Fish Population Dynamic and Stock Assessment (2+1)

Problem

To estimate L$$\infty$$ and Z by Powell and Wetherall method, the length interval L₁-L₂ is the primary data to be taken. The number of specimens caught for each length group interval are to be recorded. Using the following data, estimate K and L$$\infty$$ .

Sl.No.	Length interval	Number caught
1.	3-5	37
2.	5-7	56
3.	7-9	86
4.	9-11	129
5.	11-13	188
6.	13-15	258
7.	15-17	319
8.	17-19	352
9.	19-21	351
10.	21-23	324
11.	23-25	283
12.	25-27	239
13.	27-29	196
14.	29-31	158
15.	31-33	123
16.	33-35	93
17.	35-37	69
18.	38-39	48
19.	39-41	31
20.	41-43	18
21.	43-45	10
22.	45-47	3

1.For Calculation of mean length of fish ($$\overline{L}$$) for different length intervals

1. $$\overline{L}$$45-47 = $${46\times3}\over 3$$ = 46

2. $$\overline{L}$$ 43-45 = $${46\times3\times44\times10}\over {3+10}$$ = 44.462

3. $$\overline{L}$$  41-43 = $${46\times3\times44\times10+42\times18}\over {3+10+18}$$  = 43.032

Calculate ($$\overline{L}$$)for other length intervals

2. Calculation of $$\overline{L}-{L^'}$$

(i) For 39-41 length group 41.516-39 = 2.516

(ii) For 41-43 length group 43.032-41 = 2.832

Similarly calculate $$\overline{L}-{L^'}$$ for other length groups