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

Adopting a risk tolerance of 50% indicates that the maximum exploitation rate that would allow the biomass objective to be achieved under average temperature conditions (mean tem- perature scenario 1990–2019) or where productivity had no dependence on temperature (Null) was about 7% and 6% under a density independent and density-dependent assump- tions, respectively (Fig 7, Table 1). For the 0.5˚C colder scenario, these values were about 9% and 8%, respectively and this translates to a climate conditioning factor greater than 1 (the fac- tor to multiply the exploitation rate in order to achieve risk equivalency i.e., maintain the same level of risk associated with the advice) and is resulting from plausible CC scenarios and risk- equivalent exploitation rates are summarised in equivalent to about 1.3 for both density depen- dent and independent models. Under the 0.5˚C warmer and increased temperature variance scenarios, the biomass objective was not possible to achieve (Table 1 - “NP”) thereby corre- sponding to a CCCF equal to 0.0 (no exploitation). This does not mean that the objective would be achievable in the absence of exploitation. Rather, it means that there are no options Fig 4. Four temperature scenarios for the environmental variable in the Gulf of St Lawrence over the next 10 years. The black line is status quo, i.e. the future is simply sampled from the past temperature distribution. The red line is the status quo temperature distribution with mean shift 0.5˚C warmer, the blue line the status quo temperature distribution shifted 0.5˚C colder and the green

line is the status quo mean but with the standard deviation of the distribution increased by a factor of 1.5. https://doi.org/10.1371/journal.pone.0239503.g004 PLOS ONE Climate-change conditioned risk-equivalent fisheries advice PLOS ONE | https://doi.org/10.1371/journal.pone.0239503 February 19, 2021 11 / 22