Measuring the balance between fisheries catch and fish production

Abstract

Balanced harvesting has been proposed as a fisheries management strategy to mitigate the impacts of fisheries removal on ecosystem structure. One definition of balanced harvest is that all species should be harvested in proportion to their annual production. However, most marine ecosystems lack comprehensive production estimates necessary to empirically measure the degree of balance. We developed and tested 2 new methods for estimating fish biomass production at the species level with limited data requirements. Application of our techniques to 4 ecological production units in the northwest Atlantic (Mid-Atlantic Bight, Georges Bank, Gulf of Maine, and western Scotian Shelf) from 1991-2013 provided a direct estimate of 1.9 million t yr-1 of total fish production. The degree of balance between catch and production distributions at the species level, assessed using the proportional similarity index, ranged from 0.34 to 0.83 on a scale from near 0 to 1. Increased balance was positively associated with yield in the Gulf of Maine (Spearman’s, p = 0.04). Increased balance was negatively associated with an ecosystem impact indicator in the Gulf of Maine (Spearman’s, p = 0.03) and Mid-Atlantic Bight (Spearman’s, p = 0.02). These case studies provide some evidence of benefit to humans and reduced ecosystem harm from more balanced harvest. More importantly, we provide a unique empirical metric of balanced harvest at the species level, and develop potential indicators and methods for ecosystem-based fisheries management.