Ensis sp. fishery in Scotland

• Also known as razor shells, razor clams and “spoots”

• Vessels were often “multi purpose” Light trawl, scallop diving, dredges, lobster and crab pots etc.

• Recent regulation has licensed vessels specifically for Ensis fishery

• Diving operations usually in depths 4 – 10m. • The main market for Ensis spp is as a live export

to southern Europe and Asia (in particular China, and Japan)

Distribution and landings by ICES rectangle (2005- 2014)

Updated map required

Data prepared by Rui Catarino MS-S

Landings (Tonnes) 1997 - 2014

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1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

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Ensis sp. Burying mechanism

Description of burying mechanism

The digging cycle of Ensis sp. The broken lines between adjacent valves indicate movement of the shell in relation to the sand (stippled).

•A, foot probing downward, siphons and fourth pallial aperture (4) open (i);

•B, siphons closed, valves adducting, water ejected from mantle cavity, maximum pressure in pedal haemocoele (iii);

•C, adduction complete, maximum dilation of the foot (Schwellform), retraction commencing (iii)-(iv);

•D, retraction complete, siphons reopened, ejection of water from 4th pallial aperture, slight withdrawal of foot from sand, leaving cavity below (s) (iv)-(v);

•E., relaxation of adductors complete, valves held firm in sand as foot probes (vi); movement of shell, including opening of valves; O ejection of water from mantle cavity; <<, probing of foot; <, hydrostatic pressure of haemocoale derived primarily from adduction, secondarily from retraction; >--<, contraction of adductor of retractor muscles. [Source: Trueman, 1967]

Harvesting techniques and rates• Intertidal hand collection by digging. <100 per hour

• Intertidal hand collection by saline. 1000+ per tide

• Hand collection by divers by digging. <100 per hour

• Hand collection by divers by saline. 3000+ per tide

• Hydraulic dredge. 5000+ per day

• Divers using electro gear. 5000+ per day.

Data from Seafish report SR652

Scottish fishing rig (anecdotal)

Diver –

collects Ensis emerging from substrate

Generators –providing electrical power

“Fly-dragging” –heaving in against an anchor used to tow the gear at ~3m/min

Electrodes –on the seabed, create an electric field

Case Studies for ensis

• South and West Wales.– Previously un-fished area. Ensis present. Control and

worked areas. Environmental impact study on non-target species. Post survey inspections for up to 28 days.

• Southern Ireland.– Inshore diving for shellfish is banned. Mechanical

collection of ensis using electrical stimulus in front of dredge rather than fluidising seabed using hydraulic system.

Effects of Electrofishing for Ensis spp. on benthic macrofauna, epifauna and fish speciesDr. Andrew Wooler (1), Evonne Maxwell (1), William Lart (2)

1) Salacia-Marine

2) Sea Fish Industry Authority

June 2011

Prepared for the South and West Wales Fishing

communities Ltd as part of Electrofishing for Razorfish

(Ensis spp.) Project (FIFG 57437)

Seafish report SR652 ISBN-978-1-906634-58-2

www.seafish.org

Generator ( AC plus DC welding)

Comparison between positive (left) and negative (right) electrodes after several hours use

Fishing trials

• Four trial areas of 100m * 100m were selected as having suitable sediment type for razorclams and also large diversity of other species.

• Areas had not previously been fished as in “protected area”.

• Areas were randomly divided (N/S)• One half of each area was subjected to intensive

coverage with electro-rig energised. • The four ”control areas” were not fished in any

way.

Fishing trials (cont)

• Cameras on electro-rig recorded reactions to electric field.

• Observer on vessel monitored bird, mammal and cetacean interaction with electro-rig.

• Details of system performance (current and voltage), vessel location, weather conditions etc recorded in tow log.

Species observed in electric field

• 4 species of crustacea.• 5 species of Mollusca• 3 species Echinodermata• 8 species of fish• Collected data includes type of effect, description

of behaviour and recovery time.• Short term (1 day post fishing) and long term (up

to 28 days post fishing) studies of macrofauna, epifauna and fish carried out in all areas.

Conclusions

• (Heavily paraphrased.)• “At the currents and voltages used in these trials

Ensis spp can be effectively harvested without serious negative effects on the epifaunal and macrofaunal benthic community.”

• “Given the commonly reported negative effects of alternative approaches, toothed and hydraulic dredges. The results of this study suggest further development work is warranted to develop less disturbing fishing gears”.

BIM pulse dredge trials• Stimulus. “ Pulsed” AC or DC at 20 volts ~ 100 Amps. 4 or

6 electrodes.– Dredge penetration 1 to 5 cm.– 15 minute tows– Dredge stationary for 40 – 60 seconds to stimulate

ensis. Dragged though patch and then halted.– Overall 18% of retained razors damaged. ( 8 – 28% by

haul)• Comparison with published results ( Fahy and Carroll

2007) for hydraulic dredge. – 3 bar water pressure to fluidise the sediment to a depth

up to 30 cm.– 60% of retained razors damaged.

BIM collector rig