Gulland (1965) has defined the various yield 

 categories, but it might be beneficial to restate 

 these terms as follows: 



(1) P'/R = exploited population weight in 



grams per recruit; that is, F times 

 the average total weight of lobsters 

 divided by the number of recruits in 

 the exploited phase. 



(2) Y/R = yield in weight per recruit; that 



is, the yield in grams per lobster 

 entering the fishery under a different 

 For t c . 

 (S)N'/R = numbers per recruit in the ex- 

 ploited population; that is, the aver- 

 age number in the exploited phase; 

 so that, if there were one million 

 lobsters caught and N'lR = 0.5 at a 

 specific For t c , then this population 

 size is two million. 



(4) C/R = catch in numbers per recruit; 



that is, the fraction of the stock 

 caught for a specific F or t c ; so that, 

 as F increases so does the fraction 

 of the numbers caught. Conversely, 

 as t c increases, the fraction of the 

 stock caught decreases. 



(5) W = mean weight of individual lob- 



sters; so that, as F increases, the 

 mean weight per lobster decreases. 

 Conversely, as t c increases so does 

 the mean weight. 



With either type of expansion, there usually 

 is agreement at least in the increasing or de- 

 creasing trend (other parameters constant) of 

 the yield in weight per recruit with assumed 

 age at first capture t c (Table 11). Therefore, 

 we included with the binomial expansion the 

 values from the cubic expansion in order to 

 demonstrate their use and potential value in 

 lobster management. 



Because of the range in natural mortality 

 estimates, we decided to plot the yield estimates 

 with at least two different instantaneous values. 

 I chose (1) 0.2664 and (2) 0.1000 so that we 

 could determine the effect this change has on 

 the yield estimates. 



With this reasoning, if the instantaneous 

 natural mortality (M) were 0.1000 with all 

 other parameters as estimated, then the cubic 

 and binomial methods demonstrate an increas- 



ing yield in weight per recruit with the older 

 assumed age groups of the same assumed age 

 class (trend line [F] for both expansions, Fig. 

 18). Conversely, if M were 0.2664 with identical 

 other parameters, then the best yield with the 

 cubic expansion would still be at the older 

 assumed age or molt groups (trend line [C] 

 cubic, Fig. 18) while the binomial expansion 

 shows a better yield at the younger assumed 

 age or molt groups (trend line [D] binomial, 

 Fig. 17). 



As discussed earlier, I believe the lower na- 

 tural mortality estimates approximate the ac- 

 tual value. Therefore, the information under 

 [F] for both expansions should be the more 

 logical to use in terms of selecting the correct 

 size or assumed age or molt class for maximum 

 sustainable yield. 



For this reason, I strongly advocate raising 

 the minimum size to at least some convenient 

 measure near t c+ i . The size for this assumed 

 age or molt group is 91-mm carapace length 

 (3-9/16 inches). For the convenience of all 

 concerned parties, it would be logical to set 

 the new minimum size at 3- ¥2 -inch carapace 

 length. This size would be much more com- 

 patible with the size at maturity for females 

 and logically should eliminate the maximum 

 size regulation. 



This proposed size could increase the catch 

 by about 18% . For example, if the catch were 

 20 million lb. with the 3-3/16 inch regulation, 

 with the size limit set at 3-Vfe inches, the catch 

 would have increased 3.6 million lb. over the 

 20 million lb. In value, the fishermen would 

 receive an estimated increase of $3,312,000. 



The increase to S-V2 inches could be achieved 

 by raising the minimum size one-sixteenth of 

 an inch each year until the desired size is 

 reached. This would delay the net benefit of 

 18% for at least this period of years. 



I must reiterate that if recruitment varies 

 from its present level (numbers shedding into 

 the legal size range each year), this percentage 

 of yield increase would be over what the yield 

 would have been without the change in mini- 

 mum size. That is to say, if a catch of 20 

 million lb. occurred last year and a catch of 

 18 million occurs this year with the 3-3/16 

 inch size limit, these same years with a size 

 limit of 3-V2 inches would have produced a 

 catch of 23.6 and 21.24 million lb. respectively. 



51 



