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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



been the season of poorest fishing. The fish have 

 been consistently more available during the third 

 quarter of the year, and while a closed season at 

 that time would cause a greater reduction in the 

 total catch it offers no obvious advantage in 

 growth of the fish which might result in a greater 

 catch after the period of restraint. 



A minimum size limit may offer some small 

 theoretical advantages, but we suspect that the 

 practical difficulties in its application will over- 

 balance any advantages. We cannot calculate the 

 effect of a minimum size limit on yellowtail stocks 

 because we do not know the natural mortality and 

 therefore, cannot use the method developed by 

 Ricker (1945). In principle, however, if natural 

 mortality is low and growth rate high, it is de- 

 sirable to save the fish to a larger size before cap- 

 ture because they will grow more than the group 

 will lose through death. The reverse is also true: 

 if natural mortality is high and growth rate low, 

 the fish should be harvested as early as practicable. 

 By the time the yellowtail enter the fishery, they 

 have passed through the period of maximum 

 growth in their second summer (1 annulus). 

 When they are fully available at 3 years of age 

 or older, the growth rate lias slowed down mark- 

 edly; therefore, we doubt whether even with a 

 very moderate natural mortality, there would be 

 a significant advantage from setting a size limit. 



A second consideration that frequently enters 

 into the establishment, of a size limit is protection 

 of the fish until they have had an opportunity 

 to spawn. The southern New England yellowtail 

 spawns at such an early age that during the period 

 of our study only a negligible portion of the 

 landings were immature; consequently, we could 

 not advocate a size limit on this basis. 



A serious limitation on the effectiveness of a 

 size limit would ensue from the use of the otter 

 trawl in the fishery combined with the certainty 

 that virtually all small yellowtail, after being 

 landed on deck and sorted in the usual manner, 

 would die before or shortly after their return to 

 the water. Consequently, an effective minimum 

 size limit would have to be accompanied by a 

 minimum mesh size, which would be most difficult 

 to apply in a fishing fleet that seeks numerous 

 other species of varying body shapes and minimal 

 acceptable sizes along with the yellowtail. 



There may, however, be a need to prohibit the 

 landing of fish smaller than are acceptable for 

 filleting. Such a need arises from the develop- 

 ment of the trash fishery on and near the former 

 yellowtail grounds and the possible inclusion of 

 yellowtail among the fish destined to be reduced 

 to fish meal. After commencement of the trash 

 fishery, there were scattered reports of yellowtail 

 being included in the catch, but evidently the pro- 

 portion was small, for in the samples from trash- 

 fish catches (Snow 1950) no significant quantities 

 of yellowtail were included. If, however, an un- 

 usually successful spawning of yellowtail occurs, 

 large quantities of young below filleting size may 

 be attractive to the trash-fish boats. Such yellow- 

 tail would be in their most rapid period of growth 

 and it might be more economical to allow them 

 to remain in the sea to become available as food 

 fish later. A prohibition against landing small 

 fish should be effective, because the trawlers usu- 

 ally can avoid concentrations of such fish. 



The closure of certain fishing areas has some- 

 times been recommended to protect spawning fish, 

 young fish, or fish especially vulnerable to an effi- 

 cient gear. Such a measure offers no solution in 

 the yellowtail because only one kind of gear, the 

 otter trawl, has ever caught significant quantities 

 of them, the fish have been scarcer during their 

 spawning season than at other times, and we have 

 found no well-defined spawning or nursery area. 



A restriction of the total catch might well have 

 saved some of the fish and prolonged the fishery 

 during and after the period of our study if our 

 hypothesis of a large accumulated stock being 

 gradually caught is correct. On the other hand, 

 such a restriction might have meant a lowering 

 of the total catch because the fish saved would have 

 suffered some natural mortality that might or 

 might not have been compensated by growth. 

 Even a loss might have been desirable if it evened 

 out the landings over a longer period. Advocacy 

 of the measure for this reason requires studies be- 

 yond the scope of this report. 



CONCLUSIONS 



If, as appears probable, the abundance of the 

 yellowtail is determined largely by natural causes 

 beyond our control, no definite size or kind of 

 catch can be expected from a given fishing effort. 

 No action is necessary to prevent extinction of the 



