Fish Production Correlated with Primary Productivity, not the Morphoedaphic Index1 John A. Downing, Celine Plante, and Sophie Lalonde DGpartement de Sciences Biologiques, University de Montreal, C.P. 6128, Succursale 'A', Montreal, Qu4. H3C 317 Canada Downing, J.A., C. Plante, and S. Lalonde. 1990. Fish production correlated with primary productivity, not the morphoedaphic index. Can. J. Fish. Aquat. Sci. 47: 1929-1936. Estimates of the biological production of entire lake fish communities were collected from the published literature on lakes covering a wide range of geographic areas and trophic status. Correlation analysis shows that fish production is uncorrelated with the morphoedaphic index (p>0.05) but closely correlated with annual phytoplankton production (^ = 0.79), mean total phosphorus concentration (^ = 0.67), and annual average fish stand ing stock (r2 = 0.67). Empirically derived regression equations are presented and compared with previous models based on catch and yield data. Analysis of these equations suggests that conversion of phytoplankton into fish production is 100 times more efficient in oligotrophic lakes than hyper-eutrophic ones, but that a much lower fraction of fish production can be channeled to sustainable yield in oligotrophic lakes. Sustained yields were frequently as little as 10% of the annual community fish production. On a releve", dans les ouvrages publics, des estimations de la production biologique de communaute's entieres de poissons provenant de lacs couvrant une grande e"tendue ge"ographique et une vaste gamme d'e*tats trophiques. L'analyse de correlation de"montre que la production de poissons n'est pas correMee avec I'incide morphoe"daphique (p>0,05), mais qu'elle est etroitement corre'le'e avec la production annuelle de phytoplancton (r2 = 0,79), la concentration moyenne de phosphore total (r2 = 0,67) et la biomasse annuelle moyenne de poissons (r2 = 0,67). On pre"sente des Equations de regression obtenues empiriquement et on les compare avec des modeles ante"rieurs reposant sur des donne"es relatives aux captures et aux rendements. L'analyse de ces Equations revele que la conversion de phytoplancton en production de poissons est centfois plus efficace dans les lacs oligotrophes que dans les lacs hypereutrophes, mais qu'une fraction beaucoup plus faible de la production de poissons contribue a un rendement gquilibre" dans les lacs oligotrophes. Dans de nombreux cas, les rendements equilibre's repre"sentaient aussi peu que 10% de la production annuelle des communaute's de poissons. Received October 11, 1989 Accepted April 19,1990 Recu le 11 octobre 1989 Accepte" le 19 avril 1990 (JA337) At equilibrium, unexploited fish stocks produce exactly enough biomass to balance natural mortality. The aim of fisheries management is to replace the greatest pos sible fraction of natural mortality with fishing mortality without exceeding the rate of renewal of the stock (e.g. Schaefer 1968). The renewal of fish stocks is provided by production, which is the "amount of tissue elaborated per unit time per unit area, regardless of its fate'1 (Clarke 1946). Models for the prediction of freshwater fish productivity abound (review by Leach et al. 1987). These models disagree about the characteristics of lakes that have the greatest influence on fish production (Table 1). Early models were based on sim ple morphometric measures like mean depth (Z) or lake area (Rounsefell 1946; Rawson 1952, 1955). Later ones, like the famous "morphoedaphic" model, augmented morphometric data with indicators of lake fertility like alkalinity (Hayes and Anthony 1964) and total dissolved solids (Ryder 1965). The simplicity of the morphoedaphic index (MEI) model has made it a staple of lake fisheries management (Ryder 1982; Leach et al. 1987). In the 1970's, models frequently linked fish pro duction to phytoplankton (Hrbacek 1969; Melack 1976; McConnell et al. 1977; Oglesby 1977) and benthos (Matuszek 'Publication No. 370 of the Groupe d'Ecologie des Eaux douces, University de Montreal. Can. J. Fish. Aquat. Sci., Vol. 47, 1990 1978) productivity. Most recent studies have used the old approaches on new fish production data bases (Liang et al. 1981; Jenkins 1982; Jones and Hoyer 1982; Oglesby etal. 1987) or have reanalyzed the old data (i.e. Ryder 1965) using new combinations of variables (e.g. Hanson and Leggett 1982; Youngs and Heimbuch 1982) or methods (Prepas 1983; Schnei der and Haedrich 1989). Some recent multivariate models pre dict yields of single species fisheries (e.g. Godbout and Peters 1988). Individual models have advanced alkalinity, algal bio mass (chlorophyll a), air temperature, area, benthos standing crop, body size, fishing effort, mean depth, phytoplankton pro ductivity, total dissolved solids, total nitrogen concentration, and total phosphorus concentration as the most important pre dictors of lake fisheries production. Probably the most important deficiency of current lake fish