a highly significant correlation coefficient of r 

 = 0.981 (P < .01, 12 df). Thus, whether 

 standard vessel days or vessel weeks were used, 

 the conclusions would be similar. 



On the basis of these analyses it appears that 

 the standard vessel landing day probably well 

 represents the trend of the fishing effort for 

 Atlantic menhaden but underestimates the 

 actual amount of fishing. Even the landing days 

 themselves are a fairly reliable index of the 

 changes in fishing effort over a number of 

 years, although landing days make no allow- 

 ance for differences between vessels. As 

 pointed out previously, there even is a good 

 correlation between standard vessel days and 

 vessel weeks. With reduced stocks, however, 

 the amount of unsuccessful fishing has in- 

 creased and the standard vessel landing days 

 and the landing days are underestimating fish- 

 ing effort even more in recent years. However, 

 this can and should be corrected through the 

 use of logbook data. 



The standard vessel day as originally calcu- 

 lated makes no allowance for changes that have 

 increased the efficiency of the fishing fleet, 

 particularly since the early 1950's. Besides the 

 introduction of newer and larger boats, innova- 

 tions such as power blocks, fish pumps, nylon 

 nets, and airplanes have been added (Henry, 

 1968). The airplanes, in particular, have greatly 

 increased the searching ability of the menhaden 

 fleet. These factors have not been considered 

 in calculating the standard vessel days; how- 

 ever, most of these improvements occurred 

 rather rapidly in the mid-1950's so effort since 

 that time would be comparable. A comparison 

 between effort before and after the mid-1950's 

 would be of more doubtful validity. 



Another undesirable feature of the standard 

 vessel day is that since catch comparisons were 

 made only in certain years for specific vessels 

 there was no consistent and precise method to 

 assign a weighting factor to new vessels that 

 subsequently entered the fishery. Con- 

 sequently, it is important if some physical 

 feature of a menhaden vessel can be related to 

 the catching ability of the vessel. A number of 

 features, including horsepower, gross tonnage, 

 net tonnage, and age of vessel were examined. 

 In other fisheries, including the Gulf menhaden 

 and Peruvian anchovy (Schaefer, 1967), gross 

 tonnage of the fishing vessel has been related to 



CATCH /STftNDflRO VESSEL DftY (TONS) 



Figure 16.— Relation between catch of Atlantic men- 

 haden per standard vessel day and per vessel week in 

 Chesapeake Bay, 1955-68. 



I 2 3 4 5 6 



WEIGHTING FACTOR FOR RELATIVE FISHING POWER 



Figure 17.— Relation between weighting factor for rela- 

 tive fishing power and gross tonnage of purse seine 

 vessels in Chesapeake Bay. 



the catches by the vessel. This relation is not 

 advantageous to the Atlantic menhaden fish- 

 ery, however (Fig. 17). Chesapeake Bay data 

 are used in these analyses since the major 

 amount of fishing in recent years has occurred 

 in that area. Although the mean values indicate 

 increased catches with increased gross tonnage, 

 at least for the smaller weighting factors (the 

 method of calculating these weighting factors 

 was discussed previously), the amount of over- 

 lap masks any possible significant relation. One 

 reason for this may be that the Atlantic fishery 

 includes many converted vessels not specifi- 



