(DRAFT) - Taxonomy
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
TAXONOMY
NAME - shrimp, sand
OTHER COMMON NAMES - grass shrimp and common shrimp
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - ,
CLASS AND SUBCLASS - Crustacea,
ORDER AND SUBORDER - Decapoda, Natantia
FAMILY AND SUBFAMILY - Crangonidae,
GENUS AND SUBGENUS - Crangon,
SPECIES AND SSP - franciscorum,
SCIENTIFIC NAME - Crangon franciscorum
AUTHORITY - Stimpson
TAXONOMY REFERENCES - 257
COMMENTS ON TAXONOMY -
Tribe: Caridae.*257*
Taxonomy - 1 (DRAFT) - Status
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
STATUS
Coded Status
Sport Fish
Commercial
Commercial/consumption
Commercial/bait
REFERENCES FOR STATUS - 257
COMMENTS ON STATUS -
The crangonid shrimp of the California coast have been fished commercially
since the 1800's. This commercial fishery was centered in San Francisco
Bay. Before the 1960's, most of the catch was dried and shipped to the
Orient, but part of it went to the fresh fish markets. After the 1960's,
the fishery became primarily a bait fishery, and annual harvests were less
than 200,000 pounds.*257*
The sport fishermen of the region will probably continue to support a bait
fishery landing 68-91 t of crangonid shrimp annually. The prospect of
expansion of the fishery is poor.*257*
Status - 1 (DRAFT) - Distribution
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine FL2
Marine FL3
REFERENCES FOR NWI - 257
COMMENTS ON HABITAT ASSOCIATIONS -
Crangonid shrimp are abundant in bays on mud and sand bottoms and offshore
in deeper waters.*257*
Habitat Associations - 1 (DRAFT) - Food Habits
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 257
LIFESTAGE FOOD FOOD PART
Larva Copepods Not Specified
Adult Crustaceans Not Specified
Adult Polychaetes Not Specified
Adult Molluscs Not Specified
Adult Plants Not Specified
Adult Cirripeds
Adult Fish Egg/Fetus stage
Adult Bryozoans Not Specified
Adult Hydrozoans Not Specified
Adult Arachnids Not Specified
Adult Ostracods Not Specified
Adult See Comments; Food
REFERENCES FOR ADULT FOOD - 257
REFERENCES FOR LARVAE FOOD - 257
COMMENTS ON FOOD -
Little is known about the ecology of larval and postlarval crangonids. The
larvae are presumably predators on small zooplankters, such as copepods.
Larvae have been maintained in the laboratory on a diet of Artemia
naulii.*257*
Juvenile and adult crangonids are predaceous, their dietary
differences being related to shrimp size and prey availability. Seasonal and
geographical dietary studies have indicated that crangonid prey in the diet
is generally proportional to their occurrence in an estuary. Researchers who
studied the feeding ecology of sand shrimp in San Francisco Bay, found that
these species feed on a similar array of benthic prey made up of
crustaceans, polychaetes, mollusks, foraminiferans, and plant material.
Amphipods were the most frequently ingested; barnacle exuvia, fish eggs,
bryozoans, hydrozoans, and mites were occasionally ingested. Larger
crangonids ate larger prey. Foraminiferans, copepods, and ostracods were
taken by small shrimp, while shrimp, polychaetes, and isopods were taken by
large shrimp.*257*
In the less saline regions of the San Francisco Bay
Estuary--the delta region--the most important food of sand shrimp is the
opossum shrimp, Neomysis mercedis, which occurred in 62%-84% of all sand
shrimp gastric mills containing prey. Larger crangonids ate larger mysids.
Sand shrimp are suggested to affect the population structure and abundance
of mysids in the delta.*257*
The distribution of N. mercedis does affect the
Food Habits - 1 (DRAFT) - Food Habits
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
distribution of sand shrimp in the San Francisco Bay Delta. Not only is
crangonid density much greater in locations where mysids are abundant, but
crangonids in areas of high mysid density take more prey than those in areas
of low prey density. The delta region of San Francisco Bay has impoverished
benthic communities and thus the region has few potential prey organisms.
