1. Introduction

In an agreement between NORAD, FAO and Institute Scientifique des Pêches Maritimes, Casablanca, the R/V "DR. FRIDTJOF NANSEN" was scheduled to carry out an acoustic survey on the stocks of small pelagic fish between Safi and Cape Blanc in the period August- September 1989.

The main objectives were to map the distribution of the main pelagic species, and provide estimates on their abundance. In addition as time and conditions would permit, there would be carried out target strength measurements on the principal pelagic species. A newly installed electronic equipment for analysis of echo from the sea bottom were to be tested. The purpose of this was to set up a system for automatic, logging of the quality of the sea bottom, calibrated by ground truthing.

If possible intercalibrations with the R/V Sharif El Idrissi were to be carried out.

The shelf was planned to be covered with acoustic transects at average 10 nm apart. In areas with high densities the sampling intensity could be increased, in order to obtain a more accurate mapping of the distribution limits of the aggregations. In areas with low densities or absence from fish the survey grid could be opened to 20 nm between the transects.

Participation

The scientific staff from Casablanca was:

Salah Bencherifi
Abdelhak Lahnin

The scientific staff from IMR was:

Tore Strømme
Helge Ullebust
Ingvald Svellingen
Martin Dahl

From Marine Microsystems, Dublin participated:

John Murphy (until 5 Sept.)

Narrative:

During the summer layup the vessel was under repair at Las Palmas. This work proved out to be much more extensive as planned and the departure was abt. 14 days delayed, with respect to the original plan.

At departure on 27 Aug the vessels acoustic system was calibrated in the harbour of Las Palmas. The vessel steamed to Safi, where the Moroccan scientists embarked. The survey started in the north at Cape Safi on 30 August. The vessel called on Agadir on 2 Sept. to disembark the engineer from Marine Microsystems and exchange the vessels officers. At Agadir the vessel met Sharif el Idrissi and a intercalibration session was planned. "Dr. Fridtjof Nansen" surveyed the waters off Agadir for 12 hours to find suitable targets for intercalibrations. The fish was however distributed to shallow to permit a controlled calibration, and the session had to be cancelled.

The R/V "Dr. Fridtjof Nansen then continued the acoustic coverage southwards. The vessel was regularly in contact with Institute Scientifique de Pêches Maritimes in Casablanca, reporting fish aggregations as they were encountered, together with the ships position. The survey was closed by passing Cape Blanc on 18 September.

The survey input in the various regions was:

Cape Safi to Agadir : 2 days, 375 nm sailed.
Agadir to Cape Juby : 7 days, 1200 nm sailed
Cape Juby to Cape Bojador : 2 days, 500 nm
Cape Bojador to Dakhla : 3.5 days, 810 nm.
Dakhla to Cape Blanc : 4.5 days, 1100 nm.

The weather conditions were good during the whole survey. The vertical distribution of the pelagic fish were at most time favorable for acoustic research, i.e. surface schooling were not frequent. The fish off Agadir and partly east of Cape Juby were however distributed fairly close to the shore, and the vessel could for navigational reasons not fully cover the inner distribution limits. This should however not constitute a major error in the estimates, as the vessel at most turning points were less than 1 nm from the shore.

Figure 1 and 2 show the course track with fishing stations.

Annex III gives a description of the acoustic instruments and the fishing gear used.