LIFE HISTORY OF THE COMMON SHRIMP 
17 
Only those findings of Spaulding, Gates, and Viosca relating to the spawning and 
young will be given here. Spaulding thought that the breeding began about the 
middle of June and that spawning took place “in the deeper water of the larger bays 
or even in the Gulf.” He interpreted his data as showing either a long breeding season 
during the summer or two breeding seasons a year. Two years later (1910) Gates 
reported that there was only one breeding season and that “this extends from, approxi- 
mately, the first of May to the last of July.” Our investigations show that the period 
given by Gates covers the most intensive portion of the spawning season and that the 
entire season may be longer by a month or two on either end. Contrary to Gates’ 
assertion that “the smaller the shrimp the earlier it spawns”, we find that the larger 
shrimp mature first, consequently they also probably spawn first (fig. 7). 
Viosca states that Penaeus setiferus spawns in the Gulf, chiefly on the evidence 
that sexually mature shrimp are found only in outside waters. The young are said to 
live in the plankton of the Gulf until a size of 1% inches is reached. “By May, 
reasonable numbers of baby shrimp appear in the shallow waters near the coast line 
and a large proportion gradually migrate into brackish waters, all growing rapidly 
throughout the summer.” 
That the sexually mature shrimp are more abundant in the Gulf than in the inside 
waters agrees with our experience, but that no mature are taken in the bays is too 
sweeping a statement. Although always strikingly less abundant, especially in the 
more mature stages, we have records of many shrimp in advanced stages of ovary 
development from the inside waters both of Louisiana and of Georgia. 
Viosca was led, apparently, to infer that the larvae live in the plankton up to a 
length of 1 % inches by his inability to obtain smaller young. The largest larvae found 
by Muller were 4.5 mm long, the smallest post-larval young about 5 mm. We have 
obtained young as small as 7 mm. Obviously the larvae do not reach a length of 
iy 4 inches (31.75 mm). Either this size was inferred but not actually seen, or, if 
seen, some other crustacean was mistaken for Penaeus, We have been unable to 
find young of this size on the outside, either in the plankton, the trawl material, or on 
the ocean beaches, although we have obtained them in inside waters in all four States 
in which we have worked. 
Although a gradual inward migration of young such as pictured by Viosca would 
be a reasonable process, the presence of many young of 7 mm and up in the creeks, 
bayous, and lakes, and their complete absence on ocean beaches show that the larvae 
often pass directly to shallow brackish waters. Like Viosca we have found that the 
larger young of 20 to 50 mm move, in general, seaward through the summer and fall, 
so that there is always a gradient of decreasing size from the waters of greater salinity 
toward fresh water. 
Owing to the extended spawning season, the advent of the young into the com- 
mercial catch is followed week by week by new contingents which move into the 
fishing zone and become large enough to be taken by the trawls. As a result, the lower 
limit of size in the commercial catch is approximately constant through the summer 
and into the fall, as might be expected, since the limit is set by the selective action of 
gear and the movements of the young and not by growth. It may be affected, how- 
ever, in a minor way by changes in temperature or by changes in the fishing areas 
which are not always strictly comparable from month to month. 
