Note: 



THOUSAND TRAPS 



Two-digit numbers indicate years 



Figure 6. — Relation between catch and fishing effort (traps) for the inshore American 



lobster fishery, 1905-72. 



D. Dynamic Pool Models. 



Thomas (1973) has applied the yield per recruit 

 model to the Maine lobster fishery. Depending on the 

 methodology, the instantaneous total mortality (Z) 

 ranged from 1.1363 to 2.9188 while the instantaneous 

 natural mortality {M) ranged from 0.0202 to 0.3467. 

 Therefore, the estimates of the instantaneous fishing 

 mortality (F) ranged from 0.7896 to 2.8986. According 

 to Thomas, the lower natural mortality and higher fish- 

 ing mortality were more plausible. In order to com- 

 plete the necessary inputs for the dynamic pool model, 



Thomas computed the following equations: 



L, = 266.77 [\-e -'■'''"' " + ''''~'^]; 

 W = 0.001682Z.,-»2826. 



(1) 

 (2) 



Equation (1) relates the length of the lobster fLJ to age 

 or time. This is essentially the growth function for 

 lobsters. Equation (2) relates the lobster weight (ffj to 

 length. Based upon the above equations Thomas' es- 

 timates of M (instantaneous natural mortality); W^ 

 (maximum expected weight); K (constant proportional 

 to catabolic rate); /o (hypothetical age at zero weight); 

 tc (assumed age at first capture); tr (assumed age at 



Table 12. — Estiinated relation between catch, effort, and seawater temperature for the Maine lobster fishery (yield functions).' 



Equation 



Years 



MSY 



(lbs.) 



£max 



(traps) 



D.W. 



(\) Q = -35.6442 -I- 0.0814E -0.(X)0061£-2 + 0.6363r 

 (10.96) (8.16) (3.85) 



(2) Q = -8.4992 -I- 0.0954E -0.000073£^ 

 (12.80) (9.12) 



0.933 



0.909 



667,000 



642,000 



0.97 



1.19 



/-values in parentheses 



'The years 1897-1904 were omitted 

 from the regression since no observations 

 on seawater temperature were available. 



Source: Data from Sea and Shore Fisheries. 

 See Appendix B. 



Q = Catch in million pounds 

 E = Effort in thousand traps 

 T = Annual seawater temperature "F for 

 Boothbay Harbor 



16 



