There are two online sources of length weight relationships that I am aware of. They have been around a while so some fish may be out of date. Here is one:
https://www.dnr.state.mi.us/publications/pdfs/ifr/manual/smii%20chapter17.pdfHere is another:
http://www.nativefishlab.net/library/textpdf/15123.pdfMore often I will take a current chart and regress the formula underlying the chart. The function in decimal is a power function, but this can be linearized by taking the logarithm of both sides of the power equation. Being now linear, one only need two points to resolve the coefficients. Once you have a spreadsheet, you can regress any chart for any fish. The method goes like this.
You need 4 columns. Length, Weight, Log10(Length), and Log10(Weight). Put the labels for these in the cells A1,B1,C1,D1 respectively.
In column A enter the smallest length in A2 and the longest length in A3. In column B, enter the corresponding weights. In cell C2 enter the formula
=LOG10(A2) and then copy that formula to C3. In cell D2 enter the formula
=LOG10(B2) and then copy the formula to D3.
You are now ready to regress the formula Log10(W) = Log10(a) + b* Log10(Length). Log10(a) is the intercept and (b) is the slope of the linearized function. In cell F1 enter "Intercept" and in cell G1 enter "Slope". In F2 enter the equation
=INTERCEPT(D2:D3,C2:C3). In G2 enter the equation
=SLOPE(D2:D3,C2:C3). And there you have it. The equation that uses these coefficients to compute standard weight is SW= 10^(intercept coefficient + slope * LOG10(length)).
I like to use the power relationship instead. It is in the form:
SW =afactor * Length^Slope where afactor = 10^Intercept.
If you prefer this too, just add the equation into F3
=10^F2. Just substitute the value of F3 for afactor above.
