Acoustic surveys are generally carried out on spawning and pre-spawning aggregations of fish. Outside of the spawning season many pelagic species are generally very scattered over a large geographical area and difficult to detect using acoustic methods. A cruise track is first formulated with data from previous surveys, commercial catch data and the help of the fishermen and fishing industry.
Purpose of Survey
The aim of an acoustic survey is to determine the relative abundance of the target species. This information is then used to determine catch rates and management advice for the following year.
How Acoustic Surveys Work
These surveys use sound waves emitted from a "transducer" to estimate the density of plankton and fish shoals. The survey vessel tows the transducer under water, which is linked to an echo sounder in the vessel which records the shoals of fish as "marks" on a screen or paper trace.
'Mark' of herring as seen on acoustic screen. The solid red line is the seafloor.
The species composition of each mark is then identified by taking trawl samples. The density and number of marks are then converted into biomass (weight) of the different species. Acoustic surveys are particularly effective on shoaling species that have a large swim bladder, such as herring and blue whiting.
Marine Institute Acoustic Survey Programme
We carry out acoustic surveys for three main species:
- Blue Whiting
Herring Acoustic Survey
Every year FEAS carries out two Herring Acoustic Surveys on the RV Celtic Explorer, the Northwest Herring Acoustic Survey (NWHAS) in early July and the Celtic Sea Herring Acoustic Survey (CSHAS) in the fourth quarter of the year. Each of these surveys takes three weeks to complete and covers around 3000nm of survey transects. As well as studying the target species, each survey also collects oceanographic data as well and provides a platform for students to carry out their own research, and for observers to record seabird and marine mammal activity.
Typical survey tracks of herring acoustic surveys.
Blue Whiting Acoustic Survey
Ireland participates in an International Blue Whiting Acoustic Survey (IBWAS), which as well as the RV Celtic Explorer from Ireland, involves vessels from Norway (RV G.O. Sars), Russia (RV Fridtjof Nansen), the Faeroe Islands (RV Magnus Heinason) and the Netherlands (RV Tridens) in spring each year. The total combined area coverage extends from the Faroe Islands in the north (60.30°N) to south of Ireland (52°N), with east -west extension from 6°-17° W. The 2014 survey was the 11th coordinated international blue whiting spawning stock survey since 2004.
Cruise track of all vessels involved in International Blue Whiting survey.
Boarfish are the newest species surveyed by FEAS. Boarfish surveys are carried out on commercial fishing vessels as part of an industry/science partnership. They take place each July.
The International Ecosystem survey in the Nordic Seas
Ireland also takes part in the International Ecosystem survey in the Nordic Seas. This is an acoustic survey for Atlanto-Scandian herring and blue whiting in the Norwegian and Barents seas. It takes place each May on board the Danish research vessel the RV Dana. Ireland sends biologists or acouticians each year. In turn, Danish and German scientists join us on our Blue Whiting Survey each March.
Recent Survey Results
Download the most recent and past survey reports from the Herring, Blue Whiting and Boarfish Acoustic Surveys which on our Open Access Repository.