Workshop on mitigation measures to reduce bycatch of short-beaked common dolphins in the Bay of Biscay (WKEMBYC2)
29/06/2023: Update with three annexes (annexes 6, 7 and 8). Two of these annexes relate to mitigation scenarios applied to the Bay of Biscay (Subarea 8) only. In the initial WKEMBYC2 workshop and report that took place in November 2022, mitigation scenarios were applied to both the Bay of Biscay (ICES Subarea 8) and Iberian waters (ICES Division 9a). In order to facilitate direct comparison with previous work when only the Bay of Biscay was considered (ICES Subarea 8), an additional evaluation of mitigation scenarios, considering ICES Subarea 8 only, was conducted in May 2023 (See Annexes 7 and 8 in this report). Taking into account data from 2019–2021 and bycatch mortality estimates based on strandings data, none of the fifteen proposed mitigation scenarios can reduce bycatch of the common dolphin in the Bay of Biscay below the potential biological removal (PBR) limit. Based on data from 2019–2021 and bycatch estimates derived from at-sea monitoring data, six of the fifteen proposed mitigation scenariosare are likely to reduce bycatch of the common dolphin below the PBR limit.
Following the special request from the DG MARE, the Workshop on mitigation measures to min-imize bycatch of short-beaked common dolphins in the Bay of Biscay (WKEMBYC2) was estab-lished by ICES. WKEMBYC2 was tasked with updating and revaluating the scenarios previously proposed in the ICES special request advice in 2020. The group was asked to consider recent data on bycatch of common dolphins in commercial fisheries and total fishing effort in the Bay of Biscay and Iberian Coast ecosystem, as well as taking into account results from any mitigation trials carried out since the meeting in 2020.
In section 2 of this report the efficacy of the scenarios provided during WKEMBYC in 2020 were reassessed using updated bycatch estimates calculated from at-sea monitoring and stranding data collected between 2019 and 2021. Scenarios and methods remained unchanged, to ensure comparability between both evaluations. Similarly, PBR values considered in the 2020 scenarios were again considered here, with the addition of the mPBR which was developed by OSPAR since the last workshop.
The annual mortality due to bycatch inferred from French strandings in the Bay of Biscay and along the Western Channel was estimated at about 9,040 (95%CI [6,640 - 13,300]) common dol-phins between 2019 and 2021. In the Bay of Biscay and Iberian Coast (areas 8 and 9), the mean annual bycatch estimated from at-sea observations between 2019-2021 across all métiers was 5938 (95% CI 3081-9700) common dolphins. The abundance estimate and PBR values used in this report were the same as those used in 2020; with common dolphin abundance estimated to be 634 286 (CV=0.307) for the European Atlantic Assessment Unit, and PBR for the species calcu-lated as 4926 individuals per year. The management objective of PBR is to ensure that “a popula-tion will remain at, or recover to, its maximum net productivity level (typically 50% of the populations carrying capacity), with 95% probability, within a 100-year period”.
A modified PBR (mPBR) value of 985 was also used, with the management objective of ensuring “a population should be able to recover to or be maintained at 80% of carrying capacity, with probability 0.8, within a 100-year period”. Considering bycatch estimates calculated from at-sea monitoring, scenarios with a combination of pingers on OTM/PTB and at least 4-week closure in winter can reach the management objective of bycatch remaining below the PBR. The removal bycatch over a three-month period between the January and March winter period, and an addi-tional month closure in July/August potentially reduces bycatch below the mPBR level for at-sea monitoring bycatch estimates alone. Considering estimates inferred from strandings, a mini-mum of 6-week closure combined with pingers can achieve the objective of reducing bycatch below PBR. None of the scenarios can reduce bycatch below mPBR for either monitoring and stranding bycatch estimates. The narrower the fishery closure, the higher the risk of not achiev-ing the management objective, as the peak of mortality can be missed.
In section 3 of the report the workshop participants chose to further explore the scenarios with bycatch rates and estimate bycatch at a finer spatial and temporal scale and to consider addi-tional mitigation measures based on results of newly conducted preliminary trials. This explora-tory analysis allowed particular areas, métiers or periods with evidence of elevated bycatch rates to be identified at higher resolution, however, this approach requires significant at-sea monitor-ing in all strata. If such data were available, this method could be used to highlight specific areas, métiers and periods where particular effort in vessel observation should be deployed or mitiga-tion measures implemented.
WKEMBYC2 also recommended a series of monitoring actions to improve bycatch estimates, monitoring to data analysis, mitigation and the assessment of the northeast Atlantic common dolphin.
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