The consequences of balanced harvesting of fish communities

Balanced harvesting, where species or individuals are exploited in accordance
with their productivity, has been proposed as a way to minimize the
effects of fishing on marine fish communities and ecosystems. This calls
for a thorough examination of the consequences balanced harvesting has
on fish community structure and yield. We use a size- and trait-based
model that resolves individual interactions through competition and predation
to compare balanced harvesting with traditional selective harvesting,
which protects juvenile fish from fishing. Four different exploitation
patterns, generated by combining selective or unselective harvesting with
balanced or unbalanced fishing, are compared. We find that unselective
balanced fishing, where individuals are exploited in proportion to their productivity, produces a slightly larger total maximum sustainable yield than
the other exploitation patterns and, for a given yield, the least change in
the relative biomass composition of the fish community. Because fishing
reduces competition, predation and cannibalism within the community,
the total maximum sustainable yield is achieved at high exploitation rates.
The yield from unselective balanced fishing is dominated by small individuals,
whereas selective fishing produces a much higher proportion of large
individuals in the yield. Although unselective balanced fishing is predicted
to produce the highest total maximum sustainable yield and the
lowest impact on trophic structure, it is effectively a fishery predominantly
targeting small forage fish