Atlantic cod in the Celtic Sea, Demersal otter trawl
The spawning stock biomass of Celtic Sea cod increased from outside safe biological limits (below Blim) in the early 2000s and was inside precautionary levels(above Bpa and MSY Btrigger) in 2012 and 2013 decreasing back down to just outside safe biological limits more recently (below Blim). The decrease in spawning stock biomass is in part due to successive low recruitment events in recent years. Recruitment estimates in recent years were well below the average of the time-series with the exception of 2014 is estimated to be above the average of the time-series. Fishing mortality has been on a fluctuating, declining trend since 2005 and is currently inside precautionary levels (below Fpa) but above FMSY which would be optimal for maximum sustainable yield (ICES, 2017a).
Figure 1. Cod in Divisions 7e–k (Celtic Sea cod). Summary of stock assessment (weights in thousand tonnes). The assumed recruitment value is unshaded (ICES, 2017a).
Stock structure and recruitment
Tagging work by Ireland and the United Kingdom supports the idea that there is a self-contained, resident cod stock in the Celtic sea and the western English Channel (7e-k). Although minimal population mixing occurs between cod stocks in the Irish Sea and the Celtic Sea, cod are migratory and undertake a limited degree of population mixing in other areas. Both conventional tagging and data storage tag (DST) information indicates that the distribution of the cod population in Division 7g (where the majority of landings are taken) remained spatially constrained within the division and the highest abundances were found in central areas between January and March. The cod population in the Northern Celtic Sea (Division 7g) was more widely dispersed throughout the division between April and June. Fish tagged in the Bristol Channel (Division 7f) tended to mix with offshore populations in Divisions 7g and 7h. In contrast, some of the fish tagged in the western English Channel (Division 7e) migrated into the Eastern Channel (Division 7d) for at least part of the year. Juveniles found close to the southeast Irish Coast (south of Division 7a) are considered to be part of the Celtic Sea stock and the landings adjusted accordingly since 2004 (ICES, 2017a).
Data gaps and research priorities
Routine monitoring of temporal and spatial changes in landings, fishing effort and landings per unit effort (lpue) for the main fleets catching cod in Division 7e–k has been recommended. This monitoring uses maps of landings and landings per unit effort by ICES rectangle (ICES, 2017b) and was carried out in 2016.
A degree of uncertainty exists in the catch statistics for this stock. Misreporting, discard practices and high grading are a main cause of uncertainty in the catch data, especially when quotas have been particularly restrictive in the 2003–2008 period as well as 2011 (ICES, 2009).
ICES. 2009. Report of the Benchmark and Data Compilation Workshop for Roundfish (WKROUND), 16–23 January 2009, Copenhagen, Denmark. ICES CM 2009/ACOM:32.
ICES. 2016. Report of the Working Group on Celtic Seas Ecoregion (WGCSE) 4–13 May 2016 Copenhagen, Denmark; stock annex
ICES. 2017a Cod (Gadus morhua) in divisions 7.e–k (Western English Channel and southern Celtic Seas). ICES Advice 2017
ICES. 2017b. DRAFT Report of the Working Group on Celtic Seas Ecoregion (WGCSE) 9-18 May 2016 Copenhagen, Denmark
MMO 2016 Landing obligation (discard ban) 2017: Guidance https://www.gov.uk/government/publications/landing-obligation-discard-ban-2017-guidance