(DRAFT) - Taxonomy
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

TAXONOMY

NAME - shrimp, brown

OTHER COMMON NAMES - brownie, green lake shrimp, redtail shrimp, red shrimp, golden shrimp, native shrimp and summer shrimp

ELEMENT CODE -

CATEGORY - Aquatic Crustaceans

PHYLUM AND SUBPHYLUM - Arthropoda, Crustacea

CLASS AND SUBCLASS - Malacostraca, Eumalacostraca

ORDER AND SUBORDER - Decapoda, Dendrobranchiata

FAMILY AND SUBFAMILY - Penaeidae,

GENUS AND SUBGENUS - Penaeus,

SPECIES AND SSP - aztecus,

SCIENTIFIC NAME - Penaeus aztecus

AUTHORITY - Ives, 1891

TAXONOMY REFERENCES - 197, 127, 14 and 252

Taxonomy - 1 (DRAFT) - Status
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

STATUS

Coded Status
Commercial
Commercial/consumption

REFERENCES FOR STATUS - 127

COMMENTS ON STATUS -
The brown shrimp is prey to a host of finfish species and is the major
contributor to the Gulf of Mexico shrimp fishery, the most valuable fishery
in the United States.*127*

Status - 1 (DRAFT) - Distribution
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

DISTRIBUTION

Distribution - 1 HABITAT ASSOCIATIONS

HABITAT - AQUATIC

REFERENCES FOR HABITAT - 14

NATIONAL WETLAND INVENTORY CODES

NWI NWICLS NWIMOD NWISPEC

Estuarine UB3 R 5
Marine OW0 5
Marine OW0 R 5

REFERENCES FOR NWI - 127

COMMENTS ON HABITAT ASSOCIATIONS -
Spawning is reported to occur primarily in offshore waters deeper than 18 m
(60 ft), possible as deep as 137 m (450 ft) or more. Young brown shrimp
remain in shallow estuarine areas near the marsh-water, mangrove-water
interface or in seagrass beds which provide both predator protection and
feeding habitat.*127*
Eggs occur offshore and are demersal. Larvae occur offshore and begin to
immigrate to estuaries as postlarvae around 8-14 mm TL. Juveniles and
subadults prefer shallow marsh areas and estuarine bays. Adults occur in
neritic Gulf waters. Larvae and juveniles inhabit soft, muddy areas,
especially in association with plant/water interfaces. Adults are
associated with terrigenous silt and muddy sand substrate.*252*

Habitat Associations - 1 (DRAFT) - Food Habits
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

FOOD HABITS

TROPHIC LEVEL -
OMNIVORE

REFERENCES FOR TROPHIC LEVEL - 127

LIFESTAGE FOOD FOOD PART
Larva Zooplankton Not Specified
Larva Phytoplankton Not Applicable
Larva Rhizophoraceae Not Applicable
Larva Detritus Not Applicable
Larva See Comments; Food
Juvenile Polychaetes Not Specified
Juvenile Crustaceans Not Specified
Juvenile Detritus Not Applicable
Juvenile Ostracods Not Specified

REFERENCES FOR GENERAL FOOD - 127

REFERENCES FOR JUVENILE FOOD - 127

REFERENCES FOR LARVAE FOOD - 127

COMMENTS ON FOOD -
All actively feeding stages of the brown shrimp are omnivorous and feeding
begins with the first protozoeal stage. Larval stages feed on phytoplankton
and zooplankton. Postlarvae feed on epiphytes, phytoplankton, and detritus,
but faster growth is attained on food of animal origin. Juveniles and
adults forage nocturnally on available food, including polychaetes,
amphipods, chironomid larvae, but also detritus and algae.*252*

