HOUDE ABUNDANCE AND POTENTIAL YIELD OE SCALED SARDINE 



TABLE 10. — Estimated numbers and percentages of survivors of scaled sardines at hatching, 5.5 mm SL, and 15.5 mm SL in 1973. 

 Estimates are made at three possible growth rates (see Table 9). Duration of the nonfully vulnerable larval stage was set at 1.0 day 

 for 1.1 to 3.0 mm larvae. The number of spawned eggs was based on the estimate in Table 4. Predicted numbers at hatching, 5.5 mm, 

 and 15.5 mm are calculated from exponential functions based on Table 9 data. 



'Hatching assumed to occur at 0.81 day. 



Estimated survival of scaled sardines at hatch- 

 ing and 5.5 mm was lower than that for thread 

 herring or round herring (Houde 1977a, b). In 

 1973 scaled sardines apparently experienced high 

 mortality during embryonic and young larval 

 stages, which quickly reduced the initial number 

 of eggs to relatively few larvae. Thread herring 

 and scaled sardine mortality rates may be similar 

 for larvae in the fully vulnerable length classes. 

 Round herring larvae had a lower estimated mor- 

 tality rate than either scaled sardines or thread 

 herring. But, the probable slower growth rate of 

 round herring larvae at cooler temperatures 

 (Houde 1977a) caused estimated numbers at 

 15.5 mm to be only 40 to 120 survivors/10,000 

 spawned eggs, which was comparable with the 

 thread herring estimate of 60 to 200 survivors/ 

 10,000 eggs, but higher than the 5 survivors/ 

 10,000 eggs estimated for scaled sardines. 



SUMMARY 



1. Scaled sardines spawned from January to 

 September in the eastern Gulf of Mexico, with 

 most spawning occurring during spring and sum- 

 mer. They spawned in waters <30 m deep, mostly 

 within 50 km of the coast. 



2. Eggs were collected where surface tempera- 

 tures ranged from 20.8° to 30.7°C and surface 

 salinities were 29.9 to 36.9%<». Larvae «5.0 mm SL 

 were collected at surface temperatures from 18.4° 

 to 30.5°C and at surface salinities of 27.3 to 36.9%o. 

 Most eggs and =£5.0-mm larvae occurred where 

 surface temperature exceeded 24°C and surface 

 salinity was above 35%<>. 



3. Estimates of annual spawning increased in 

 each year, 1971-73. Biomass estimates increased 

 from 16,000 to 390,000 metric tons during 

 those years. The mean biomass estimate for the 

 3-yr period was 184,527 metric tons. Concentra- 

 tions of adult biomass between the coast and the 

 30-m depth contour were: 1971—2.8 kg/ha; 

 1972—24.7 kg/ha; 1973—64.8 kg/ha. 



4. Estimated annual potential yields to a fishery 

 were: 1971—4,177 to 8,354 metric tons; 1972- 

 37,064 to 74,128 metric tons; 1973—97,153 to 

 194,305 metric tons. Potential yield, based on the 

 3-yr mean biomass estimate, was between 46,132 

 and 92,264 metric tons, or 7.7 to 15.4 kg/ha. 



5. Larvae were more abundant in 1973 than 

 in 1971 or 1972. Larval mortality, relative to 

 length and to estimated ages, was estimated for 

 1973 data. For length, the instantaneous coeffi- 

 cient was Z = 0.3829, corresponding to a 31.8% 

 decrease in larval abundance per millimeter in- 

 crease in length. For age, the most probable esti- 

 mate is Z = 0.2835, which corresponds to a 

 24.1% daily loss rate. 



6. It is probable that more than 99.99<- mortality 

 occurred between spawning and the 15.5-mm 

 stage in 1973. Only 5 larvae/ 10,000 spawned eggs 

 were estimated to have survived to 15.5 mm at 

 20 days of age in that year. 



ACKNOWLEDGMENTS 



People and agencies that were acknowledged 

 for their support of this project by Houde (1977a) 

 are thanked once again. Harvey Bullis reviewed 

 an early draft of the paper. This research was 

 sponsored by NOAA Office of Sea Grant, Depart- 

 ment of Commerce, under Grant 04-3-158-27 to 

 the University of Miami. 



LITERATURE CITED 



AHLSTROM, E. h. 



1968. An evaluation of the fishery resources available to 

 California fishermen. In The future of the fishing indus- 

 try of the United States, p. 65-80. Univ. Wash. Publ. 

 Fish., New Ser. 4. 



ALVERSON, D. L., AND W. T. PEREYRA. 



1969. Demersal fish explorations in the northeastern 

 Pacific Ocean — an evaluation of exploratory fishing 

 methods and analytical approaches to stock size and yield 

 forecasts. J. Fish. Res. Board Can. 26:1985-2001. 



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