Megrim, Celtic Sea, Beam trawl
The assessment method used is described as ‘data limited’ and described as indicative of trends. Whilst an assessment model was fitted a lack of confidence in the data means that the results can only be interpreted as indicative of trends; there are no reference points available. These trends shown below indicate an increasing spawning stock biomass and a decreasing relative fishing mortality, with both catches and recruitment of young fish stable. Discards have not been fully quantified across all fleets so total catch has not been fully estimated.
Stock structure and recruitment
The assessment is for megrim (Lepidorhombus whiffiagonis) but the reported catches and TAC are for megrim and four spot megrim (L boscii) which is a relatively minor (circa 5%) component of the catches. There is evidence for strong genetic differentiation within the ICES Sub Areas VI and VII, VIII and IX which would tend to support the existence of relatively localised populations. However, apart from the observation that juveniles prefer to inhabit depths between 150 and 280 m and that females tended to dominate shallower catches west of Ireland with males more common in deeper water there is not much information on population distributions and migrations (MacDonald 2014 and literature cited).
Whilst this information suggests that the management stock in ICES divisions VIIb-k and VIIIabd may consist of a number of subpopulations the assumption by ICES since the 1970s has been that the stock is adequately defined for management purposes (ICES 2012).
Data gaps and research priorities
The most urgent data gap which needs filling is the need for discard data from all fisheries exploiting the stock. The situation has improved in recent years with the addition of one year’s French data in addition to the data from other nations, but the discard rates have been variable in recent years so a longer time series is needed to quantify total catches, hence the advice given is for landings only. Whilst there has been a ‘benchmarking workshop’ in 2012 (ICES 2012) where the modelling process was developed agreed, a lack of confidence in the data means that the absolute results for this model were not used so improved data is a priority. Ultimately assessment reference points for spawning stock biomass and fishing mortality are required for a full assessment of this stock.
ICES (2012) Report of the Benchmark Workshop on Flatfish Species and Anglerfish (WKFLAT); 1–8 March 2012 Bilbao, Spain
ICES (2014) Celtic Sea and West of Scotland Megrim (Lepidorhombus whiffiagonis) in Divisions VIIb–k and VIIIa,b,d ICES Advice 2014
ICES (2015) Megrim (Lepidorhombus whiffiagonis) in Divisions VIIb–k and VIIIa, b, d (West and
Southwest of Ireland, Bay of Biscay) ICES Advice 2015
MacDonald P (2014) Increasing understanding of a data poor species to improve resource (Lepidorhobus whiffiagonis) in the Northern North Sea PHD thesis University of Aberdeen