Rapport de Campagne - Station Biologique de Roscoff

COMPTE RENDU DE CAMPAGNE A LA MER SUR UN NAVIRE Ifremer
H OP E 99
URM 7
Nom : HERRING
Prénom : Peter
Campagne : HOPE 99
Navire : L'ATALANTE - Submersible: NAUTILE
Organisme maître d'oeuvre : URM 7
Chef de mission : F. LALLIER
Première partie: du 9 au 26 avril 1999
Participants associés:
Ben BOORMAN
Institution : SOUTHAMPTON OCEANOGRAPHY David EDGE
CENTRE, UK
Rappel des Objectifs
The programme of trawling with the RMT system was aimed at identifing the fauna in
the water column immediately above the 13° N active sites. This would show whether any of
the mobile fauna seen at the sites during the submersible dives, or their larvae, extended
upwards into the overlying water column.
Travaux réalisés
Twelve nighttime trawls were achieved, each with three sets of nets. Ten trawls were
along the ridge axis over the active sites: 2 of these covered the depths from the surface to
1500m, 2 were between 2000and 2400m, 3 sampled at 2400-2500m, 1 at 2500-2550m and 2
were fished ~50m above the bottom. Net 2 was always open as the trawl passed over the main
region of active sites. Two samples were lost through technical problems but 28 were
successfully achieved.
Two off-axis trawls were made, for comparison with the tows down the ridge. One
was fished across the ridge and the other was in deeper water several km to the west of the
ridge. Both were fished at the same depth as the main trawls along the ridge axis (2400-
2500m).
Exploitation à terre
The RMT8 samples will be sorted and the major faunal components identified. The
catches of net 2 and of nets 1 and 3 will be compared to see if there is any clear influence of
the active sites on the respective samples. Biomass determinations will be made on the basis
of displacement volume. The RMT1 samples will be examined for the larger larval forms.
The pelagic fauna over the EPR will then be compared with that over the MAR sites,
sampled in 1997 during the MARVEL and FLAME cruises.
Commentaires
The first impressions of the trawl samples are that they comprise a typical
bathypelagic fauna, and that the active hydrothermal sites have little influence on the fauna
above them. Even the two trawls fished perilously close to the bottom (closest approach was
~25m) lacked any obvious components derived from the vent fauna. Despite the presence of
many Lebbeus at some locations, none were taken in any of the nets. However, 2 specimens
of Nematocarcinus sp. were taken, superficially similar to the species observed during
several dives. Juveniles of vent-associated animals included several postlarval macrurids and
three very young specimens of a cirrate octopod.
HOPE 99 Page 189 RAPPORTS SCIENTIFIQUES