STUDIES ON THE STRIPED BASS OF THE ATLANTIC COAST 59 



different conditions of the fishery and thus determine which is the most advantageous, 

 not only from the point of view of profit to the fisherman, but also in the light of what 

 is known about the life history of this species. In other words, it is desirable to dis- 

 cover at what age (or length) it is most advantageous to start the fishery for striped 

 bass; i.e., whether the fishery gets the most profit out of taking the fish for the first 

 time when they are 2-year-olds (averaging roughly three-quarters of a pound and 12 

 inches in length) as it does at present, or whether it would benefit by allowing the fish 

 one or two more growing seasons before catching them. 



In order to find the answers to these questions it is essential that the fishing 

 mortality at different ages — the percentage of fish of each age taken by the fishery — 

 and the natural mortality, be known. This can only be done accurately by careful 

 studies and the collection of detailed statistics on the annual catches of striped bass 

 over long-term periods, although the present work has given some information along 

 these lines. Considering the dominant 1934 year-class, it has been assumed from 

 the percentage of tag returns (see p. 57) that approximately 40 percent of its members 

 were taken by the fishery as 2-year-olds in 1936 and 1937, and that about 25 percent 

 of the 3-year-olds of 1937 and 1938 were also taken by the fishery. It is known 

 from various catch records from Virginia to Rhode Island that only about one- 

 quarter as many 3-year-old striped bass were caught in 1937 as the 2-year-olds that 

 were taken in 1936. This is demonstrated in figure 4, where the catches of a pound- 

 net fisherman at Fort Pond Bay, Long Island, N. Y., were approximately four times 

 as great by number in 1936 as they were in 1937, and where the catch was over 90 

 percent 2-year-olds in 1936 and 3-year-olds in 1937. Given this information it is 

 possible to estimate the natural mortality in 1936 by the following equation: 



NM=S 1 -(FM l +S 2 ), 



wherein NM is the natural mortality in 1936, Si the stock available in 1936, FM t 

 the fishing mortality in 1936, and S 2 the stock available in 1937. Si can be given 

 any arbitrary value, for example, 1,000. If FM X is assumed to be 40 percent of Si 

 (see above), FMi is 400. S 2 is equal to approximately Ay.FM 2 , where FM 2 is the 

 fishing mortality in 1937, for tagging experiments indicate that roughly 25 percent of 

 the 3-year-olds were taken in 1937. FM 2 is known to be % FM U as only one-quarter 

 as many 3-year-olds were taken in 1937 as there were 2-year-olds taken in 1936. 

 Under these conditions FM 2 therefore becomes 100, and in the equation above, where Si 

 was assumed to be 1,000, S 2 becomes 400. Substituting these values in the equation, 

 the natural mortality in 1936 attains a value of 200. Thus of the original 1,000 fish 

 in 1936, 400 were caught as 2-year-olds, and of the remaining 600 fish, 200 were lost 

 through natural mortality. It is therefore apparent that if the estimates on which 

 the figures making up this equation are based are correct, natural mortality accounted 

 for about one-third of the 2-year-olds in 1936 which were not taken by the fishery. 

 It should be pointed out, however, that slight variations in the percentages assigned 

 to FMi and FM 2 , which are only rough approximations, can materially change the 

 value obtained for NM. 



Taking the figures in the equation above, since they seem to be the best available, 

 it is possible to get some estimate of the yield from the stock under the existing con- 

 ditions of the fishery. Table 1 is a theoretical treatment of 1,000 striped bass of the 

 1934 year-class to show the rate of removal by the fishery and natural mortality, the 

 numbers and poundage caught, and the market value, when the fish of this age group 

 were caught over a 5-year period from 1936-40 (as 2-, 3-, 4-, 5-, and 6-year-olds). 

 This treatment, in other words, considers the value when the fishery starts catching 

 striped bass for the first time as 2-year-olds, which is exactly what occurred in 1936 

 along the Atlantic coast. The natural mortality is figured at one-third of the popu- 

 lation, excluding those taken by the fishery. The fishing mortality was estimated to 

 be 40 percent in 1936, 25 percent in 1937, 15 percent in 1938 (when the members 

 of the 1934 year-class were 4-year-olds), 10 percent in 1939 (5-year-olds), and 5 per- 

 cent in 1940 (6-year-olds) — a declining fishing mortality that undoubtedly represents 

 as sharp a decrease in the percentage of fish of any year-class caught each year as 

 could possibly exist, and probably over-estimates the decline in the percentage taken 

 by the fishery as the members of a year-class become older. It will also be noted in 

 table 1 that the price per pound varies with the different size categories under con- 



