Distributional Patterns, Habitat Overlap and Trophic Interactions of Species Caught by Trawling in the Ragay Gulf, Philippines

Issue Date

3-2009

Abstract

The impact of trawlers on the fisheries ecosystem was investigated using the distribution of trawl fisheries catch in Ragay Gulf, the degree of overlap of species caught with those from other coastal fisheries and the trophic flow structure of the components of the system. Multivariate analysis of the exploratory trawl-fishing survey revealed northern and southern species clusters associated with prevailing circulation patterns and phytoplankton density in the gulf. Further analysis of the trawl catch composition showed two more clusters which indicate spatial distribution and intensity of the trawl fishery. These areas were differentiated as "highly fished" and "less fished." More than 50% overlap in species from these different habitats (coral reef, seagrass, mangrove and soft bottom) caught in the multispecies fisheries has implications on municipal water jurisdictions, especially on coastal communities where trawling is a source of living and food. The 45-yr historical reconstruction of trawl fisheries in the gulf using ECOSIM showed a significant decrease in the biomass of large, high-value fish groups and also an increase in small reef-associated carnivores and cephalopod biomass, because of ecosystem overfishing. The subsequent 100-yr simulation showed a shift to small reef-associated species as an effect of trawling activity. Minimal change on the small reef-associated species is noted when there is a complete ban on trawl fishing in the gulf but shows an increase in large carnivores. Coastal zoning schemes should consider the benefits derived from the ban on trawl fishing as also affirmed by anecdotal fisher accounts. In addition, the implications of the effects of trophic interaction and ontogenetic habitat connectedness have a profound influence on the overall dynamics of the fisheries ecosystem.

Source or Periodical Title

Philippine Agricultural Scientist, The (Formerly: The Philippine Agriculturist)

ISSN

0031-7454

Volume

92

Issue

1

Page

46-65

Document Type

Article

Frequency

quarterly

Physical Description

maps ; graphs ; tables ; references

Language

English

Subject

distribution pattern, ECOSIM, species composition overlap, trawl biomass, trawl fisheries, trophic flow structure

En – AGROVOC descriptors

TRAWLING; TRAWLERS; HABITATS; MULTISPECIES FISHERIES; COASTAL FISHERIES; COASTAL ECOSYSTEMS; GULFS; MULTIVARIATE ANALYSIS; INTEGRATED COASTAL ZONE MANAGEMENT

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