HUNTSMAN ET AL.: YIELD PER RECRUIT MODELS 



FIGURE 18. — Yield per recruit in weight of 



scamp where M = 0.17 (from Matheson, 



Manooch and Huntsman, see Table 1). 



Scamp M 0.17 



Yield Per Recruit in Weight 



0.2 0.4 0.6 0.3 1.0 1.2 1.4 1.6 1.8 2.0 

 FISHING MORTALITY (F) 



For instance, we believe that our yield per recruit 

 models allow preliminary estimates of MSY, 

 estimates required in fishery management plans pro- 

 mulgated under the Fishery Conservation and 

 Management Act. Current catches are an estimate of 

 MSY if three fairly safe assumptions, concerning 

 fishing effort, amount of recruitment, and recruit- 

 ment ages, are fulfilled. The first is that current effort 

 is sufficient to take most of the yield. As early as 



1975, F for most important species was great enough 

 that 70 to 859< of the maximum yield was taken. The 

 most cursory observation would reveal that commer- 

 cial fishing has increased an enormous amount since 



1976. Consequently F should now be more than suffi- 

 cient to take all the yield practically available. The 

 second assumption is that recruitment was sufficient 

 to fully populate the reefs. The major factor limiting 

 reef fish abundance is the scarcity of habitat (Ehrlich 

 1975), rather than scarcity of recruits. Reef fishes in 

 general have long-lived larval stages allowing 

 replenishment of local populations from distant 

 spawning stocks. Observations of natural and artifi- 

 cial reefs suggest that recruits are almost always 

 abundant (e.g., Anonymous 1971; Stone et al. 1979). 

 The third assumption is that recruitment ages 

 remain within a range that will allow maximum yields. 

 It appears that current recruitment ages for major 

 species either are within, or close to, this range. 



Allocation of the catch to various sectors of the 

 fishery may eventually become important. Allocators 



will need to understand the relative impact of various 

 types of gear on the stock and the relationship be- 

 tween effort and mortality. To provide a preliminary 

 estimate of relative impact, we calculated a crude 

 measure of the relative fishing power of the three 

 most important vessel types in the Carolina area. 

 Handline vessels operating from South Carolina 

 ports averaged 321 kg/d (Ulrich et al. 1977), "high- 

 rise" trawlers took 958 kg, and headboats caught 208 

 to 250 kg (Huntsman 1976b; Huntsman et al 1978). 

 Thus handline boats were about 1.3 to 1.5 times as 

 effective and trawlers about 3.8 to 5.2 times as ef- 

 fective as headboats. We cannot perfectly equate the 

 three types, however, because each takes different 

 species (Ulrich et al. 1977). 



The disparity in species vulnerability might allow 

 partitioning the resource without conflict — red snap- 

 per to trawlers; groupers to handliners; porgies, 

 grunts, and vermilion snapper to headboats. But we 

 do not believe such partitioning is desirable. Large 

 trophy fish constitute only a small portion of the 

 headboat catch but are probably extremely impor- 

 tant in motivating the fishermen. Further we believe 

 pursuit of large fish catalyzes the taking of smaller 

 and more abundant species in offshore areas. Only 

 about 30,000 groupers and red snapper (totaling 

 about 182 t) were taken annually by headboats in 

 North Carolina and South Carolina from 1972 to 

 1974, compared with some 400,000 individuals of 

 other species (excluding black sea bass) totaling 



693 



