Working Group on Marine Mammal Ecology (WGMME)

The Working Group on Marine Mammal Ecology met in 2021 to address new information on marine mammal ecology relevant to management.ssessments. Two terms of references were standing ToRs; under the first of these, ToR A, new and updated information on seal and cetacean population abundance, population/stock structure, management frameworks as well as anthropogenic threats to individual health and population status were reviewed along with findings on threats to marine mammals such as bycatch, pollution, marine debris and noise. ToR B is a cooperation with WGBIODIV to review species-specific foraging distributions (considering horizontal and vertical dimensions depending on data availability) and to estimate consumption by marine mammal species representative in case study areas. ToR C was implemented to review aspects of marine mammal fishery interactions not covered by ICES WGBYC. ToR D is the second standing ToR and concerns updating the WGMME seal database, which was updated with the latest data.
Regarding ToR A, seal stocks in the North Atlantic are generally growing and stable, except both grey and harbour seals in Iceland, which have both declined dramatically in recent decades. Also, harbour seals in some areas of northern UK are declining, and the southern Baltic ringed seal subpopulation is threatened by climate change. Suggestions for calculation of Potential Biological Removal (PBR) for grey seals in OSPAR regions I, II and III are also provided. Recent surveys for estimating cetacean species abundance are presented as well as updates on anthrophonic threats, such as pollution.
Under ToR B it was emphasized that when estimating diet and prey consumption of marine mammals, aspects like (1) non-representativeness of samples (e.g. stomachs from stranded or bycaught individuals or scats from seal haul outs) for the population, (2) not recoverable remains of some prey items and (3) the partially (and maybe completely) digestion of hard prey remains in the gastro-intestinal tracts of the predator, are important to consider. To illustrate the available data and metainformation some example case studies were summarised. An outline methodology for combining and analysing data useful for prey guild modelling and ECOPATH modelling is presented.
Under ToR C, Regulations for acoustic deterrent devices to mitigate marine mammal bycatch and legislation requirements for monitoring of bycatch were reviewed along with updated information on bycatch. A questionnaire survey to European stranding networks mapped information pertinent to bycatch assessments.