GEAR TRIALS IN THE NORTHERN IRELAND NEPHROPS FISHERY (Phase 2) (Project No CO4/039733/06)

Transcription

1 GEAR TRIALS IN THE NORTHERN IRELAND NEPHROPS FISHERY (Phase 2) (Project No CO4/39733/6)

2 BACKGROUND PHASE 1: Results indicated that neither option had a significant affect on catches. Control Option 1 Option 2 Existing 7mm/8mm prawn trawl 16mm X 5 mesh cover and existing 3m X 9mm. As control but with second

3 PHASE 2 Project Steering Group Walter Crozier Richard Briggs Pieter-Jan Schön Terry Cunningham Jim Hamilton Ian Humes Paddy Campbell Dick James Ian Kelly Alan McCulla John Cassidy Norman Graham (by Video link) AFBI AFBI AFBI TC Nets James Hamilton Trawl Nets DARD DARD NIFPO NIFPO ANIFPO ANIFPO Marine Institute (Gear Technologist) Skipper of MFV Carreen: Andrew Annett Observers: Gary Dunlin Gary Hughes Robert Phillips

4 CONTROL GEAR CON TROL Standard Nephrops net 3 bars wide Standard 8mm 2.1m from extension 3m Standard 8mm 2.1m 5 meshes 1.5m x 82m m 1.5m 4mm P/E braid 4.5m 84mm 4.5m X 5.6mm compact netting 12 round 5 meshes round cover 21mm int x 11.5m deep All s are knotless and 3 m etres long

5 EXPERIMENTAL OPTIONS EXPT 1 EXPT 2 EXPT 3 EXPT 4 EXPT 5 EXPT 6 12mm - Usual position 12mm Dynema 12mm in ROI position codend 12mm 12mm split (not Dynema) In ROI position 12 mm Knotless 5mm twine Standard 8mm 2 bars wide 3 bars wide Strip of diamond mesh in centre (12 meshes wide) 12mm m normal 5mm twine standard 8.85m 8mm 8.85m 3 bars wide 2.1m 2.1m 12mmm 82mm 82mm 82mm 12mm normal 1.5m 4mm P/E 1.5m Dynema 1.5m 4mm P/E 1.5m 5mm 1.5m 4mm P/E twine 6m Codend 6m 52mm mesh 4.5m 4.5m 4.5m 4.5m 4.5m 84x5.6mm 84x5.6mm 84x5.6mm 84x5.6mm 84x5.6mm compact compact compact compact compact netting netting netting netting netting 12 round 12 round 12 round 12 round 12 round Expt 1 12mm 2.1m from extension 12 tows Expt 2 12mm of Dynema near codend 12 tows Expt 3 12mm 8.85m from extension 13 tows Expt 4 8mm 2.1m from extension Square Mesh Codend Expt 5 12mm normal mesh near codend 4 tows Expt 6 12mm split 8.85m from extension 8+8=16 tows 12 tows

6 AREA OF OPERATION: 15 September 29 October 28 (+) 54.8N and extension study 2-5 March 29 (o) E3 E4 E5 54.6N N 54.2N N 53.8N N 53.4N W 6.2W 6.W 5.8W 5.6W 5.4W 5.2W 5.W 4.8W 4.6W

7 DATA PRESENTATION (1) Catch Bulk (2) Catch at length Nephrops, Haddock and Whiting (3) Relative catch at length (4) Mean proportions P of total catch retained at length l: P = C exp C exp + C control C exp and C control = catch numbers If P =.5 no selection difference

8 RESULTS 3 25 Mean Catch (error bars = SE) Control Expt Expt mm 2.1m from extension 12 tows bars wide Nephrops Haddock Whiting 12mm m normal 5mm twine 1 8 Haddock: Catch at Length Experiment 1 2.1m MLS 3cms 82mm 1.5m 4mm P/E Length (cm) Whiting: Catch at Length 4.5m 84x5.6mm compact netting 12 round Experiment 1 MLS 27cms Length (cm)

