Relation Between Catch and Effort 



A Schaefer-type curve and relation is a 

 useful method for examining catch and effort 

 data. 1 have constructed a Schaefer-type curve 

 (Fig. 37) for the Chesapeake Bay fishery to 

 show the relations between the total effort and 

 (1) catch per unit of effort and (2) total catch. 

 Although the Schaefer-type analysis does not 

 use all available mortality and growth data and 

 Chesapeake Bay menhaden admittedly do not 

 constitute a closed population, Chesapeake Bay 

 and the South Atlantic are the two areas where 

 the fish are exploited at a very early age (1 and 

 2 years) and are not, to any great extent, 

 exposed to an intensive fishery in some other 

 area earlier. In my opinion the data in Figure 



37 give every indication in recent years of at 

 least economic overfishing if not biological 

 overfishing. It is interesting to compare similar 

 data for the South Atlantic Area which also 

 fishes on the age groups before they are heavily 

 exploited in other areas (Fig. 38). Fishing 

 effort in this area has been relatively low in 

 recent years. I believe the effort in this area is 

 at such a low level as to have virtually no effect 

 on the stock present. The high mortality 

 estimate was due primarily to migrations from 

 the area. Since the stocks in the other three 

 fishing areas are heavily dependent on what 

 escapes from the Chesapeake Bay and South 

 Atlantic Areas, a similar analysis for the other 

 areas is not warranted. 



I have hmited the analyses in Figures 37 and 



38 to data collected since 1955 when our age 

 analyses were initiated. The analyses were also 

 limited to these years because drastic changes 

 have taken place in the menhaden fishery, 

 beginning about the middle of the 1950's, 

 including the use of airplanes and power-blocks 

 (Henry, 1968). These changes have markedly 

 increased the efficiency of the fleet. The extent 

 of the increased efficiency of the gear is not 

 known, but it is obviously substantial. There- 

 fore, a comparison of data in recent years with 

 inaccurate catch per-unit-of-effort data from 

 previous years would be of little value and 

 could give a completely false impression. The 

 fact that the catch per-unit-of-effort has 

 declined rather drastically in spite of the 

 greatly increased efficiency makes the situation 

 even more alarming. Although accurate 



estimates of natural mortality are not available, 

 preliminary analyses indicate that with any 

 reasonable natural mortality (0.5 or less) the 

 total yield would be increased if the catch of 1 

 and 2 years old fish in Chesapeake Bay were 

 reduced. 



The very low levels of abundance; continued 

 high level of fishing effort on young, immature 

 fish; low catch per unit of effort; and the 

 continued absence of a strong year class for 10 

 consecutive years are all disturbing signs that 

 should not be taken lightly. 



3" 



TOTAL STANDARD VESSEL DAYS (TMbUSANOSl 



Figure 37.— Analysis of catch- effort statistics. Chesa- 

 peake Bay menhaden purse seine fishery, 1955-68. 



S 75- 



^5 



-,2 50 



< Z 



o w 



°8 



25 



50 - 



- tr 

 I <r 



<5 



25 



"I 



- 50<o 



"° 



55 



25xg 



"2 



500 1,000 



TOTAL STANDARD VESSEL DAYS 



1,500 



Figure 38.— Analysis of catch-effort statistics, South 

 Atlantic menhaden purse seine fishery, 1955-68. 



21 



