Oclesnv, R. T. 1977. Relationships offish yield to lake phytoplankton standing crop, production, and morphoedaphic factors. J. Fish. Res. Board Can. 34:2271-22'79.Fish yield is related to annual pfimary production, summer phytoplankton standing crop, and the morphoedaphic index for lakes representing a wide variety oftypologies by a series of models in the form of 1og-log regressions. Tentative boundary conditions are established by which lakes inappropriate to the models can be excluded. Confidence intervals for predicted values about the mean are given for the fish yield-phytoplankton standing crop regression. From this relation, potential yields for the lakes studied are reduced from a range of 10,000 to one of 25-fold. Efficiencies with which carbon is transferred from primary production to fish yield vary by 2Io3 orders of magnitude and are highest for small, intensively managed ponds and lowest for large, deep, cold-water lakes. Models based upon fish yicld as a function of phytoplankton production or standing crop are inherently more accurate and subject to fewer exceptions than are those related to morphoedaphic factors. The former appear to be capable of substantial refinement but even in their present state might be employed to make useful predictions for groups of lakes. A suggested supplement to existing approaches in fishery management involves the following sequence: (1) use ofexpectation-variability diagrams to obtain an overview ofthe problem, (2) selection ofan appropriate model or models to predict yield, (3) prediction ofa range ofyields, and (4) implementation ofregulations proved successful for other lakes in the same yield category.

Gleotrichia echinulata was planktonic in Green Lake (Seattle, Washington) during summer, making its initial appearance between May and early July and disappearing during September. It apparently spent 8 to 10 months of the year on the bottom where colonies developed from spores deposited by the preceding year’s bloom. The depth of spore deposition may be important in determining the success of spore maturation, and solar radiation may be a primary factor in inducing the annual return of this alga to the plankton. The maximum growth rate in 1886 was about 0.124 colony doublings per day. The vertical distribution of the colonies was controlled primarily by wind‐induced currents. The colonies had no measurable effect on light penetration even at a maximum density of over 400 colonies per liter. Laboratory studies indicated that G. echinulata can fix nitrogen. Only one herbivore in Green Lake, Lindia euchromatica, is known to feed on this species.

An interrelated series of regression equations is derived to define the response of lake ecosystems to mixed zone phosphorus loadings in terms of simple and readily determinable parameters. Data used were collected over 14 yr for 16 lakes in central New York State characterized by a wide variety of morphometries, hydrologies, and phosphorus loadings. The regressions describing the dependence of summer phytoplankton standing crop and winter total P concentration on loading and of standing crop on total P were linear. Those characterizing water transparency as a function of standing crop and winter total P were parabolic. All regressions showed high correlation coefficients. The overall model composed of these regressions establishes a quantitative basis for the concept that phosphorus supplied to lakes exerts a uniquely controlling role on phytoplankton standing crop. The regressions may be used for trophic state description and in the development of management strategies for lakes.