Stock and recruitment in North Sea herring (Clupea harengus); compensation and depensation in the population dynamics

Macroscopic maturity staging data are widely used to distinguish between reproductive and non-reproductive individuals. The implicit assumption is that these data are accurate. The accuracy of macroscopic maturity staging of North Sea herring (Clupea harengus) has not been checked since the macroscopic scale was produced in 1961. The aim of this study was to assess the accuracy of macroscopic maturity staging of female North Sea herring by comparison to histological staging and the gonadosomatic index (GSI). Ovary samples were collected during the North Sea Herring Acoustic Survey in 2006 on-board FRV ‘Scotia’ (Scotland) and in 2007 on-board FRV ‘Scotia’ and RV ‘Johan Hjort’ (Norway). Commercial samples were also collected by Marine Scotland, Aberdeen in both years. The maturity staging error was relatively low in 2006 (21% error) but was much higher on-board FRV ‘Scotia’ (57%) and RV ‘Johan Hjort’ (47%) in 2007. There was estimated to be a 27% under-estimation of the spawning stock biomass (SSB) in 2007 due to the differences in the proportion mature but no change in SSB estimates in 2006. GSI cut-off scores, estimated by means of multinomial regression models were successfully able to separate immature females from both mature-active and recovering females; however, there was some overlap between the mature-active and recovering individuals. We conclude that an effective and low-cost means of reducing error in herring maturity studies is the combined use of a four-point macroscopic maturity scale with routinely collected GSI data, the latter acting to validate and fine tune macroscopic staging.

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Comparison of two periods of North Sea herring stock management: success, failure, and monetary value

ICES Journal of Marine Science ◽

10.1093/icesjms/fsm045 ◽

2007 ◽

Vol 64 (4) ◽

pp. 686-692 ◽

Cited By ~ 21

Author(s):

E. John Simmonds

Keyword(s):

North Sea ◽

Scientific Information ◽

Clupea Harengus ◽

Stock Management ◽

Monetary Value ◽

Management Actions ◽

Spawning Stock ◽

Critical Issues ◽

Management Advice ◽

Management Issues

Abstract Simmonds, E. J. 2007. Comparison of two periods of North Sea herring stock management: success, failure, and monetary value. – ICES Journal of Marine Science, 64: 686–692. At two points in the past (1970 and 1995), North Sea herring (Clupea harengus) abundance and catches have been in a similar situation: the stock had declined from an earlier high and reached a depleted state with a spawning-stock biomass of around 400 000 t, well below the agreed biomass limit reference point of 800 000 t. Catches were also similar at 600 000 t annually, and too high to be sustainable. A comparison of the scientific advice, the management actions, and their effects on population trends over the periods following these two critical years provides insight into important management issues. The benefits to the industry of the value of the cumulative catch resulting from successful management of this large stock have been proven to outweigh by far the costs of obtaining good management advice. The conclusion is that sound scientific information plays an important role when difficult management issues have to be confronted. However, there are other critical issues, such as the stakeholders' wish to preserve the stock at all costs and a management organization that has authority to take decisions.

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