The stock assessment, for each Functional Unit (FU), is based on one Under Water Television (UWTV) survey linked to yield-per-recruit analysis from length data. UWTV improved since 2007 due to an enhancement in the record position by Global Positioning System (GPS), increasing accuracy of abundance estimates; values prior to 2007 were revised. Discard and bycatch data are included in the assessment (ICES, 2012a).
ICES advice is for each FU and, under the Maximum Sustainable Yield (MSY) transition scheme, is at 1,400 tons for 2013 for FU 6 (Farn Deeps) and at 18,120 tons for all FU in the North Sea. ICES has presented mixed-species advice for the North Sea for the first time in 2012, spanning a range of options. Cod is the limiting species due to bycatch in North Sea demersal fisheries – to strictly enforce the cod management plan, catches of Norway lobster in this fishery should be limited to 1,100 tons (ICES, 2012a).
Current management, at the ICES Division level instead for each FU, is not considered to represent the local effort and safeguard the sustainability of Nephrops stocks (ICES, 2012a)
Reference points based on the precautionary approach have not been defined (ICES, 2012a), and neither have limit reference points. Candidate maximum sustainable yield (MSY) points have been explored, and determined for males and females, separately and combined. Under the new ICES MSY framework, a proxy of FMSY, based on F35%SPR for males was determined taking into account differences in exploitation rates between sexes, stock resilience, factors affecting recruitment, population density, knowledge of biological parameters, the nature of the fishery, historical landings and stock status. MSY Btrigger was revised (due to UWTV survey improvement) and set at 890,000 million individuals (ICES, 2012a).
The stock has been recovering since 2009 and in 2011 was at 870,000 million, below MSY Btrigger. The harvest rate at 11.4% is above FMSYproxy of 8%. Total landings, in a decreasing trend, are at 20,000 tons; for FU 6 are at around 2,100 tons – Farn Deeps is the only FU in a diminishing landings trend. Effort in this FU can increase, has happened in 2006, due to lower abundance in other FU which is inadvisable as signs of overexploitation have been shown in former years (ICES, 2012a).
The abundance index was revised. After the maximum value registered in 2005 (1657 millions) abundance has been decreasing until 2009 (683 millions), coincident with the increase in the effort level, and since then has been recovering but is still below MSY Btrigger. Except for 2008 at 6.4%, the effort level has always been above FMSY. Landings oscillated around 18,000 tons between 1992 and 2003, and since then increased to higher levels, at about 29,000 tons in 2007 and 2009.
Landings in Farn Deeps (FU 6) were at average 2,200 tons between 1996 and 2004 and increased to 4,868 tons in 2006 (62% above ICES advice), in consequence of improvement in catches’ reporting but also due to additional effort increase – this possibly resulted in alterations in breeding success and recruitment (ICES, 2012a).