By Teppo Vehanen, Jouni Aspi
Fisheries Research, Volume 27, Issues 1-3, June 1996, Pages 37-49, ISSN 0165-7836, DOI: 10.1016/0165-7836(96)00472-9.

Because there are some 15 000 Finnish lakes exceeding 10 ha in area, there is a pressing need in Finland for the development of effective stocking strategies for various types of Finnish lakes. The most common predatory fish employed in stocking in Finland for the past few decades has been brown trout (Salmo trutta (L.) m. lacustris), and the brown trout yield in lakes relies almost solely on stocking. Since the recourses of the fisheries managers are limited, it would be useful if an empirically derived lake classification scheme were made available for them, to enable them to plan and implement monitoring programmes to suit each individual lake.
A cluster analysis (Ward's minimum-variance method) was used to classify 33 lakes in northern Finland on the basis of the yields of seven most common species: brown trout, vendace, whitefish, perch, pike, burbot and roach. The success achieved in the stocking of brown trout was compared between the various lake clusters. A discriminant analysis was used to develop a discriminant criterion to classify each lake into one of the clusters on the basis of species composition and ten environmental variables.
The results suggested that, when based on catch statistics, cluster analysis can produce an objective classification scheme. Relative brown trout yield (kilograms per thousand fish released) seemed to be higher in the cluster with a higher proportion of vendace. The importance of the use of proper stocking rate for different kind of lakes was also revealed. Discriminant criterion based on both species composition and environmental variables rather reliably classified the lakes to correct clusters (76% and 70%, respectively).
A scheme employing lake clusters could, thus, be used as a basis for management decisions on suitable stocking rate and which of the lakes are to be included into the stocking programmes of brown trout. The study produced some useful guide-lines to management programmes reducing the need to study all individual lakes in detail.
Keywords: Brown trout; Community analysis; Fish yield; Species composition

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