COMMENTS ON JUVENILE FOOD -
Jones found that 45- to 65-mm juveniles "selected the organic fraction of
the sediment" and termed them "opportunistic omnivores." Those over 65-mm
began to disperse to deeper waters and became more predaceous, but
occasionally ingested both detritus and algae and were termed "omnivorous
predators." Prey items included polychaetes, amphipods, nematodes,
chironomid larvae, and ostracods. Based on laboratory feeding experiments,
Ogle and Price (1976) suggested that mysids may also serve as food for
juvenile in northeastern gulf coast estuaries. Darnell (1958) described
feeding habits for 91- to 142-mm brown shrimp from Lake Pontchartrain,
Louisiana, similar to the findings of Jones (1973) for brown shrimp over 65
mm.*127*
Juveniles are primarily encounter-feeders whereas adults are selective
omnivorous predators.*252*

COMMENTS ON LARVAE FOOD -
Larvae are reported by Van Lopik et al. (1979) to feed in the water column
on both phyto- and zooplankton. After moving into estuarine nursery areas,
postlarvae become demersal and feed at the vegetation (marsh grass,
mangrove, or seagrass) -water interface. Jones reported that postlarvae
Food Habits - 1 (DRAFT) - Food Habits
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

from 25 to 44 mm indiscriminately ingested the top layer of sediment, which
contained detritus (comprised primarily of Spartina), algae, and
microorganisms, and termed them "omnivorous encounter feeders."*127*

Food Habits - 2 (DRAFT) - Environment Associations
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

ENVIRONMENTAL ASSOCIATIONS

G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
L
L
L
L
A Bottom Type [Aquatic]: Mud or silt
A Bottom Type [Aquatic]: Organic debris
A Bottom Type [Aquatic]: Sand
G Bottom Type [Aquatic]: Specified in Comments
G Aquatic Vegetation [specified type]: Specified in comments
G Water Depth Preference: Specified in Comments
G Water Temperature: Specified in Comments
G

REFERENCES FOR ENVIRONMENTAL ASSOC_ - 127

REFERENCES FOR RESTING ADULT ENVIRONMENTAL ASSOC_ - 127

REFERENCES FOR RESTING LARVAE ENVIRONMENTAL ASSOC_ - 127

COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Temperature. Brown shrimp have been collected at water temperatures as low
as 2 degrees C (36 degrees F), but few are normally taken below 10 degrees
C (50 degrees F), with highest catches taken above 20 degrees C (68 degrees
F). Temperatures of 4.4 degrees C (40 degrees F) or less may cause mass
narcosis and mortality. Kutkuhn (1966) reported that shrimp taken in
waters of greater than 32.2 degrees C (90 degrees F) "are usually flacid
and highly sensitive to stresses induced by handling." This is consistent
with the observations of Zein-Eldin and Aldrich (1965) that growth and
survival were both reduced above 32.2 degrees C (90 degrees F) with a
suggested maximum tolerable temperature for postlarvae of just over 35
degrees C (95 degrees F).*127*

Optimum temperature for larval development has been reported as 28 degrees
to 30 degrees C (82 degrees to 86 degrees F). Estuarine recruitment of
postlarval penaeids was recorded by Christmas et al. (1966) only at
temperatures of greater than 12 degrees C (54 degrees F). Postlarval
growth was reported by Zein-Eldin and Aldrich (1965) to begin between 11
degrees and 18 degrees C (52 degrees and 64 degrees F), increase rapidly
between 18 degrees and 25 degrees C (64 degrees and 77 degrees F), and peak
Environment Associations - 1 (DRAFT) - Environment Associations
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

at 32 degrees C (90 degrees F). No growth was seen by St. Amant et al.
(1965) when water temperature dropped below 16 degrees C (61 degrees F).
Venkataramaiah et al. (1972) found maximum growth, survival, and efficiency
of food utilization at 26 degrees C (79 degrees F) (vs. 21 degrees and 31
degrees C [70 degrees and 88 degrees F]). They also found that with a
rapid change in temperature (direct transfer from 26 degrees to 21 degrees
C [79 degrees to 70 degrees F]), postlarvae and juveniles became inactive,
often convulsed, and in some cases developed muscular paralysis. Direct
transfers between salinities varying from 8.5 to 34 ppt had no adverse
effects.*127*

