Management and Restoration of Crayfish Stocks Phase 2

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:

1. 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.                                                                                                                                                                                 

2. 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.  

3. 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.

4. 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.