This may be an important factor linking the distributions of crangonids and
mysids in the delta region of San Francisco Bay.*257*
Crangonid shrimp
recycle nutrients during their feeding activities. Agitation of bottom
sediments by crangonids searching for food and shelter has been suggested as
an important mechanism of nutrient recycling in estuaries. Nitrogen
excretion by large populations of crangonids can have important effects on
the nitrogen budget of estuarine systems.*257*
COMMENTS ON ADULT FOOD -
Juvenile and adult crangonids are predaceous, their dietary
differences being related to shrimp size and prey availability. Seasonal and
geographical dietary studies have indicated that crangonid prey in the diet
is generally proportional to their occurrence in an estuary. Researchers who
studied the feeding ecology of sand shrimp in San Francisco Bay, found that
these species feed on a similar array of benthic prey made up of
crustaceans, polychaetes, mollusks, foraminiferans, and plant material.
Amphipods were the most frequently ingested; barnacle exuvia, fish eggs,
bryozoans, hydrozoans, and mites were occasionally ingested. Larger
crangonids ate larger prey. Foraminiferans, copepods, and ostracods were
taken by small shrimp, while shrimp, polychaetes, and isopods were taken by
large shrimp.*257*
In the less saline regions of the San Francisco Bay
Estuary--the delta region--the most important food of sand shrimp is the
opossum shrimp, Neomysis mercedis, which occurred in 62%-84% of all sand
shrimp gastric mills containing prey. Larger crangonids ate larger mysids.
Sand shrimp are suggested to affect the population structure and abundance
of mysids in the delta.*257*
The distribution of N. mercedis does affect the
distribution of sand shrimp in the San Francisco Bay Delta. Not only is
crangonid density much greater in locations where mysids are abundant, but
crangonids in areas of high mysid density take more prey than those in areas
of low prey density. The delta region of San Francisco Bay has impoverished
benthic communities and thus the region has few potential prey organisms.
This may be an important factor linking the distributions of crangonids and
mysids in the delta region of San Francisco Bay.*257*
Crangonid shrimp
recycle nutrients during their feeding activities. Agitation of bottom
sediments by crangonids searching for food and shelter has been suggested as
an important mechanism of nutrient recycling in estuaries. Nitrogen
excretion by large populations of crangonids can have important effects on
the nitrogen budget of estuarine systems.*257*
Food Habits - 2 (DRAFT) - Food Habits
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
COMMENTS ON LARVAE FOOD -
Little is known about the ecology of larval and postlarval crangonids. The
larvae are presumably predators on small zooplankters, such as copepods.
Larvae have been maintained in the laboratory on a diet of Artemia
naulii.*257*
Food Habits - 3 (DRAFT) - Environment Associations
Species shrimp, sand
Species Id M070012
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
A Water Temperature: Specified in Comments
A
A Dissolved Oxygen: Specified in Comments
A Bottom Type [Aquatic]: Mud or silt
A Bottom Type [Aquatic]: Sand
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 257
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 257
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Water temperature is a critical factor not only in survival but in the
regulation of most life functions of cold-blooded organisms such as
crangonid shrimp. Water temperature affects metabolic, growth, and feeding
rates, osmoregulation, movement, habitat selection, and survival. The
discharge of heated effluents may restrict the distribution of crangonids
or other cold-blooded organisms in estuarine systems, and sudden
temperature changes may be lethal.*257*
The seasonal migrations of crangonids have been linked to changing water
temperatures. The spring onshore migration of juveniles may be a migration
to warmer waters and the fall-winter offshore movement of mature shrimp may
be a migration to cooler waters.*257*
Crangonids of the Pacific Southwest have been collected over a wide range
of temperatures. Sand shrimp have been collected from 6.3 to 23.9 degrees
C. Sand shrimp are abundant at >15 degrees C.*257*
Crangonids are euryhaline, occurring at salinities from nearly fresh water
to seawater. Sand shrimp have been collected from San Francisco Bay at
salinities of 0.1 - 34.3 ppt.*257*
The seasonal distribution of crangonids, particularly sand shrimp, along
the California coast is closely related to salinity. Although the sand
shrimp inhabits brackish water during much of its life cycle, it requires
relatively high salinities for reprocuction. Ovigerous females are rarely
collected where salinity is low. Ovigerous females are found year-round in
San Francisco Bay, but almost never in the less saline portions of the bay.
