THE USE OF SHAPE FOR CLASSIFYING FISH INTO ECOLOGICAL GROUPS

For management purposes it is suggested to break down fish into groups of species that lend themselves to the same management regime, i.e., have a similar ecology in terms of feeding habits, growth, reproduction, and environment. Such groups could then be used to i) improve our understanding of the respective group by summarizing the knowledge available for the members of the group and to ii) estimate important parameters for those members of the group for which no data are available. A precondition to the latter is the ability to classify "unknown" fish into the appropriate ecological group. The use of morphometrics in combination with discriminant analysis is evaluated. The results indicate that the method is well suited for this task. ICLARM contribution No. 756 Fish are the most numerous group of vertebrates and live almost wherever there is water. For management purposes it is desirable to break down this large, heterogeneous group into smaller homogeneous groups, above the species level. Preferably these units should contain species that lend themselves to the same management regime, i.e., have a similar ecology in terms of feeding habits, growth, reproduction, and environment. Such a lumping of species has been suggested or practiced by a number of authors, e.g., Kesteven (1973), Lackey (1974), Royce (1972). Appeldorn & Lindeman (1985, page 509) suggest that "such a unit can be treated in many respects as a single species" and that it can be managed in the same way as an unispecies stock. While the taxonomic status can be used for forming species clusters in some cases, it is not helpful in others when members of the same family occupy different niches. The family of Gadidae, for example, brings together a benthos feeder (Melanogrammus aeglefinus), a pelagic predator (Pollachius virens), and a pelagic plankton feeder (Boreogadus saida) not to speak of Lota lota, the lone freshwater gadid. For statistical purposes finfish have been broken down into 13 commodity groups by the 'International Standard Statistical Classification of Aquatic Animals and Plants' or ISSCAAP (FAO 1990). The ISSCAAP code is regularly used in the FAO yearbook of fishery statistics (e.g., FAO 1988). It has also been used for other purposes such as allocating resources for research (Fearn & Davis 1991). For management purposes the ISSCAAP code has problems similar to the taxonomic status because it joins, for example, all gadoids in one group. There is thus a need to create new groups of fish based on the above mentioned ecological criteria. Such ecological groups could then be used to i) improve our understanding of the respective group by summarizing the knowledge available for the members of the group and to ii) estimate important parameters for those members of the group for which no data are available. The practicality of the latter has been demonstrated, for example, by Pauly (1980, 1989) who derived empirical models for obtaining values of important but hard-to-estimate parameters such as natural mortality or food consumption from easy to obtain variables such as growth parameters, water temperature, or morphometric measurements. He applied his models to large, heterogeneous groups of species