Evidence for metapopulation structuring in cod from the west of Scotland and North Sea

Abstract

The scale of population structuring in cod Gadus morhua from the west of Scotland (ICES stock area VIa) and northern North Sea was investigated using a combination of non-genetic methods. Site fidelity of spawning aggregations was examined using historic tag-recapture experiments and individual geolocation estimates from data storage tagged fish. The extent of movements from spawning areas indicated by these two tagging approaches was broadly similar. Between 67 and 97% of adult cod remained within 100 km of spawning areas throughout the year, suggesting resident spawning groups. A small proportion of cod, however, did appear to stray between spawning areas. A comparison of the elemental signature of the otoliths of 0 year-group and the 0 year-group component from the same year-class at age 2 years indicated that most adults originate from local nursery areas. Moreover, there did not appear to be detectable exchange between spawning areas >200 km apart, such as the Clyde and Minch or Shetland and the Inner Hebrides. As such, population processes may operate at a smaller spatial scale than the stock level, with spawning aggregations functioning as local populations within a metapopulation. The relevance of this scale of dynamics is discussed in relation to recently imposed closed areas in the region. # 2006 Crown copyright

Decline and Recovery of Atlantic Cod (Gadus morhua) Stocks throughout the North Atlantic

“…Ames (2004) provides evidence that some of this substock structure may have disappeared, or have been reduced, even before the initiation of scientific study of the Atlantic cod resources. The existence of metapopulation structure has been supported and amplified by recent studies using advanced techniques in fields such as genetics (Ruzzante et al 1999), otolith chemistry (Jónsdóttir et al 2006), and tagging (Wright et al 2006). The view of stock dynamics afforded by SPA (Fig.…”

Migratory behaviour of Atlantic cod Gadus morhua: natal homing is the prime stock-separating mechanism

“…Further integration of results from tagging studies with new molecular and chemical approaches will help to further clarify the role of behaviour in determining stock structure, especially concerning degree of reproductive isolation between spatially closely located spawning aggregations (cf. Wright et al 2006).…”

“…To obtain observational records, archival tag technology represents a relatively new opportunity to reconstruct fish migratory pathways which may -separately or jointly with other methods -reveal more complex migratory patterns (e.g. Wright et al 2006).…”

Temporal trends in age and size at maturation of four North Sea gadid species: cod, haddock, whiting and Norway pout

“…Several gadids are of commercial importance, including our 4 model species. North Sea cod is widely distributed throughout the North Sea and is structured in many sub-populations (Hutchinson et al 2001, Wright et al 2006, Wright et al 2011b. North Sea haddock usually occurs north of the Dogger Bank (a sandbank located at 54.5°N), with major spawning areas in the northern North Sea and off the Scottish east coast, possibly corresponding to 2 different subpopulations (Wright et al 2011a).…”