Fish harvesting advice under climate change: A risk-equivalent empirical approach

information and data to define a functional relationship between stock production and an environmental E variable, which can be modified and improved as more information becomes available in a manner consistent with a plausible hypothesis. Development of an EM model does not preclude the development of more detailed approaches later on that may capture uncertainty better, but they do allow us to proceed in the present rather than waiting for future developments before advice can be provided. CC is accelerating [2] and there are indications of non-linearity and possibly tipping points in many features of the environment affected by CC [36,37], particularly in Canadian and other higher latitude waters [38]. The time scales of many of the projections in the IPCC reports are consistent with CC driven factors potentially affecting fish production within rela- tively short time frames (e.g. 10 years) and where fisheries management advice that does not consider that change could be rendered invalid within that period. Many jurisdictions have requirements for setting of fishery objectives (e.g. target and limit reference points for biomass and exploitation rate) or established recovery targets and plans for collapsed stocks embedded in legislation and policy. The ability to comply with such targets, limits and/or rebuilding plans can be affected by non-stationary environmental conditions that can be driven by cli- mate and ecosystem change. These types of requirements and management standards increase

the need to provide fisheries advice that considers CC impacts as part of the body of advice for fishery managers. Developing this advice in a risk-based framework that informs decisions about risk equivalent exploitation is a particularly direct and transparent way for science to inform decision makers of the risk implications of their choices. Such advice has the strengths of being evidence-based, uses the available information about the how the environment impacts of environmental conditions on stock productivity, and clearly articulates the CC- related risks to the resource under various management options as risk increments (positive or negative) from status quo risk when CC is not considered (and the environment is assumed to be stationary). Similarly to how EMs are used to predict SLR from global temperatures with large-scale data and hypothesis directed [12], we have followed the same approach to make broad predictions about future states expressed in the form of incremental risk and risk-equiv- alent advice conditioning factors. The CC conditioning here considers first order non-stationarity where that non-stationar- ity is characterised by the P/B vs E relationship. Higher orders of non-stationarity could exist as well though they are rarely considered in fisheries. For example when a researcher surmises that the P/B vs E relationship itself has changed which could result from evolutionary impacts of fishing or through another driver of P/B change and physiological adaptation of the species

or the stock. Greenland halibut in the Gulf of St. Lawrence are stenothermic [39]. This lack of adaptability to a large range of temperature conditions of the stock combined with low oxygen conditions of bottom waters in the GSL (that are projected to worsen) means that there is a low adaptive capacity of this stock to compensate production losses with climate change. It has been conservatively predicted that this stock may lose up to 55% of its best habitat over a 20– 40 year period [39] with CC. The relationship between P/B and E used here captures some of this effect concurring that the habitat loss is likely to lead to important productivity losses for the stock and there is little compensatory capacity for adaptation. Development of EMs is an effective way to condition fishery advice to CC in the short- to medium-term. These models are relatively quick to implement and they tend to be robust because they are driven by broad phenomenological relationships and take advantage of emer- gent phenomena and constraints present in the climate forcing feedback system [40]. The EM approach should not be seen as a substitute for detailed mechanistic approaches but comple- mentary. EM methods can incorporate process-based understanding as knowledge increases, and when knowledge is sufficient, mechanistic approaches can take many of the elements of PLOS ONE Climate-change conditioned risk-equivalent fisheries advice PLOS ONE | https://doi.org/10.1371/journal.pone.0239503 February 19, 2021 17 / 22