ICES French Southern Atlantic Bottom Trawl Survey for commercial fish species

The dataset includes age- and length-based catch per unit effort data for commercial fish species collected by the French trawl survey EVHOE.
For the 1987 to 1996 period, the Survey EVHOE has been conducted in the Bay of Biscay on an annual basis with the exception of the years 1993 and 1996. It has been conducted in the third or fourth quarter except in 1991 where it took place in May. In 1988 two survey were conducted, one in May the other in October.

The Celtic Sea was surveyed from 1990 to 1994 but the sampling was restricted to a small geographical area. The duration is between 40 to 45 days depending on year and availability of ship. Since 1997, the survey covered all the Celtic Sea and Bay of Biscay during the 4th quarter.

The French demersal survey began in 1987. The survey area was first limited to the Bay of Biscay (ICES Divisions VIIh, VIIIa,b,c and d) and in 1990, the survey area was extended towards the north to cover the grounds of Celtic sea deeper than 100 meters (ICES Divisions VIIe,f,g,h and j). 

Prior to 1997, the sampling designs were as follows: In the Bay of Biscay (ICES Divisions VIIh, VIIIa,b,c and d) a stratified sampling scheme was originally used. 

The area was divided according to latitude into 3 blocks and the hauls were distributed in seven depth zones (15-30, 31-80, 81-120, 121-160, 161-200, 201-400, 401-600 m). 100 hauls were made at fixed locations and 35 at changeable stations from year to year. Since 1989, all the hauls (mean number by survey 135) are made at the same locations.

In the Celtic Sea (ICES Divisions VIIe,f,g,h and j) the sampling design was systematic, stations were located at the intersection points of a grid of lines 25 nautical miles apart both in latitude and in longitude. The mean number of sets was 56.

From 1997 onwards the whole area has been separated in 5 geographical strata or sectors: southern Bay of Biscay (GS) and northern Bay of Biscay (GN), southern Celtic Sea (CS), central Celtic sea (CC) and northern Celtic sea (CN). In each sector a depth-stratified sampling strategy has been adopted with 7 depth ranges: 0-30, 31-80, 81-120, 121-160, 161-200, 201-400 and 401-600 m. 

The sampling design is a stratified random allocation. The number of hauls per stratum is optimised by a Neyman allocation taking into account the most important commercial species in the area (hake, monkfish and megrim). Minimum of two stations per stratum is sampled and 140 fishing stations are planned every year. This number of hauls is adjusted according to the ship time available at sea. 

Catch weight and catch numbers were recorded for all species, only selected finfish and shellfish species were measured until 1990. Since 1991, all finfish and a selection of shellfish (mainly nephrops and squids) are measured. 

Since 1997, the French survey has been carried out on the R/V Thalassa, a stern trawler of 73.7 m length by 14.9 m wide, gross tonnage of 3022 t. The fishing gear used is a GOV 36/47 without exocet Kite which is replaced by 6 additional floats. In average, the gear has a horizontal opening of 20 m and a vertical opening of 4 m. The doors are plane-oval with 1350 Kg.