ICES Advice 2013, Book 9 1

9.3.3.7 Special request, Advice October 2013 ECOREGION Widely distributed and migratory stocks SUBJECT NEAFC request to ICES to evaluate the extra harvest control rule options

for the long-term management plan for blue whiting Advice summary ICES reaffirms the precautionary reference points given in its response of June 2013 to the special request from NEAFC on the long-term management plan for blue whiting, (Section 9.3.3.1). ICES confirms that the value of F0.1 is currently estimated to be 0.22. ICES advises that the value of FMSY is considered to be 0.30 and this replaces the F0.1 proxy for FMSY of 0.18 from the advice of September 2012 (Section 9.4.4). For the fixed target Fs of 0.22, 0.25, and 0.30 the HCRs are shown to meet the ICES precautionary requirements of less that 5% probability of SSB< Blim over a ten-year period. The proposed multistage HCRs are shown to meet the ICES precautionary requirement of less that 5% probability of SSB< Blim for the recruitment regimes simulated over a 40-year period (12 years of normal recruitment followed by 8 years of high recruitment and, finally, followed by 20 years of low recruitment). The request proposes a new multistage HCR with two optional values for a slope parameter (a2). The results of the evaluations showed that the HCRs gave similar performance with both values and no differences could be seen in the plots of SSB and F. The increase in F at high biomass leads to greater catch variability and 4% higher yields over the 40-year period simulated (particularly during periods of high recruitment). The multistage HCR leads to higher interannual variability (IAV) in TAC during the period of declining stock as recruitment changes from the high to the low regime. IAV for the multistage HCR is 33% compared to 25% for the F target of 0.22. Two extreme cases of banking and borrowing were evaluated (either continually banking or borrowing the full allowable amount). Both showed negligible differences in terms of F, SSB, or probability of SSB< Blim. The advice for TAC levels (2014) according to the different target F options (0.22, 0.25, and 0.30) outlined in this request were also provided in the advice issued in October 2013 (Section 9.4.5). For the multistage HCR with either slope option the target F for 2014 is 0.30, which is also provided as a catch option in the October 2013 Advice. Request ICES delivered an advice to a special request from NEAFC on blue whiting management strategy in June 2013 (ICES, 2013a). This advice was presented by ICES at the NEAFC PECMAS meeting in June 2013. Following some discussion by PECMAS it was concluded that a few elements would be good to have further clarified and a few more scenarios would be useful to get tested. Therefore, NEAFC forwarded the following request to ICES:

“ICES is requested:

1) To advise on whether the precautionary and MSY reference points given in its response of June 2013 to the special request from NEAFC on the long term management plan for blue whiting, are considered to be valid, in particular

a) That the value of F0.1 is considered to be 0.22 rather than 0.18, as stated in the advice of September 2012 b) That the value of Fmsy is considered to be 0.30 rather than 0.18, as stated in the advice of September 2012

2) To confirm whether the current harvest control rule with three different F targets, 0.22, 0.25 and 0.30, is precautionary. In

addition ICES is requested to evaluate the F targets referred to in this point with an inter-annual quota flexibility of +/- 10 %.

3) To evaluate the “proposed HCR form”, as referred to in its response of June 2013, with the parameters shown below Figure 1, and with an inter-annual quota flexibility of +/- 10%.

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• A lower bound of F= 0.05 below Blim = 1 500 000 tonnes;

• A linear sliding scale with slope a1 starting at Blim and ending at Trigger

B1 = 2 250 000 tonnes; • A standard level between Trigger B1 and Trigger B2 at ICES best estimate of F0.1; • A linear sliding scale with slope a2 above Trigger B2, where Trigger B2 is

4 000 000 tonnes; and • An upper bound at higher stock sizes at ICES best estimate of Fmsy.

The evaluations should be done using values for the slope a2 of 2.0 and 3.0 as defined in table 9.3.3.1.5 of the ICES response of June 2013. ICES is also invited to suggest alternative values of the slope if these would be more precautionary or reduce inter-annual TAC variability.

4) To compare and tabulate the results in 2 and 3, as well as result of the current HCR, on the basis of effects on long-term

development of stock size, inter-annual variability in the catch and probability of stock size falling below Btrigger (B1).

ICES is requested to deliver its advice together with its October 2013 advice on widely distributed stocks. ICES is also requested to give advice for TAC levels (2014) according to the different options outlined in this request.”