Energetic demands of osmoregulation at low slainities may preclude egg
Environment Associations - 1 (DRAFT) - Environment Associations
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
development and thus reproduction in low salinity waters. Studies showed
that low salinities retard egg development in crangonids. Salinity is
thus important in larval survival; preliminary investigations suggested
that survival of larval sand shrimp declined at salinities below 12
ppt.*257*
Little information is available relating crangonid distribution to
substrate type. Crangonids are found on substrates ranging from mud to
peat to sand. They appear to be particularly suited to sand-mud substrates
by being able to nestle and bury themselves into the substratum using
their pleopods and walking legs. Some crangonid species are reported from
the rocky intertidal zone.*257*
Other environmental factors, such as dissolved oxygen concentration, metals
concentrations, pesticides, and other agricultural, municipal, and
industrial pollutants may affect the distribution and abundance of
crangonids.*257*
Low dissolved oxygen concentrations, in combination with high water
temperatures, are believed to limit the occurrence of crangonids in several
streams tributary to San Francisco.*257*
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Water temperature is a critical factor not only in survival but in the
regulation of most life functions of cold-blooded organisms such as
crangonid shrimp. Water temperature affects metabolic, growth, and feeding
rates, osmoregulation, movement, habitat selection, and survival. The
discharge of heated effluents may restrict the distribution of crangonids
or other cold-blooded organisms in estuarine systems, and sudden
temperature changes may be lethal.*257*
The seasonal migrations of crangonids have been linked to changing water
temperatures. The spring onshore migration of juveniles may be a migration
to warmer waters and the fall-winter offshore movement of mature shrimp may
be a migration to cooler waters.*257*
Crangonids of the Pacific Southwest have been collected over a wide range
of temperatures. Sand shrimp have been collected from 6.3 to 23.9 degrees
C. Sand shrimp are abundant at >15 degrees C.*257*
Crangonids are euryhaline, occurring at salinities from nearly fresh water
to seawater. Sand shrimp have been collected from San Francisco Bay at
salinities of 0.1 - 34.3 ppt.*257*
The seasonal distribution of crangonids, particularly sand shrimp, along
the California coast is closely related to salinity. Although the sand
shrimp inhabits brackish water during much of its life cycle, it requires
relatively high salinities for reprocuction. Ovigerous females are rarely
collected where salinity is low. Ovigerous females are found year-round in
San Francisco Bay, but almost never in the less saline portions of the bay.
Energetic demands of osmoregulation at low slainities may preclude egg
development and thus reproduction in low salinity waters. Studies showed
that low salinities retard egg development in crangonids. Salinity is
Environment Associations - 2 (DRAFT) - Environment Associations
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
thus important in larval survival; preliminary investigations suggested
that survival of larval sand shrimp declined at salinities below 12
ppt.*257*
Little information is available relating crangonid distribution to
substrate type. Crangonids are found on substrates ranging from mud to
peat to sand. They appear to be particularly suited to sand-mud substrates
by being able to nestle and bury themselves into the substratum using
their pleopods and walking legs. Some crangonid species are reported from
the rocky intertidal zone.*257*
Other environmental factors, such as dissolved oxygen concentration, metals
concentrations, pesticides, and other agricultural, municipal, and
industrial pollutants may affect the distribution and abundance of
crangonids.*257*
Low dissolved oxygen concentrations, in combination with high water
temperatures, are believed to limit the occurrence of crangonids in several
streams tributary to San Francisco.*257*
Environment Associations - 3 (DRAFT) - Life History
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
LIFE HISTORY
MORPHOLOGY/IDENTIFICATION AIDS: The crangonid shrimp of the Pacific
Southwest are easily distinguished form other members of the tribe Caridea
by four features; (1)-the rostrum is very short, generally not extending
beyond the eyestalks, (2)-the body is dorsally flattened, (3)-the chelipeds
are not strongly developed, i.e., they are subchelate in form, and (4)-the
eyes are not covered by the carapace. Shrimp of the genus Crangon are
further distinguished by a single median spine in the gastric region of the
carapace.*257*
The three species of Crangon are easily distinguished by the structure of
the Cheliped or the presence of distinctive markings. The "hand" of the
cheliped of sand shrimp is slender and elongate, and the "finger," when
closed, turns back almost longitudinally.
The differences in cheliped shape are not always distinctive in small
shrimp, but sand shrimp have a pair of spines on the fifth abdominal segment
that can be used to separate small sand shrimp from small black shrimp.*257*
The sexes of mature crangonid shrimp are easily distinguished. Sand shrimp
sexes can be distinguished at about 26-30 mm.
