  Zhou and Smith (2017) investigate different multi-species harvesting
scenarios using a simple Holling-Tanner model. Among these scenarios are two
methods for implementing balanced harvesting, where fishing is distributed
across trophic levels in accordance with their productivity. This note examines
the effects of a different quantitative implementation of balanced harvesting,
where the fishing mortality rate is proportional to the total production rate
of each trophic level. The results show that setting fishing mortality rate to
be proportional to total production rate, rather than to productivity per unit
biomass, better preserves trophic structure and provides a crucial safeguard
for rare and threatened ecological groups. This is a key ingredient of balanced
harvesting if it is to meet its objective of preserving biodiversity.