In the text below, ‘current HCR’ refers to harvest control rules that exclude Trigger B2, Slope a2, and the upper bound (i.e. includes everything to the left of Trigger B2 in Figure 1 of the request). ‘Proposed multistage HCR’ refers to HCRs that include all the elements contained in Figure 1 in the request. Elaboration on the advice An improved version has been developed of the analysis tool “HCS program for simulating harvest control rules” (Version HCS13_4) using previous analyses (ICES, 2013a). Software description and instructions for users are available from the ICES Secretariat. The previous approach assumed knowledge of the current recruitment regime; however, this information would not be available in practice. Therefore, the simulations given here are based on short-term forecasts being based on the geometric mean of perceived recruitments from year −5 to year −2, relative to the intermediate year. The new evaluations also include a higher observation error (CV increased from 0.24 to 0.30) to account more completely for uncertainty in the assessment. Previous analyses only included assessment model errors. The simulations evaluate the proposed HCR by assuming a normal–high–low recruitment scenario, i.e. a normal recruitment for a period of 12 years until the regime shifts to high recruitment for a duration of eight years, followed by a low recruitment period until the end of the time period in the analyses year 2052 (see Figure 9.3.3.7.1). This specific regime was chosen as it was thought it would give a suitable test for the multistage HCR. Low recruitment has not previously been observed for a period of longer than five years, so the simulation of low recruitment for 20 years was considered a worst-case scenario and likely an extreme test. Thus, the risk of SSB being below Blim in the period 2043–2052, estimated to be greater than 5% in some of the simulations, is likely to be an overestimate. Therefore, the results for this period are not included in considerations of the ICES precautionary criteria.

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Re-evaluation of reference points The results of the new analysis are consistent with the precautionary and MSY reference points given by ICES in June and October 2013 (ICES, 2013a, 2013b). Evaluation of options for HCRs Following the overall approach used by ICES in June 2013 (ICES, 2013a) ICES has evaluated some additional HCR scenarios to answer the request above (ICES, 2013c). Summary performance statistics in terms of the development of stock size, interannual variability in the catch, and probability of stock size falling below Trigger B1 of all the HCRs evaluated for this request are provided in Table 9.3.3.7.1. The results for runs that include banking or borrowing are not shown because there is little difference in the performance statistics. Basis of the advice Background A management plan was agreed by Norway, the EU, the Faroe Islands, and Iceland in 2008 (ICES, 2012b). The plan uses:

i) a target fishing mortality (F = 0.18) if SSB is above SSBMP (= Bpa), ii) a linear reduction to F = 0.05 if SSB is between Bpa and Blim, and iii) F = 0.05 if SSB is below Blim.

In order to facilitate discussions between Coastal States on possible modifications to the long-term management plan for blue whiting in the Northeast Atlantic, ICES was requested by NEAFC to conduct an evaluation of the harvest control rule elements under the existing long-term management plan (ICES, 2013b). ICES provided a response in June 2013 (ICES, 2013a) and following that advice, NEAFC requested a few further options to be evaluated, as outlined in the request description above. Results Reference points The new data were consistent with the data used by ICES in June 2013 in terms of weight-at-age, maturity-at-age, and exploitation pattern. The small revision of the software tool used did not result in different estimates of F0.1 or FMSY compared to those presented by ICES in June 2013. Proposed HCR Harvest control rule with F targets (0.22, 0.25 and 0.30) The request required the evaluation of the current HCR with alternative F targets (0.22, 0.25, and 0.30). Figure 9.3.3.7.1 shows the performance of these alternatively parameterized HCRs compared with the current HCR (F = 0.18). Realised F values differ from the target F values due to observation and model errors included in the setting of the TAC (i.e. imperfect information from the true population) and because the stock often falls below the Trigger B1 under normal and low recruitment regimes. At the beginning of the high recruitment period F values decrease sharply since recruitment has increased, but as this would be unknown at the start of the high recruitment period it is not yet accounted for in the TAC setting procedure This assumes recent three-year average recruitment in the forecast. Conversely for similar reasons, F values increase when the recruitment regime changes from high to low. Under the low recruitment regime at the end of the time period, for all F target values the stock stabilizes at a level below the Trigger B1, leading to lower Fs. These lower Fs allow the stock to stabilize above Blim on average for all F targets. As the stock increases under the high recruitment regime, the higher target Fs result in higher TACs and restrict stock growth. Under lower target Fs, since the stock reaches a larger size this results in slightly higher TACs when the stock decreases after the change in regime from a high to a low recruitment. Under the normal and high recruitment periods the maximum annual probability of SSB< Blim is less than 5% (Figure 9.3.3.7.2). However, after seven years of the low recruitment the probability of SSB< Blim exceeds 5% when an F target of 0.30 is used. This risk increases to 8–9% over the last ten years of the simulation. Likewise, an F target of 0.25 leads to a greater than 5% probability of SSB< Blim in the last ten years of the simulation. Low recruitment has not previously been observed for a period of longer than five

