Estimasi Potensi Produksi Ikan Di Danau Laut Tawar Berdasarkan Morphoedaphic Index

Laut Tawar Lake is located in Aceh Tengah District is the largest lake in Aceh Province. The lake, located at an altitude of 1230 meters above sea level, produces about 13 species of freshwater fish. Fish depik (Rasbora tawarensis), eyas (Rasbora sp.), and relo (Rasbora sp.) are endemic species of Laut Tawar Lake. This study aims to estimate the potential of fish production based on the value of morphoedaphic index. The observation was conducted for one year, from October 2016 until September 2017. The measurement of electric conductivity value of lake waters was conducted on 7 (seven) stations selected purposively in the lake area about 5870 hectares. The results showed that morphoedaphic index value of Laut Tawar Lake ranged from 5.10 to 7.84 with an average of 6.14. Potential of fish production in the lake is 33.47 kg/ha/yr with total potential of fish production of 196.49 ton/yr. The value shows a decrease of 10.93 kg/ha/yr over a period of 22 years. This decrease is caused by changes in morphometry parameters and water quality of Laut Tawar Lake.

Can growth be used as a surrogate measure of walleye (Sander vitreus) abundance change?

We examined several models to determine the relative contributions of density-dependent and density-independent factors on walleye (Sander vitreus) growth in the ceded territory of Wisconsin from 1990 to 1999. We then used independent data from 2000 to determine how well each model predicted walleye growth and examined several models to determine if growth could be used to predict density. Adult density best predicted the mean size of age-3 males ( [Formula: see text]3m) and age-5 females ( [Formula: see text]5f). Density-independent measures of pH, the morphoedaphic index, maximum depth, and conductance had a positive influence on growth, while adult density negatively affected growth. The solely density-dependent models predicted [Formula: see text]3m and [Formula: see text]5f poorly in 2000. The addition of density-independent factors improved model predictions of [Formula: see text]3m and [Formula: see text]5f. Walleye growth did not predict adult walleye densities. Regional patterns in walleye growth were correlated with surrogate measures of lake productivity and to a lesser extent adult density. Density dependence had a relatively weak affect on growth patterns, suggesting that growth cannot be used as a surrogate method for monitoring abundance change.

Production of Fish Populations in Lakes

Biological production estimates of 100 fish populations from 38 lakes worldwide were gathered from the literature. The relationship between the annual production of fish populations (P, kilograms per hectare per year), annual mean standing biomass (B, kilograms per hectare), and maximum individual body mass (W, grams) was approximately log10P = 0.32 + 0.94 log10B − 0.17 log10W (R2 = 0.84). This relationship is similar to one observed for lotic invertebrate populations and shows that P declines with W. Major axis regression indicated that the P/B:W relationship had an exponent similar to that predicted by allometric theory. The residuals from this multivariate equation suggest that fish production is positively correlated with temperature, lake phosphorus concentration, chlorophyll a concentration, primary production, and with pH. The results suggest a general bottom-up control of lake ecosystem components. The morphoedaphic index is not a good predictor of the production of fish populations. Assuming that sustainable yield is about 10% of production, sustainable yield would be less than 15% of the standing biomass for the majority of fish populations analyzed. Exploited populations were found to be about 70% more productive, on average, than unexploited populations of the same standing biomass and body-mass.

Biotic and Abiotic Determinants of the Diet of Brook Trout, Salvelinus fontinalis, in Lakes of the Laurentian Shield

From a survey of 12 lakes containing brook trout, Salvelinus fontinalis, 12 lakes containing brook trout and creek chub, Semotilus atromaculatus, and 13 lakes containing brook trout and white sucker, Catostomus commersoni, we built seven multiple linear regression models to account for the mean percent weight of different prey categories in the diet of brook trout. Presence of chub and sucker, zooplankton community structure, sampling date, morphoedaphic index, and the importance of rock outcrops accounted for 88% of the variation in weight of zoobenthos eaten by trout, which was the preferred prey in allopatry. Thirty percent of the variation in weight of zooplankton eaten by trout was explained by the importance of macrophytes and other refuges for fish. Models for amphipods, dipteran pupae, swimming insects, terrestrial insects, and prey-fish explained between 36 and 63% of the variation. The presence of white sucker or an index of their impact (mean length or density of Cladocera) and the characteristics of littoral habitats appeared in six of seven models. Littorasl habitats seemed particularly determinant for the inclusion of prey-fish in the diet, more prey-fish being eaten when regufes were abundant. Variables related to lake morphometry and physicochemistry appeared less regularly in the models.

Use of the Morphoedaphic Index to Predict Nutrient Status and Algal Biomass in Some Canadian Lakes

The underlying assumptions of the morphoedaphic index (MEI; total dissolved solids (TDS)/mean depth), which has been used to predict fish yields in lakes, and its power for predicting biomass at lower trophic levels were examined using published data. The assumptions included the relationship between mean depth of lakes and various hydrologic characteristics (flushing rate and stratification regime), water transparency characteristics (water color and turbidity), and the stoichiometric relationship among ions (expressed as a proportion between TDS and the concentration of primary nutrients, total phosphorus (TP) and total nitrogen (TN)). Although these basic assumptions could be supported empirically, the predictive power of the MEI became progressively weakened with increasing trophic level. MEI accounted for up to 85% of the variation in TP and TN, less than 50% of the variation in [Chl a], and none of the variation in the biomass of herbivorous zooplankton. The functions relating TDS to both TP and TN were fundamentally different: as lakes increased in salinity, the TN:TP ratio decreased dramatically so that TP almost exceeded TN concentrations in extremely saline lakes. This necessitated the development of separate MEI–nutrient relationships for saline (TDS > 1000 mg/L) and nonsaline lakes.

A Statistically Valid Model of the Morphoedaphic Index

The morphoedaphic index (MEI) has been criticized because of the use of ratio variables in linear regression. Computationally simple, the continued use of the index is questionable given the widespread access fisheries biologists now have to computerized statistical packages. We present a statistically valid analogue to the MEI, the morphoedaphic model (MEM), that utilizes multiple regression to characterize the morphometric and fertility properties of lakes to predict annual fish yield. Surface area, lake volume, and total dissolved solids (TDS) are used to predict annual fish yield for the lake and to derive associated confidence limits. Predicted yield of the newly derived model was compared with predictions from the original MEI Comparisons were also made based on models derived from Ontario sport and commercial fisheries data sets. The MEM derived from these partitioned data sets more accurately modelled the observed long-term yields for these lakes. Analysis of the remaining outliers suggests that several additional variables and stratification may be required to further develop the precision of the statistical model.

Fish Production Correlated with Primary Productivity, not the Morphoedaphic Index

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 uncorrected with the morphoedaphic index (p > 0.05) but closely correlated with annual phytoplankton production (r2 = 0.79), mean total phosphorus concentration (r2 = 0.67), and annual average fish standing 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.

Ratios in Aquatic Sciences: Statistical Shortcomings with Mean Depth and the Morphoedaphic Index

Researchers in aquatic sciences frequently employ empirically derived models to predict productivity, yield, and abundance of fish. We demonstrate that predictive models employing ratios of standardized biomass and lake morphometric variables are biased by spurious correlations due to mathematical transformations and the use of inappropriate null models. Our findings emphasise that studies incorporating ratios like mean depth or the morphoedaphic index require cautious interpretation. Future research should focus on more appropriate analytical approaches such as regression-based models like the analysis of covariance. Alternatively, where ratios are employed and spurious correlations are likely, statistical evaluations must incorporate randomization tests to assess the significance of such results.