The Taxonomic Status and Nomenclature of Some Atlantic and Pacific Populations of Yellowfin and Bluefin Tunas

Abstract

T HE chief object of this paper is to analyze certain taxonomic data that have been previously published by authors regarding some populations of the yellowfin and bluefin tunas, to see what reasonable taxonomic conclusions can be drawn therefrom. Included also are some original data which have been determined on the western Atlantic bluefin tuna. In taxonomic papers on the family Scombridae, used in a broad sense, the geographic distribution of many species is often stated to be cosmopolitan. (For recent brief resumes of the species of this family, see Fraser-Brunner, 1950, and Rivas, 1951.) However, it should be remembered that such statements, in general, represent the subjective opinion of the author, unsupported by adequate data. This supposition is probably based on the impression that these fishes, being powerful swimmers, roam the seven seas at will. However, in at least one instance where a detailed study of comparable data has been made, namely, the comparison of the populations of bluefin tunas from the American Atlantic and Pacific coasts by Godsil and Holmberg (1950), the cosmopolitan distribution of a single species of bluefin tuna is disproved, as discussed below. It is altogether within the realm of likelihood that other so-called cosmopolitan species will prove to be composites of more than one species, on an objective study of adequate data. Some evidence is here presented which indicates that the two bluefin tuna populations on the opposite Atlantic coasts apparently belong to two distinct species. Also, evidence gleaned from the literature, although inadequate, seems to indicate that the yellowfin tuna populations should also be assigned to more than one species, or at least a number of subspecies should be recognized. This paper of course is not a definitive finished treatment of the tunas and it is not meant to be taken as such, since extant data are meager and inadequate to solve the various taxonomic problems involved. It is rather meant to present a certain viewpoint to be taken into consideration in future attempts to solve the problem. In the absence of adequate data we must lean heavily on the known facts of the geographic distribution of fishes in general to draw plausible conclusions. Based on these two factors, our scant knowledge of the taxonomic characters of these fishes taken in conjunction with what we know of zoogeography of fishes in general, the tentative conclusions here arrived at seem to be justified. As the main reliance here is based on zoogeographic rather than morphologic considerations, and because of the necessarily tentative nature of this paper, all Latin names used are binomial, although in some instances the inadequate data would rather indicate that trinomials should more properly be used.