The research project was organized into four work packages. WP1 assessed the extent and impact of seal depredation on coastal and inshore fisheries. Two approaches were taken. First, fishers in the pollock static-net fishery of SW Ireland were provided survey sheets to self-report fish catch and depredation. Results suggested high depredation rates averaging ~14% with some vessels experiencing rates exceeding 40%. Second, GPS tracks of grey seals were collated from across Ireland, the UK, and France (in collaboration with La Rochelle and St Andrews University’s) and analysed in relation to fishing activity obtained from the Global Fishing Watch database. Results suggest seals are more likely to switch to foraging behaviours when co-occurring with fishing activity, although overall co-occurrence between the two is low (<5% of seal foraging co-occurs with fishing activity). Moreover, co-occurrence varied between individuals, with some individuals not foraging at all in co-occurrence with fishing boats despite transiting through areas where fishing activity was recorded. Together, these results suggest co-occurrence of seal foraging and fishing activity is linked to only a small proportion of individuals across a limited proportion of their total foraging time and does not necessarily suggest seals seek out nets to depredate, with nets possibly encountered opportunistically.
WP2 aimed to identify and quantify ‘hidden’ depredation events, resulting from whole fish removal by seals (and thus making the depredation event uncountable from visual assessment following hauling). Fishing nets from the static-net pollock fishery were equipped with accelerometers, and upon hauling the locations of fish and evidence of depredation were recorded in relation to the location of accelerometers. Accelerometer data streams were analysed using an algorithm to detect jerks in movement, possibly associated with a fish getting caught in the net, and then bitten/removed by a seal. Analyses thus far have been hindered by noise in the data streams likely resulting from net movements with underwater currents and turbulence. Refinement to the algorithms to improve functionality is ongoing.
WP3 assessed the effectiveness and practicability of targeted acoustic startle technology (TAST) to deter seals from static-net fisheries targeting pollock and reduce depredation rates. By eliciting a startle response mediated by an autonomous reflex arc in the brainstem, TAST deters seals from a localized area. Moreover, individuals do not become habituated to the sound, as is often the case with standard acoustic deterrent devices. The approach only requires low noise doses, and uses brief isolated sound signals emitted at low duty cycles at a specific frequency band where seal hearing is much more sensitive than that of non-target species such as dolphins and harbour porpoise. A prototype TAST device was tested during 19 days of dedicated at-sea boat survey trials, during which the presence of dolphins and porpoise was also monitored via underwater hydrophones. Results showed an overall decrease in depredation with the use of TAST. TAST had no detectable impact on patterns in the presence of dolphins and porpoise during trials.
WP4 aimed to assessed how fishers found the practical use of the mitigation system. Via continuous engagement with static net fishers during survey trials and TAST engineers, several improvements were implemented in the design of the TAST prototype improving its practicability.
Results of the research will be reported in 2-4 peer-reviewed articles (one under review, two in preparation, and another one planned following the incorporation of additional supporting data). A technical report was delivered to the National Parks and Wildlife Service. The work was selected for an oral presentation at Society for Marine Mammalogy International Conference in Perth, Australia (2024). Several public outreach activities were completed including a visit to a further education college in Cork, and presentations at several cultural events (e.g. Feile na Bealtaine Festival in Dingle, Kerry).
