Monitoring, modelling and management of Irish Sea mussel stocks

Transcription

1 Monitoring, modelling and management of Irish Sea mussel stocks Gavin Burnell Aquaculture and Fisheries Development Centre University College Cork Ireland The Shellfish Association of Great Britain, Annual Conference, May, 2007 Image: GLOBEC/Glynn Gorick

2 Irish Sea benthic mussel seed is an important resource It needs to be exploited sustainably

3 The Irish Sea mussel seed fishery (tonnes) , , ,861 (source DCMNR, BIM, DARD)

4 Marine Institute of Ireland Resource and Risk assessment of mussel seed in the Irish Sea to understand the biology and ecology of mussel seed beds in the Irish Sea in order to assess their abundance and sustainability to suggest management strategies for the sustainable exploitation of the mussel resource in the Irish Sea

5 Partners from UCC, UCD and QUB Dr Carter Newell USA Dr Aad Smaal RIVO, Netherlands Prof Ray Seed School of Ocean Studies,UK Mary Ferns ISA and SESCO Dr Terrence O Carroll - BIM Micheal O Cinneide Marine Institute Dr Francis O Beirn Marine Institute

6 Project work packages Reproduction Recruitment UCC (coordination) UCD Hydrodynamic modelling Seabed Surveys Aquafact and Alternative sources of seed QUB Management strategies - ALL

7 Question 1 Where does the seed come from?

8 broodstock habitats: estuarine intertidal subtidal the spawning season: spring / summer / autumn?

9 Sample sites estuarine intertidal subtidal

10 Results - Spawning periods Intertidal Estuarine & Subtidal May July May Oct June Dec 300 Gonad Index J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J

11 Question 2 When does the seed settle?

12 Work package B - Recruitment (a) Clogherhead Recruits present every month sampled Mussel Recruitemnt per 9cm 2 pad ( SD) (b) Dalkey Island Clogherhead (a): Peak recruitment in July Peak recruitment in June, July and September Dalkey Island (b): - No peak in recruitment Does intertidal mirror subtidal recruitment? O04 S04 A04 J04 J04 M04 A04 M04 F04 J04 D03 N03 O03 S03 A03 J03 J03 M03

13 Question 3 Do seed beds survive overwinter in the Irish Sea?

14 Density of mussel seed from the Blackwater bed in 2005 Mytilus density (6250cm 3 ) Position within the bed Edge (west) Middle Edge (east) 0 FEB APR JUN Some seed beds survive from autumn recruitment to early summer Mussel size varied depending on position within the bed

15 Question 4 Can we model the behaviour of mussel larvae?

16 Historical map of seed collection areas and model simulation sites Seed area 6 model release sites

17 Larval patterns of distribution Factors: 1. Site 2. Time period (May-June, July-August) 3. Phase (Spring/Neap) 4. State (Flood, Ebb, HW, LW) 5. Zone (Top, Middle, Bottom) 1l samples (n=120)

18 Larval density and position varies with tidal state High nos. during flood tides Low nos. during ebb tides Larvae closer to seabed during high, low and ebb tides Mixed during flood tides Mean Larval Density (m -3 +SD) Flood Ebb High Low Mean Larval Density (m -3 +SD) per depth zone Top Middle Bottom Flood Ebb High Low

19 Dispersal Models Lagrangian Part icle Tracking ( Coherens* * ) Lagrangian SPM Module Initial Particle Position River & Open Boundary Input Inputs: Local hydrodynamics Local meteorology Advective Transport Diffusive Transport Assumptions: Currents Updated Particle Position Turbulence Passive particle vs. active advection Larval duration (41d) * Marine Science and Technology Program

20 Larval concentration Coherens Model Southern Irish Sea release (50,000particles) Model without behaviour 100 hrs 200 hrs 400 hrs 600 hrs 800 hrs 1000 hrs Model with behaviour 100 hrs 200 hrs 400 hrs 600 hrs 800 hrs 1000 hrs

21 Results: Larvae are retained within estuarine and coastal regions by a combination of their behaviour and tidal currents

22 Work package D Alternative sources of seed Hatchery Spat settlement on longline collectors wild seed from other areas

23 Are there alternatives to bottom dredged seed? Stand alone mussel hatcheries are not currently economic Relaying of rope seed on bottom is being evaluated by BIM / Industry

24 Q5: How can we use our knowledge to sustain the mussel seed fishery? Key results even small seed are reproducing there are 2 main spawning seasons for the subtidal mussel seed early summer and late autumn modelling shows that these larvae are largely retained near the area of release some seed overwinters in the Irish Sea

25 Work package E recommendations for management strategy How can we put all this information together to support a sustainable bottom mussel industry?

26 Possible management options for Irish Sea mussels carry out annual survey with agreed protocols to map the resource identify stable overwintering beds and conserve a portion of them as broodstock areas protect subtidal beds until after summer spawning (open from mid July)

27 Conclusions There is a need for ongoing scientific management to ensure a sustainable future for the Irish Sea bottom mussel industry

28 Acknowledgements Thanks to all the partners and advisors for allowing me to borrow their tables, figures and pictures.