ery production models is that few actually predict rates of bio logical production; instead, many predict variables like "catch" or "yield" (Table 1). The many different "fish production" models yield predictions of quite different dependent variables and thus are difficult to compare and interpret. Short-term sport or commercial fishing yields probably do not bear a constant relationship to long-term or sustainable yields. Further, the relationship between catch and actual fish production is unknown because both the amount of fishing effort expended 1929 Table 1. Number of lakes examined, coefficients of determination (r2), and variables employed in various models for the prediction of fish production in lakes. Year is the year of publication, Area indicates lake area, Z is the lake mean depth, Alk. is the alkalinity, TDS is total dissolved solids, PP is the water column primary production, Chi a is the chlorophyll a concentration in the water column, Benthos indicates the standing biomass of benthic invertebrates, TP is the water column total phosphorus concentration, TN is total nitrogen concentration, Air T is the mean annual air temperature, and Effort is the annual fishing effort. 12 39 13 138 0.73 Area 0.40 0.80" Area 0.67b Area,Z,Alk Ryder 23 0.73 TDS/Z 1969 Hrb&ek 13 0.72 TN 1969 1976 Hrb&ek Melack 11 24 0.72c 0.56 PP PP 1977 McConnell et al. 6 0.93 PP 1977 Oglesby 19 0.74 PP 1977 Oglesby 19 0.84 Chi a 1978 Matuszek 11 0.80 Benthos 1981 Liang et al. 18 0.76 PP 1982 Hanson and Leggett 20 0.58 Benthos/Z 1982 Hanson and Leggett 21 0.87 TP 1982 Jenkins 290 0.08 TDS/Z 1982 1982 Jones and Hoyer Schlesinger and Regier 25 43 0.83c 0.74 Chlo Air T 1982 Youngs and Heimbuch 27 0.72 Area 1983 1983 Prepas Schlesinger and McCombie 23 92 0.70 0.61 Z Effort 1946 Rounsefell Rounsefell 1952 Rawson 1964 Hayes and Anthony 1965 1946 Production estimate Predictor Author Year Z Commercial fishing yields Sport fishing yields 25 yr average commercial catch Long or short term sport or commercial catches weighted by trophic chain length "Catch records for several years, or from published estimates based on intensive fishery surveys1' Net growth increment in stocked carp ponds Net growth increment in carp ponds Three consecutive years average commercial yield Net growth increment in experimental swimming pools Fish catch "...in lakes with moderate to intensive fishing pressure" Fish catch "...in lakes with moderate to intensive fishing pressure" Average annual catch over the 15 yr period of maximum commercial yield Net (1-yr) growth increment in stocked ponds and lakes "Long term commercial and sport harvest" (Oglesby and Ryder) "Long term commercial and sport harvest" (Oglesby and Ryder) "Mean of all available annual (catch) estimates" Sport fish harvest from creel census Commercial and sport yields "...assumed to be a close approximation of the lake's MSY." Yield data from Ryder, Oglesby and Matuszek "Catch records" of Ryder Sport fish yields from creel census. •Computed from Rawson's (1955) table 3. bLog of yields weighted by trophic chain length. CFY not as logarithms. and the capture efficiency have a large influence on the amount offish actually landed (Schlesinger and McCombie 1983; Godbout and Peters 1988). The meaning of the variables predicted by many of these models to either the practical management of lake fisheries, or the theoretical study of ecology is difficult to discern. Oglesby (1977) has stated that it would be preferable to establish fish production models from rigorously defined and repeatable measurements like fish production rather than rough indices of average catch, but suggested that reliable, whole community production data were too rare, during the mid 1970's, to permit this. All fisheries management models assume that sustainable fish yield is correlated with fish production. If this correlation exists, then we would expect fish production to be correlated with the same lake characteristics as long-term fish yield measures. This research draws together existing measurements of production of whole fish communities to find which of the proposed lake characteristics is most closely correlated with fish productivity. 1930 Methods Data on the production of entire fish communities were gleaned from an exhaustive survey of the primary ecological literature published since 1969. We only retained data where the production of all significant fish species in each lake had been measured. Fish communities that had been subject to recent stocking were not included in the data set because pro duction by recently stocked fish might not reflect the natural ecosystem productivity. Data on biotic and abiotic characteristics of lakes were derived from published works or in some cases were completed through direct communication with the authors of the produc tion studies. Morphometric characteristics collected were lake area, volume, mean and maximum depth, and area of watershed. Lake productivity indicators were phytoplankton productivity, total phosphorus, nitrogen and chlorophyll a con centrations in the water column, and conductivity (as a measure Can. J. Fish. Aquat. 