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AN ACOUSTIC SURVEY OF ORANGE ROUGHY AGGREGATIONS TO THE WEST AND NORTH OF THE PORCUPINE BANK
Weitere Beteiligte (Hrsg. etc.): O'Donnell, Ciaran
|BK - Klassifikation:
||21.3 Küsten- und Hochseefischerei
|Sonstige beteiligte Institution:
||Bericht / Forschungsbericht / Abhandlung
||Irish Fisheries Investigations (Bd. 3-15, 17-20, 24)
|Kurzfassung auf :
||The survey was carried out over a 14 day period from the 5th – 20th February 2005 onboard the
65m RV Celtic Explorer. The main focus of this pilot survey was to acoustically survey orange
roughy (Hoplostethus atlanticus) spawning aggregations. In total, 7 commercially fished and one “pristine” area were investigated during the survey. Of the commercially fished areas 6 were made up of seamounds or hill features and one flat seabed area. The relative abundance of orange roughy recorded for all sites combined was 19,000t with a c.v of 40%, 62% if taken as an absolute estimate of abundance. Fishing operations were carried out by the 25m stern trawler the FV Mark Amay. A total of 32 successful trawls were undertaken. Fishing operations yielded a total of 39 species, with orange roughy dominating catches. Other main component species by weight include baird’s smoothead (Alepocephalus baiirdi); black scabbard (Aphanopus carbo)
and roundnose grenadier (Coryphaenoides rupestris). Flat ground areas produced the highest species diversity and the greatest length range of orange roughy. Hill features yielded fewer species in greater numbers, with larger orange roughy present around hill features. The physical properties of the water column at each of the 8 survey areas were measured using a total of 34 vertical CTD casts. Conditions varied between survey areas due to local bathymetric conditions.
Overall, Eastern North Atlantic Water (ENAW) dominated the first 1000m. From 1000m, a hyper-saline warm water mass of Mediterranean Sea Outflow Water (MOW), was identified in all areas to the south of 52°N and none in areas north of 54°N. A detailed investigation of two hill features (one fished and one pristine) using high-resolution multibeam, video and still imaging was carried out using the ROV Aglantha. ROV dives commenced at depth and advanced to the summit of the target feature. The commercially fished site was dominated by coral rubble; trawl door scars and degraded coral skeletons. At the “pristine” site species diversity was greater with coral thickets of reef forming species, soft coral bushes and little sign of anthropogenic impact. A total of 210 individual cetacean sightings were recorded (long-finned pilot whale and the bottle nosed dolphin) in addition to 12 seabird species.