The necessity to move from a traditional fishery
management to an ecosystem approach is now acknowledged. Indicators are
required to support the development of this approach. For example, community
indicators have been proposed to assess the impact of fishing. We tested
here the applicability of one such community indicator, the
abundance-biomass comparison (ABC method), as a measure of the impact of
bottom trawling (years of sampling: 2001 and 2003) on the benthic
invertebrates – typically starfishes, crabs, squat lobsters, shrimps and
large hard-shelled molluscs- of “Grande Vasière”, a major French
fishing zone, in the Bay of Biscay. The ABC method is generally used as an
impact indicator for different types of physical, biological and
anthropogenic disturbances on benthic communities. This method is based on
the assumption that increasing disturbance shifts communities from dominance
by large-bodied species with low turnover rates toward dominance by
small-bodied species with high turnover rates. At less disturbed areas the
average biomass of individuals is greater than at more heavily disturbed
areas. The ABC method measures this effect by comparing the ranked
distributions of abundance and biomass within a given community. We applied
the ABC method and compared the size structure and the species diversity at
two areas exposed to moderate and high bottom trawl effort. Species
diversity was lower in the most exploited area. The highly trawled area was
dominated by opportunistic organisms, mainly one species of swimming crab
Liocarcinus depurator, one species of squat lobster Munida rugosa and Norway lobsters
Nephrops norvegicus, which are large-bodied
species. Consequently, the results of the ABC method were inconsistent with
the theoretical expectation for these particular macrofaunal communities and
the measured levels of fishing intensity.
