Balanced harvest: concept, policies, evidence, and management implications

Abstract

Balanced harvest has been proposed to reduce fishing impact on ecosystems while simultaneously maintaining or even increasing fishery yield. The concept has attracted broad interest, but also received criticisms. In this paper, we examine the theory, modelling studies, empirical evidence, the legal and policy frameworks, and management implications of balanced harvest. The examination reveals unresolved issues and challenges from both scientific and management perspectives. We summarize current knowledge and address common questions relevant to the idea. Major conclusions include: balanced harvest can be expressed in several ways and implemented on multiple levels, and with different approaches e.g. métier based management; it explicitly bridges fisheries and conservation goals in accordance with international legal and policy frameworks; modelling studies and limited empirical evidence reveal that balanced harvest can reduce fishing impact on ecosystem structure and increase the aggregate yield; the S. Zhou (&) CSIRO Oceans and Atmosphere, Rev Fish Biol Fisheries (2019) 29:711-733 https://doi.org/10.1007/s11160-019-09568-w( 0123456789().,-volV) (0123456789().,-volV) extent of balanced harvest is not purely a scientific question, but also a legal and social choice; a transition to balanced harvest may incur short-term economic costs, while in the long-term, economic results will vary across individual fisheries and for society overall; for its application, balanced harvest can be adopted at both strategic and tactical levels and need not be a full implementation, but could aim for a ''partiallybalanced'' harvest. Further objective discussions and research on this subject are needed to move balanced harvest toward supporting a practical ecosystem approach to fisheries.

Accounting for the bin structure of data removes bias when fitting size spectra

“…Size-spectra parameters have been selected by the European Union as one of several indicators used to evaluate sea-floor integrity (European Commission 2010, Rice et al 2012), and size-spectrum models continue to be widely applied (e.g. Taniguchi et al 2014, Álvarez et al 2016, Stasko et al 2016, Mindel et al 2018, van Gemert & Andersen 2018, Woodson et al 2018, Zhang et al 2018, Zhou et al 2019. Such applications require consistent calculation methods, especially when used for providing practical advice to fisheries (or ecosystem) managers.…”

Exploring Balanced Harvesting by Using an Atlantis Ecosystem Model for the Nordic and Barents Seas

“…Implementation of BH requires information on the production or productivity of all species, but the literature does not provide a single clear answer of how these should be used to set fishing mortality. There is an ongoing debate (Heath et al, 2017;Zhou et al, 2019) on whether fishing mortality should be set in proportion to productivity (P/B with the unit 'per time, ' as in this study) or in proportion to production (P with the unit 'mass per time'). The key difference between the two is that production (BH1) is density-dependent, while productivity (BH2) can be density-independent (Eqs.…”

“…The gross production was divided by the corresponding biomass to get a "per capita" productivity rate, often referred to as a P/B-ratio. This approach, setting fishing mortality proportional to the productivity or P/B ratio, is one of the alternatives suggested amongst BH-scientists (Jacobsen et al, 2014;Kolding et al, 2016;Zhou et al, 2019) and was the approach chosen for this study. It should be noted that there are other possible formulations (for a discussion of this, see Zhou et al, 2019).…”

“…If BH results in mimicking the natural mortality with predationlike fishing mortality, the evolutionary selection on life-history traits would be expected to be reduced. An implementation of BH would result in a more diverse fishing fleet with a wider range of fishing gears, and the risk of fishery induced selection on any trait is reduced (Zhou et al, 2019).…”

“…We merely aim to investigate what might occur if BH were to be implemented in an Atlantis model of the Barents Sea, and hope that the results of our work give some more concrete input into the overall debate. This paper does not focus further on this discussion, which is covered in a recent review of Zhou et al (2019), except to note that by using the Atlantis model we aim to include as much species realism in our analysis as is currently possible. Where species-specific details are poorly captured, we note this in the discussion.…”