The stock is surveyed by underwater TV (UWTV), covering the main part but not all of the grounds (Functional Units, FU), meaning abundance may be underestimated. A yield-per-recruit analysis is then conducted based on length frequency data. There is uncertainty around many of the population’s biological parameters such as growth (ICES, 2012a). 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 10,000 tons for 2013 for FU 7 (Fladen Ground) 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 3,900 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 was selected as F0.1 = 10.3% for sexes combined and based on the likely low productivity and on historical harvest ratios. MSY Btrigger was revised (due to UWTV survey improvement) and set at 2767,000 million individuals (ICES, 2012a).
Fladen Ground is the largest Nephrops ground. The spawning biomass size has decreased in the last three years but is above its MSY reference point, and fishing mortality is below its MSY target. Current abundance levels, suggesting low productivity, are linked to the depleted North Sea cod stock and the ensuing reduced predation; although biomass can be underestimated by the current methodology used (ICES, 2012a).
Since 2000 abundance has been higher than previous values achieved in the 1990s. After the maximum values registered in 2007-2008 (around 7000 millions) abundance has been decreasing progressively, coincident with the increase in the effort level until 2010. Even though the effort level has always been below FMSY except in 2010. Total 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. In Fladen Ground (FU 7) landings were below 6,500 tons until 2000 but since then have been increasing, attaining 13,330 tons in 2009 in consequence of improvement in catches’ reporting (ICES, 2012a).