Crayfish stocks are heavily depleted in Irish waters. This depletion has been driven by over exploitation since the introduction of tangle netting in the 1970s. The restoration potential relies on acquiring better data on crayfish essential habitat, information on migration and stock structure and in managing fishing interactions. The specific project objectives and tasks are:
- Characterisation of crayfish habitat at selected sites to improve knowledge for spatial management including the value of reserves.
Crayfish habitat will be characterised and mapped using a combination acoustic data from the national seabed survey and SCUBA and vessel based surveys at selected sites. The extent of reef habitat is available from the national seabed survey data. The extent of reef suitable for crayfish is a subset of this. Crayfish live in physically complex elevated and structured reef habitat. Analysis of slope and elevation of existing shaded relief data for reef habitat can be used to further define the extent of reef that may definable physically as crayfish reef. The physical structure of crayfish reef can be described and ‘ground-truthed’ for a number of areas using SCUBA to further inform the classification of reef habitat. SCUBA will also be used in a limited number of areas to classify crayfish reef to Eunis level 4 or 5 based on characterisation of species diversity in these areas. This will be extended using vessel based camera and video surveys. The output will be a crayfish essential habitat map which has been biologically characterised. This provides the basis for Task 2 (modelling larval dispersal and recruitment from and onto reef), indicates the potential for crayfish stock restoration given available unoccupied habitat, is linked to National Seabed survey priorities for development of habitat maps for priority inshore waters and provides additional data for conservation objective setting of reef which is an Annex I habitat in the Habitats Directive. This work began in 2017 and due to logistics and weather delays the contract issued to MERC Ltd will run into 2019 but with no additional funding over that allocated in 2017.
Assessment of crayfish movement, migration, growth and stock status using mark recapture data.
The work undertaken in 2017 and 2018 will continue. Significant numbers of re-captures were recorded in 2017 and 2018 from the 2017 tag release programme. The industry forums have proposed to give legal protection to marked tagged crayfish from 2019 to facilitate research and to increase spawning potential. The tagging programme will be funded by the BIM inshore fisheries scheme in 2019.
Assessment of catch and by-catch species composition in the commercial tangle net fleet. Observer data in 2017 and Skipper data from 2 vessels in 2018 provided comprehensive information on size composition, catch rate, tag recaptures and by-catch. This work will continued in 2019 and 2020.
- Management measures for stock recovery and to reduce the effects of the fishery on biodiversity.
This could include changes from netting to potting or temporary time closures, spatial closures, and monitoring of changes in population.
The project has a 2 year duration and runs between 2019 and 2020.
- Data sets: size composition, catch and effort, tag releases, tag recaptures, georeferenced data, acoustic map data on seabeds, biological data on reef fauna, distribution of crayfish reef habitat, modelled larval dispersal data and maps. To be incorporated into existing Marine Institute data bases where appropriate.
- Report on fine scale acoustic mapping of crayfish reefs and the distribution of crayfish reef habitat.
- Report on larval dispersal modelling.
- Report on catch and by-catch in the crayfish fishery.
- Report on tag release and recapture of crayfish.
- Incorporation of data and new information into stock assessment and scientific advice and publications/dissemination thereof.
Management of crayfish stocks: Information from the project will be collated and used to design management measures for the fishery with the objective of re-building crayfish stocks and reducing the environmental effects of the current set net fishery. Particular emphasis will be placed in areas where by-catch is significant and where the reef data shows potential for re-building. Measures might include the increased use of spatial reserves for crayfish, changing from set nets to trap fisheries and temporary closures to enable stock recovery or inclusion of additional technical conservation measures. Improved scientific knowledge on the essential habitat, stock structure and life cycle/connectivity of crayfish stocks in SW Ireland. Overall Expected benefits are:
1. Improved scientific knowledge on the fishery and its impact on target stock and biodiversity
2. Proposed management measures to restore crayfish stocks and protect biodiversity impacted by the fishery taking account of the above.
3. Dissemination of results and related management consideration at regional/national inshore management fora.