The most distinguishing characteristic separating the sexes is the structure
of the endopodite of the second pleopod. Males have an appendix masculina
on the endopodite of the second pleopod, whereas females do not, i.e., the
first, second, and third pleopods look alike. The structure of the
endopodite of the first pleopod is short and curved inward in males and long
and straight in females. The location of the gonopore is still another
distinguishing characteristic, but it is often difficult to recognize in
preserved shrimp. The gonopore is at the base of the fifth pair of walking
legs in males and at the base of the third pair of walking legs in females.
*257*
SPAWNING AND LARVAE: Crangonid shrimp carry their eggs under the abdomen
attached to and between the basal joints and inner rami of the pleopods.
The distribution and abundance of ovigerous females is a useful index of
reproductive activity. Several investigators have reported that the
spawning season of crangonid shrimp is long. Ovigerous females have been
reported to occur during 9 to 12 months of the year in various
populations.*257*
Ovigerous females of the three species reviewed in this report can be found
year-round along the California coast. Ovigerous sand shrimp are usually
most abundant in the spring and summer in coastal embayments but are
abundant offshore in winter. *257*
Studies reported that both male and female sand shrimp live for about one
year. More recent investigations suggest that females may live 1.5 to 2.5
years and males 1.5 years. Repeated spawning has been demonstrated by the
presence of females bearing ovarian stages 5-7, early in the spawning season,
as well as eggs on their egg pad.*257*
The brood sizes of crangonid shrimp are related to shrimp size and species.
Researchers determined the best fit relationship between brood size of sand
Life History - 1 (DRAFT) - Life History
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
shrimp from San Francisco Bay and total length to be:
Log N = -3.66 + 4.09 Log TL,
where N = number of eggs and TL = total length (mm). (Lengths given refer
to total length, from the tip of the rostrum to the distal end of the
telson.) Brood size ranged from about 1200 eggs for shrimp 48 mm long to
about 7000 eggs for females 65 mm long. Kinnetics Laboratories reported a
linear relationship between sand shrimp brood size and length:
N = -16,542 + 339.6(TL).
Brood size ranged from 2499 to 8840 eggs for shrimp from 55 to 71 mm long.
Both relationships account for 81% of the variation in brood size and
predict similar brood sizes for shrimp >55 mm but differ in their
predictions of brood sizes of smaller shrimp. Studies reported a similar
range of brood size for sand shrimp from Yaquina Bay, Oregon: brood sizes
ranged from 1900 to 4800 eggs in shrimp of similar lengths.*257*
Eggs hatch directly into late zoea-stage larvae, which swim dorsal sides up
and with abdomens hanging vertically. Sand shrimp are reported to require
seven larval stages to complete metamorphosis to post-larva, which required
19-20 days at laboratory temperatures of 20 degrees C and 20-25 days 16
degrees C. The larval stages are believed to require 30-40 days at field
temperatures. *257*
Early stage larvae are generally found in near-surface waters and late stage
larvae near the bottom. Early larvae would be expected to occur in the
nearshore zone, transported there by offshore surface currents or released
from reproductive females. Late-stage larvae are more likely to be
transported onshore or upstream in the shoreward moving lower layer of the
water column. Abundance of crangonid larvae generally corresponds to this
expected pattern. Seasonal abundance of larvae is generally bimodal, with
a large spring peak and a smaller fall peak.*257*
POSTLARVAE AND JUVENILES: Postlarvae, the smallest juvenile stages of
crangonid shrimp, are 5-10 mm long and cannot be distinguished to species.
Postlarvae occur over a wide range of salinity, from seawater to nearly
fresh water, but are concentrated in more saline water. The preference of
crangonid postlarvae for bottom waters places them in favorable currents
for onshore and upstream transport. Postlarvae are abundant in San
Francisco Bay in spring to early summer.*257*
Crangonids longer than 10 mm can be identified to species and are considered
juveniles. Most investigators have considered them to be juvenile or
immature until they develop sexual characteritstics, at lengths of 22-30 mm,
although shrimp larger than this can still be immature. The abundance of
juvenile crangonid shrimp commonly peaks in spring and summer; a smaller
peak may develop in late summer and fall.*257*
The abundance of juvenile sand shrimp generally peaks in spring and summer
in low salinity waters of coastal embayments. Juveniles occur in nearly
fresh water (<1 ppt) but move to water of higher salinity as they mature.
Life History - 2 (DRAFT) - Life History
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
*257*
MIGRATIONS: Sand shrimp migrate to deeper, more
saline water as they mature. This out-migration from low-salinity water
appears to be related to reproduction, as it coincides with the development
of sexual characteristics. The migration is particularly pronounced in sand
shrimp. Juveniles are often found in the upper reaches of estuaries, in
nearly fresh water. As the shrimp mature, they move to water of higher
salinity, which may result in size gradients in sand shrimp populations.
