Studies on the Life History and Ecology of the Bigmouth Buffalo, Ictiobus cyprinellus (Valenciennes)

Abstract

The field study of the bigmouth buffalo (Ictiobus cyprinellus (Valenciennes)), conducted mainly in 1955 and 1956, was concentrated on two small eutrophic lakes in the Qu'Appelle River drainage of Saskatchewan. The bigmouth buffalo reaches its northern limit of range in the Qu'Appelle drainage. Migration into Saskatchewan was probably through postglacial connections at the headwaters of the Mississippi and Red River systems. In the lakes studied, the species prefers water shallower than 5 m.The relation of standard length to fork length and of fork length to weight is presented graphically, and the latter described by the equation: weight in pounds = (0.00097 fork length in inches)^2.91. Length–frequency distributions and age determinations from scale reading show that the population studied was largely the very successful 1948 year-class, produced in a year of extensive flooding. Annulus formation occurred during the second or third week in June. Growth of the 1948 year-class in Pasqua Lake was extremely slow, probably influenced by the cool climate and population density here.Food of young buffaloes was mainly Cladocera and Copepoda. Larger buffaloes ate about 75% Entomostraca and 15% chironomids, the latter more important as the size of fish increased. Analysis of the living habits of the food eaten, and the feeding mechanism of the buffalo, shows that they occupy a food niche overlapping both bottom feeders and limnetic plankton feeders.Sexual maturation, especially of females, was extremely slow both in age and size as compared with southern populations. Examination of gonads suggests spawning occurs about May 18–25. Egg measurements indicate that females do not all spawn each year. The contention by other investigators that spawning is "triggered" by addition of fresh water analogous to normal spring floods of the Mississippi River is supported by the present study.The population in the Qu'Appelle drainage is probably dependent on the very sporadic production of strong year-classes. A more stable population would require association with regular spring floods of a nearby river or marsh. Commercial removal from the viewpoint of greatest productivity is most economical at the smallest marketable size, as yearly weight gains are probably more than offset by natural mortality.