technical methods to mitigate seal ... - webgate.ec.europa.eu · there have been various attempts...

© Natural Resources Institute Finland © Natural Resources Institute Finland

Technical methods to mitigate seal-

induced damages in trap-nets

&

Satellite monitoring of grey seals

caught in pontoon trap-nets in the

Gulf of Finland 2010-2012

Farnet field-trip

26.5.2016 Helsinki

Esa Lehtonen

Natural Resources Institute Finland

© Natural Resources Institute Finland

Technical methods to mitigate

seal-induced damages in

trap-nets

© Natural Resources Institute Finland 3

40 000-54 000 grey seals in the entire Baltic Sea area

(counted around 32 000 in year 2015, 60-80 % of the total stock).

In Finnish waters around 11 500 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.

Grey seals (Halichoerus grypus) cause the main damage

in the coastal fishery

© Luke, Esa Lehtonen © Luke, Esa Lehtonen © Luke, Esa Lehtonen


Traditional trap-net models for salmon nowadays just a historical gear ->

Seals have learned to catch fish inside the trap-net

Catching of fish by gilling (mesh bar length 75 mm),

free access for greyseals -> not useful method anymore

Seal-safe Dyneema fish bag

Wire grid

Middle

chamber

Fish bag

Wings

”Sharp

corners”,

3 funnels

© Luke, Esa Lehtonen


Various seal trap

modifications and

designs tested =>

Without success

Seal trap




Around 250 pontoon trap-nets already in use along the Finnish coast

(main target species: salmon, whitefish, sea trout)

2-layer Dyneema seal-safe

fish chamber

Hauling with air-compressor

Pontoon trap-net = Push-up trap-net


Stoppnät:

Pontoon trap-net:

hoop ø 3 m: bar length 200 mm, ø 2 mm dyneema netting

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

Methods to prevent seals from entering into

the pontoon trap-net fish bag

Middle chamber

Fish chamber



Protection netting of steel wire, possible to

mitigate seal caused damages in pontoon

trap-nets

Bar length 200-240 mm,

steel wire ø 1 mm

Water visibility and

colour -> effects on

fish behaviour ?



Satellite monitoring of grey seals

caught in pontoon trap-nets in the

Gulf of Finland 2010-2012



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 2010-2012.

• 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.



Method published: E. Lehtonen, P. Suuronen 2010.

Live-capture of grey seals in a modified salmon trap. Technical note. Fisheries Research 102 (2010) 214-216

Seal trying to reach fish in chamber releases the gate behind

Drawing by Iconex Ltd



Adapter

Shuttle

Message to mobile phone when

the seal is caught in the trap-net

Middle chamber


GPS antenna ->

GSM antenna ->

Weight 400 g



Name Weight

kg

Monitoring

start

Monitoring

end

Days Locations

Kasimir, KA-10 125 1.7.2010 2.11.2010 124 2391

Crispen, CR-10 88 25.10.10 14.3.2011 140 4223

Otro, OT-10 123 13.11.10 24.4.2011 162 5683

Stig, ST-11 133 5.6.2011 12.6.2011 7 99

Ahti, AH-11 113 22.6.2011 18.4.2012 301 6030

Arnold, AD-11 156 7.8.2011 27.10.2011 81 781

Tyko, TY-11 173 24.8.2011 14.10.2011 51 479

Benjamin, BE-11 121 30.8.2011 4.2.2012 156 979

Voitto, VO-11 128 16.9.2011 10.3.2012 175 1662

Monitoring of grey seals in the Gulf of Finland 2010-2012


Pontoon trap-net

Trap-net (hoops)

Fish farm

Main foraging areas 2011

Locations of 4 seals

4 grey seals feeding

in trap-nets

Catching & release site, Loviisa Söderby +

Tyko

Ahti

Benjamin Arnold

Ahti

Arnold

Benjamin

Tyko

Satellite monitoring of grey seals in 2011, main foraging areas


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


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 28.3.2012

Grey seal ”Voitto” (128 kg)

”Baltic Sea cruiser”


• Some grey seal individuals specialise in foraging in and close to

the trap-nets (in 2010-2011 tagging experiments 6 out of 8 grey

seals).

• Only male grey seals of different ages visit the pontoon trap-

nets. 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.

RESULTS


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.

RESULTS (continue)



Tagging project financed by: Ministry of Agriculture and Forestry (2008-2009), FGFRI, South Finland FLAG ESKO and Sandmans stiftelse (2010-2011)

The report published in April 2013, Riista- ja kalatalous Tutkimuksia ja selvityksiä

1 /2013 and in Marine Ecology Progress Series Vol.507:297-308, 2014


Thank you!

31.5.2016 21


technical methods to mitigate seal ... - webgate.ec.europa.eu · there have been various attempts...

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