The mean length of sand shrimp collected in midsummer in the San Francisco
Bay Estuary ranged from 31 mm near the upstream limit of their distribution
(1 ppt) to >50 mm in the central bay.*257*
Further evidence for an outward migration related to reproductive state is
provided by information on mean salinity of occurrence of females bearing
eggs of various stages.
Females bearing stage-1 eggs are found at salinities of 1.0 to 33.8 ppt
(mean 20 ppt). Ovigerous sand shrimp are generally found only at
salinities greater than 14.6 ppt. The average salinity appears to increase
with egg stage (up to 24.6 ppt for those with stage-4 eggs. Females
bearing stage-4 eggs were not collected from waters of salinity less than
3.7 ppt.*257*
The outward migration of crangonid shrimp is believed to be related to
temperature-salinity interactions. Ovigerous females are found in coastal
embayments in summer but are uncommon in them in winter; they seemingly
migrate offshore in winter, possibly in response to water temperature
fluctuation. This offshore population then contributes larvae and
postlarvae for the spring abundance peaks.*257*
Sand shrimp also undergo diel vertical migrations. Researchers first
reported a diel pattern in which the shrimp enters the water column and
disperses through the water column at night but remains on or near the
bottom during daylight. The ecological significance of this behavior
remains unknown, but the habit may serve to allow feeding near the surface
while protected by darkness from visual feeding predators (fish). Migration
into the water column may also be a response to the movement of their
primary food, Neomysis mercedis, into the water column. Additional studies
substantiated the diel activity patterns of sand shrimp and N. mercedis.
*257*
ADULTS: Male sand shrimp matured at 34 mm. Ovigerous females as short as
43.6 mm for sand shrimp were reported in Oregon waters. These
lengths at maturity agree well with findings in California.*257*
Studies reported a seasonal variation in the sex ratio of sand shrimp from
San Francisco Bay; males predominated before the breeding season and females
predominated during the peak of the breeding season. This variation can be
attributed to the short life span of males, which are believed to die soon
after copulation, and the longer life span of at least some of the breeding
females. In general the sex ratios of crangonid populations of the Pacific
Southwest appear to be about 1:1. This ratio is expected in
nonsynchronously spawning populations in which a portion of the population
Life History - 3 (DRAFT) - Life History
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
has more than one brood.*257*
GROWTH: In all crangonids, males and females grow at different rates. The
length of male sand shrimp from San Francisoco Bay rarely exceeded 50 mm
although some individuals as long as 71 mm long have been collected. Female
sand shrimp longer than 70 mm were commonly collected.
The length of crangonids in San Francisco Bay are somewhat greater than in
Oregon, where studies reported maximum lengths of 50 mm (males) and <62 mm
(females) for sand shrimp. The shrimp may grow larger in San
Franciso Bay because water temperatures are higher there than in Oregon,
presumably leading to faster growth or longer growing seasons.*257*
Offshore populations of crangonids may reach much larger lengths.
Collections of sand shrimp off the mouth of the Columbia River indicate a
population with a mean length >80 mm and maximum lengths of 110 mm.
Researchers suggested that reduction in size of marine animals, although
generally slight in higher Crustacea living in brackish water, is
comparable to Bergmann's Law: size is related to features of the physical
environment. The reduction may be attrributable to the physiological
effects of salinity, reduced food availability, or a combination of these
and other factors. Studies of osmotic regulation indicated that smaller
sand shrimp are capable of better hyper-regulation but larger ones are
capable of better hypo-regulation. Thus, the migration of larger shrimp to
high salinity waters would be energetically advantageous and may lead to
faster growth.*257*
Growth rates are extremely difficult to estimate from size-frequency
histograms derived from field collections of crangonid shrimp. Immigration,
emigration, temperature and salinity effects, and differential mortality
combine to obscure growth patterns. Researchers estimated that the growth
of juveniles ranged form 0.76 to 1.37 mm per week in Oregon. Growth rates
of crangonids in California are somewhat higher. Kinnetics Laboratories
(1984) estimated male and female sand shrimp >30 mm long to grow 1.7 to 2.4
mm per month.*257*
Length-weight relationships for juvenile, male, and female sand shrimp were
given by Siegfried (1980). The regression equations describing these
relationships follow:
juveniles: Log W = -5.41 + 2.58 LogTL
males: Log W = -6.12 + 3.27 LogTL
females: Log W = -6.62 + 3.57 LogTL
where W = dry weight in grams and TL = length in mm. Analysis of covariance
revealed significant differences in slopes between the length-weight
regressions of juvenile and mature shrimp. The difference is at least
partly attributable to gonadal development.*257*
MORTALITY: Annual abundance of crangonid shrimp varies widely. Annual
abundance indices for sand shrimp in San Francisco Bay were several orders
of magnitude higher in some years than in others from 1980 to 1985. Annual
abundance of crangonid shrimp appears to be determined mostly by mortality
of larvae and postlarvae. Mortality due to predation is undoubtedly high
Life History - 4 (DRAFT) - Life History
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
and may explain geographic patterns of abundance within embayments.