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years, so this worst-case scenario which simulates low recruitment for 20 years is likely to be an extreme test. However, considering the low likelihood of consistently low recruitment and that density-dependent growth and maturity as well as cannibalism are not accounted for in the present analysis, the actual risks are expected to be smaller. Thus, the risk of SSB being below Blim in 2043–2052, estimated to be greater than 5% in some of the simulations, is likely to be an overestimate. Therefore, this aspect is not included in considerations of ICES precautionary criteria. Banking and borrowing Banking and borrowing was found to have a very limited effect for all alternative F targets (Figures 9.3.3.7.3 and 4). Figure 9.3.3.7.3 shows the performance of the HCR with an F target of 0.30 compared to the same HCR under scenarios of constant banking and constant borrowing. The most notable difference comes following the change from a high recruitment period to a low recruitment period. A scenario of constant banking leads to a delay in the reduction of TACs, leading to slightly higher F values and slightly lower SSB values. A similar pattern is seen for all alternative F target values (results not shown here). For higher F targets, after a sustained period of low recruitment there is a slightly higher but negliglible probability of SSB< Blim under constant banking and a slightly lower probability of SSB< Blim under constant borrowing (Figure 9.3.3.7.4). Proposed multistage HCR The request proposed specific parameters of the new HCR. The evaluations were done using these parameters, with values for the slope a2 of 2.0 and 3.0 (Figures 9.3.3.7.5 and 9.3.3.7.6). These two slope values perform almost identically (the lines overlap in Figure 9.3.3.7.5). The proposed rule leads to higher Fs at all stock sizes compared to the current HCR. When SSB is greater than Trigger B2 (4000 kt) the proposed rule leads to higher Fs and TACs and lower SSB. Following the transition from a high recruitment regime to a low one, the current HCR provides higher TACs since the F values are reduced to similar levels for both HCRs while the stock size is allowed to be larger during the periods of high recruitment under the current HCR. After a period of sustained low recruitment, the probability of SSB< Blim is slightly higher under the proposed HCR than the current HCR (Figure 9.3.3.7.6). However, even under this unlikely scenario of sustained poor recruitment, the maximum annual probability of SSB< Blim remains below 5% for both rules. The reason for the minor difference between the two different slope options is that they are both rather steep and that the F of the HCR switches very quickly from 0.22 to 0.30. Methods The main differences from the approach used in June 2013 (ICES, 2013a) were the higher observation error and the decision process where recruitment predictions in the short-term forecast were different. In June 2013 these were according to a deterministic stock–recruitment function, with parameters representing the regime at the beginning of the projection period which was not realistic. To address this issue, the present simulations are based on the geometric mean of perceived recruitments from year −5 to year −2, relative to the intermediate year. Sources ICES. 2012a. Report of the Working Group on Widely Distributed Stocks (WGWIDE), 21–27 August 2012, Lowestoft,

UK. ICES CM 2012/ACOM:15. 931 pp. ICES. 2012b. Blue whiting in Subareas I–IX, XII, and XIV (Combined stock). In Report of the ICES Advisory

Committee 2012. ICES Advice, 2012, Book 9: 100–113. ICES. 2013a. NEAFC request to ICES to evaluate the Harvest Control Rule element of the long-term management plan

for blue whiting. In Report of the ICES Advisory Committee 2013. ICES Advice, 2013, Book 9, Section 9.3.3.1. ICES. 2013b. Blue whiting in Subareas I–IX, XII, and XIV (Combined stock). In Report of the ICES Advisory

Committee 2013. ICES Advice, 2013, Book 9, Section 9.4.5. ICES. 2013c. ICES Ad Hoc Group on blue whiting management plan evaluations. Authors: David C. M. Miller and

Dankert Skagen. ICES CM 2013/ACOM:76.

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Figure 9.3.3.7.1 Mean performance of the current management plan HCR with F target options of 0.18, 0.22, 0.25, and 0.3 under the changing recruitment scenario of normal (ten years), high (eight years), and low (20 years) recruitment. No banking or borrowing is included.

