FISHERY BULLETIN: VOL. 76, NO. 1 



and pigmentation, so that by a length of 15 mm 

 only one to four melanophores of that series are 

 still visible, and these only under favorable light- 

 ing conditions. 



Summary of Contrasting Characters 



The precaudal and caudal vertebral counts, 



14 + 17 in S.Japonicus and 13 + 18 (or 12 + 19) 

 inS. scombrus, are distinguishable in S.Japonicus 

 as small as 7.6 mm and in S. scombrus at 8.6 mm. 

 First dorsal fins, with 10 or 11 spines in S. 

 japonicus and 12 to 17 spines in S. scombrus, at- 

 tain their full complement by 13.0 and 17.0 mm in 

 the two species, respectively. In S. japonicus a 

 total complement of 13 or 14 first-dorsal-fin 

 pterygiophores is attained by 20.2 mm while in S. 

 scombrus a total complement of 22 to 25 is at- 

 tained by 32.0 mm. Because anterior pterygio- 

 phores ossify before posterior ones, and the counts 

 differ between the two species, counts of pterygio- 

 phores in the second through fifth or sixth inter- 

 neural spaces serve to identify S.japon/cus by 11.7 

 mm and in S. scombrus by 18.2 mm (Table 1). 



The relative position of the first anal 

 pterygiophore and the first haemal spine is first 

 observable in S. japonicus at 11.7 mm and in S. 

 scombrus at 32.0 mm. In S.Japonicus the first anal 

 pterygiophore is anterior to the first haemal spine 

 while in S. scombrus it is posterior. 



Scomber japonicus larvae are deeper bodied at 4 

 to 1 1 mm and have greater preanus lengths at 3 to 



15 mm than comparably sized S. scombrus larvae. 

 Scomber scombrus larvae are more heavily 



pigmented and acquire pigmentation earlier than 

 S. japonicus at lengths less than about 15 mm 

 (Figure 4). Of the two species S. scombrus is ear- 

 lier in developing melanophores on the snout and 

 lower jaw. Some specimens of both species possess 

 a few minute melanophores on the ventrum of the 

 abdomen, but their occurrence is more frequent in 

 S.Japonicus larvae <4.2 mm. At given sizes up to 

 12 mm, where additional dorsal trunk pigmenta- 

 tion is developing in both species, the 

 melanophores are more numerous and larger in S. 

 scombrus than in S.Japonicus. At lengths greater 

 than about 12 mm this character is equally de- 

 veloped in both species. Melanophores are not 

 found at the symphysis of the cleithra in any S. 

 japonicus larvae, but are present in S. scombrus 

 larvae as small as 3.7 mm, then in increasing 

 frequency of occurrence so that all S. scombrus 

 larvae >8 mm possess this pigmentation 



DISTRIBUTIONS OF EGGS 

 AND LARVAE 



Scomber scombrus. Egg Distributions 



During the May cruise, S. scombrus eggs were 

 taken from Martha's Vineyard to below the mouth 

 of Chesapeake Bay and were concentrated from 

 Fire Island, N.Y., to Cape Henry, Va. (Figure 5). 

 Spawning apparently extended northward in the 

 inshore portion of shelf water in an area whose 

 northeastern boundary roughly paralleled the 

 surface isotherms. The egg distribution extended 

 out to at least the edge of the continental shelf off 

 Maryland to North Carolina on transects F, G, J, 

 and K. 



By the time of the June cruise, spawning of S. 

 scombrus had shifted to the northeast. Eggs were 

 taken only on the three northernmost transects, 

 the majority occurring in the inner half of shelf 

 waters (Figure 6). 



Scomber scombrus. Larva Distributions 



During May, S. scombrus larvae were caught 

 between Chespeake Bay and Oregon Inlet, N.C., 

 across the breadth of the continental shelf and 

 south of the area where eggs were taken during 

 this cruise (Figure 7). These larvae were small, 

 ranging from 2.5 to 8. 1 mm long with a mode of 3.0 

 to 3.9 mm. 



During the June cruise we took S. scombrus 

 young over a greater area than in May. Larvae 

 occurred from the offing of Martha's Vineyard, 

 which was probably not the northern limit of their 

 distribution, south to the offing of Currituck 

 Beach, N.C. (Figure 8). The distribution of larvae 

 overlapped that of eggs on the three northernmost 

 transects and extended across the entire breadth 

 of the continental shelf between Martha's Vine- 

 yard and New Jersey. The largest numbers oc- 

 curred off Montauk Point, N.Y. Most larvae taken 

 in June were north of the area of larva occurrence 

 in May. 



A marked increase in lengths of young, progres- 

 sing from north to south, is shown in length- 

 frequency data for this cruise (Figure 9). This in- 

 crease may be due to earlier spawning or higher 

 temperatures to the south which may enable the 

 larvae to grow faster. 



The inordinately large increase in lengths be- 

 tween transects D and E and decrease in lengths 

 south of transect E may have been caused by the 



104 



