ICES provides advice on two sea bass (Dicentrarchus labrax) stocks; a ‘northern’ stock in divisions 4.b-c, 7.a, and 7.d-h (central and southern North Sea, Irish Sea, English Channel, Bristol Channel and Celtic Sea), and a southern stock in divisions 8.a-b (Bay of Biscay). This Workshop reviewed evidence and proposed plausible stock structure scenarios for the ICES sea bass benchmark in 2023 (WKSEABASS). In summary, evidence suggests that the current ICES stock units do not reflect the biological boundaries and connectivity of sea bass within these areas. Evidence from genetic (section 2.1), tagging (section 2.3) and larval/juvenile pelagic drift (section 2.4) studies, revealed a high degree of connectivity between the northern and southern sea bass stock units. Furthermore, genetic (section 2.3) and tagging (section 2.3) evidence revealed potential boundaries within the northern sea bass stock, particularly between the North Sea and the Celtic/Irish Sea. The group agreed that evidence suggested a single meta-population structure, meaning a group of spatially separated populations interacting at some level (i.e. migrating, reproducing, feeding). Based on evidence provided, three plausible population scenarios were identified: · Hypothesis 1: Three subpopulations, Irish Sea (7.a), North Sea (4b-c), southern Bay of Biscay (8.b); with mixing among the Celtic Sea (7.f-g), Bristol Channel (7.h), English Channel (7.d-e) and Northern Bay of Biscay. Mixing is seasonally dependant with more mixing occurring during summer compared to winter. · Hypothesis 2: Three subpopulations, Irish Sea (7.a), North Sea (4.b-c) and Bay Biscay (8.a-b); with mixing among the Celtic Sea (7.f-g), Bristol Channel (7.h) and English Channel (7.d-e). Mixing is seasonally dependant with more mixing occurring during summer compared to winter.· Hypothesis 3: Three subpopulations, Irish Sea (7.a), North Sea/eastern English Channel (4.b-c, 7.d) and Bay Biscay (8a-b); with mixing among the Celtic Sea (7.f-g), Bristol Channel (7.h) and western English Channel (7.e). Mixing is seasonally dependant with more mixing occurring during summer compared to winter. |
