Yield Properties and Structure of Boreal Percid Communities in Ontario

Abstract

A synoptic review of yield data for 70 northern Ontario lakes from 1917 to 1973 showed that percids mainly walleye (Stizostedion vitreum vitreum) constituted about one-third, by weight, of the total fish yield. This relationship, which was independent of fishing effort, lake size, and lake productivity, is considered to be an emergent property of this type of fish community and represents a degree of homeostasis within the community under exploitation. The relation of percid yield to theoretical yield (based on the morphoedaphic index — MEI) reflected organizational structure and suggested the existence of a community (percid) component within the MEI, and from this we recommend upper limits of percid harvest for boreal percid lakes.Most (83%) of the 70 lakes had an average total yield of less than 2.5 kg∙ha−1∙yr−1, 53% (37 lakes) yielding less than one-half of the theoretical yield (average 3.4 kg∙ha−1∙yr−1). Long-term average yields exceeded the theoretical maximums in only 11 lakes. Mesotrophic to slightly eutrophic waters appeared as optimum for percid yields.Inferences from the data suggest an unexploited boreal percid community is characterized by high community stability and low net community production with resiliency low because of the low productive capacity of the waters. A yield index (RYI), which was assumed to reflect both effort and vulnerability to exploitation, showed that fishing intensity tended to be higher on the smaller, less productive lakes in this study. Key words: Percidae, Stizostedion, community ecology, yield properties, management implications