5c/., Vol. 47, 1990 Table 2. Whole fish community production data and lake characteristics drawn from the published literature. Abbreviations indicate, FP: fish production (kg-na^yr"1), FB\ fish biomass (kg-ha"1), PP: primary production (g C-m~2-yr"1), TP: total phosphorus (jxg-L"1), Cond.: conductivity (jiS-cm"1, 20°C), Z: mean depth (m). na indicates that the datum was not available. Lakes Alinen Mustajarvi Batorin Big Turkey (1985) Big Turkey (1988) Botjam Char Dalnee FP FB 30.3 73.0 83.0 1.2" 3.8 17.3 2.0 Horkkajarvi La Luisa 276.9 Little Turkey (1985) Little Turkey (1988) Marion Myastro Nakuru Naroch 0vre Heimdalsvatn Red deer Sabanilla Vitalampa Washington Wishart (1985) Wishart (1988) 7.0 TP 39.3 Cond. 24.3 Z 3.0 Data sources Rask and Arvola 1985; Arvola (pers. comm.) 398.0 228.5 15.5 Demenets PP 163.0 5.2" 7.3 30.3 104.0 197.0 372.2 32.2 351.6 na na 0.3 0.3 2.6 4.2 41.1 4.6 13.5 41.1 25.0 4.1 3.8 196.0 10.2 487.0 na na 31.5 na na na 3.3 5.6 114.5 43.3 7.0 1.4 6.0 3.0 12.2 12.2 3.3 145.8 325.7 10.9a 11.2 28.9 125.0 59.4 44.0 14.7 81.0 19.8 97.3 na na 9.0 11.5 14.7 15.3 4.7 28.9 11.6 311.7 na na 35.1 220.5 na na na 3.7 0.6 9.8 89.4 20.2 93.4 4.5 157.0 16.5 34.8 18.0 2.8 81.1 33.0 2.8 2.8 5.1 33.3 33.3 2.2 3.9a 4.7 21.5 64.0 5.6a 24.4a 5.7 24.4 na na na 0.7 0.7 8.0 314.8 881.0 6.2 5.0 38.8 na 38.8 18.2 na na 9850.0 18166.7 5.0 6.0 2.4 5.4 2.3 2.2 Winbergetal. 1972 Kelso 1985; Lam et al. 1986 Kelso 1985, 1988; Lam et al. 1986 Nyberg 1979; Ramberg 1976 Rigler 1972, 1975 Krogius et al. 1972 Gulin and Rudenko 1973 Rask and Arvola 1985; Arvola 1983; (pers. comm.) Hoiafk 1970 Kelso 1985; Lam et al. 1986 Kelso 1985, 1988; Lam et al. 1986 Efford 1972 Winberg et al. 1972 Vareschi and Jacobs 1984, 1985; Plante 1987; Vareschi (pers. comm.) Winberg et al. 1972 Kloster 1987; Lien 1978, 1981; Tangen and Bretum 1978 Chadwick 1976 Hoieik 1970 Nyberg 1979; Ramberg 1976 Edmondson 1977, (pers. comm.); Eggers et al. 1978 Kelso 1985; Lam et al. 1986 Kelso 1985, 1988; Lam et al. 1986 "Production and biomass of 1+ fish and older. of total ion concentration). Phytoplankton production data were converted to total net annual production per unit lake area. Results and Discussion Chlorophyll, nitrogen, and phosphorus concentrations were Fish community production data were obtained for 20 lakes (Table 2) in a wide range of geographic locations (Fig. 1). All estimates were actual measures of biological production (as opposed to catch or yield), and were mostly estimated using cohort, Allen curve, or instantaneous growth methods (Chap man 1971; Rigler and Downing 1984). Two independent pro duction estimates were obtained for Turkey, Little Turkey, and Wishart Lakes (Kelso 1985, 1988) yielding 23 whole com munity fish production estimates in all. This is a number of estimates similar to that used in the majority of previous studies examining average catch data (Table 1). The fish communities consisted of between one and 22 species of fish, but there was no correlation between species richness and lake trophic status (e.g. both the unproductive Char Lake and the tropical Lake Nakuru had only one important fish species). Lakes varied in mean annual fish standing stock from 5.2 kg-ha"1 in the oligotrophic Turkey Lake on the Canadian Shield (Kelso 1985) to collected as annual averages. The chlorophyll concentrations of lakes Alinen-Mustajarvi, Botjarn, Vitalampa and 0vre Heimdalsvatn were estimated using the least-squares regres sion relationship between log,o chlorophyll and log,0 total phosphorus found in the data set (r2 = 0.82; n= 10). Total dis solved solids (TDS) was inferred from conductivity measure ments using Rodhe's (1949) table 2. This procedure yielded predicted TDS values that were closely correlated (^ = 0.95; n = 6) with TDS measurements in an independent set of data (Oglesby 1977). Annual mean air temperature, which is closely correlated with surface water temperature (StraSkraba 1980), was used instead of water temperature (see also Schlesinger and Regier 1982) because of its greater availability in climatic reports (Wernstedt 1972). Annual average pH data were also collected because of the possible influence of pH on the pro duction of invertebrates (Plante and Downing 1989). Geo graphic variables, latitude and altitude, were also noted where possible. Analysis of relationships between fish community produc tion and lake characteristics were performed using simple and multiple regression (Draper and Smith 1981; Gujarati 1978) after logarithmic transformation, where necessary, which sta bilized the variance, linearized the responses, and normalized the residuals. Residuals were examined following the protocol of Draper and Smith (1981). Can. J. Fish. Aquat. ScL, Vol. 47, 1990 372 kg-ha"1 in the small, eutrophic Lake Demenets in the Pskov province of