cally built for menhaden fishing, leading to a 

 variety of vessel types in the fishing fleet. 

 Although there is a relation between gross 

 tonnage and net tonnage, at least for the larger 

 vessels, there also is tremendous variability for 

 the smaller vessels (Fig. 18). This variabihty 

 clearly emphasizes the diverse nature of the 

 fleet menhaden vessels. On the other hand, a 

 significant relation between length of vessel 

 and catch does exist (Fig. 19), although one 

 group of vessels in the 30- to 50-m range is 

 much more effective (weighting factor of 5 vs. 

 3). 



It might be appropriate at this point to 

 summarize briefly the results of my analyses on 

 a suitable unit of fishing effort for Atlantic 

 menhaden. A number of possible units of 

 effort were examined including: (1) vessel fish- 

 ing days, (2) vessel landing days, (3) vessel 

 weeks, and (4) standard vessel landing days. In 

 addition, vessel tonnage and length were re- 

 lated to the relative fishing power of the vessel. 

 In this report I have used the standard vessel 

 landing day as a measure of fishing effort. 

 However, all these units were rather similar and 

 any one of them could have been used without 

 altering the results and conclusions I reached in 

 this report. 



I 2 3 4 5 6 



WEIGHTING FACTOR FOR RELATIVE FISHING POWER 



Figure 19.— Relation between weighting factor for rela- 

 tive fishing power and length of purse seine vessels in 

 Chesapeal^e Bay. 



The major drawbacks for the units of effort 

 other than standard vessel day were as follows: 



(1) for vessel fishing days— data not readily 

 available, needs to be estimated from logbooks; 



(2) for vessel landing days— makes no allowance 

 for differences in fishing power of the various 

 vessels or for days of zero catches, and (3) for 



CO 



z 

 o 



- 200 o 



100 



100 



200 3O0 



GROSS TONS 



400 



500 



Figure 18.— Relation between gross tons and net tons on Chesapeake Bay 

 menhaden vessels. 



10 