Salinity. Postlarval brown shrimp have been captured in salinities from
essentially fresh to 69 ppt, but few have been taken in waters of less than
5 ppt. Venkataramaiah et al. (1972) successfully reared brown shrimp at
1.7 ppt, but had no survival at 0.5 ppt. These findings coincide closely
with those of Gunter et al. (1964), who suggested a minimum salinity of 0.8
ppt. Tagging studies by White and Boudreaux (1977) indicated that heavy
freshwater introduction into marsh nursery areas may cause juveniles to
migrate to deeper or laterally towards offshore shallows (i.e., to higher
salinity habitats) earlier than under normal hydrographic conditions.
White and Boudreaux also discussed the fishery implication of such early
migration. The field observations of Barrett and Gillespie (1973) led them
to suggest a salinity optimum of 19 ppt for brown shrimp.*127*

Temperature-Salinity Interaction. A wide range of temperature-salinity
combinations seems to be tolerated by brown shrimp, with interactive
effects becoming most evident at the extremes of the repsective tolerance
ranges. The highest growth and survival rates were found at
temperature-salinity combinations of 26 degrees C or 79 degrees F (vs. 21
degrees and 31 degrees C [70 degrees and 88 degrees F]) and 8.5 or 17 ppt
(vs. 25.5 and 34 ppt). A wider range of salinities was tolerated at 26
degrees C (79 degrees F) than at the higher or lower temperatures. An
increased range of salinity tolerance at temperatures above 21 degrees C is
consistent with the findings of others. The combination of low salinity
and low temperature has repeatedly been shown to be damaging to brown
shrimp.*127*

Substrate and System Features. Field observations have repeatedly
suggested that postlarval brown shrimp recruit in greatest abundance to
soft bottom, shallow areas of estuaries in or near marshes or seagrass
beds. Settling postlarvae have a significant preference for softer,
muddier substrates with decaying vegetation. Apparently, field-observed
recruitment patterns, in this case, accurately reflect a specific
preference rather than a misinterpretation of the result of several related
processes (e.g., random recruitment combined wtih differential mortality
rates between available habitats to give the resultant impression of
apparent habitat selection). If this is indeed the case, the maintenance
of such interface habitats is critical in the species life history and to
the continuity of normal development. Possible reasons for this
association with vegetation-water interfaces have been discussed in
previous sections. Adults are taken in greatest abundance on mud or silt
bottoms, but are also taken on mud-sand, sand, or shell bottoms.*127*

Environment Associations - 2 (DRAFT) - Environment Associations
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

The relation of brown shrimp harvest to temperature and salinity can be
summarized in the following manner, a good brown shrimp year can be
expected after a warm, relatively high salinity spring in coastal nursery
areas. Mean temperature and salinity threshold values (i.e., above which
harvest was good and below which harvest was poor) of 20 degrees C (68
degrees F) and 10 ppt during the primary recruitment and growth period for
brown shrimp along the North Carolina coast.*127*

The importance of the surrounding vegetational system has been emphasized
in a study, which found total shrimp yield to be directly proportional to
marsh acreage in Louisiana, and to acreage of marsh plus seagrass in the
northeastern Gulf of Mexico. It found no significant relationship of
shrimp yield with water surface area, mean water depth, or volume of the
estuaries investigated. Experimental perturbations (blocking off wetlands
with levees and bulkheads) have been shown to decrease postlarval and adult
densities.*127*

COMMENTS ON LIMITING ENVIRONMENTAL ASSOC_ -
Brown shrimp are consumed by many finfish species and by large crustaceans.
The loss of marsh habitat and reduction in freshwater inflow into the bays
have come under recent scrutiny as major factors influencing shrimp
production.*252*

COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Brown shrimp greater than 75 mm tolerate temperatures between 4 and 36
degrees C. with a preferred range of 14.9 to 31.0 degrees C. Adults
tolerate salinities of 0.8 - 45 ppt with an optimum range of 24 - 38.9 ppt.
Salinity and temperature effects are more conspicuous at either
extreme.*252*
Temperature and Salinity. Adverse temperatures or salinities reduce brown
shrimp survival. Under laboratory conditions, larvae did not complete
development at temperatures below 24 degrees C. The survival rate of brown
shrimp nauplii was higher at 24 degrees C than at 20, 28, or 32 degrees
C, and both protozoeal and mysis survival rates increased with temperature
from 24 to 32 degrees C. Survival rates of postlarvae increased with
temperature from 15 to 20 degrees C, remained above 90% from 20 to 25
degrees C, and decreased at temperatures greater than 25 degrees C. At
salinities below 27 ppt or above 35 ppt, hatching was inhibited and
survival of larvae decreased.

Researchers have observed convulsions and disoriented movements of brown
shrimp at salinities less than 2 ppt. Brown shrimp have been collected,
however, at salinities as low as 0.2 ppt in Alabama estuaries. Although
brown shrimp can tolerate wide ranges of salinity and temperature,
interactive effects occur when one or both of these factors are unfavorable.
The salinity tolerance of brown shrimp was reduced at temperatures below 20
degrees C, and tolerance to salinities below 10 ppt was markedly reduced at
temperatures below 15 degrees C.

commercial brown shrimp production in Louisiana was low when postlarvae
recruited early to areas of low salinity (less than 8 ppt) and temperature
(less than 20 degrees C), but was higher when shrimp recruited at later
dates to areas with temperatures greater than 20 degrees C and salinities
greater than 15 ppt.*14*

COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
It was demonstrated that postlarval burrowing in temperatures below 18
degrees C. Extended exposure to temperatures below 20 degrees C may be
detrimental to population survival.*252*
Juvenile brown shrimp are distributed from 0-45 ppt, but prefer 10-20
ppt.*252*

COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Larvae tolerate salinities ranging from 24.1-36 ppt. Postlarvae have been
collected from salinities of 0.1 - 69 ppt and have shown good growth at
2-40 ppt.*252*

COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Eggs will not hatch at temperatures below 24 degrees C. Postlarvae have
been collected from temperatures of 12.6 and 30.6 degrees C. It was
demonstrated that postlarval burrowing in temperatures below 18 degrees C.
Extended exposure to temperatures below 20 degrees C may be detrimental to
population survival. Brown shrimp greater than 75 mm tolerate temperatures
between 4 and 36 degrees C. with a preferred range of 14.9 to 31.0 degrees
C.*252*

Environment Associations - 4 (DRAFT) - Life History
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

LIFE HISTORY

PHYSICAL DESCRIPTION:

Brown shrimp may be distinguished from white shrimp and pink shrimp by the
following features:
Adrostral grooves and crests long, extending almost to hind margin of
carapace; postrostral crest well-developed as far back as adrostral grooves;
gastrofrontal crests present; dorso-lateral grooves on last abdominal
section well-defined and broad; ratio of height of dorsal keel to width of
dorso-lateral groove usually less than 2.25; dark lateral spot at junction
of third and fourth abdominal segments usually absent.*127*

REPRODUCTION:

Since the actual spawning event by brown shrimp has not been observed in
situ, statements regarding the site and time of spawning are based upon the
capture of eggs, larvae, or spent adults. Spawning is reported to occur
primarily in offshore waters deeper than 18 m (60 ft), possibly as deep as
137 m (450 ft) or more. The major spawning season extends from September
through May, but may occur throughout the year, particularly at depths
greater than 46 m (150 ft). While a single spawning peak, February to
March, has been reported along the southeastern Atlantic coast, several
studies have suggested two peaks, September through November and April to
May, in the northern Gulf of Mexico.

