Estimating fishing exploitation rates to simulate global catches of
pelagic and demersal fish
Abstract
Robust projections of future trends in global fish biomass, production
and catches under different fishing scenarios are needed to inform
fisheries policy in a changing climate. Trust in future projections,
however, relies on establishing that the models used can accurately
simulate past relationships between exploitation rates, catches and
ecosystem states. Here we use fisheries catch and catch-only assessment
models in combination with effort data to estimate regional fishing
exploitation levels (defined as the fishing mortality relative to
fishing mortality at maximum sustainable yield, F/FMSY). These estimates
are given for large pelagic, forage and demersal fish types across all
large marine ecosystems and the high seas between 1961 and 2004; and
with a ‘ramp-up’ between 1841-1960. We find that global exploitation
rates for both large pelagic and demersal fish are consistently higher
than for forage fish and reached their peaks in the late 1980s. We use
the exploitation rates to globally simulate historical fishing patterns
in a mechanistic fish community model. We find a good match between
model and reconstructed fisheries catch, both for total catch as well as
catch distribution by functional type. Simulations show a clear
deviation from an unfished model state, with a 25% reduction in fish
biomass in large pelagic and demersal fish in shelf regions in the most
recent years and a 50% increase in forage fish, primarily due to the
release of predation pressure. These results can set a baseline from
which the effect of climate change relative to fishing could be
estimated.