Community Research and Development Information Service - CORDIS

Deliverable: otolith core chemistry classification of harvest location of cod

Using the microchemistry of otolith cores to place cod back to their origin gave the following results. There were no significant differences between areas in otolith core concentrations of Mg or Pb. The otoliths of fish from the Baltic had significantly more Mn and Ba, and lower Sr that those of fish from other areas. The three sampling seasons were grouped together for discriminant analysis. Classification was based on 8 elements: Na, Mg, Mn, Cu, Rb, Sr, Ba and Pb. Pb made no significant contribution to the discrimination. The most important elements in the classification were Rb, Mn, Sr, Ba. However, better classification was achieved using 7 elements, excluding Pb. The percent correct classifications ranged from 71% for Baltic fish to 38% for Celtic Sea fish.

The cross validated success of the Artificial Neural Network (ANN) was mixed, ranging from 0 to 82.4%. With the exception of CTB (Celtic Sea) and CTF (Norwegian waters), the classification success was above the expected random probability. In the case of CTF, there were relatively few samples with which to train, cross validate or test the ANN. CTC (Icelandic waters), CTD (Irish Sea), CTE (North Sea) and CTG (Icelandic fish farm) all had a similar classification success of between 45 and 60%. The clearest classification success was with CTA (the Baltic) despite a relatively small number of samples analysed.

In the case of CTB (Celtic Sea) the highest proportion of misclassified samples was to CTD (Irish Sea). CTB (Celtic Sea), CTC (Icelandic waters) and CTD (Irish Sea) all had been 15 and 22% of the fish misclassified as coming from CTE (North Sea). No fish were misclassified as coming from CTF (Norwegian waters), however, the training data set was small for this area.

The linear regression of the ANN model was relatively high for the Baltic (CTA) and the Scottish fish farm (CTH), reflecting the high correct percentage of classification. The regression coefficient for the Icelandic waters (CTC) and, surprisingly, the Norwegian waters (CTF) also had reasonably high regression coefficients. All other areas had a relatively low linear regression coefficient that reflected the relatively low level of classification success.

Testing: Autumn (feeding aggregation) core samples.
The cross validated success of the ANN was mixed, ranging from 0 to 60.0%. Where test data existed, with the exception of CTB (Celtic Sea) the classification success was above the expected random probability. The highest classification success was with the two fish farms CTG (Icelandic fish farm) and CTH (Scottish fish farm).

In the case of CTB (Celtic Sea) the highest proportion of misclassified samples was to CTD (Irish Sea) with a reasonably large proportion also in to CTC (Icelandic waters). The majority of the CTE (North Sea) were misclassified as coming from the Irish Sea (CTD). No fish were misclassified as coming from CTF (Norwegian waters) or CTB (Celtic Sea).

The highest linear regression of the ANN model were for the two fish farms (CTG and CTH) reflecting the reasonably high correct percentage of classification. All other areas had a relatively low linear regression coefficient that reflected the relatively low level of classification success.

Reported by

THE UNIVERSITY OF BERGEN
DEPARTMENT OF RESEARCH MANAGEMENT, PO BOX 7800
N-5020 BERGEN
Norway
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