Methods 



Squilla empusa were collected fortnightly along 

 a transect in the Gulf off Freeport, Tex. (Fig. 1) 

 aboard a chartered shrimp trawler using twin 10.4 

 m (34-ft) trawls with a 4.4 cm stretched mesh cod 

 end and tickler chain. Except for August and Sep- 

 tember 1979, a day and a night cruise were made 

 each month in the period July 1979-October 1980 

 i Table 1). Data for Squilla were obtained from the 

 first of two 10-min tows (bottom time) made at 

 depths of 5, 9, 13, 18, 24, 27, 36, 47, 55, 64, 73, 82, 

 86, and 100 m, from 4 tows at 16 m, and from 12 

 tows at 22 m. 



All S. empusa were culled from the catch, pre- 

 served in 10'r Formalin' 2 , washed in fresh water, 

 then stored in 70% ethanol. Specimens from the 

 period July 1979-June 1980 were later processed to 

 determine sex, total length (TL), and total wet 

 weight (TW). Carapace length (CL), abdominal 

 length ( AL), abdominal width (AWD), and abdom- 

 inal wet weight (AW) were measured on all speci- 

 mens collected during seven cruises. Mea- 

 surements follow Manning (1969), except that 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service. NOAA. 



TABLE 1.— Total length compositionstatisticsimmiby cruise for 

 Squilla empusa from the Gulf of Mexico off Freeport, Tex., July 

 1979-October 1980. Night and day cruises are indicated by N 

 and D. 



abdominal length was measured along the dorsal 

 midline from the anteriormost portion of the first 

 abdominal somite to the apices of the submedian 

 teeth of the telson. Females collected during the 

 period July 1979-October 1980 were assigned 

 gonad maturity stages described in Table 2. Typi- 

 cal maximum size was approximated as a length 

 l L correlated with the Beverton-Holt yield model 

 parameter t L (Gulland 1969) following Alverson 

 and Carney's (1975) definition that only 0.5-1% of 

 the catch exceeds age ti . All length measurements 

 presented herein are total length unless stated 

 otherwise. 



TABLE 2. — Descriptions of gonad maturity stages assigned to 

 female Squilla empusa. 



Stage 



Description 



1 Immature. Spent, 

 or Resting 



2 Early Developing 

 3. Late Developing 



4 Gravid 



Ovaries narrow transparent tubes. We could 



not distinguish visually between Immature, 



spent, or resting individuals, nor assign 



age based on length frequency analysis. 



Ovaries with slight yellow coloration occupy 



0-25% of abdominal cavity. 



Ovaries with orange coloration occupy 



25-50% of abdominal cavity; little or no 



expansion of ovaries within each segment. 



Ovaries deep orange in color 



occupy 50-100% of abdominal cavity; 



ovaries in each segment definitely expanded 



Results 

 Bathymetric Distribution and Diel Periodicity 



Squilla empusa were collected from 5 to 86 m 

 depths. Maximum abundance (male: 14.4-16.2 

 individuals/tow; female: 17.5-19.6 individuals/ 

 tow) occurred at 9-16 m (Fig. 2). Abundance was 

 much lower at 5 m (male: 4.6 individuals/tow; 

 female: 5.9 individuals/tow) and approximated 

 that at 27 m. Abundance was even lower but uni- 

 form ( <2.0 individuals/tow) from 36 to 55 m; only 

 one specimen each was collected at 64 and 86 m. 



Size compositions of S. empusa varied with 

 depth, although trends were similar for each sex. 

 Individuals from the entire observed size range 

 (26-132 mm) occurred in depths of 5-27 m (Fig. 3); 

 size compositions of each sex were similar 

 throughout these waters. Deeper waters were 

 occupied primarily by individuals in each sex 

 greater than the average size of 77 mm. Few indi- 

 viduals <80 mm {<17c ) occurred deeper than 27 

 m, and no individuals < 80 mm occurred deeper 

 than 55 m. 



Catches of S. empusa were greatest at night. 

 Mean catch/tow during the 1-yr period October 

 1979-September 1980, when both day and night 



420 