Figure 9.3.3.7.2 Annual probability of SSB< Blim for the current management plan HCR with alternative F target options of

0.18, 0.22, 0.25, and 0.3 under the changing recruitment scenario of normal (ten years), high (eight years), and low (20 years) recruitment. No banking or borrowing is included.

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Figure 9.3.3.7.3 Mean performance of the current management plan HCR with an F target option of 0.3 under the changing recruitment scenario of normal (ten years), high (eight years), and low (20 years) recruitment.

Figure 9.3.3.7.4 Annual probability of SSB< Blim for the current management plan HCR with alternative F target options of 0.18, 0.22, 0.25, and 0.3 under the changing recruitment scenario of normal (ten years), high (eight years), and low (22 years) recruitment. No banking or borrowing is included.

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Figure 9.3.3.7.5 Performance of the proposed HCR compared to the current HCR under the high recruitment scenario.

(Normal and low recruitment are not relevant here – these scenarios are illustrated above (Figure 9.3.3.7.1) because the stock seldom gets above Trigger B2.) The proposed HCR is: F = 0.05 below Blim (1500 kt), Trigger B1 = 2250 kt, standard F = 0.22 between Trigger B1 and Trigger B2, Trigger B2 = 4000 kt, and F increases to an upper bound of F = 0.30 along a slope a2 = 3 (red) or a2 = 2 (blue). Note that the blue line is overshadowed by the red line in each plot because the results are almost identical.

Figure 9.3.3.7.6 Performance of the proposed HCR compared to the current HCR under high recruitment scenario. The

proposed HCR is: F = 0.05 below Blim (1500 kt), Trigger B1 = 2 250 kt, standard F = 0.22 between Trigger B1 and Trigger B2, Trigger B2 = 4000 kt, and F increases to an upper bound of F = 0.30 along a slope a2 = 3 (red) or a2 = 2 (blue). Note that the blue line is overshadowed by the red line in each plot because the results are almost identical.

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Table 9.3.3.7.1 Summary performance statistics of all the HCR evaluated for the second request. Results for runs including banking or borrowing are not shown since these performed very similarly to runs without banking or borrowing. During sustained low recruitment the stocks will on average stabilize at a level above Blim for all HCRs, though for target Fs of 0.25 and above the probability of SSB< Blim exceeds 5%. Low recruitment has not previously been observed for a period of longer than five years, so this worst-case scenario which simulates low recruitment for 20 years is likely to be an extreme test. Thus, the risk of SSB being below Blim in 2043–2052, estimated to be greater than 5% in some of the simulations, is likely to be an overestimate. Therefore, this aspect is not included in considerations of ICES precautionary criteria.

2013–2017 First 5 years (Short term)

HCR* Catch F SSB TAC IAV % Max annual P(SSB< Blim) Max annual P(SSB< Btrigger)

Current MP 636 0.18 4292 25 0.001 0.132

0.22 721 0.22 4109 30 0.002 0.227

0.25 775 0.25 3983 33 0.010 0.306

0.30 850 0.29 3795 40 0.029 0.423

New MP_a2 = 2 778 0.25 3941 36 0.012 0.278

New MP_a2 = 3 781 0.25 3934 37 0.012 0.28

2043–2052 Last 10 years (Low recruitment equilibrium)

HCR* Catch F SSB TAC IAV % Max annual P(SSB< Blim) Max annual P(SSB< Btrigger)

Current MP 291 0.16 2274 35 0.009 0.626

0.22 294 0.17 2118 45 0.033 0.721

0.25 296 0.18 2044 51 0.058 0.764

0.30 300 0.20 1958 60 0.105 0.836

New MP_a2 = 2 289 0.17 2102 46 0.036 0.724

New MP_a2 = 3 289 0.17 2102 46 0.036 0.723

2012–2052 All years (Including normal, high, and low recruitment periods)

HCR* Catch F SSB TAC IAV % Max annual P(SSB< Blim) Max annual P(SSB< Btrigger)

Current MP 635 0.17 4424 26 0.009 0.626

0.22 677 0.20 4068 32 0.033 0.721

0.25 701 0.22 3857 37 0.058 0.764

0.30 730 0.25 3581 45 0.113 0.836

New MP_a2 = 2 709 0.22 3758 36 0.036 0.724

New MP_a2 = 3 709 0.22 3753 36 0.036 0.723

*No banking or borrowing.