# Weight and length measurements for 37 Mekong River fish species of the ‘Dai’ fishery

## Cite this dataset

Koning, Aaron et al. (2024). Weight and length measurements for 37 Mekong River fish species of the ‘Dai’ fishery [Dataset]. Dryad. https://doi.org/10.5061/dryad.dr7sqvb5h

## Abstract

The Lower Mekong Basin supports some of the world’s largest and most diverse inland fisheries by supplying nutrition to over 60 million people and an estimated 11 billion USD of economic activity each year. Despite the nutritional and economic importance of the fishery, there are limited data available on which fishery officers and managers can build fishery stock management plans. Traditional fishery stock management relies on models of individual and population growth that in turn rely on robust individual-based data sets, preferably collected over long time scales. One such fishery for which there are robust data sets are for the “dai,” or bagnet, fishery located on the Tonle Sap River that connects the Mekong River mainstream with the Tonle Sap Lake. However, datasets from the dai fishery are not publicly available, limiting their utility for understanding how catches in this fishery have changed over time. Several papers have utilized the data from the dai fishery, but none have made the data publicly available. By partnering with commercial fishers who participate in the dai fishery and in partnership with the Cambodian Department of Fisheries and the Inland Fisheries Research and Development Institute we collected weight and length data bi-monthly for fish captured at two dai operations starting in November 2020 and continuing to February 2021, totaling 32,274 measurements of length and weight for 37 species. Here we report weight and length data for individuals captured during this timeframe as well as calculated weight-length relationships for total length and standard length for all 37 species for which there were ³30 measurements. Plots of all weight-length regressions are also included in the data package. Finally, we report equations for converting standard length measurements to total length estimates and vice versa.

## README: Weight and length measurements for 37 Mekong River fish species of the ‘Dai’ fishery

https://doi.org/10.5061/dryad.dr7sqvb5h

### Description of the data and file structure

The data package contains 6 .csv files and 4 folders containing plotted output of regressions.

Dai_2020_2021_TL.csv

This .csv file contains 32,274 observations of total length (tl) and weight measurements collected from November 2020 to March 2021 from two "dai" nets on the Tonle Sap River, Cambodia. Further details can be found in the methods.

The table contains three rows: Column "Genus_species" is the genus species name of each fish identified and measured; Column "tl.cm" is the total length measured to the nearest 0.1 centimeters (cm) and reported in centimeters; Column "W.g" is the weight of each fish measured to the nearest 0.1 grams (g) and reported in grams.

Dai_2020_2021_SL.csv

This .csv file contains 32,205 observations of standard length (sl) and weight measurements collected from November 2020 to March 2021 from two "dai" nets on the Tonle Sap River, Cambodia. Further details can be found in the methods.

The table contains three columns: Column "Genus_species" is the genus species name of each fish identified and measured; Column "sl.cm" is the standard length measured to the nearest 0.1 centimeters (cm) and reported in centimeters; Column "W.g" is the weight of each fish measured to the nearest 0.1 grams (g) and reported in grams.

Dai_2020_2021_TL_reg_results.csv

This .csv file contains the summary information for simple linear regression of log10(total length (cm)) against log10(weight (g)) data for 37 species found in "Dai_2020_2021_TL.csv".

The table contains 7 columns: Column "Genus_species" is the genus species name of each species for which there were 30 measurements of total length and weight; "num_obs" is the total number of observations of total length and weight used in the regression; "A.tl" is the model parameter alpha (α) of the regression and "B.tl" is the model parameter beta (β) in the equation: W_i = αL_i^β*10^(ϵ_i), where W_i is the weight of individual (i), L_i is the total length of the same individual, and ϵ_i is the residual. We fit our data using the linearized form of the equation:log_10(W_i)= log_10(α) + β log_10(L_i) + ϵ_i; Column SE.B.tl is the standard error in the estimate of β from the same equation; p_value is the p-value indicating whether the null hypothesis that the slope of the equation is equal to 0 is rejected at an alpha of 0.05; R2_adj is the adjusted R-squared for the model fit of for each regression by each species.

Dai_2020_2021_SL_reg_results.csv

This .csv file contains the summary information for simple linear regression of log10(standard length (cm)) against log10(weight (g)) data for 37 species found in "Dai_2020_2021_SL.csv".

The table contains 7 columns: Column "Genus_species" is the genus species name of each species for which there were 30 measurements of total length and weight; "num_obs" is the total number of observations of total length and weight used in the regression; "A.sl" is the model parameter alpha (α) of the regression and "B.sl" is the model parameter beta (β) in the equation: W_i = αL_i^β*10^(ϵ_i), where W_i is the weight of individual (i), L_i is the standard length of the same individual, and ϵ_i is the residual. We fit our data using the linearized form of the equation:log_10(W_i)= log_10(α) + β log_10(L_i) + ϵ_i; Column SE.B.tl is the standard error in the estimate of β from the same equation; "p_value" is the p-value indicating whether the null hypothesis that the slope of the equation is equal to 0 is rejected at an alpha of 0.05; "R2_adj" is the adjusted R-squared for the model fit for each regression by each species.

Dai_2020_2021_TL_SL_Convert.csv

This .csv file contains the summary data for simple linear regression of log10(total length) against log10(standard length) for 37 species for which both total length and standard length were reported from the catch of 2 dai nets between November 2020 and March 2021. These regressions allow for conversion of standard length measurements to total length measurements.

The table contains 7 columns: Column "Genus_species" is the genus species name of each species; "num_obs" is the total number of observation of both total length and standards length used in the regression.; "M" is the slope of the regression line (coefficient on the standard length measurement); "b" is the intercept of the regression line; "p_value" is the p-value indicating whether the null hypothesis that the slope of the equation is equal to 0 is rejected at an alpha of 0.05; "R2_adj" is the adjusted R-squared for the model fit for each regression by each species.

