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The ICES has issued its assessment of a new rebuilding plan for western horse mackerel to the EU Commission and PELAC
The ICES has issued its assessment of a new rebuilding plan for western horse mackerel (Trachurus trachurus) in ICES Subarea 8 and divisions 2.a, 4.a, 5.b, 6.a, 7.a–c, and 7.e–k.
ICES advises that the evaluated rebuilding plan as proposed by PELAC shows potential to reach the specified target (three consecutive years > Bpa) within the time frame specified in the plan (< ten years) and is considered to be precautionary in the long term. The time frame to rebuild the stock is estimated to be two years longer following the rebuilding plan (by 2028) compared to zero catch (by 2026) given current starting conditions.
Once rebuilding is achieved, ICES advises that alternative harvest control rules (HCRs) should be examined for long-term management of the fishery to satisfy maximum sustainable yield (MSY) objectives.
On 19 October 2020, ICES received the following request from the European Commission, accompanied by a PELAC evaluation report (Pastoors et al. 2020): ICES is requested to evaluate the proposal for a rebuilding plan for Western Horse Mackerel as prepared by the Pelagic Advisory Council in July 2020:
- In particular, ICES is requested to assess whether this plan is seen as precautionary on the short term as well as on the long term.
- ICES is furthermore requested to assess whether the plan is consistent with the objectives to ensure stock recovery and bringing the biomass above sustainable levels within the indicated timeframes, and whether it is consistent with the maximum sustainable yield objectives of the CFP.
- Should the proposed plan include elements that are in contradiction with ensuring that the stock is fished and maintained, also in the future, at levels which can produce MSY, ICES is requested to comment specifically on such elements, and their consequences for ensuring MSY.
ICES has not yet defined fixed criteria for evaluating rebuilding plans, this plan has been evaluated against the targets and time frames set out in the plan (Annex 1). The western horse mackerel stock is currently estimated to be close to Blim, so for any harvest rule there will always be some risk in the short term of SSB being below Blim. The proposed rebuilding plan has a rebuilding time frame of a maximum of ten years.
The stock is considered to be rebuilt when SSB is estimated to have been above Bpa with a 50% probability for three consecutive years.
The application of the proposed double breakpoint rule with a target fishing mortality of F = 0.074 (FMSY) shows a high probability of rebuilding of the stock in the short term. Based on the 2020 assessment, the first year that the rebuilding probability is estimated to be more than 50% is 2028. The probability of SSB being below Blim is estimated to be less than 5% by 2025.
The rebuilding plan HCR is based on a target fishing mortality of FMSY and is considered to be precautionary in the long term.
The timing of rebuilding of the stock has been shown to be sensitive to the recent higher recruitment. If that higher recruitment does not materialize or is fished sooner than expected, the rebuilding of the stock will be delayed. Recovery is still expected (2031–2035) but may exceed the ten-year time frame. This evaluation was conditioned on the 2020 assessment; if future assessments downscale the stock size estimates significantly, this will also delay the time required to reach the targets outlined in the plan.
Should the reference points for this stock be revised before rebuilding has been achieved, it will be necessary to re-evaluate the performance of the HCR.
The 20% TAC constraint defined in the rebuilding plan allowed for quicker rebuilding times but contributed to long-term fishing mortality being below the target F. The rebuilding plan showed that large reductions in TAC could occur when the SSB was below Btrigger and TAC constraints did not apply. Once the stock subsequently climbed above Btrigger, the 20% TAC change limits applied to a low starting TAC led to fishing mortalities below the target F. Therefore, once rebuilding has been achieved, ICES recommends examining alternative HCRs for long-term management of the fishery to satisfy MSY objectives.
Articles 3.1 and 5.2 of the proposed rebuilding plan states: “…all attempts will be made to realise that target within five years.” It could be more clearly specified whether five or ten years is the preferred rebuilding time frame.
Article 3.2 could more clearly specify what probability of exceeding Bpa is expected before rebuilding is considered to have been achieved.
The development and adoption of a management plan for the provision of catch advice has been a long-term goal of the Pelagic Advisory Council (PELAC) since a plan was first proposed in 2008, and in 2020 a PELAC technical focus group was established to identify and evaluate a number of potential harvest strategies. Given the continued estimates of low stock size and recognizing that the risk to Blim in the short term will remain above the precautionary 5% threshold, the focus group evaluated candidate harvest rules on the basis of proposing a rebuilding plan. The PELAC submitted the evaluation for consideration to the European Commission, who requested that ICES review the evaluation (ICES, 2021a).
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