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Acoustic biomass estimates of pelagic forage species in the offshore waters of the Lesser Antilles

Scientific Basis for Ecosystem-Based Management in the Lesser Antilles Including Interactions with Marine Mammals and Other Top Predators (LAPE)







Scientific Basis for Ecosystem-Based Management in the Lesser Antilles Including Interactions with Marine Mammals and Other Top Predators: Acoustic biomass estimates of pelagic forage species in the offshore waters of the Lesser Antilles, by Melvin, G, P Fanning2, C O'Donnell, M Dahl, L Edwards, R Gardner, H Simon and D Theophille, FAO, Barbados, 2008. viii + 46 pp., 6 Tables and 7 Figures, FI:GCP/RLA/140/JPN. Technical Document No. 6


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    Cetacean surveys in the Lesser Antilles - 2000-2006
    Scientific Basis for Ecosystem-Based Management in the Lesser Antilles Including Interactions with Marine Mammals and Other Top Predators (LAPE)
    2007
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    Sighting surveys are the principal means of obtaining information about the species, abundance, distribution and movements of marine mammals and other air-breathing groups. During the course of the project a number of cetacean sighting surveys were conducted in both near-shore (small-scale) and offshore (large-scale) waters of the Lesser Antilles Pelagic Ecosystem (LAPE). In addition, the results from additional surveys, conducted in the same area for the period 2000-2003, were compi led and incorporated into the present analysis. With one exception, statistical analysis of the surveys was not possible due to small numbers of sightings. In the one case where an analysis was completed it was based on species aggregated into groups of similar behaviour (for sighting purposes). Estimates of the abundance of the aggregate groups had high coefficients of variation, ranging from 0.34 to 0.89. The species identified in the surveys were all known to be present in the reg ion although one important group of cetaceans reported to be in the region, the killer whales (e.g. Orcinus orca, Pseudorca crassidens, Feresa attenuate), was not observed during any of the LAPE project surveys.
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    Cruise No 1/95 First version - Studies of survey methodology for hake, 16 January - 19 February 1995
    Cruise Reports Dr. Fridtjof Nansen
    1995
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    The main objective of the gear experiments under Part I is to study the effective fishing width of the standard bottom trawl for hake. Experiments will be made with different sweep lengths to study herding effects. Observations of possible escapement over the headline will be attempted. Required experimental conditions include reasonably good catch rates, good range of fish size and favorable bottom conditions. SCANMAR instruments will be used for monitoring and all catches will be measured and sampled. If a main part of the hake lifts from the bottom at night, target strength measurements will be attempted and "acoustic density" and "swept area density" compared. A further objective is to test and possibly calibrate the new type of otter board against the standard type. These tests must include different depths and other fishing conditions. Studies will also be made of the large mid water trawl fishing for pelagic hake.
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    Cruise report for the LAPE ecosystem survey on RV Celtic Explorer (CE0607)
    Scientific Basis for Ecosystem-Based Management in the Lesser Antilles Including Interactions with Marine Mammals and Other Top Predators (LAPE)
    2006
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    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.

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