the eastern USSR. Primary Production Only three of the 16 lake characteristics were significantly (p<0.05) correlated with fish community production (Table 3), thus many of the published correlations between fish yield and various lake characteristics do not hold for fish community pro duction. Although the top three variables in Table 3 yielded 1931 -60 -180-150-120 -90 -60 -30 DEGREES 6 30 OF 60 90 120 150 180 LONGITUDE Fig. 1. Location of 20 lakes for which fish community production data were obtained from the published literature. Table 3. Coefficients of determination (r2) for the relationship: \og,oFP = a + b logloX, for the fish production data in Table 2. n is the number of observations included in the regression, and p is the 3- probability that an equal or greater r2 value would be obtained by chance alone. Values of p are corrected for the number of tests performed (Kirk 1982). Variable n r2 o Primary production Fish biomass Total phosphorus Latitude" TDS/Z(MEI) 19 23 14 18 9 23 16 pHa Air temperature Conductivity Zmax 16 22 16 23 <0.001 <0.001 0.002 0.058 0.149 0.519 0.593 Z Lake area Total nitrogen Lake volume Altitude 23 23 16 23 14 0.79 0.67 0.67 0.34 0.57 0.15 0.20 0.18 0.13 0.16 0.10 0.04 0.02 0.01 0.01 0.00 Watershed area Chlorophyll a 0.727 0.741 0.812 0.871 1.000 1.000 1.000 1.000 1.000 "Independent variable not log,0 transformed. r2 values that were not significantly different from each other (r-test; Sokal and Rohlf 1981; p<0.05), the correlation coef ficient for the relationship between annual phytoplankton pro duction (PP; g C-m^-yr"1) and fish production (FP; kg-ha~l-yr~1) was the highest. The coefficient of determina tion for the relationship: (1) log]OFP = 0.600 + 0.575 logloPP (Fig. 2) was 0.79 (n= 19;/?<0.001). This coefficient of deter mination is greater than all but six of those found in studies of correlations between lake characteristics and fish catch or yield in the published literature (Table 1). The correlation is even better than the relationship seen between fish yield and primary production in stocked ponds (Hrbacek 1969; Liang et al. 1981). The lower residual variation around Eq. (1) is probably because 1932 PRODUCTION DATA (THIS PAPER) ooooe CATCH DATA (OGLESBY 1977) O O -1 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 LOG PRIMARY PRODUCTION (g C-m-yr ) Fig. 2. Relationship between fish and phytoplankton production for literature data on whole fish community production (closed squares) and Oglesby's (1977) fish catch data (open circles). Dashed lines indi cate approximate 95% confidence bands for predicted values of the mean logloF/> (Prepas 1984). Oglesby's fish yield values were con verted to wet mass by multiplying by four (Oglesby 1977) and the Asian data where gross production of phytoplankton was measured or where a range of fish catch values was given are not plotted. The solid line is predicted from Eq. (1). The four lowest points are fisheries yield data from Lakes Superior, Huron, Michigan and Ontario. The four highest points are the average of three consecutive years of com mercial yield from three Indian ponds and the annual yield from an unnamed carp pond in Israel. our FP data are uninfluenced by variations in fishing effort. Confidence intervals for predicted values show that 95% of pre dicted mean fish production rates will be not less than about half and not more than about twice the production indicated by Eq. (1). Can. J. Fish. Aquat. ScL, Vol. 47, 1990 3.0 Equation (1) suggests that the conversion of phytoplankton into fish production (assuming 1 gC = 10g fresh mass; Oglesby 1977) is about 1% efficient in very unproductive, oli gotrophic lakes like Big Turkey Lake, and as little as 0.002% efficient in hyper-eutrophic lakes like Lake Nakuru. Our results oppose those of Oglesby (1977). He found that ratios of fish catch to primary production covered the same range as ours, but the transfer of primary production to fish yield was most efficient in hyper-eutrophic carp ponds. Oglesby stresses, how ever, that his analysis does not necessarily represent true bio logical efficiency because his yield data were subject to several factors like fishery management practices, or incomplete catch records. Our data on biological fish production suggest that the transfer of energy from algae to fish production is several orders of magnitude more efficient in oligotrophic ecosystems than in eutrophic ones. Oglesby's (1977) fish-catch data are nearly always lower than our fish production rates (Fig. 2). This may be because the sport and commercial yields in Oglesby's model do not account for the production of all fish, only those landed by fishermen. Another possibility is that the fishing yields summarized by Oglesby (1977) are sub-maximal, especially considering that the catches that were lowest, compared to measured production values, were found in the Great Lakes (Lakes Superior, Huron, Michigan, and Ontario) where distances are large and effort