Pink shrimp, continued 



Migrations and Movements : Larval stages are capable 

 of vertical migration to control their position in the water 

 column (Costello and Allen 1970, Allen et al. 1980). 

 Both larval and juvenile stages show phototaxic re- 

 sponses in their movements (Ewald 1965, Costello 

 and Allen 1970, Jones et al. 1970). Larvae migrate 

 vertically away from the water surface during the day, 

 and juveniles move to the water surface during full 

 moon tides. Pink shrimp postlarvae enter estuarine 

 nursery areas during the summer months after 21 to 28 

 days of larval and postlarval development and remain 

 there for 2 to 6 months (Costello and Allen 1 970, Jones 

 et al. 1970, Copeland and Bechtel 1974, Allen et al. 

 1980). Entry into estuaries may be facilitated by net 

 inflows of sea water after periods of low water levels. 

 The annual rise in sea level that occurs during the 

 warmer months when spawning is occurring may facili- 

 tate current-borne movement of postlarvae from the 

 continental shelf into these nursery areas (Allen et al. 

 1980). Late juveniles and early adults (95-100 mm 

 total length (TL)) migrate to deeper offshore waters as 

 they grow, often migrating 150 nautical miles (Joyce 

 1965, Costello and Allen 1970). There is no evidence 

 that adults from different spawning stocks migrate to 

 different spawning grounds (Costello and Allen 1 966). 

 The intensity of the migrations at the surface appears 

 to be associated with moon phase, with greater num- 

 bers captured during full moon tides compared to 

 captures during new and quarter moon tides (Beardsley 

 1970, Costello and Allen 1970). Although emigration 

 occurs throughout the year, the main activity peak 

 occurs in the fall with a secondary peak in the spring. 

 Decreasing watertemperature triggers the pink shrimp 

 to move into deeper waters (Joyce 1 965, Costello and 

 Allen 1970, Copeland and Bechtel 1974). In Florida 

 during this time, maturing juveniles move from Florida 

 Bay westward into the Tortugas fishery area (Costello 

 and Allen 1966, Allen et al. 1980, Gitschlag 1986). 

 Western Gulf of Mexico pink shrimp typically move 

 southward as they mature into adults, but some move- 

 ment to the north has been observed (Klima et al. 

 1 987). Movement patterns are influenced by patterns 

 in fishing effort (Sheridan et al. 1989, Sheridan pers. 

 comm.). Shrimp stocks in northern Mexico and south 

 Texas cross the U.S. -Mexico border and probably 

 comprise a single management entity. The pink shrimp 

 may also overwinter in estuaries by burrowing into 

 sediment (Williams 1955b, Joyce and Eldred 1966, 

 Costello and Allen 1970, Copeland and Bechtel 1974, 

 Bielsaetal. 1983). 



Reproduction 



Mode : Sexual reproduction occurs through external 

 fertilization by sexually dimorphic (gonochoristic) male 

 and female individuals (Costello and Allen 1970, 

 McKenzie 1981). 



Mating/Spawning : Spawning occurs in sea water at 

 depths of 4 to 48 m and probably in deeper waters as 

 well (Perez-Farfante 1 969). Mating may occur several 

 times during a female's growth and development and 

 is not always associated with spawning. Mating occurs 

 between midnight and early morning between a hard- 

 shell male and a soft-shell female (Eldred 1958). A 

 spermatophore is placed on the female's abdomen 

 during mating. When the female releases eggs the 

 spermatophore releases sperm and fertilization occurs 

 externally (Costello and Allen 1970, McKenzie 1981, 

 Williams 1984). In one study, the smallest impreg- 

 nated female observed was 89 mm, and the smallest 

 ripe female was 101 mm. In the Gulf of Mexico, the two 

 principal spawning grounds are the Sanibel and Tortuga 

 shelf regions between depths of 15 to 48 m. The 

 Tortugas shrimp grounds receives emigrants from 

 nursery areas between Florida Bay and Indian Key, 

 and the Sanibel grounds receives shrimp from nursery 

 areas between Indian Key and Pine Island Sound. 

 Although ripening females and postlarvae have been 

 observed throughout the year, the number of larvae 

 indicates the height of spawning activity occurs from 

 April through September in the Florida Bay region 

 (Costello and Allen 1970, Roesslerand Rehrer 1971, 

 McKenzie 1 981 , Williams 1 984). Similar but season- 

 ally more abbreviated patterns are seen in areas to the 

 west and north of south Florida. Spawning occurs as 

 water temperatures rise, and water temperature is 

 apparently critical to reproductive development 

 (Cummings 1 961 , Costello and Allen 1 966, Jones et al. 

 1970, Allen et al. 1980, Bielsa et al. 1983). Most 

 spawning activity in the Florida Tortugas grounds is 

 during the waning moon (Costello and Allen 1970, 

 Roesslerand Rehrer 1 971 ), and occurs between 20° to 

 31 °C with maximum activity between 27° and 30.8°C 

 (Roessler et al. 1 969, Jones et al. 1 970). 



Fecundity : Shrimp with a weight of 1 0.1-66.8 g contain 

 44,000 to 534,000 developing ova (Martosubroto 1 974). 



Growth and Development 



Egg Size and Embryonic Development : The average 

 egg diameter is 0.31-0.33 mm. At 27-29°C, nauplii 

 emerge 13-14 hours afterthe eggs are spawned (Dobkin 

 1961). 



Age and Size of Larvae : Pink shrimp larvae undergo 5 

 naupliar stages with length ranges of 0.35-0.40, 0.40- 

 0.45, 0.45-0.49, 0.48-0.55, and 0.53-0.61 mm. There 

 are 3 protozoeal stages with length ranges of 0.86- 

 1.02, 1.5-1.9, and 2.2-2.7 mm. There are 3 mysis 

 stages with length ranges of 2.9-3.4, 3.3-3.9, and 3.7- 

 4.4 mm. Two postlarval stages have been described, 

 with length ranges of 3.8 to 4.8 mm, and 4.7 to nearly 

 10.0 mm (Ewald 1965, Costello and Allen 1970, Allen 

 et al. 1980). The pink shrimp grows from nauplius to 



67 



