Wednesday, 15 February 2012

Counting fish

An adult and a pre-recruit toothfish.  
The adults can reach over 2 metres in length
 and weigh in excess of 150 kg.
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.
Drs Hanchet and Jo discussing the finer points 
of fish identification.  
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.

Picking up our scientists from Cape Bird.
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.