Acknowledgements SGHERWAY 2008-2010 Dr Emma Hatfield This project would not have been possible without the input of the following people: Steven Beggs, Maurice Clarke, Afra Egan, Clementine Harma, Niels Hintzen, Beatriz Roel, Norbert Rohlf and John Simmonds Pelagic RAC. 11 th October 2010 SGHERWAY Assessment and management units Current Replace with: Study Group on the evaluation of assessment and management strategies of the western herring stocks o Convened in 2008 to explore and evaluate recommendations of WESTHER project: 1. assess two stock units - Malin Shelf (VIa North, VIaS and VIIb, c, Clyde and Irish Sea (VIIaN)) and Celtic Sea (the current Celtic Sea and VIIj stock) 2. combined survey on non-spawner distributions mixing on the Malin Shelf 3. management plans should recognise there is a population in the Celtic Sea and VIIj and a metapopulation centred on area VIa SGHERWAY ToRs 1. Combined assessment of the three stocks. Results o poor retrospective pattern in each scenario 1. investigate combined assessment of the VIaN, VIaS, Irish Sea (VIIaN) – the Malin Shelf metapopulation o combined assessment is not sensitive to the choice of settings 2. evaluate sustainable alternative management strategies for the metapopulation of VIaN, VIaS and VIIaN, through Conclusions simulation o combined assessment does give important 3. evaluate the utility of a synoptic acoustic survey in the information on the Malin Shelf metapopulation, summer for the Hebrides, Malin and Irish shelf areas, in unlikely to be useful for management advice purposes conjunction with WGIPS surveys of VIaN and the North Sea o it is unlikely that it will replace individual assessments of the constituent stocks. However, it is necessary to segregate these stocks in the Malin Shelf acoustic surveys 1
2. A lternative Management Strategy Evaluation 2. Alternative Management Strategy Evaluation o Populations : the populations of the three different ICES areas, In total, four different processes or scenarios were varied VIaN, VIaS/VIIb,c and VIIaN are assumed to each represent a to evaluate whether management of the ICES stocks spawning population. During spawning they only occupy the area is precautionary or not: they are named after, while during the feeding season parts of a o level of mixing between populations population can migrate to other areas where they are susceptible to the fishery active within the area o accuracy of correctly splitting the Malin Shelf survey o Fisheries : within each of the three management areas, the into three different survey indices fishery is targeting the biological populations during the feeding o number of samples taken in the Malin Shelf survey season when mixing between populations occurs. Hence, each fishery only has the fish occurring in the management area they o management target are active in available to it o Surveys : within the simulation framework only one survey is These procedures were modeled including feedback loops where, over time, the outcomes of management actions designed and this is an acoustic survey over the Malin/Hebrides Shelf, targeting the combined population of VIaN, VIaS/VIIb,c affect the biological population the year after which, in and, depending on the scenario investigated, VIIaN, and it reports its turn, affects the fishery and management on all ages 2. MSE. Mixing 2. MSE. Population Identification success Modelled SSB Modelled SSB 2. MSE. Survey samples / design 2. MSE. Survey samples / design. II. Deviance from true age-pattern Modelled SSB 2
2. MSE. Discussion 2. MSE. Conclusions No sustainable management of metapopulation. In none of the scenarios where the VIIaN population is included in the Malin Shelf survey can the VIIaN ICES stock be sustainably managed. Sustainable management possible for the VIaN and VIaS/VIIb,c ICES stocks Strong trade-offs between level of mixing, uncertainty in stock identification and sustainable fishing mortality 3. A synoptic Malin Shelf acoustic survey 3. A synoptic Malin Shelf acoustic survey Distribution of biomass per rectangle Acoustic Density 2008 2009 Adults Juveniles 60.0° N 60.0° N 59.5° N 59.5° N 60° N 60° N Bio juv 2008: 59.0° N 59.0° N 59° N 59° N 58.5° N 58.5° N 58.0° N 58.0° N Bio 2008: 0% 18% 38% 58° N 58° N 57.5° N 57.5° N Bio juv 2009: 57.0° N 57.0° N 57° N 57° N 0% 21% 44% 56.5° N 56.5° N Bio 2009: 0% 23% 47% 56.0° N 56.0° N 56° N 56° N 55.5° N 55.5° N 0% 9% 18% 55° N 55.0° N 55.0° N 55° N 54.5° N 54.5° N 54° N 54° N 54.0° N 54.0° N 53.5° N 53.5° N 53° N 53° N -13° -12° -11° -10° -9° -8° -7° -6° -5° -4° -3° -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 53.0° N 53.0° N W W W W W W W W W W W W W W W W W W 12° 11° 10° 9° 8° 7° 6° 5° 4° 12° 11° 10° 9° 8° 7° 6° 5° 4° Blue circles ML Aberdeen, green circles MI Galway and red circles AFBI, Belfast 3. A synoptic Malin Shelf acoustic survey SGHERWAY conclusions o it is unlikely that a combined assessment will replace individual assessments of the constituent ICES stocks (VIaN, VIaS/VIIb,c and Irish Sea). However, it is o the amount of mixing between stocks cannot be resolved necessary to segregate these stocks in the Malin Shelf by the current sampling regime in the Malin Shelf survey acoustic surveys o consequently, a sampling programme has been o MSE shows that sustainable management is possible developed to enable proper identification of fish stock for the VIaN and VIaS/VIIb,c ICES stocks but not for the origins, making use of otolith and body shape techniques Irish Sea ICES stock when it is included in the and analyses that will be compared to the fish of known metapopulation model (and survey) spawning origin collected during the EU project o the amount of mixing between stocks cannot be WESTHER resolved by the current sampling regime in the Malin o this sampling programme has been initiated in the 2010 Shelf survey but a new sampling regime should resolve summer surveys population identification o there are strong trade-offs between the level of mixing, uncertainty in stock identification and sustainable fishing mortality 3
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