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Species Name: 
Sicyonia brevirostris Stimpson, 1871

Common Name:
Brown rock shrimp, rock shrimp

Species Description:
Sicyonia brevirostris  is the largest of the rock shrimp occurring in the vicinity of the IRL, with mature individuals measuring more than 10 cm (4 inches) carapace length (CL).    It is differentiated from other penaeoid

shrimp species by its robust body form and heavy, stone-like exoskeleton.Short hairs cover the body surface and appendages.  The rostrum is short, bifid or trifid at the tapered tip, and bears 3 (occasionally 4) teeth.  The rostrum maybe elevated 5° - 45°.  A high postrostral carina is present and has 4 forward-facing teeth.  Laterally, the hepatic area is somewhat swollen and has a well developed hepatic spine.  An abdominal carina spans the first 5 segments.  The first abdominal segment has a tooth directed anteriorally.  Pleural plates overlap those of the next posterior segment.  The telson is long and tapers to a robust point, with a pair of spines on either side of it.  Eyes are large and deeply pigmented.  The carapace is off white to pinkish in color, with the dorsal surface darker and blotched or barred with lighter shades.  Legs are red to reddish-purple and barred with white. 

Synonymy:
Eusicyonia brevirostris Burkenroad, 1934

Similar Species:
Rock shrimp resemble penaeid shrimp in general size and body form, but they can be easily separated from other penaeoid shrimp species by their thick, rigid, stony exoskeleton. 

Sicyonia brevirostris is similar to a related species,  S. laevigata, that is occasionally found within the IRL.  The two are differentiated based on size and on the number of rostral teeth. While S. brevirostris grows over 11 cm (4 inches) and usually has 3 rostral teeth behind the tip of the rostrum, S. laevigata reaches only 5 cm (2 inches) and has only 2 rostral teeth. 

 
II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Sicyonia brevirostris occurs in the Western Atlantic from approximately Norfolk, Virginia south along the Atlantic coast to Florida and the Gulf of Mexico to the Yucatán, including Cuba, and the Bahamas.  Centers of abundance occur in the waters off North Carolina near Cape Lookout;  Cape Canaveral in Florida, and the Yucatán. 

IRL Distribution:
The brown rock shrimp is rare to occasional within the Indian River Lagoon, but it supports a large commercial fishery in nearshore and offshore waters from Jacksonville to St. Lucie Inlet where they inhabit waters 18 – 73 meters deep (Anderson 1956).  Juveniles are occasionally found on the rocks of jetties, in tidal creeks, and on protected beaches (Ruppert and Fox 1988).

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Maximum total length is 15.3 cm (6.02 inches); however, most individuals found in shallow water areas are less than 5 cm (2 inches).  Males reach approximately 11.6 cm (4.5 inches) while females reach 11.8 cm (4.6 inches).   

Typical grow rates are approximately 2-3 mm CL per month in juveniles, and 0.5 – 0.6 mm CL per month in adults.  Females grow slightly faster than males, but males gain weight faster in proportion to CL in all class sizes (Kennedy et al.  1977). Growth is more rapid in summer months.     

Maximum life span is approximately 20 – 22 months (Kennedy et al. 1977).

Abundance:
While not abundant within the Indian River Lagoon, brown rock shrimp populations can be large in nearshore and offshore waters.  In a 3-region area of Florida which spanned from Amelia Island near Jacksonville, Florida south to St. Lucie Inlet, Florida, rock shrimp were found in all regions when water depth was between 18 – 73 m (60 - 240 feet) (Anderson 1956).  Highest densities of Sicyonia brevirostris occurred between 34 – 55 m (110 – 180 feet), with density decreasing both inshore and offshore of this range.  The deep water limit to rock shrimp occurrence is likely habitat related, as suitable bottom type decreases beyond 55m depths.  The shallow water limit of rock shrimp occurrence is largely unknown, but the species is known to be scarce on muddy substrata. 

Shelf currents near Cape Canaveral tend to keep larvae and recruits on the Florida Shelf and may transport them inshore in springtime (Kennedy et al. 1977). 

Reproduction:
Female maturation size ranges from 17 - 24 mm (0.6 – 0.9 inches) CL (carapace length) or larger (Kennedy et al. 1977).  Males mature when they reach approximately 18 mm CL (0.65 inches).     

Rock shrimp have separate sexes, with copulation occurring between hard-shelled individuals.  Fecundity, as in many shrimp species, is high, and increases with increased body size.  Fertilization takes place as eggs and sperm are simultaneously expulsed from the female.  Spawning occurs year-round, with females releasing eggs 2 -3 times during the year, but peaks between November and January (Kennedy et al, 1977).  Larvae are present in the water column throughout they year. 

Kennedy et al. (1977) identified 5 ovarian stages in the brown rock shrimp, one more than was found in penaeid shrimp:  1)Undeveloped; 2) Developing; 3) Nearly Ripe; 4) Ripe; and 5) Advanced Ripe.

