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Mapping fish and fish eggs

The abundance and distribution of six variables related to fish and fish eggs were modelled in the archipelago between Sweden and Finland, but the distribution of herring eggs was also modelled in Lithuania. Despite the increased mobility of fish compared to vegetation and most sessile invertebrates, and despite the fact that the performance of fish models were slightly poorer than for other groups, the available evidence suggest that models can be used to predict abundance and distribution also of fish!

Figure 1. Performance (mean±se) of models of fish in two case-study areas using different criteria. Better performance is characterised by large r2 and AUC, but small nrmse.

Modelling abundance
The performance of models predicting abundance of fish was evaluated with respect to explained varaince (r2) and precision (nrmse). Species (e.g. pike, pikeperch and perch) performed very well the archipelago (all of 5 responses achieving nRMSE values lower than 0.2, corresponding to average prediction error less than one fifth of the range of abundance values for the modeled species). Of the fish, sticklebacks and pikeperch young-of-the-year were modelled best.

Modelling distribution
The performance of models predicting distribution (i.e. the presence vs. absence) of fish species and eggs in a particular site was evaluated usingh the AUC-statistic. As a rule of thumb, a value of 0.8 is often considered ”good” while 0.9 is considered excellent.

Models predicting the distribution of the spawn and young-of-the-year of a number of fish species performed reasonably well across the Archipelago Sea and in Lithuania (5 of 7 species modelled attained AUC values of 0.85 or more), although the lowest AUC value across all of the studied groups (invertebrates, fish and macrophytes) was observed for pike young-of-the-year (AUC = 0.67). None of the fish response variables were modeled in more than one area so differences between areas could not be assessed on the basis of a certain species. Of the fish, perch spawn and pikeperch young-of-the-year were modelled best.



 

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