Cruise report for the LAPE ecosystem survey on RV Celtic Explorer (CE0607)

Abstract

The LAPE project has completed an ecosystem survey using the research vessel R/V Celtic Explorer, operated from Galway, Ireland by the Marine Institute. The survey collected information on the abundance, biomass and distribution information for pelagic forage species, as well as sampling for trophic relationships and physical and biological environmental sampling. This includes samples from numerous species rarely or never observed when sampling from fisheries catches. Acoustic bioma ss estimates have not been completed however the greatest biomass of forage species detected, both acoustically and by trawling, is predominantly mesopelagic fish, squids and crustaceans. The catches of epipelagic species were mostly juveniles of oceanic pelagic, coastal pelagic and reef species. This survey did not target, and did not catch, the commercially important pelagic species of the region. Flyingfish (Exocetidae) and dolphin (Coryphaena hippurus) are known to occur only w ithin a few meters of the surface, above both the acoustic transducers and the minimum fishing depth of the trawls. In addition, these and the adults of the other large pelagic species (Istiophoridae, Scombridae, Xiphiidae) are too fast and agile to be easily caught using pelagic trawls. The ecosystem survey also provided in-situ measures of biological oceanographic parameters to calibrate satellite estimates of primary productivity as well as information on key physical parameters of the water masses in the region. Preliminary inspection of the cruise results are all largely consistent with expected conditions in oligotrophic tropical oceanic waters (Longhurst, 1999). The primary production is limited to deep chlorophyll layers with essentially no chlorophyll or fluorescence measurable in near-surface waters. A cetacean sighting survey was conducted during daylight along the same transects. Although previous surveys have shown that the region does not have high concentrations of cetaceans the cetacean results are still surprisingly low. Since data are too few for a statistical analysis, a careful review of the cetacean survey is required to understand these extremely low results.