Marine

MRV Scotia Survey 0814S – Herring Acoustic Survey Complete

July 31, 2014 by Marine Directorate Communications No Comments | Category Marine Directorate general, Marine Directorate Science, Research Vessel Surveys

MRV Scotia has now completed the annual HERAS ( HERring Acoustic Survey), returning to Aberdeen on 17 July 2014. HERAS is an International Council for the Exploration of the Sea (ICES) co-ordinated survey with five countries taking a “snapshot” of herring stocks with coverage from the southern North Sea to north of Shetland and down the shelf edge as far as the Republic of Ireland. Unlike demersal surveys which rely on fishing hauls for stock estimation, the vessels involved in HERAS use echo-sounders to bounce sound off any shoals of fish. The more energy being returned, the more fish are there. Simple!  Further information about how stocks are assessed can be found in a short, very readable and appropriately named publication, Fish Stocks: Counting the uncountable?

Stock estimation is a difficult process;  it is akin to being asked to count the number of worms in your back garden. Ask yourself how would you go about it when you only have a teaspoon to do any digging.  That’s the problem that scientists have to tackle but with an exceptionally large garden and using vessels with acoustic systems as the teaspoon.

That’s the problem that scientists have to tackle but with an exceptionally large garden and using vessels with acoustic systems as spades.

MRV Scotia surveyed around 2,300 miles of track and carried out 42 pelagic (mid-water) tows to obtain biological information including species identification, sex, age and maturity of the fish. The catches were predominantly herring with a small quantity of mackerel mixed through. Other species noted were Norway pout, 0 group (< 1 year old) gadoids and  a couple of confused lumpsuckers.

Data from this cruise will be further  analysed and presented to an ICES working group in which the scientists from each survey will combine the data. The combined data will then be scrutinised by the Herring Assessment Working Group, they will add landings and observer data  and then an estimate will be made of the Spawning Stock Biomass (SSB). It is that estimate that eventually filters through to the pelagic fisherman as the Total Allowable Catch (TAC) and individual country quotas.

P J Copland
Scientist-in-charge on Scotia Survey 0814S

Comments