Externally fertilized, semibuoyant eggs are released into the water column
and hatch within 24 hours into the first naupliar stage. Brown shrimp
larvae, as with other penaeids, pass through five naupliar, three
protozoeal, and three mysis stages over a 10- to 25-day period before
transforming into postlarvae. It has been suggested that these early stages
require the more constant environment of the open ocean.*127*

BEHAVIOR:

Peak recruitment of postlarval brown shrimp to the estuaries may occur
months after the peak in spawning. While most authors refer to all stages
from hatching to estuarine recruitment as planktonic (pelagic), it has been
observed that overwinterinng brown shrimp in the Gulf of Mexico may burrow
into the bottom and "await the advent of warmer temperatures" before
entering the estuaries. There is laboratory evidence of this burrowing
behavior in postlarval brown shrimp at temperatures below 18 degrees C (64
degrees F). From this evidence it was concluded that brown shrimp
postlarvae winterover in a state of reduced activity as inshore water
temperatures decline.

Postlarvae are reported to move into the estuaries primarily at night on
incoming tides, and to take on a demersal habit as they move to shallow,
soft-bottom areas of the estuarine nursery grounds. Transformation to the
juvenile stage occurs within 4 to 6 weeks after entering the estuary.
Growth and survival during the postlarval and early juvenile stages are
thought to be criticial factors affecting the harvestable adult population
size.*127*
Life History - 1 (DRAFT) - Life History
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

Adult. After exiting the estuaries, brown shrimp move rapidly to about 18 m
(60 ft) and then slowly make their way to spawning depths of 46 to 91 m (150
to 300 ft). Several studies have suggested that offshore adult populations
in the northern Gulf of Mexico tend to move westward with the prevailing
currents. That the Mississippi River is not an absolute barrier to such
westward movement by shrimp migrating from estuaries east of the delta was
shown by the tagging studies.*127*

Emigration. Young brown shrimp remain in shallow estuarine areas near the
marsh-water, mangrove-water interface or in seagrass beds which provide both
predator protection and feeding habitat. As they reach 60 to 70 mm, they
move away from these interface areas into deeper, open water "staging areas"
and at 90 to 110 mm begin their gulfward migration. One study found
emigrants as small as 50 mm in western Louisiana that were apparently
prompted to leave the estuaries early by a strong freshwater input which has
reduced nursery area salinities to 3 to 4 ppt. It has been suggested that
crowding or competition for food might be the basis for the inverse
relationship between population density on the nursery grounds and the size
of migrating adolescent shrimp.

The period of May through August, particularly June to July, is often cited
as peak months of emigration. The combined effect of increased tidal height
and current velocities associated with full moons during these months has
been suggested as a stimulus to emigrate. One study reported little
day/night difference which conflicts with a study which reported that the
highest percentage of emigration occurs at twilight. The latter study also
reported a diel variation in use of the water column during migration, with
peak densities near the bottom in day-light hours, midwater at twilight, and
near the surface at night.*127*

Predators. Juvenile brown shrimp may escape fish predation by burrowing
into the sediment. In either clear or turbid water, the presence of sand
in which to burrow decreased predation by southern flounder but not by
Atlantic croaker. The latter fish appears well-adapted to feeding upon
burrowed organisms. The effects of clear versus turbid water on predation
rates is more complex. Whether sand for burrowing was present or not,
turbid water (compared to clear water) increased predation by southern
flounder but decreased predation by Atlantic croaker. In clear water, sand
reduced predation by pinfish. In turbid water, however, the presence of
sand did not reduce predation by pinfish; shrimp burrowed less when the
water was not clear. Predation by fishes may be the major cause of natural
mortality to brown shrimp in estuaries.

Postlarvae and juveniles prefer vegetated over unvegetated bottom for
protection from predators and for food resources.*14*

LIMITING FACTORS:

Temperature and Salinity. Adverse temperatures or salinities reduce brown
shrimp survival. Under laboratory conditions, larvae did not complete
development at temperatures below 24 degrees C. The survival rate of brown
shrimp nauplii was higher at 24 degrees C than at 20, 28, or 32 degrees
Life History - 2 (DRAFT) - Life History
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

C, and both protozoeal and mysis survival rates increased with temperature
from 24 to 32 degrees C. Survival rates of postlarvae increased with
temperature from 15 to 20 degrees C, remained above 90% from 20 to 25
degrees C, and decreased at temperatures greater than 25 degrees C. At
salinities below 27 ppt or above 35 ppt, hatching was inhibited and
survival of larvae decreased.

