Abstract
There is evidence that the importance of the different spawning grounds of North Sea autumn-spawning herring has changed. It has been hypothesised that as herring stocks collapse, the diversity of spawning sites also collapses. This was found to be the case in the Sea autumn-spawning herring, which collapsed in the late 1970s. The ICES International Herring Larval Survey has been carried out since 1972 and covers most of the potential and historic spawning grounds of herring. recovery of the stock did take place as predicted in terms of biomass, and re-colonisation of old spawning sites also did occur. We show that, despite the delayed response in re-colonisation of the southern spawning areas, there is almost no change in the number of spawning locations where the highest abundances of larvae (top 50%) are found from collapse to recovery (approximately 9 sites). It was a change in these core sites and the spread to other locations with lower larval abundance that caused the spread of herring spawning. We show that larval surveys are a useful tool for describing the dynamics of sub-stock structure in heterogeneous populations such as herring.
Highlights
Fish stocks in the different stages of collapse or recovery show many changes in population demographics, ecology and productivity (Shelton et al, 2006; Melvin and Stephenson, 2007; Nash et al, 2009)
One of the classic examples of a fisheriesinduced collapse followed by stock recovery is North Sea herring (Simmonds, 2007)
Spawning components collapsed from south to north (Cushing, 1992) and the herring became more limited in distribution (Saville and Bailey, 1980)
Summary
Fish stocks in the different stages of collapse or recovery show many changes in population demographics, ecology and productivity (Shelton et al, 2006; Melvin and Stephenson, 2007; Nash et al, 2009). One of the classic examples of a fisheriesinduced collapse followed by stock recovery is North Sea herring (Simmonds, 2007). The collapse of North Sea herring was not spatially homogeneous. Spawning components collapsed from south to north (Cushing, 1992) and the herring became more limited in distribution (Saville and Bailey, 1980). Recovery was different for each spawning com-
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