Investigating the role of prey depletion in cetacean distributions and population dynamics

34th European Cetacean Society Conference, O Grove, 16-20 April 2023A key driver in determining the distribution and demography of cetaceans is the dispersion of their prey, in terms of availability, abundance and quality. A Working Group on Resource Depletion has been established within ASCOBANS to review current knowledge and develop recommendations for research and action. It includes members with expertise in veterinary and fishery science, cetacean biology, ecology and conservation. The group has eight terms of reference - reviewing and collating recent information on resource depletion and its impacts, prey distribution and abundance, health and condition indicators, small cetacean diet, spatio-temporal trends in small cetacean species, emerging technologies, integrating information from multiple data sources, and making recommendations for possible mitigation measures to aid conservation. As a first step, the group has summarised information on the diets of all small cetacean species regularly occurring in the ASCOBANS Agreement Area, and explored the parameters required to assess cetacean health and condition at both an individual and population level. The need to better understand prey choice in terms of prey availability and caloric content is highlighted along with the development of indicators of food shortage through necropsies of dead animals and photographic assessments of body condition in live animals. Future research, monitoring and conservation needs include refining the definition of prey depletion, developing prey depletion reference points, and articulating associated conservation objectives. We also need a better understanding of the relationships between cetacean physiology, energetics, body condition, health and diet, and of the population and ecosystem level consequences of prey depletion (e.g. based on the use of ecosystem models). Improved monitoring of prey and cetacean distribution and abundance at relevant spatiotemporal scales would facilitate estimation and mapping of resource depletion riskN

Initiatives to investigate and improve bycatch data from cetacean strandings

ICES Annual Science Conference 2023, 11–14 September 2023, Bilbao, SpainCetacean strandings can provide key information to assess and understand bycatch mortality and its potential impact on populations (as for common dolphins in the Bay of Biscay) but the extent to which this is currently feasible varies widely across Europe. Several initiatives are presently underway to improve and standardize bycatch diagnosis from carcasses, streamline reporting of strandings data, and establish a common database. The ICES Working Group on Bycatch routinely gathers available information (currently far from comprehensive) on annual stranding records by member states, including information on evidence of bycatch, which feeds into the ICES advisory process on bycatch of Protected, Endangered and Threatened Species (PETS). In 2021, ICES Working Group on Marine Mammal Ecology initiated a questionnaire survey of European strandings networks to gather information on their organization, resources, protocols for data and sample collection, and bycatch diagnosis, in cetaceans and other PETS. ACCOBAMS completed a similar initiative in 2022 and we are presently consulting West African strandings networks about the information they collect on PETS bycatch. The utility of strandings to quantify bycatch is being investigated in several projects in Spain. The IWC has current bycatch and strandings initiatives, and ASCOBANS and ACCOBAMS have developed protocols for cetacean necropsy and bycatch diagnosis. In April 2023, two relevant workshops are planned, the ECS/ASCOBANS workshop on “Scoping the development of a European marine strandings database” and the ACCOBAMS-ASCOBANS workshop on “Current cetacean bycatch issues in European waters”, This presentation will briefly describe the various ongoing initiatives and their results to date. Based on the WGMME questionnaire survey, cetacean bycatch is an important cause of death for harbour porpoises, pelagic delphinids and baleen whales. Several regions reported upward trends in bycatch mortality in these groups and in seals. Bycatch was associated with a wide variety of gear (e.g. static, towed and floating gears, traps, pots, and pole and line). Highlighted needs include better coordination of data collection, standardised pathological investigations and consistent reporting nationally and internationally. Reported strengths and weaknesses of the networks, as well as identified assessment and data gaps, provide useful information to enhance the potential of these networks to contribute to bycatch assessment. Finally, we consider how the utility of information arising from strandings could be maximised, including the application of drift models and life tables, placing bycatch in the context of population health status, and the need for good quantification of survey effort by stranding networksN