Community Research and Development Information Service - CORDIS

Deliverable: otolith morphometic classification of harvest location of cod

1. Data on otolith shape has been extracted as Fourier coefficients and thereafter compiled into a database of descriptors that have been delivered for further analysis of combined data.
2. Otolith shape does not discriminate well between a large set of sample origins. In this study mean classification success ranged from 58.8% to 61.9% for 7 sample sites that were replicated three times.
3. Low variation in shape descriptors between sample origins does not necessarily imply that the classification success will increase. Otoliths from the Baltic were more easily distinguished from other otoliths compared to otoliths from the North Sea despite that both sample sites had a low variation in shape.
4. The number of samples of otolith shape from different origins needs to be balanced in order to secure a proper statistical analysis. Furthermore the subtle differences between otoliths suggest that sample size should exceed 1000 specimen in order to be representative.
5. Otolith shape appears to vary between seasons. Reference samples of otolith shape therefore need to be taken in the same time period as the samples that need to be discriminated.
6. Otoliths are readily available in large numbers from practically all fishery labs around the NE Atlantic. The otolith shapes are fairly easy to determine by standard image systems. Therefore investigations that need to discriminate between stocks and detect the harvest origin of individual cod can be made swiftly and with a relatively low budget compared to other discriminating methods.
7. Fishery managers and legislators are often more interested in fish that may derive from only two areas. Thus, investigations of fish origin are usually initiated when a fisherman are accused of fishing in closed areas but claim that he has been fishing in an adjacent area. This study suggests that otolith shape can predict the fish origin between two areas with a high accuracy.

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