might be small relative to the productive area. The latter seems improbable, however, because Lawrie and Rahrer (1972) and Wells and McLain (1972) suggest that the Great Lakes were being overfished during the period when these catch data were recorded. It is plausible that Rounsefell (1946) was correct, that extremely large lakes with little perimeter, littoral zone, or allochthonous energy input yield low rates of fish production rel ative to autochthonous primary production. The separation between catch and actual production meas urements seems largest in oligotrophic lakes (Fig. 2). The dif ference between fish production and sustainable yield should reflect either the fraction of fish community production that is unexploited (i.e. rough fish, juveniles) or the amount of fish production that cannot be channeled into fishing mortality. Rough fish are generally more abundant in eutrophic lakes, therefore it is unlikely that the difference between Oglesby's (1977) yield measurements and our production data is only the production of unfished populations. If Oglesby's data are an accurate reflection of real maximum sustainable yields of exploited populations, then it appears that sources offish mor tality are different in oligotrophic and eutrophic lakes. Because nearly all fish production can be harvested on a sustainable basis when primary production is high, it appears that natural mortality can be substantially replaced by fishing mortality through exploitation in eutrophic lakes. This would occur if most mortality of biomass falls upon harvestable adult fish and reduction of adult density assuages natural mortality. In oli gotrophic systems, however, a smaller proportion of the fish production can be harvested on a sustainable basis, and it appears that nearly all fish production is required to balance natural mortality. Natural mortality therefore must fall on a part of the population that is not harvested, and for which decreased adult density provides little increase in growth potential or decreased density-dependent mortality. The data therefore sug gest that fish production in eutrophic lakes is highly dependent on adult density, while in oligotrophic lakes a much greater fraction of the annual community energy budget goes toward reproduction and juvenile mortality. Can. J. Fish. Aquat. Sci., Vol. 47, 1990 v 2.5 D .C (FPrRiIOkDoSUgCNH"o o -J 2.0 - 1.5 - 1.0 - 0.5 - o.o 0.5 1.0 1.5 2.0 2.5 3.0 LOG FISH STANDING BIOMASS (kg-ha"1) Fig. 3. The relationship between mean annual fish standing stock and fish community production in lakes. The solid line represents Eq. (2). Dashed line indicate approximate 95% confidence bands for predicted values of the mean log1oFP (Prepas 1984). This interpretation is speculative, however, because the degree to which Oglesby's catch data reflect actual sustainable yields is unknown. For example, ignoring the four lowest and four highest points in Oglesby's data (Fig. 2), representing the Great Lakes fisheries and Indian and Israeli pisciculture ponds, renders the two data-sets approximately parallel, offset by about one log unit, suggesting that fishing yields are about 10% of net fish community production. Standing Biomass Fish production in lakes was found to covary with fish com munity standing biomass (FB; annual mean kg-ha"1) as: (2) log10F/> = -0.42 + 1.084 logloFB (^ = 0.67; w = 23;/><0.001). These two variables are closely correlated (Fig. 3) because, in general, production is propor tional to the product of growth and standing biomass (Plante and Downing 1989). Fish production in the arctic Char Lake falls far beneath the general trend, probably because the aver age annual air temperature near Char Lake is - 16°C. The slope for log10Ffi close to 1 in Eq. (2) suggests that PIB does not vary significantly with FB. The annual production to biomass ratio {FPIFB) ranged from 0.02 in Char Lake to 2.73 in the equa torial Lake Nakuru (average FPIFB = 0.76; n = 23; 5£=0.15; median = 0.52). Total Phosphorus Fish community production was also correlated with the total phosphorus concentration (TP\ jxg-L~l) of the water column: (3) log,0F/> = 0.332 + 0.531 \o%iQTP (t2 = 0.67;n= 14;^ = 0.002). The relationship between log, q and \ogl0TP appears to be non-linear when the very rich Lake Nakuru is included in the data (Fig. 4). The non-linear relation is approximated by: 1933 ,*-N O.U _' 2.5 - i -1 (4) (^ = 0.79; n=14; ;?