Landings records support these laboratory findings. Researchers found that
commercial brown shrimp harvests were low after periods of low after
temperature and salinity in Pamlico Sound, North Carolina, and high
after periods of high salinity and temperature. Another study reported that
commercial brown shrimp production in Louisiana was low when postlarvae
recruited early to areas of low salinity (less than 8 ppt) and temperature
(less than 20 degrees C), but was higher when shrimp recruited at later
dates to areas with temperatures greater than 20 degrees C and salinities
greater than 15 ppt.*14*

Substrate and System Features. Availability of cover is an essential
requirement for brown shrimp nursery areas. One researcher reported that
the abundance and type of commercially important penaeids is directly
related to the amount of intertidal vegetation available for nursery
habitats. The size of shrimp reaching commercial fishing grounds may be
density dependent, and in years of high recruitment, there may not be enough
nursery habitat for maximum production.

Bulkheading, ditching, disposal of dredged material, and drainage from
agricultural or silvicultural areas may reduce the suitablitity of some
estuaries as nursery areas. Bulkheading reduces the marsh-water interface
that is critical habitat to postlarval and juvenile stages of brown shrimp.
Excessive surface drainage into estuaries can affect salinity patterns, and
contribute substantial amounts of pesticides and sediment to the ecosystem.
Ditches and canals can also affect salinity patterns in estuaries and
prevent the influx of shrimp. The disposal of dredged material covers
nutritive substrates used by shrimp and may result in gill erosion and egg
suffocation. Existing estuarine areas must be preserved to ensure the
continued commercial production of brown shrimp.*14*

Other Environmental Requirements. Other factors regulating the occurrence
and development of brown shrimp are water circulation and turbidity.
Currents generated by wind and tide govern the distribution of chemical
components, temperature, suspended matter and planktonic organisms in the
water column. Although turbidity has not been conclusively linked with
shrimp distribution, aerial photographs have shown a positive relation
between turbid areas and concentrations of shrimp in the Gulf of Mexico.
Life History - 3 (DRAFT) - Life History
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

Turbidity may reflect the nutritive potential of the water, and serve to
protect shrimp from predation.

Dissolved Oxygen. Brown shrimp can detect and avoid oxygen-depleted water.
Juveniles 65-86 mm long avoid 1.5-2 ppm dissolved oxygen (D.O.). Mean
lethal D.O. for juveniles of this size was 0.8 ppm after 1.4 ppm/h
reduction, and it was 0.5 ppm after 2.6 ppm/h reduction. Adults are
unstressed at greater than 4.0 ppm D.O..*14*

Researchers noted a decrease in brown shrimp abundance at altered marsh
sites in Texas, where dissolved oxygen concentrations were below 3.0 mg/l.
Researchers also reported oxygen consumption rates of brown shrimp increased
significantly with temperatures from 18 to 33 degrees C, but that difference
in oxygen consumption rates at test salinities of 10 ppt, 20 ppt, and 30 ppt
were negligible. At 20 ppt 3.7-g brown shrimp used significantly more
oxygen per gram than did 6.7-g brown shrimp; there was no significant
difference between sizes at 10 ppt and 30 ppt.*14*

Parasites and Diseases. Bacteria isolated from blood of brown shrimp were
predominantly Vibrio, Aeromonas, and Pseudomonas. Peritrichous ciliate and
suctorian protozoans may be attached to the gills. Gregarine sporozoan
protozoans may occur in the digestive tract. Brown shrimp may be infected
with larval nematodes and larval cestodes. Diseases and parasites probably
do not cause significant direct mortality but may reduce vigor and increase
predation rates.*14*

One study reviewed the major parasites and diseases affecting brown shrimp.
Microsporidian protozoans, which destroy muscle tissue and gonads, may be
the most important brown shrimp parasite.*14*

The effects of several environmental pollutants and pesticidies on brown
shrimp have been studied as well. Malathion, toxaphene, methyl parathion,
and DDT are among the pesticides detrimental to brown shrimp.*14*

POPULATION ATTRIBUTES:

Growth rates of brown shrimp may vary considerably due to differences in
water temperature, salinity, and food availablity. Nearly all published
brown shrimp growth data relate to postlarvae and juveniles because of their
availability for study and because such data are useful for predicting
commercial harvests.

