Sustainable exploitation of Ontario's aquatic resources calls for a new management approach. This vast resource includes more than 250,000 lakes and offers angling opportunities for many popular species (e.g., walleye Sander vitreus (formerly Stizostedion vitreum), lake trout Salvelinus namaycush, brook trout S. fontinalis, northern pike Esox lucius, smallmouth bass Micropterus dolomieu, largemouth bass M. salmoides, and muskellunge E. masquinongy). In pioneer days, the “apparently inexhaustible abundance of resources” fostered an open‐access policy promoting the recreational use of these resources for the benefit of the economy. After World War II, there was a rapid increase in angling effort and by the 1970s many lakes were being overexploited. Clearly, an unrestricted, open‐access policy was no longer appropriate. The result has been a rapid proliferation of fishing regulations as exceptions to divisionwide regulations that were created to protect lakes where problems were detected. The growing complexity of these regulations is the result of a management approach that has focused on individual lakes. This complexity is not popular with the angling public, and evaluation of its benefits has proven difficult because a change in regulations on one lake may affect fishing effort on other lakes. We argue that a larger spatial and temporal scale of management is needed when a resource is widely dispersed across a large population of lakes. This new approach should incorporate (1) consensus on biologically achievable objectives, (2) periodic, unbiased assessment of the state of the resource, (3) periodic evaluation to decide whether current management practices are meeting objectives, and (4) adaptive management in choosing among alternative management actions. Recent progress towards establishing this management approach in Ontario is discussed.

Growing degree-days (GDD, °C·days) are an index of ambient thermal energy that relates directly to an ectotherm’s cumulative metabolism but is rarely used to describe growth and development in fish. We applied GDD to length and maturity data from 416 populations of walleye ( Sander vitreus ) from Ontario and Quebec, Canada (mean annual GDD = 1200 to 2300 °C·days). On average, males matured after they had experienced 6900 °C·days and reached 350 mm total length (L) (n = 77 populations), and females matured after 10 000 °C·days and at 450 mm L (n = 70). Across 143 populations, GDD accounted for up to 96% of the variation in the length of immature walleye but also revealed a twofold difference in growth rate that was indicative of variation in food availability. When applied to data from eight populations in which walleye abundances have changed dramatically over time, GDD revealed a 1.3-fold increase in immature growth rate when abundance was low compared with when it was high. Our results both demonstrate the explanatory power of GDD with respect to fish growth and maturity and inform the development of regional management strategies for walleye.

Marshall, T. E., and P. A. Ryan. 1987. Abundance patterns and community attributes of fishes relative t o environmental gradients. Can. I. Fish. Aquat. Sci. M(Suppl. 2): 198-215.Seventy-five lakes s f the Canadian boreal forest were examined for patterns of fish species abundance and community structure in relation to gradients of four environmental variables: (1) Bake area, (2) mean depth,(3) Secchi disk transparency, and (4) rnorpkoedaphic index (MEI). Mean depth appeared to exert the greatest control o n the relative abundance of the species considered. The remaining variables influenced abundance i n unique ways, although, as witk mean depth, this influence was mainly a consequence of changes in thermal and nutrient regimes. An examination s f lower trophic components indicated that these regimes appear to structure food webs, with distinctly different patterns in food webs occurring in dimictic and polymictic Bakes. Major shifts in aquatic biota occur in the transition region between Bake types. Lakes witk these characteristics are at a Bower successional state due t o environmental unpredictability, as demonstrated by an increasing importance of rover K-strategists.O n a etudie 75 lacs de la for& boreale canadienne pour la recherche de tendances de I'abondance des especes de poisscln et de la structure des comrnunautes par rapport aux gradients de quatre variables envirsnnernentales : 1) superficie d u lac, 2) profondeur msyenne, 3) transparenceau disque de Seccki et4) indice rnorpho6daphique. La prsfondeur moyenne sernble &re le parametre qui exer~ait la plus grande influence sur B'abondance relative des especes etudi6es. Les autresvariables influaient sur I'abondance de faqon particuliere mais, comrme dans le cas de la profondeur moyenne, cette influence resultait surtout de modifications d u regime thermiqkse et de celui des rnatieres nutritives. Un examen des csrnposantes trophiques inferieures a montre queces regimes structuraient Bes reseauxalimentaires qui prgsentaient des allures tres differentes dans les lacs dimictiques et polymictiques. Les princigales modifications du biote aquatique, entre lacs de types differents, etaient notees dans la none de transition. Les lacs presentant ses caracteristiques sont un niveaee evolutif inferieur A cause de facteuas environnementaux imprevisibles, cornme le demontre la predominance de plus en plus importante des strategies r sur les strategies K.