Farnet field-trip Helsinki. Esa Lehtonen. Natural Resources Institute Finland. Natural Resources Institute Finland

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1 Technical methods to mitigate sealinduced damages in trap-nets & Satellite monitoring of grey seals caught in pontoon trap-nets in the Gulf of Finland Farnet field-trip Helsinki Esa Lehtonen Natural Resources Institute Finland

2 Technical methods to mitigate seal-induced damages in trap-nets

3 Grey seals (Halichoerus grypus) cause the main damage in the coastal fishery grey seals in the entire Baltic Sea area (counted around in year 2015, % of the total stock). In Finnish waters around grey seals. Seal caused damages and economic losses are most severe in salmon, whitefish and pikeperch fishery There have been various attempts to mitigate seal-induced damage in the northern Baltic. Seal-safe trap-net modifications (made of dyneema netting) have shown to be one potential way to reduce the damage. However, no single gear modification or scaring device has been shown to provide complete protection from seal-induced damages so far. Luke, Esa Lehtonen Luke, Esa Lehtonen Luke, Esa Lehtonen 3

4 Traditional trap-net models for salmon nowadays just a historical gear -> Seals have learned to catch fish inside the trap-net Seal-safe Dyneema fish bag Luke, Esa Lehtonen Fish bag Sharp corners, 3 funnels Middle chamber Wings Wire grid Catching of fish by gilling (mesh bar length 75 mm), free access for greyseals -> not useful method anymore

5 Seal trap Various seal trap modifications and designs tested => Without success Luke, Esa Lehtonen

6 Pontoon trap-net = Push-up trap-net 2-layer Dyneema seal-safe fish chamber Hauling with air-compressor Around 250 pontoon trap-nets already in use along the Finnish coast (main target species: salmon, whitefish, sea trout) Luke, Esa Lehtonen 6

7 Methods to prevent seals from entering into the pontoon trap-net fish bag Pontoon trap-net: hoop ø 3 m: bar length 200 mm, ø 2 mm dyneema netting Stoppnät: Middle chamber Fish chamber Luke, Esa Lehtonen The large-mesh protection net in the middle chamber allows fish (salmon, whitefish, sea trout etc.) to enter the fish chamber but leave seals outside. Developed by fishermen & KANRA / KEHRA projects 7

8 Protection netting of steel wire, possible to mitigate seal caused damages in pontoon trap-nets Water visibility and colour -> effects on fish behaviour? Bar length mm, steel wire ø 1 mm Luke, Esa Lehtonen 8

9 Satellite monitoring of grey seals caught in pontoon trap-nets in the Gulf of Finland Luke, Esa Lehtonen 9

10 Aims of the satellite monitoring study To study the temporal and spatial behaviour of Baltic grey seals (Halichoerus grypus) captured with pontoon trap-nets in collaboration with professional fishermen To compare foraging locations of grey seals to locations of the trap-nets on the southeast coast of Finland. The knowledge can be used for mitigating seal-fishery interactions and for management of the Baltic grey seal stock. Luke, Esa Lehtonen

11 Drawing by Iconex Ltd Seal trying to reach fish in chamber releases the gate behind Method published: E. Lehtonen, P. Suuronen Live-capture of grey seals in a modified salmon trap. Technical note. Fisheries Research 102 (2010)

12 Message to mobile phone when the seal is caught in the trap-net Middle chamber Adapter Shuttle Luke, Esa Lehtonen 12

13 GSM antenna -> GPS antenna -> Weight 400 g Luke, Esa Lehtonen 13

14 Monitoring of grey seals in the Gulf of Finland Name Weight kg Monitoring start Monitoring end Days Locations Kasimir, KA Crispen, CR Otro, OT Stig, ST Ahti, AH Arnold, AD Tyko, TY Benjamin, BE Voitto, VO

15 Satellite monitoring of grey seals in 2011, main foraging areas Arnold Benjamin Ahti Tyko Ahti Arnold Benjamin Tyko Main foraging areas grey seals feeding in trap-nets Locations of 4 seals Pontoon trap-net Trap-net (hoops) Fish farm Catching & release site, Loviisa Söderby +

16 Russian border Itäkivi 2011 tagged grey seals stayed the entire summer and fall period in the Eastern Gulf of Finland. Frequent visits from haul-out sites to trap-net fishing sites 16

17 Grey seal Voitto (128 kg) Baltic Sea cruiser Migration from Gulf of Finland tagging site to the southern Baltic in fall 2011 (900 km). During four months winter period the total migration distance of 2600 km. The last location was received from the Gulf of Finland seal sanctuary Sandkallan

18 RESULTS Some grey seal individuals specialise in foraging in and close to the trap-nets (in tagging experiments 6 out of 8 grey seals). Only male grey seals of different ages visit the pontoon trapnets. The movements concentrated near the coasts during the autumn. Important prey species of grey seals as well as commercial trap-net fishing can be found in the same area. The grey seal habitat use changes in winter, as they avoid ice-covered areas.

19 RESULTS (continue) Luke, Esa Lehtonen A 88 kg male grey seal Crispen was released three times from the same pontoon trap-net in Gulf of Finland 2010 => evidense of specialisation Selective removal of grey seals overlapping with fishery can be considered a effective locally focused method to mitigate damages caused to fishery.

20 Tagging project financed by: Ministry of Agriculture and Forestry ( ), FGFRI, South Finland FLAG ESKO and Sandmans stiftelse ( ) The report published in April 2013, Riista- ja kalatalous Tutkimuksia ja selvityksiä 1 /2013 and in Marine Ecology Progress Series Vol.507: ,

21 Thank you! Luke, Esa Lehtonen

22 22 Teppo Tutkija