Dai_2020_2021_SL_TL_Convert.csv

This .csv file contains the summary data for simple linear regression of log10(standard length) against log10(total length) for 37 species for which both total length and standard length were reported from the catch of 2 dai nets between November 2020 and March 2021. These regressions allow for conversion of total length measurements to standard length measurements.

The table contains 7 columns: Column "Genus_species" is the genus species name of each species; "num_obs" is the total number of observation of both total length and standards length used in the regression.; "M" is the slope of the regression line (coefficient on the total length measurement); "b" is the intercept of the regression line; "p_value" is the p-value indicating whether the null hypothesis that the slope of the equation is equal to 0 is rejected at an alpha of 0.05; "R2_adj" is the adjusted R-squared for the model fit for each regression by each species.

Dai_2020_2021_TL_plots

This folder contains the plots of log10(total length (cm)) versus log10(weight (g)) regressions for the 64 species found in the data file "Dai_2020_2021_TL.csv" and reported in "Dai_2020_2021_TL_reg_results.csv".

Plots show all observations included in the analysis (grey, filled circles), the regression line (red line), the untransformed model equation with α and β parameter estimates from the regression, the number of observations (n = ), and the R2 adj value indicating model fit.

Dai_2020_2021_SL_plots

This folder contains the plots of log10(standard length (cm)) versus log10(weight (g)) regressions for the 63 species found in the data file "Dai_2020_2021_SL.csv" and reported in "Dai_2020_2021_SL_reg_results.csv".

Plots show all observations included in the analysis (grey, filled circles), the regression line (red line), the untransformed model equation with α and β parameter estimates from the regression, the number of observations (n = ), and the R2 adj value indicating model fit.

Dai_2020_2021_TL_SL_Convert_plots

This folder contains plots for standard length (cm) versus total length (cm) regressions for the 63 species for which there were standard length and total length measurements for > 30 individuals.

Plots show all observations included in the analysis (grey, filled circles), the regression line (red line), the linear model equation with slope (M) and intercept (b) estimates from the regression, the number of observations (n = ), and the R2 adj value indicating model fit. Total length estimates can be calculated from this model by multiplying the standard length measurement in cm by M and adding b.

Dai_2020_2021_SL_TL_Convert_plots

This folder contains plots for total length (cm) versus standard length (cm) regressions for the 63 species for which there were total length and standard length measurements for > 30 individuals.

Plots show all observations included in the analysis (grey, filled circles), the regression line (red line), the linear model equation with slope (M) and intercept (b) estimates from the regression, the number of observations (n = ), and the R2 adj value indicating model fit. Standard length estimates can be calculated from this model by multiplying the total length measurement in cm by M and adding b.

## Methods

Since at least the year 2000 the Cambodian Department of Fisheries has monitored the commercial fisheries catch at the ‘dai’ fishery on the Tonle Sap River. The dai fishery consists of a barrage of fishing extending laterally across the river at 15 locations (dai rows). Dai rows are numbered 2-16 and can include up to seven individual fishing platforms that deploy and raise large fishing nets into the water column. These nets measure approximately 25 meters in width, while the depth of the net is determined by the depth of the water column. At their peak, individual dai nets capture thousands of kilograms of fish per day. Monitoring of fish catch by the Department of Fisheries, now the Fisheries Administration (FiA), is conducted twice per month, corresponding with the high catch period in the seven days preceding the full moon, and the low catch period during the rest of the month during the period of time in which the Tonle Sap River flows from Tonle Sap Lake to the Mekong Mainstream at Phnom Penh. This fishing season (October – March) corresponds with the out-migration of fish from the Tonle Sap Lake, where they travel to feed and reproduce, before returning to the deeper waters of the Mekong River prior to the onset of the prolonged dry season (December – May). The protocol for collecting weight and length data is based on sub-sampling of the large haul from the dai trap net. Individuals of economically and culturally important species is identified to species, weighed, and measured for total length (anterior-most point to distal margin of compressed caudal fin) and standard length (anterior-most point to last vertebra). Fish weights are measured in the field using a digital balance with precision to 0.1 g and all lengths are recorded to the nearest 0.1 cm. Further details on the dai fishery can be found in (Halls et al. 2013, Ngor et al. 2018)

Using these data we established length-weight relationship for all fish species following a two-parameter power function with a multiplicative error term:

*W*_{i }= *αL _{i}^{β}*10

^{∈i}

where and are model parameters, *W _{i}* and

*L*are the weight and length (TL or SL), respectively, of individual

_{i}*i.*For all species for which we collected >30 length measurements, we regressed length-weight relationships using the linearized form of the equation:

log_{10}*W _{i}* = log

_{10}(

*α)*+

*β*log

_{10}

*L*+ ∈

_{i}_{i}

For total length-weight relationships, 32,274 individual fish were measured belonging to 37 different species. All relationships were statistically significant (p < 0.001), and adjusted R^{2} values were generally high (> 0.9), indicating good model fits. Likewise, standard length-weight relationships for 32,205 individuals belonging to 37 species were all strongly significant (p <0.001) and generally showed good model fits. Model fits for particularly small species (< 5cm) are not as strong due to a lack of scale precision at low values.

**Acknowledgments**

The authors would like to acknowledge Chin Channa who collected the field data, Srey Keo Sopheak, the deputy head of Siem Reap Fisheries Administration Cantonment for help in coordinating field sampling in Chong Kneas, Siem Reap, Cambodia, the fishers helping with fish collection, and Chea Seila for coordination and logistics support.

## Funding

United States Agency for International Development, Award: AID-OAA-A-16-00057