Jo King: Jo King: Introduction � the WESTHER objectives The scientific implications of the EU � the WESTHER null and alternative Project WESTHER (Q5RS - 2002 – 01056) hypotheses for the first three objectives to the assessment and management of � results of the first three objectives the herring stocks to the west of the � interpretation of results and implications for British Isles. assessment Emma M.C. Hatfield & � recommendations from WESTHER to HAWG the WESTHER consortium � next steps WESTHER Objectives Techniques used � estimation of genetic and phenotypic 1) body morphometry differentiation between spawning 2) otolith morphometry aggregations 3) meristic analysis (pyloric caeca counts) � determination of stock origins and life 4) microsatellite DNA analysis of tissue history of juveniles 5) fish parasite assemblages � determination of composition of adult 6) parasite genetics feeding aggregations 7) otolith microstructure � improved guidelines for the conservation 8) otolith core microchemistry and and management of biodiversity and stock 9) multi-disciplinary, multivariate combination preservation Current assessment and management Partners & sub-contractors � University of Aberdeen sub- DARDNI � � FRS Marine Lab. Aberdeen � Institut für Seefischerei, Hamburg � Marine Institute, Galway, Ireland � National University of Ireland, Cork � University of Liverpool sub- IMR & University of Bergen � 1
Null Hypothesis Alternative Hypotheses � AH I: the different spawning aggregations � there is only one herring population to sampled are discrete at spawning time and the west of the British Isles, with no are, therefore, separate components detectable differences between any of � AH II: there is clear distinction of juveniles the geographically and temporally separated spawning components sampled in different nursery grounds � AH III: fish from each spawning aggregation remain discrete on their feeding grounds Spawner samples collected 2003 - 2005 Alternative Hypothesis I - spawners 60 Period 1 Period 2 58 � the different spawning aggregations sampled are discrete at spawning time and 56 are, therefore, separate components 54 52 50 -14 -12 -10 -8 -6 -4 -2 0 Outgroup samples collected 2003 - 2005 Methods used to test spawning groups 75 2003 2004 1. body morphometry 2005 70 2. otolith morphometry 3. microsatellite DNA analysis of tissue 65 4. fish parasite assemblages 5. otolith core microchemistry and 60 6. multi-disciplinary, multivariate combination 55 50 -10 -5 0 5 10 15 20 25 30 2
Alternative Hypothesis I - spawners Results of testing spawning groups All methods, except the genetics � accept Alternative Hypothesis I (microsatellite DNA), showed strong evidence for a clear distinction between all � the different spawning aggregations of the spawning groups, except Donegal and sampled are discrete at spawning time Rosamhil samples and are, therefore, separate components Alternative Hypothesis II - juveniles Juvenile samples collected 2003 - 2005 60 2003 2004 2005 58 � there is clear distinction of juveniles sampled in different nursery grounds 56 54 52 50 -14 -12 -10 -8 -6 -4 -2 0 Analysis of juveniles Parasites as tags: tag prevalence � Stanton Bank is a nursery ground � the WPs on parasites and otolith where juveniles originating from microchemistry act as tags for the spawning grounds from the north-west juvenile stages of herring and therefore of Ireland and western Scotland mix. provide the best place to search for � the Irish Sea contains juveniles arising evidence of juvenile separation from spawning in both the Irish Sea and the Celtic Sea. 3
Otolith microchemistry: nursery areas Alternative Hypothesis II - juveniles � the Irish Sea contains a mixture of juveniles � accept Alternative Hypothesis II spawned in the Irish Sea, the Celtic Sea and probably the Clyde too � there is clear distinction of juveniles � Stanton Bank and the Minches likely act as sampled in different nursery grounds nursery areas for fish spawned to the northwest of Ireland and around Skye � there is, however, strong evidence that (western Scotland). � there is a lesser signal of mixing of juveniles from different spawning grounds mix in some of the nursery juveniles in the Scottish west coast sea grounds sampled lochs of fish spawned in the Clyde, and both spawning samples off the Scottish coast (Skye and Cape Wrath). Adult “mixed” samples collected 2003 - 2005 Alternative Hypothesis III – feeding adults 60 2003 2004 2005 58 � fish from each spawning aggregation 56 remain discrete on their feeding grounds 54 52 50 -14 -12 -10 -8 -6 -4 -2 0 The results suggested: Methods used to test for possible mixtures � the “mixed” aggregations collected in VIaS consisted mainly of NW Ireland spawners with possibly a small component of Irish Sea spawners 1. body morphometry � the “mixed” aggregations collected in VIaN consisted 2. fish parasite assemblages mainly of Cape Wrath spawners, with a component of other spawners recruited from Scottish coastal nurseries 3. otolith core microchemistry and and/or NW Ireland. Additionally, there was evidence for 4. multi-disciplinary, multivariate the presence of Irish Sea adults and possibly even Clyde adults within the VIa North mixed samples combination � most of the Irish Sea “mixed” aggregations comprised Irish Sea spawners, with a small component of Celtic Sea spawners � most of the Celtic Sea “mixed” aggregations comprised Dingle Bay spawners, with no indication of any component from the Irish Sea 4
Hypothetical movements of juveniles and adults to feeding Alternative Hypothesis III and spawning grounds based on historical evidence and WESTHER results � reject Alternative Hypothesis III � there is evidence to suggest mixing of adults from separate spawning components, especially in VIa North � there is evidence to suggest that the Celtic Sea and VIIj spawning ground fish do not mix with the more northerly spawners to the same extent that the more northerly spawners mix with each other � the science, therefore, suggests links between the areas, with fish spawning in different areas mixing, to varying extents, on feeding grounds Assumptions of stock assessment � the stock is a closed unit � data used in assessments are representative of the entire stock So what does this mean in terms of This implies: the current assessment and � stock gain only through birth or management of the western herring mortality, not immigration or emigration stocks? � F distributed homogenously over the stock � Data from surveys should be a relative measure of the entire stock and its geographical distribution Are we violating these assumptions Recommendations: for the western stocks? � WESTHER results suggest that both basic 1) assess the herring to the west of the British Isles as two assumptions are violated: stock units - Malin Shelf (including the current ICES stocks VIa � for VIaN the acoustic tuning index is derived North, VIaS and VIIb, c, Clyde and Irish Sea (VIIaN)) and Celtic Sea (the current Celtic Sea and VIIj stock). In the area studied in from a survey in VIaN, an area shown to contain WESTHER we can hypothesise that there are two stock units within which data can be pooled for assessment. N.B. the boundary at the a mixture of adults from different spawning northern edge is unclear and there is no evidence presented in the report which separates autumn spawners in the north of Scotland components west of 4 degrees W from autumn spawning fish east of 4 degrees W � the bulk of the VIaN fishery is currently in Q3 in (the North Sea stock). The boundary is here for convenience. the north of VIaN – not homogenously 2) survey effort should be increased or diverted to a combined survey on non-spawner distributions mixing distributed at all on the Malin Shelf � in VIaS the 2004 acoustic survey was shown to 3) the current monitoring of the spawning components comprise spawners quite different to those should be maintained, but not to the detriment of a wider scale Malin Shelf survey. Spawning ground surveys might sampled from spawner aggregations taken from provide data on the dynamics of individual stock components, which the fishery are thought to be useful for the development of a fleet-based advice 5
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