Daily growth rates of postlarvae and juveniles determined from field studies
ranged from 0.52 to 1.67 mm, and averaged 1.0-1.5 mm during the major growth
period in late spring and early summer. Average daily growth (total length)
of juveniles reared in ponds receiving heated water from an electric power
plant was 1.1-1.5 mm in spring, and 1.0-1.4 mm in summer. Researchers
indicated that postlarval growth rates increased when temperatures exceded
15 degrees C. Researchers also observed that growth from the postlarval to
the juvenile stage took less than 4 weeks in estuarine waters of
temperatures above 20 degrees C; when postlarvae moved into water at
temperatures lower than 20 degrees C, however, growth was delayed,
mortality was high, and the subsequent commercial harvest was low.
Life History - 4 (DRAFT) - Life History
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

Reseachers reported daily juvenile growth rates of 0.1, 1.0, and 1.5 mm at
temperatures of 16, 20, and 25 degrees C, respectively. It was found that
growth and food conversion were highest at 26 degrees C.

Sexual differentiation in brown shrimp typically begins at about 50 mm TL.
Growth slows markedly as shrimp reach 100 mm TL, beyond which males usually
grow slower than females. In the Gulf of Mexico, male brown shrimp reach
about 60% of the weight and 83 % of length of females.*14*

REFERENCES FOR LIFE HISTORY- 14 and 127

Life History - 5 (DRAFT) - Management Practices
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

MANAGEMENT PRACTICES

RESULT MANAGEMENT PRACTICE

Adverse Constructing/maintaining bulkheads, seawalls, and dikes
Adverse Salinity alteration
Adverse Applying pesticides
Adverse Dredging
Adverse Shoreline modification/development
Beneficial Controlling sedimentation

REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 14

REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 14

COMMENTS ON MANAGEMENT PRACTICES -
Bulkheading, ditching, disposal of dredged material, and drainage from
agricultural or silvicultural areas may reduce the suitablitity of some
estuaries as nursery areas. Bulkheading reduces the marsh-water interface
that is critical habitat to postlarval and juvenile stages of brown shrimp.
Excessive surface drainage into estuaries can affect salinity patterns, and
contribute substantial amounts of pesticides and sediment to the ecosystem.
Ditches and canals can also affect salinity patterns in estuaries and
prevent the influx of shrimp. The disposal of dredged material covers
nutritive substrates used by shrimp and may result in gill erosion and egg
suffocation. Existing estuarine areas must be preserved to ensure the
continued commercial production of brown shrimp.*14*

Management Practices - 1 (DRAFT) - References
Species shrimp, brown
Species Id M070006
Date 26 AUG 96

References

127* Lassuy, D. 1983. Species Profiles: Life Histories and
Environmental Requirements (Gulf of Mexico) -- Brown Shrimp.
U.S. Fish and Wildlife Service Biol. Rep. 82(11.1) pp 15.

14* Larson, S., M. Van Den Avyle, E. Bozeman Jr. 1989. Species
Profiles: Life Histories and Environmental Requirements of
Coastal Fishes and Invertebrates (South Atlantic)--Brown Shrimp.
U.S. Fish and Wildlife Service Biol. Rep. 82(11.90) pp 14.

252 * Monaco, M.E., T.E.Czapla, D.M.Nelson, M.E. Pattillo. 1989.
Distribution and Abundance of Fishes and Invertebrates in Texas
Estuaries. NOAA's Estuarine Living Marine Resources Project
(ed.). U.S. Department of Commerce Rockville, MD:107.

References - 1