<0.001), but this relationship is greatly influenced by the extreme TP concentration in Lake Nakuru. The close correlation between TP and fish production probably results from the close correlation of TP with most other com ponents of lake productivity (Peters 1986) and echos the close correlation found between long-term fish catch and TP (Hanson and Leggett 1982). Hanson and Leggett's (1982) model severely underestimates fish production (Fig. 4), however, but again it is not known whether this is because these catch data do not accurately represent sustainable yields or whether sus tainable yields actually fall an order of magnitude beneath bio logical fish production (Fig. 4). Equations (3) and (4) may be of greater practical use in predicting fish production in lakes D f CT 2.0 - / / i— o gi.oo a: °" 0.5- than Eq. (1) or (2) because TP is much less expensive to mea sure than either PP or FB. ^ 0.0- ■■■■■PRODUCTION DATA PREDICTED FISH PRODUCTION o HANSON AND LEGGETT (1982) o 1 log]0FP = -0.319 + 1.441 logI077> - 0.209 (logWTP)2 -0.50 , . , 12 ill 3 LOG ANNUAL MEAN TOTAL P Fig. 4. The relationship between seasonal average total phosphorus concentration of the water column and the fish community production in lakes. The solid curve is predicted from Eq. (4) while the dotted curve represents predicted yields from Hanson and Leggett's (1982) Fig. 2. Dashed lines indicate approximate 95% confidence bands for predicted values of the mean loglo FP (Prepas 1984). ■■■■■ PRODUCTION DATA (THIS PAPER) PREDICTED FROM RYDER (1965) O si Morphoedaphic Index We found weak correlations between FP and chlorophyll a concentrations and watershed area, but no other variables or combinations of variables that we tried yielded significant cor relations (Table 3). This was especially surprising for the mor phoedaphic index, which is reputed to be the best predictor of fish production in lakes. There was no significant (p>0.05) correlation between morphoedaphic index and FP (Fig. 5). This was even true when TDS and 2 were entered separately into a multiple regression (see Schneider and Haedrich 1989), either alone or in combination with other likely variables. Predictions from Ryder's morphoedaphic equation (Ryder 1965; Schneider and Haedrich 1989) were significantly (p<0.01) beneath, and uncorrelated (p>0.05) with actual fish production measure ments (Fig. 5). Ryder's (1965) analysis was based on a more geographically restricted range of lakes than ours. Ryder (1965) has suggested that MEI might not be correlated with fish pro duction if lakes are not all in the north temperate zone, if lakes at high altitude (>600 m) are considered, or if lakes are not all large (>260 ha). Excluding all tropical and high altitude lakes from our data yields an even lower correlation between log,0MEI and log]0F? (^ = 0.05; n= 14; p = 0.53). Our data do not, however, cover as large a range of MEI as did Ryder's, because we lack data on full community fish production in very deep lakes. All of our MEI values are >1. When Ryder's data on "moderately to intensively fished" lakes with MEI >1 (all but very deep or very dilute lakes) are analyzed, no significant relationship between fish yield and MEI remains (n=13; o Q O ^ = 0.02; /? = 0.82). Although Ryder's (1965) equation pro or voked a highly influential sequence of research (e.g. Oglesby 1982), it does not make valid predictions of fish community production within this range of basin morphometry. The anal ysis presented here shows that fish production is more closely correlated with primary production, phosphorus concentration, and fish standing stock in oligotrophic to hyper-eutrophic lakes Q_ o o 0.2 0.4 LOG 0.6 0.8 MORPHOEDAPHIC 1.0 1.2 INDEX Fig. 5. Relationship between fish community production and the morphoedaphic index of Ryder (1965). Not shown are data for Lake Nakuru. Where measurements of TDS were not available, they were inferred from conductivity using Rodhe's (1949) table 2. TDS = - 1.85 + 0.81 C + 0.0002 C2 (R2 = 1.00) where C is the conductivity in (iS-cm"1 and TDS is the summed concentration (mg-L~') of all major ions. The broken line is Ryder's (1965; Schneider and Haedrich 1989) equation. 1934 of moderate depth. Acknowledgments This research was supported by an operating grant to J.A. Downing from the Natural Science and Engineering Research Council of Canada (NSERC), a team grant from the Ministry of Education of the Province of Quebec, a NSERC fellowship to Mario Henri who performed some of the initial search for data, and a CAFIR grant from the University de Montr6al. We are grateful to R. T. Oglesby and two anonymous referees for suggestions on the manuscript. Can. J. Fish. Aquat. Sci., Vol. 47, 1990 References Arvola, L. 1983. Primary production and phytoplankton in two small, polyhumic forest lakes in southern Finland. Hydrobiologia 101: 105-110. Chadwick, E. M. P. 1976. Ecological fish production in a small Precambrian shield lake. Env. Biol. Fish. I: 13-60. Chapman, D. W. 1971. Production, p. 199-214. In W. E. Ricker [ed.] Meth ods for assessment of fish production in fresh waters. IBP Handbook 3, Blackwell Scientific Publications, Oxford, UK. Clarke, G. L. 1946. Dynamics of production in a marine area. Ecol. Monogr. 16: 321-335. Draper, N. R., and H. Smith. 1981. Applied regression analysis. 