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Derivation of diet compositions in the Lesser Antilles Pelagic Ecosystem

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

Year of publication 2008

Pages 77

Author Sherry Heileman, Elizabeth Mohammed and Paul Fanning;Fishery and Aquaculture Economics and Policy Division

Product type Project

Edition 1

Synopsis (short abstract) One of the medium-term objectives of the LAPE project is to enable fishery institutions in the Lesser Antilles to implement ecosystem approach to fisheries (EAF) management of the pelagic fisheries. An immediate objective of LAPE is the formulation of a food web model of the ecosystem to better understand the effects of fisheries on predator–prey relationships, and of the effects of food web dynamics on fisheries. This report presents average diet compositions of the 29 predator func tional groups, which include seabirds, marine mammals, turtles, fish, squid and zooplankton, in the LAPE model. The data were obtained through field sampling and analysis of stomach contents of a number of species of large and medium sized pelagic fish and marine mammals, as well as through a comprehensive search of published and unpublished literature. Data from 131 studies, of which about 8 percent were from the LAPE area, were used to derive the average diet compositions presented in this report. Despite the scarcity of data from within the LAPE area itself, a reasonable amount of data on same or similar species was available from adjacent areas in the Western Atlantic, including the Caribbean, and other areas mainly in the Atlantic. As expected, the availability of diet information was directly related to the commercial importance of the species. The analysis presented here does not consider differences in diet compositions arising from predator ontogenic changes and size, or seasonal changes in diets. A major problem encountered in a number of the studies was the low level of taxonomic disaggregation of the prey and relatively high proportion of unidentified prey items. Further studies are needed to better quantify diet compositions of the species in the LAPE ecosystem, including non-commercial species that might play an important ecological role.

Cite this content as:

Scientific Basis for Ecosystem-Based Management in the Lesser Antilles Including Interactions with Marine Mammals and Other Top Predators: Derivation of Diet Compositions in the Lesser Antilles Pelagic Ecosystem, by Sherry Heileman, Elizabeth Mohammed and Paul Fanning, FAO, Barbados, 2008. vii + 77 pp. 2 Tables and 1 Figure. FI:GCP/RLA/140/JPN Technical Document No. 7

Language English

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    Catch data are required for estimation of fishing mortality and for representation of fleet dynamics in the Lesser Antilles Pelagic Ecosystem (LAPE) model. The relative extractions by country and fleet type are used to investigate a range of policy scenarios (effort control) for management of shared stocks of pelagic species. A review by the LAPE project concluded that the use of the regional fisheries statistical system (CariFIS) database is still limited and that there remained dat a management issues which were major impediments to full implementation of CariFIS in national fisheries statistics systems. The additional time and technical assistance required to solve these problems are beyond the scope of the LAPE Project. It was necessary therefore to acquire the data by either extraction from international databases at Food and Agriculture Organization (FAO) and the International Commission for the Conservation of Atlantic Tunas (ICCAT) or a re-examination of country data holdings in the variety of software used (CariFIS, MS EXCEL, MS ACCESS). By preference, data were obtained from national sources; however, data were used from the international databases when individual country data proved inaccessible. This report documents the modifications to available data and assumptions made in arriving at estimates of total catch and value of pelagic fisheries in the LAPE region. It is not intended to give a detailed analysis of catches in the region, but rather to provide information in the format necessary
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    A recently completed survey of the Lesser Antilles pelagic ecosystem used a combination of multi-frequency acoustics and pelagic trawling to locate and estimate the biomass of forage species. Stratified zig-zag transects were used to investigate an area of 610 000 km2 in the waters east and west of the Lesser Antilles from Antigua to Trinidad. Distinct pelagic layers and aggregations observed acoustically were sampled using a multiple (3) codend pelagic trawl. Pelagic organisms were identified to the lowest taxon possible and categorized by the presence or absence of a swim bladder. The acoustic data were grouped into nine broad categories based on the multi-frequency returns considering backscattering strength, aggregation appearance, depth and time of day. The resulting acoustic density was converted to indicative biomass density (kg/m2) by application of target strength estimates from published sources. Relative abundance and composition of the nine acousti c categories for the 18 and 38 kHz frequencies are presented. The spatial distribution of these broad categories displayed several distinct patterns. There was an inshore-offshore segregation of some groups throughout the survey area, but there was little sign of latitudinal gradients in distribution of these broad groupings. In the open pelagic waters, diel vertical migrations were observed by several identifiable acoustic categories, particularly mesopelagic fish (largely Myctoph ormes and Stomiiformes), and squids. Dusk and dawn vertical excursions were observed daily between depths from 500 m to less than 100 m.
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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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