Biology of the Sand Shrimp, Crangon septemspinosa, in the Shore Zone of the Delaware Bay Region

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Abstract
Over 2,500 sand shrimp were collected between October 1958 and December 1960 from shallow waters along Delaware Bay shores where salinity ranged from 4.4 to 31.4‰ and temperature extremes were 0.0 and 26.0°C. The growth rate ofC. septemspinosa was estimated to be about 1.6 mm per month and no seasonal variation was observed. The smallest shrimp collected was 6 mm long while the largest was 70 mm. Three year-classes of females and two year-classes of males inhabit the shoal waters in spring. By summer the oldest year-class of both sexes disappeared from these areas. A size difference was apparent between males and females. The longest female measured was 70 mm as compared to 47 mm for the longest male. The major spawning season forC. septemspinosa was from March to October, with ovigerous females appearing the year round except for December in the shoal water samples. Berried females were collected at water temperatures ranging from 0.0 to 25.0°C. and salinity varied from 17.7 to 29.3‰ The first egg bearers in the spawning season were large females. In July smaller berried females were more numerous. The importance of this size difference is emphasized by the fact that egg carrying capacity of a female is related to her length. The largest female recorded (70 mm) carried over 7,500 eggs. Ovigerous females ranged in length from 22 mm to 70 mm. Calculated ages for these lengths are one year and about 3 1/2 years, respectively. Females outnumbered males, especially during the spawning season. A preponderance of females bearing eggs in early stages (prior to the formation of eye pigment) was noted in the field study. A high incidence of organic debris in gastric mills, as well as behavior, suggests that scavenging is an important means of supplementing the diet. The most prominent group of organisms found in gastric mills of these shrimp were planktonic Crustacea.

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