Report of the Workshop on procedures to establish herring TAC (Spring Western Baltic (WBSS) and Autumn Spawning North Sea (NSAS) stocks) in Skagerrak and Kattegat (Division IIIa) (WKWATSUP)

The  overall  outcome  of WKWATSUP  is  a  TAC  setting  procedure  alternative  to  the  procedures  suggested  evaluated  by  the  joint  request  from  the  EC  Commission  and Norway.  The WKWATSUP  suggest  that  the  TAC  should  first  be  set  for  the  WBSS  according to the FMSY or FMSY transition framework for WBSS alone. If the NSAS is greatly  impacted  by  management  of  the  WBSS,  this  rule  needs  to  be  re‐evaluated.  Following this, the fraction taken in the Eastern part of the North Sea (parts of Sub Divisions IVb and IVaE) should be subtracted from the total TAC for the WBSS before sharing the TAC between Division IIIa and Subdivisions 22‐24. Subsequently the best estimates of the proportions of the NSAS and WBSS in the catch by fleet should be used to calculate the combined catch options in compliance with the targeted catch for WBSS.
The 50:50 share of the WBSS TAC between Division IIIa and Sub Divisions 22‐24 was not  specifically  evaluated  by  WKWATSUP.  It  was  viewed  as  a  political  choice  and  thus  all  evaluations  of  TAC  setting  procedures  were  performed  applying  a  50:50 share of the TAC between Division IIIa and Sub Divisions 22‐24, though using three different  approaches  as  how  to  include  the  share  taken  in  the  North  Sea.  The  WKWATSUP  recommend  a  seasonal  closure  of  the  herring  fishery  in  parts  of  the Eastern North Sea, however, until such is implemented, the suggested approach by the WKWATSUP mentioned above should be applied.
The WKWATSUP showed that the selection patterns of the C and F fleets were very different and thus choices about the share between Division IIIa and Subdivisions 22‐24 are likely to have an impact on the sustainable exploitation of the stock.  
The WKWATSUP summarised the existing knowledge on migrations and area distri‐butions  for NSAS  and  WBSS  based  on  literature  and  recent  catch  and  survey  data. The  general  migration  routes  are  known,  however,  an  end‐to‐end  spatial  lifecycle‐closure  model  could  be  developed,  encompassing  active  migrations  of  spawning components  and  larval  drift,  to  investigate  the  connection,  interactions  and  spatial  distribution  of  herring.  There  are  large  amounts  of  empirical  data  available  with which to verify the model, although the paucity of knowledge about overwintering and feeding locations and processes will challenge its construction.
The WKWATSUP reviewed the sampling for stock proportions in the mixed catches of herring. There was clearly a mis‐match between sampling intensity and catch dis‐tribution, particularly in relation to the part of the WBSS that migrates into the East‐ern  North  Sea  during  summer  feeding  migrations  and  the  WKWATSUP  made recommendations as how to improve the sampling scheme.
The  methodology  currently  used  to  estimate  stock  proportions  at  age  in  the  mixed  catches of herring was evaluated and recent development using a statistical model‐ling  approach  was  presented  by  the  WKWATSUP.  Some  problems  are  still  unresolved,  but  the  group  recommends  further  refinement  and  peer‐review  of  this approach with an incitement to apply the approach during next HAWG.