O'Toole and King 1974), and the Japanese catch 

 was 40,400 metric tons in that year (Food and 

 Agriculture Organization 1974). The species is not 

 fished at present in the Gulf of Mexico. Salnikov 

 (1969) reported that round herring was abundant 

 in the northeastern Gulf of Mexico, and Harvey 

 Bullis (pers. commun.) stated that it was plentiful 

 in the eastern Gulf, based on acoustic traces and 

 trawl catches made by National Marine Fisheries 

 Service research vessels. Our initial surveys of 

 eggs and larvae indicated that it might be abun- 

 dant in the eastern Gulf (Houde 1973a), and Fore 

 (1971) reported round herring eggs and larvae to 

 be abundant in the northern Gulf of Mexico. In the 

 absence of a commercial fishery, catch and effort 

 statistics, and other data on abundance, I have 

 estimated the adult biomass in the eastern Gulf 

 from the abundance of eggs that were spawned 

 annually. This fishery-independent technique of 

 biomass estimation can provide preliminary 

 knowledge of fishery potential (Ahlstrom 1968) 

 and is considered to be a useful biomass estimat- 

 ing procedure (Saville 1964; Smith and 

 Richardson in press). 



METHODS 



Survey Area and Times 



Seventeen plankton surveys were made in the 

 eastern Gulf of Mexico between lat. 24°45' and 

 30°00'N (Figure 1) in 1971-74 (Table 1). Most 

 sampling stations were located on the broad conti- 

 nental shelf, where depths ranged from 10 to 200 

 m, but a few stations were over the continental 

 slope where depths were greater. Potential sam- 

 pling stations were on transects running parallel 

 to lines of latitude; transects were spaced at 15- 

 nautical-mile (27.8-km) intervals. Stations were 

 located at 15-mile (27.8-km) intervals on each 

 transect, except for those stations beyond the 

 200-m depth contour, which were placed at 30- 

 mile (55.6-km) intervals (Figure 1). Not all sta- 

 tions were sampled on each cruise (Table 1). Other 

 details of survey planning and design have been 

 reported elsewhere (Rinkel 1974; Houde et al. 

 1976; Houde and Chitty 1976). 



Beginning with cruise IS 7205 (Table 1), sam- 

 pling was restricted to stations on alternate tran- 

 sects. The three stations nearest to shore (at 

 27.8-km intervals) were sampled on each of the 

 designated transects but only stations at 30-mile 

 (55.6-km) intervals were sampled offshore. A few 



FISHERY BULLETIN: VOL. 75, NO. 1 



T" 



FIGURE 1.— Area emcompassed 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. 



additional stations were added on 1974 cruises in 

 areas where depth was less than 10 m; no round 

 herring eggs or larvae occurred at these stations 

 and they were not important with regard to 

 spawning by this species, but they were important 

 in determining spawning and distribution of other 

 Gulf clupeids. 



Plankton Sampling 



A paired 61-cm Bongo net plankton sampler was 

 used on all cruises except cruise GE 7101, in which 

 a 1-m ICITA [International Cooperative Investi- 

 gations of the Tropical Atlantic (Navy)] plankton 

 net with 505-^m mesh was towed. Meshes on the 

 Bongo sampler were 505 /xm and 333 fxm. 

 Ichthyoplankton was sorted from the 505-^tm 

 mesh net and plankton volumes were determined 

 from the 333-/u,m mesh net catch (Houde and 

 Chitty 1976). Net tows were double oblique from 

 within 5 m of bottom to surface or from 200-m 

 depth to surface at deep stations. Nets were towed 

 at approximately 3.0 knots (1.5 m/s) in 1971, but 

 towing speed was reduced on later cruises and 

 averaged 2.3 knots (1.2 m/s) (Table 2). Stations 

 were sampled whenever the ship occupied them; 

 thus, tows were made during either daylight or 

 darkness, depending on the time of arrival at a 

 station. 



Prior to cruise GE 7208, all tows consisted of 



62 



