  Sustainable yields that are at least 80% of the maximum sustainable yield are
sometimes referred to as pretty good yield (PGY). The range of PGY harvesting
strategies is generally broad and thus leaves room to account for additional
objectives besides high yield. Here, we analyze stage-dependent harvesting
strategies that realize PGY with conservation as a second objective. We show
that (1) PGY harvesting strategies can give large conservation benefits and (2)
equal harvesting rates of juveniles and adults is often a good strategy. These
conclusions are based on trade-off curves between yield and four measures of
conservation that form in two established population models, one age-structured
and one stage-structured model, when considering different harvesting rates of
juveniles and adults. These conclusions hold for a broad range of parameter
settings, though our investigation of robustness also reveals that (3)
predictions of the age-structured model are more sensitive to variations in
parameter values than those of the stage-structured model. Finally, we find
that (4) measures of stability that are often quite difficult to assess in the
field (e.g.~basic reproduction ratio and resilience) are systematically
negatively correlated with impacts on biomass and impact on size structure, so
that these later quantities can provide integrative signals to detect possible
collapses.
