factors. The number of days each vessel landed 

 menhaden was then multiplied annually by the 

 appropriate weighting factor to give the num- 

 ber of standard vessel days. The relation of a 

 vessel's weighting factor to other features of 

 the vessel such as weight and length is ex- 

 amined later in the paper. 



Figure 11 shows the relation between the 

 calculated standard vessel days and the actual 

 landing days for the Chesapeake Bay fishery. 

 Of the total standard vessel days calculated for 

 the 1968 Atlantic menhaden fishery, 58% were 

 from the Chesapeake Bay fishery. It is obvious 

 from Figure 11 that the trends for the two 

 lines are similar and that the standard vessel 

 day is a fairly constant percentage of the actual 

 landing days. 



o2000 - 



55 



YEAR 



Figure 11.— Number of vessel and standard vessel land- 

 ing days in Chesapeake Bay menhaden purse seine 

 fishery, 1940-68. 



The conclusions based on either set of data 

 would have to be the same— a significant 

 increase in fishing effort in the Chesapeake Bay 

 area in recent years. One change occurred 

 about 1964; prior to that time the number of 

 standard vessel days was always less than the 

 actual landing days, but after 1963 the annual 

 number of standard vessel days was greater. 

 This change coincided with a major change in 

 the composition of the fleet in 1964 as can be 

 seen from Figure 12. Note in particular the 

 dramatic and continuing increase in average 

 horsepower and the decline in the average age 

 of the vessels. In other words, the newer, bigger 

 vessels in recent years have increased the 

 average weighting factor used to calculate the 

 number of standard vessel days based on the 

 number of actual landing days. 



cr<,2000 





1000 



"m 240 



£z 

 ir o 

 CJI- 220 



i=g 200 



<r t- 



Luuj 160 

 32 



ULJ 800 

 OS 

 < o 



Si 600 

 ° 400 



45 

 S 40 



uia: 35 



25 

 19 



LAMOING DAYS 



GROSS TONNAGE 



HORSEPOWER 



Figure 12.— Average age, horsepower, gross tonnage, 

 and landing days of Chesapeake Bay purse seine 

 vessels, 1955-68. 



At the time the standard vessel day unit of 

 effort was developed, it was assumed that there 

 were few zero catches. Nevertheless, the unit of 

 effort developed was in reality a "standard 

 vessel landing day," which may or may not be 

 a true reflection of the actual fishing days. 

 Data have become available from some of the 

 fishing companies which permit a closer exami- 

 nation of the relation between the landing day 

 and fishing day for some of the fishing areas. 

 Unfortunately, these data are available only 

 since 1963 or 1964 through 1967, depending 

 on area. 



In Figure 13 is shown the relation between 

 the total days fished, the total days fish landed, 

 and the calculated total standard vessel days 

 for a portion of the boats in the Chesapeake 

 Bay fishery. The relation between the three 

 sets of data is remarkably consistent, and the 

 trends are almost identical. One important 

 feature of these data is the fact that no fish 

 were caught on 30 to 40% of the days fished, 

 so that the landing days are a gross under- 

 estimation of the actual fishing effort, at least 

 during this period. 



Several comparisons for other areas between 

 total days fished, total days fish landed, and 