2nd ed. John Wiley and Sons, New York, NY. 709 p. Edmondson, W. T. 1977. Recovery of Lake Washington from eutrophication, p. 102-109. In J. Cairns Jr., K. L. Dickson, and E. E. Herricks [ed.] Recovery and restoration of damaged ecosystems. University Press Vir ginia, VA. Efford, 1. E. 1972. An interim review of the Marion Lake project, p. 89-109. In Z. Kajak and A. Hillbricht-Ilkowska [ed.] Productivity problems of freshwaters. IBP-UNESCO Symposium on productivity problems of freshwaters. Warszawa. Eggers, D. F., N. W. Bartoo, N. A. Rickard, R. E. Nelson, R. C. Wissmar, R. L. Burgner, and A. H. Devol. 1978. The Lake Washington ecosys tem: the perspective from the fish community production and forage base. J. Fish. Res. Board Can. 35: 1553-1571. Liang, Y., J. M. Melack, and J. Wang. 1981. Primary production and fish yields in Chinese ponds and lakes. Trans. Am. Fish. Soc. 110: 346-350. Lien , L. 1978. The energy budget of the brown trout population of 0vre Heim dalsvatn. Holarct. Ecol. 1: 279-300. 1981. Biology of the minnow Phoxinusphoxinus and its interactions with brown trout Salmo trutia in 0vre Heimdalsvatn, Norway. Holarct. Ecol. 4: 191-200. Matuszek, J. E. 1978. Empirical predictions of fish yields of large North American lakes. Trans. Am. Fish. Soc. 107: 385-394. McConnell, W. J., S. Lewis, and J. E. Olson. 1977. Gross photosynthesis as an estimator of potential fish production. Trans. Am. Fish. Soc. 106: 417-423. Melack, J. M. 1976. Primary productivity and fish yields in tropical lakes. Trans. Am. Fish. Soc. 105: 575-580. Nyberg, P. 1979. Production and food consumption of perch, Percafluviatilis L., in two Swedish forest lakes. Inst. Freshwater Res. Drottningholm. 58: 140-157. Oglesby, R. T. 1977. Relationship offish yield to lake phytoplankton standing crop, production and morphoedaphic factors. J. Fish. Res. Board Can. 34: 2271-2279. 1982. The MEI symposium — overview and observations. Trans. Am. Fish. Soc. Ill: 171-175. Oglesby. R. T., J. H. Leach, and J. Forney. 1987. Potential Stizostedion yield as a function of chlorophyll concentration with special reference to Lake Erie. Can. J. Fish. Aquat. Sci. 44 (Suppl. 2): 166-170. Godbout, L., and R. H. Peters. 1988. Potential determinants of stable catch Peters, R. H. 1986. The role of prediction in limnology. Limnol. Oceanogr. in brook trout (Salvelinusfontinalis) sport fishery in Quebec. Can. J. Fish. Aquat. Sci. 45: 1771-1778. Plante, C. 1987. Prediction de la production secondaire en milieu aquatique. Gujarati, D. 1978. Basic econometrics. McGraw-Hill Book Co., New York, NY. 462 p. Gulin, V. V., and G. P. Rudenko. 1973. Procedure for assessment of fish production in lakes. J. Ichtyol. 13: 813-823. Hanson, J. M., and W. C. Leggett. 1982. Empirical prediction offish biomass and yield. Can. J. Fish. Aquat. Sci. 39: 257-263. Hayes, F. R., and E. H. Anthony. 1964. Productive capacity of North Amer ican lakes as related to the quantity and the trophic level of fish, the lake dimensions, and the water chemistry. Trans. Am. Fish. Soc. 93: 53-57. HOLCfK, J. 1970. Standing crap, abundance, production and some ecological aspects of fish populations in some inland waters of Cuba. Vestn. Cesk. Spol. Zool. A 33: 184-201. Hrbacek, J. 1969. Relations between some environmental parameters and the fish yield as a basis for a predictive model. Int. Ver. Theor. Angew. Limnol. Verh. 17: 1069-1081. Jenkins, R. M. 1982. The morphoedaphic index and reservoir fish production. Trans. Am. Fish. Soc. Ill: 133-140. Jones, J. R., and M. V. Hoyer. 1982. Sportfish harvest predicted by summer chlorophyll-a concentration in midwestern lakes and reservoirs. Trans. Am. Fish. Soc. Ill: 176-179. Kelso, J. R. M. 1985. Standing stock and production of fish in a cascading lake system on the Canadian Shield. Can. J. Fish. Aquat. Sci. 42: 13151320. 1988. Fish community structure, biomass, and production in the Turkey Lakes Watershed, Ontario. Can. J. Fish. Aquat. Sci. 45 (Suppl. 1): 115-120. Kirk, R. E. 1982. Experimental design: procedures for the behavioral sciences. 2nd ed. Brooks/Cole, Belmont, CA. Kloster, A. E. 1978. Physical and chemical properties of the waters of 0vre Heimdalsvatn. Holarct. Ecol. 1: 117-123. Krogius, F. V., E. M. Krokhin, and V. V. Menshutkin. 1972. The model ling of the ecosystem Lake Dalnee on an electronic computer, p. 149164. In Z. Kajak and A. Hillbricht-Ilkowska [ed.] Productivity problems of freshwaters. IBP-UNESCO Symposium on productivity problems of freshwaters. Warszawa. Lam, D. C. L., A. G. Bobba, D. S. Jeffries, and J. R. M. Kelso. 1986. Relationships of spatial gradients of primary production, buffering capac ity, and hydrology in Turkey Lakes Watershed, p. 42-53. In B. G. Isom, S. D. Dennis and J. M. Bates [ed.] Impact of acid rain and deposition on aquatic biological systems. ASTM STP928, American Society for Testing and Materials, Philadelphia, PA. Lawrie, A. H., and J. F. Rahrer. 1972. Lake Superior: effects of exploitation and introductions on the salmonid community. J. Fish. Res. Board Can. 29: 765-776. Leach, J. H., L. M. Dickie, B. J. Shuter, U. Borgmann, J. Hyman, and W. Lysack. 