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The Baltic Proper harbour porpoise population is listed as Critically Endangered by IUCN, and only a few hundred animals remain. One of the most serious threats to this population is bycatch in static net fisheries. To minimize bycatch, ICES has proposed that acoustic deterrent devices, pingers, should be used on static nets within the population’s range. However, there have previously been indications that grey seals learn to associate the pinger sounds with the presence of nets with easily accessible prey, and that pinger use therefore can increase the risk of seal depredation in static net fisheries. In recent years, pingers operating at higher frequencies have been made commercially available, the idea being that harbour porpoises will still be able to hear the sound at 50–120 kHz while this will be above or at the limit of seal hearing. This would mean that such high-frequency pingers would not induce this so-called dinner-bell effect. In this study, data were collected from active commercial static net fisheries in the Baltic Proper, using two types of high-frequency pingers operating at 50–120 and 70 kHz, respectively. Pingers were attached to nets in accordance with manufacturers’ guidelines, and fishers were asked to estimate the catch loss owing to seals in nets with and without pingers. Data were received from 646 deployments made between May 2019 and September 2020. Four generalized mixed effect models were developed with relevant variables. The results suggest using high-frequency pingers does not increase seal depredation on static nets. It is concluded that pingers could be used as an interim measure to minimize bycatch of the Critically Endangered Baltic Proper harbour porpoise population.

Wild animals are captured or taken opportunistically, and the meat, body parts, and/or eggs are consumed for local subsistence or used for traditional purposes to some extent across most of the world, particularly in the tropics and subtropics. The consumption of aquatic animals is widespread, in some places has been sustained for millennia, and can be an important source of nutrition, income, and cultural identity to communities. Yet, economic opportunities to exploit wildlife at higher levels have led to unsustainable exploitation of some species. In the literature, there has been limited focus on the exploitation of aquatic non-fish animals for food and other purposes. Understanding the scope and potential threat of aquatic wild meat exploitation is an important first step toward appropriate inclusion on the international policy and conservation management agenda. Here, we conduct a review of the literature, and present an overview of the contemporary use of aquatic megafauna (cetaceans, sirenians, chelonians, and crocodylians) in the global tropics and subtropics, for species listed on the Appendices of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). We find that consumption of aquatic megafauna is widespread in coastal regions, although to varying degrees, and that some species are likely to be at risk from overexploitation, particularly riverine megafauna. Finally, we provide recommendations for CMS in the context of the mandate of the Aquatic Wild Meat Working Group.

1. The Baltic Proper harbour porpoise is listed as Critically Endangered by IUCN, and only a few hundred animals remain. One of the most serious threats to this population is bycatch in static net fisheries. To minimize bycatch, ICES has proposed that acoustic deterrent devices, pingers, should be used on static nets within the population range. 2. However, there has previously been indications that grey seals learn to associate the pinger sounds to the presence of nets with easily accessible prey, and that pinger use therefore can increase the risk of seal depredation in static net fisheries. 3. In recent years, pingers operating at higher frequencies have been made commercially available, the idea being that harbour porpoises will still be able to hear sound at 50-120 kHz while this will be above or at the limit of seal hearing. This would mean that such high-frequency pingers would not induce this so-called dinner-bell effect. 4. In this study, data was collected in active commercial static net fisheries in the Baltic Proper, using two types of high-frequency pingers operating at 50-120 kHz and 70 kHz, respectively. Pingers were attached to nets in accordance with manufacturers’ guidelines, and fishers were asked to estimate the catch loss due to seals in nets with and without pingers. 5. Data was received from 646 deployments made between May 2019 and September 2020. Four generalised mixed effect models were developed with relevant variables. 6. The results suggest using high-frequency pingers does not increase seal depredation on static nets. It is concluded that pingers could be used as an interim measure to minimize bycatch of the Critically Endangered Baltic Proper harbour porpoise population.