Embryology:
Eggs hatch within 24 hours into nauplii larvae measuring approximately 0.3 mm (0.01 inches) total length. There are 3 protozoeal stages, 4 mysid stages, and 1 postlarval stage.  Cook and Murphy (1965) raised larvae under laboratory and reported a development time of 29 days from the nauplius to the postlarva, and an additional 30 – 60 days to the juvenile stage.  This information is summarized in the table below:

Recruitment of postlarvae to the area offshore of Cape Canaveral was found to occur to some degree in all months.  Generally, most recruitment occurs between April and August, with the largest peaks observed between July and August (Kennedy et al. 1977). 

IV.  PHYSICAL TOLERANCES

Temperature:
Temperature was found not to be an important cue for initiating spawning activity in the brown rock shrimp, but Kennedy et al. (1977) found it did trigger ovarian development to more mature stages.  During the study, water temperature off Cape Canaveral increased from August to October from 18.1 – 27.3°C (64.4 - 81°F).  In the 3 months following this temperature increase, the percentage of mature females began to increase substantially.

Salinity:
Kennedy et al. (1977) reported that bottom salinity in their study ranged only between 32 – 36.8 parts per thousand (ppt), and had little effect on either spawning activities or larval development in the waters off Cape Canaveral, Florida.

Cook and Murphy (1965) reported that larvae raised under laboratory conditions were killed at salinities above 35 ppt, or below 27 ppt. 

Other Physical Tolerances:
High lunar light intensity was found to have an effect on spawning (Kennedy et al. 1977).  At full moons, a higher percentage of near spawn and recently spawned females were observed than at new moons. 

V.  COMMUNITY ECOLOGY

Trophic Mode:
The diet of Sicyonia brevirostris consists primarily of mollusks, crustaceans and polychaete worms.  Also included are nematodes, and foraminiferans.  Gut content analysis of brown rock shrimp found ostracods, amphipods and decapods made up the bulk of the diet, with lesser amounts of tanaidaceans, isopods, cumaceans, gastropods, and other bivalves also present (Kennedy et al. 1977). 

Habitats:
Essential habitat for Sicyonia brevirostris is quartz and shell sand of fine to medium grain as occurs in nearshore and offshore Florida.  Typical water depth ranges from 25 – 65m (82 – 213 ft.).

Activity Time:
Cobb et al. (1973) reported that brown rock shrimp are nocturnally active, likely burrowing into substrata during daylight hours.

VI. SPECIAL STATUS

Special Status:
None.

Fisheries Importance:
Before the 1970s, rock shrimp were primarily captured incidentally by trawlers seeking out commercially valuable penaeid shrimps.  The fishery first emerged as viable with the first recorded rock shrimp landings in 1970.  In that year, 1200 pounds of rock shrimp were harvested, with an estimated value of $642.  In 1972, landings totaled 443,035 pounds and were valued at $258,528.  By 1977, the fishery was being studied for sustainability, and substantial rock shrimp populations offshore of Jacksonville, Cape Canaveral and Ft. Pierce were identified.

The statewide commercial catch of wild harvested hard clams, Sicyonia brevirostris, between the years 1987 - 2001 was 105.4 million pounds, with a dollar value of over $97.5 million.  The 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties) accounts for 60.3 million pounds of the total harvest, with a dollar value of $56 million.  This ranks the rock shrimp first in pounds harvested, and second in commercial value, behind only the hard clam, Mercenaria mercenaria.  

Figure 1 below shows the dollar value of the rock shrimp fishery to IRL counties by year.  All size classes of shrimp were combined in this dataset.  As shown, commercial catch ranged from a low of $445,900 in 1987 to a high of over $13.3 million in 1996.  Brevard County annually accounts for the largest percentage of the catch with 90% in total (Figure 2),  followed distantly by St. Lucie County, which accounts for approximately 10% of the catch, nearly all of which was harvested between 1994 - 1997.  The commercial harvest in Volusia county accounts for 0.22% of the total harvest.  No commercial rock shrimp catches were reported in either Martin or Indian River Counties over the time period examined.  

Tables 1 and 2 show the commercial value of the rock shrimp harvest to Indian River Lagoon counties in both dollars (Table 1) and percentage by county (Table 2).  Table 3 shows the cumulative percentage of the harvest each county accounts for over the 15-year period from 1987 - 2001.  

  Figure 1.  Annual dollar value of the commercial catch of rock shrimp to the 5-county area
        of the Indian River Lagoon. 
 

Figure 2.  Total rock shrimp dollar vale and percentage by county for the years 1987-2001.

Table 1.  Total dollar value to IRL counties of rock shrimp, Sicyonia brevirostris, between
        1987 - 2001. 

 

Table 2.  By-county annual and cumulative percentages of t