1987. A review of methods for prediction of potential fish production with application to the Great Lakes and Lake Winnipeg. Can. J. Fish. Aquat. Sci. 44 (Suppl. 2): 471^*85. Can. J. Fish. Aquat. Sci., Vol. 47, 1990 31: 1143-1159. M.Sc. thesis, Universit6 de Montreal. 129 p. Plante, C, and J. A. Downing. 1989. Production of freshwater invertebrate populations in lakes. Can. J. Fish. Aquat. Sci. 46: 1489-1498. Prepas, E. E. 1983. Total dissolved solids as a predictor of lake biomass and productivity. Can. J. Fish. Aquat. Sci. 40: 92-95. 1984. Some statistical methods for the design of experiments and analysis of samples, p. 266-335. In J. A. Downing and F. H. Rigler [ed.] A manual on methods for the assessment of secondary productivity in fresh waters. IBP Handbook 17. Blackwell Scientific Publications, Oxford, UK. Ramberg, L. 1976. Relations between phytoplankton and environment in two Swedish forest lakes. Klotenprojektet Rapp. 7. Scr. Limnol. Upsaliensia 426. 97 p. Rask, M., and L. Arvola. 1985. The biomass and production of pike, perch and whitefish in two small lakes in southern Finland. Ann. Zool. Fenn. 22: 129-136. Rawson, D. S. 1952. Mean depth and the fish production of large lakes. Ecol ogy 33: 513-521. 1955. Morphometry as a dominant factor in the productivity of large lakes. Int. Ver. Theor. Angew. Limnol. Verh. 12: 164-175. Rigler, F. H. 1972. The Char Lake Project. A study of energy in a high arctic lake, p. 287-300. In Z. Kajak and A. Hillbricht-Ilkowska [ed.] Produc tivity problems of freshwaters, Warszawa. 1975. The Char Lake project, p. 171-198. In T. W. M. Cameron and L. W. Billingsley [ed.] Energy flow — its biological dimensions. A summary of the IBP in Canada, 1964-1974. Royal Society of Canada, Ottawa, Ont. Rigler, F. H., and J. A. Downing. 1984. The calculation of secondary pro ductivity, p. 19-58. In J. A. Downing and F. H. Rigler [ed.] A manual on methods for the assessment of secondary productivity in fresh waters. IBP Handbook 17. Blackwell Scientific Publications, Oxford, UK. Rodhe, W. 1949. The ionic composition of lake waters. Int. Ver. Theor. Angew. Limnol. Verh. 10: 377-386. Rounsefell, G. A. 1946. Fish production in lakes as a guide for estimating production in proposed reservoirs. Copeia 1: 29-40. Ryder, R. A. 1965. A method for estimating the potential fish production of north-temperate lakes. Trans. Am. Fish. Soc. 94: 214-218. 1982. The morphoedaphic index — use, abuse, and fundamental concepts. Trans. Am. Fish. Soc. Ill: 154-164. Ryder, R. A., S. R. Kerr, K. H. Loftus, and H. A. Regier. 1974. The morphoedaphic index, a fish yield estimator — review and evaluation. J. Fish. Res. Board Can. 31: 663-688. Schaefer, M. B. 1968. Methods of estimating effects of fishing on fish pop ulations. Trans. Am. Fish. Soc. 97: 231-241. Schlesinger, D. A., and A. M. McCombie. 1983. An evaluation of climatic, morphoedaphic, and effort data as predictors of yields from Ontario sport fisheries. Ontario Fish. Tech. Rep. 10, Ont. Ministry Nat. Res., Toronto, Ont. 14 p. 1935 Schlesvnoer, D. A., and H. A. Regier. 1982. Climatic and morphoedaphic indices offish yields from natural lakes. Trans. Am. Fish. Soc. Ill: 141150. Schneider, D. C, and R. L. Haedrich. 1989. Prediction limits of allometric equations: a reanalysis of Ryder's morphoedaphic index. Can. J. Fish. Aquat. Sci. 46: 503-508. Sokal, R. R., and F. I. Rohlf. 1981. Biometry — the principles and practice of statistics in biological research. 2nd ed. W. H. Freeman and Co., San Francisco, CA. 859 p. StraSkraba, M. 1980. The effects of physical variables on freshwater pro duction: analysts based on models, p. 13-85. In E. D. LeCren and R. H. Lowe-McConnell [ed.] The functioning of freshwater ecosystems. Inter. Biol. Prog. 22, Cambridge University Press, Cambridge, UK. Tangen, K., and P. Brettum. 1978. Phytoplankton and pelagic primary pro ductivity in 0vre Heimdalsvatn. Holarct. Ecol. 1: 128-147. Vareschi, E., and J. Jacobs. 1984. The ecology of Lake Nakuru (Kenya). V. Production and consumption of consumer organisms. Oecologia 1985. The ecology of Lake Nakuru (Kenya). VI. Synopsis of pro duction and energy flow. Oecologia (Berlin) 65: 412-424. Wells, L., and A. L. McLain. 1972. Lake Michigan: effects of exploitation, introductions and eutrophication on the salmonid community. J. Fish. Res. Board Can. 29: 889-898. Wernstedt, F. L. 1972. World climatic data. Climatic Data Press, Lemont, PA. WlNBERG, G. G., V. A. BABITSKY, S. I. GRAVILOV, G. V. GLADKY, I. S. Zakharenkov, R. Z. Zovalevskaya, T. M. Mikheeva, P. S. Nevyadomskaya, A. P. Ostapenya, P. G. Petrovich, J. S. Potaenko, and O. F. Yakushko. 1972. Biological productivity of different types of lakes, p. 383-404. In Z. Kajak and A. Hillbricht-IIkowska [ed.] Produc tivity problems of freshwaters. IBP-UNESCO Symposium on productivity problems of freshwaters. Warszawa. Youngs, W. D., and D. G. Heimbuch. 1982. Another consideration of the morphoedaphic index. Trans. Am. Fish. Soc. Ill: 151-153. (Berlin) 61: 83-98. 1936 Can. J. Fish. Aquat. Sci., Vol. 47, 1990