Recruitment to bay populations in any one year, however, appears to depend
on environmental conditions.*257*
Recruitment of crangonid shrimp to San Francisco Bay is independent of the
abundance of ovigerous females, i.e., the parent stock. Correlations
between annual abundance of crangonid larvae and postlarvae and of
ovigerous females are non-significant, suggesting that environmental
conditions play a major role in determining annual abundance. Thus,
management to maintain crangonid populations should be aimed at maximizing
recruitment.*257*
Annual abundance of crangonid shrimp has been linked to the volume of
freshwater flow to San Francisco Bay. The volume of freshwater inflow
determines the magnitude of seaward and landward currents, the salinity
regime, temperature, and the distribution and abundance of other organisms
including crangonid predators and prey. All of these factors play major
roles in determining crangonid recruitment and mortality.*257*
DISEASE AND PARASITES: Crustaceans are subject to infection by bacteria,
fungi, protozoans, platyhelminths, and nematodes which can cause disease.
Although infestation of crangonids by these groups has been observed, there
is little information on the incidence of infection or the effects on
crangonid populations. In crangonids of San Francisco Bay, the incidence of
infection by microsporidian protozoans is often high.*257*
The bopyroidean branchial isopod, Argeia pugettensis, an extoparasite in the
branchial chamber, often infects crangonids in San Francisco Bay and in
Yaquina Bay, Oregon. It attacks shrimp
in San Francisco Bay only in higher-salinity waters. Researchers reported
only female parasitized sand shrimp in Yaquina Bay, Oregon; however, no
parasitized ovigerous females were found. In San Francisco Bay almost all
parasitized shrimp appeared to be females. Since it is unlikely that the
isopod would attack only females, and since castration by parasites is
reported for other crustacean species, it is likely taht the attachment of
A. pugtettensis results in castration in sand shrimp. Castration would
inhibit gonadogenesis and castrated male shrimp would take on feminizing
characteristics, including larger size. A larger host would presumably make
more energy available to the parasitic isopod. Since host and parasite
weights are positively correlated, early attachment of the parasite and
growth with the host is indicated.*257*
Whether female or castrated male, parasitized crangonid shrimp are still
significantly smaller than nonparasitized shrimp, as shown in a field study
conducted in Humboldt Bay. The study suggests that there are slower growth
rates in the parasitized shrimp. Preliminary laboratory investigation
reveals that parasitism by A. pugettensis depresses metabolic rates (oxygen
consumption) in sand shrimp but does not affect excretion rates.*257*
REFERENCES FOR LIFE HISTORY- 257
Life History - 5 (DRAFT) - Management Practices
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Regulating harvest - restricting weapons/gear use
Beneficial Regulating harvest - setting seasons
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 257
COMMENTS ON MANAGEMENT PRACTICES -
The local market for crangonid shrimp was saturated soon after the Chinese
began shrimp fishing. However, a profitable export trade soon developed,
based on the shipment of dried shrimp to the Orient. The use of Chinese
shrimp nets was investigated by the California Fish and Game Commision in
1897 and again in 1910, largely to assess the loss of young fish
(particularly striped bass, Morone saxatilis) in the Chinese nets. In 1901
the Califonia State Legislature established a closed season to shrimp
fishing from May to August. By 1911 the Chinese shrimp nets were
prohibited, but in 1915 a law was passed to allow limited use of the nets in
parts of San Francisco Bay.*257*
Management Practices - 1 (DRAFT) - References
Species shrimp, sand
Species Id M070012
Date 26 AUG 96
References
References - 1