9 Expt 2 12mm of Dynema near codend Mean Catch (error bars = SE) Control Expt 2 12 tows Note: Haddock only caught in 1 tow 2.. Nephrops 21 1 Haddock Whiting 1.5m 12mm Dynema Haddock: Catch at Length (from 1 tow only) MLS 3cm s Fish (cm) Experiment 2 Whiting: Catch at Length 4.5m 84x5.6mm compact netting 12 round Experiment 2 MLS 27cms Fish length (cm)

10 Mean Catch 35 (error bars = SE) Control Expt mm Knotless 5mm twine Expt 3 12mm 8.85m from extension 13 tows 8.85m tended to sag (see Expt 6) Number Nephrops 5 Haddock: Catch at length Haddock MLS 3cms Whiting Experiment 3 82mm Fish Length (cm) 1.5m 4mm P/E Whiting: Catch at Length 4.5m 84x5.6mm compact netting 12 round Experiment 3 MLS 27cm Fish length (cm)

11 Expt 4 8mm 2.1m from extension Mean Catch (error bars = SE) 25 2 Control Exp 4 Square Mesh Codend tows Standard 8mm 3 bars wide standard 8mm 3 bars wide Nephrops Haddock Whiting 2.1m % Nephrops: Relative size Relative size frequency Control Expt Haddock: Catch at length Fish Length (cm) MLS 3cms Expt 4 4 6m 6m Codend 52mm mesh Carapace lengths (mm) No improved Nephrops selectivity Whiting: Catch at length Expt 4 MLS 27cms Fish length (cm)

12 Expt 4: Codend comaprisons on hauling 8mm Diamond Mesh codend 5-55mm Square Mesh codend

13 Expt 5 12mm normal mesh near codend 4 tows Baskets Mean Catch (error bars = SE) Control Exp Nephrops Haddock Whiting Haddock: Catch at length 1.5m 12mmm normal 5mm twine MLS 3cms Experiment Fish Length (cm) Whiting: catch at length 4.5m 84x5.6mm compact netting 12 round Experiment 5 MLS 27cms Fish length (cm)

14 7 6 Mean Catch (error bars = SE) 25 2 Control Exp Baskets % reduction % reduction Strip of diamond mesh in centre (12 meshes wide) 1 Nephrops Bulk Haddock Whiting Expt m 7 Haddock: Catch at length 12mm split m from extension 16 tows Experiment 6 MLS 3cms 82mm 1.5m 4mm P/E Fish Length (cm) 6 Whiting: Catch at length 5 Experiment m 84x5.6mm compact netting 12 round 3 2 MLS 27cms Fish length (cm)

15 Proportions of total catch retained at length Haddock Proportion of haddock in Exp 6 net 1. Strip of diamond mesh in centre (12 meshes wide) Expt m Proportion mm split m from extension 16 tows 82mm 1.5m 4mm P/E Whiting Proportion Length cm Proportion of whiting in Exp 6 net m 84x5.6mm compact netting 12 round Cod Length cm Haul Gear Total Exp Control Total

16 CONCLUSIONS Increasing the size of the from 8mm to12mm positioned 2m in front of the codend did not change the selection properties of the net. Significant escapes of juvenile haddock and whiting occurred when a 12mm was inserted 8m from the codend extension. This reinforces the findings of earlier studies (Briggs et al., 1996, Anon and Armstrong et al., 1998). The loss of some Nephrops with a 12mm in this position could be due to sagging of the panel A 5-55 mm square mesh extension resulted in losses of 44% haddock, 75% whiting and 58% Nephrops by number sagging was remedied in Experiment 6 by placing a 12 mesh strip of 8mm diamondshaped netting between a halved for support. This configuration reduced discards of juvenile haddock by 54% and juvenile whiting by 65% (number) with no loss of Nephrops.