ross Sea fishery is mainly based on adult fish and although we have a really good idea of the sizes (and thus the ages) of these, we know less about the population structure of the smaller fish which will replace them in the years to come. We know from previous work that the younger and smaller fish hang out here in the shallower water in the southern Ross Sea (the shelf). So we are fishing 65 different locations in order to collect these younger fish. We catch them, and then measure many of their characteristics such as their length, weight, sex, and some organ weights - we remove and store their otoliths (to get their ages), and then take tissue samples for a raft of other projects ashore.
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Drs Hanchet and Jo discussing the finer points
of fish
identification.
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What do we hope to understand from this work? Firstly,
whether there are differences in the numbers of young fish that survive after
hatching from year to year - and if so how much this varies from one year to
the next. We might then then be able to determine what environmental
factors influence this success. It is also an additional insurance policy
for the fishery, as this work will give advanced notice as to what we might
expect in the adult population a few years down the track.
Who is doing it? Well we have two scientists aboard –
Dr Stu Hanchet from New Zealand (NIWA) who
was one of the proponents of the work; and Dr Hyun-Su Jo from Korea’s National
Fisheries Research and Development Institute (NFRDI). There are also
two of us from Sanford and our two
scientific observers. All vessels working in CCAMLR Exploratory fisheries
like the Ross Sea must carry two observers at all times. We work 24/7
with three of us on a watch doing the sampling.
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Picking up our scientists from Cape Bird.
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On 4 February we picked up our scientists from Cape Bird on
Ross Island after we
finished our normal season. Thanks to a great break in the weather and the much
appreciated assistance and organisation of Antarctica New Zealand‘s Peter
McCarthy we got them aboard without difficulty. Most aboard also got
their first view of Ross Island, Mt Erebus and Mt Terror as
we rarely get close to the continent during normal operations. I really
hope the rest of our Our
Far South crew get a similar day when they get down here.
Next blog – our fine vessel.
