FISHERY BULLETIN: VOL. 75. NO. 3 



METHODS 



Adult biomass was determined from estimates 

 of annual abundance of spawning products, a 

 knowledge of the mean relative fecundity of 

 thread herring, and an assumed sex ratio of 1:1 

 (Saville 1964; Ahlstrom 1968). Methods to deter- 

 mine thread herring egg and larval abundance, 

 distribution, adult biomass, potential yield to a 

 fishery, and mortality during egg and larval 

 stages were analogous to methods reported in de- 

 tail for round herring (Houde 1977a). Other de- 

 tails of survey design and planning also have been 

 published (Rinkel 1974; Houde and Chitty 1976; 

 Houde et al. 1976). Temperature and salinity data, 

 as well as some egg and larvae data, from these 

 surveys are stored in the National Oceanographic 

 Data Center, Washington, D.C., under the 

 MAFLA file. 



The survey area was located on the broad conti- 

 nental shelf off western Florida in the eastern Gulf 

 of Mexico, between lat. 24°45'N and 30°00'N (Fig- 

 ure 1). In 17 cruises (Table 1) from 1971 to 1974, 

 plankton was collected with a 61 -cm bongo net 

 sampler fitted with 505- and 333-fMm mesh nets. 

 Most stations were over water depths from 10 to 

 200 m, except in 1974 when some stations as shal- 

 low as 5 m were added to the sampling plan. These 

 shallow stations were added to determine if thread 

 herring and scaled sardine, Harengula jaguana, 

 spawning increased significantly nearshore where 

 there had been no previous sampling. Thread her- 



k-^-^ 



30' 



28' 



26° 



24' 



200m 



86° 



84° 



82° 



80° 



FIGURE l.— Area encompassed by the 1971-74 eastern Gulf of 

 Mexico ichthyoplankton surveys. Plus symbols ( + ) represent 

 stations that were sampled during the survey. The 10-, 30-, 50-, 

 and 200-m depth contours are indicated. 



ring eggs and larvae were identified using descrip- 

 tions by Houde and Fore (1973) and by Richards et 

 al. (1974). 



Egg and larval abundances at stations in the 

 cruise area, over the time period represented by a 

 cruise, and on an annual basis, were estimated 

 using techniques similar to those outlined by Sette 

 and Ahlstrom (1948), reviewed by Saville (1964), 

 and most recently discussed by Smith and 



TABLE 1. — Summarized data on cruises to the eastern Gulf of Mexico, 1971-74, to estimate abundance of thread herring eggs and 

 larvae. GE = RV Gerda, 8C = RV Dan Braman, TI = Tursiops, 8B = RV Bellows, IS = RV Columbus Iselin, CL = RV Calanus. 



Cruise 



Dates 



Number 



of 

 stations 



Positive 

 stations 

 for eggs 1 



Positive 



stations 



for larvae 2 



Mean egg abundance under 1 m 2 Mean larvae abundance under 1 m 2 

 All stations Positive stations All stations Positive stations 



GE7101 3 

 8C7113 



TI7114 

 GE7117 

 8C7120 



TI7121 

 TI7131 



8B7132 



GE7127 

 8B7201 



GE7202 

 GE7208 

 GE7210 

 IS7205 

 IS7209 

 IS7303 

 IS7308 

 IS7311 

 IS7313 

 IS7320 

 CL7405 

 CL7412 



13 



4 





 4 

 2 

 

 

 

 4 



12 

 

 

 



10 



47 

 13 



11 



0.00 



28.42 

 0.85 



0.72 



0.00 



276.82 

 14.39 



42.46 



75.92 

 17.09 



999.46 

 137.98 



75.53 



0.00 



27.67 

 17.48 



11.02 



0.00 



52.63 

 51.87 



79.91 



'Positive station is a station at which thread herring eggs were collected. 



2 Positive station is a station at which thread herring larvae were collected. 



3 An IOTA 1-m plankton net was used on this cruise. On all other cruises a 61 -cm bongo net was used. 



494 



