(DRAFT) - Taxonomy
Species shrimp, blue-spotted
Species Id M070014
Date 26 AUG 96
TAXONOMY
NAME - shrimp, blue-spotted
OTHER COMMON NAMES -
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 - nigromaculata,
SCIENTIFIC NAME - Crangon nigromaculata
AUTHORITY - Lockington
TAXONOMY REFERENCES - 257 and 231
COMMENTS ON TAXONOMY -
Tribe: Caridea.*257*
Taxonomy - 1 (DRAFT) - Status
Species shrimp, blue-spotted
Species Id M070014
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, blue-spotted
Species Id M070014
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, blue-spotted
Species Id M070014
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 257
LIFESTAGE FOOD FOOD PART
Larva Copepods Not Specified
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*
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 - 1 (DRAFT) - Environment Associations
Species shrimp, blue-spotted
Species Id M070014
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. Blue-spotted shrimp have been collected from 7.8 to 20.2 degrees
C. Blue-spotted shrimp are abundant at 14-18 degrees C.*257*
Crangonids are euryhaline, occurring at salinities from nearly fresh water
to seawater. Blue-spotted shrimp are generally abundant only in water with
salinity >23 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*
Environment Associations - 1 (DRAFT) - Environment Associations
Species shrimp, blue-spotted
Species Id M070014
Date 26 AUG 96
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. Blue-spotted shrimp have been collected from 7.8 to 20.2 degrees
C. Blue-spotted shrimp are abundant at 14-18 degrees C.*257*
Crangonids are euryhaline, occurring at salinities from nearly fresh water
to seawater. Blue-spotted shrimp are generally abundant only in water with
salinity >23 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 - 2 (DRAFT) - Life History
Species shrimp, blue-spotted
Species Id M070014
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 blue-spotted shrimp is intermediate
in form--not as elongate as that of sand shrimp and not as robust
as that of black shrimp. The differences in cheliped shape are not
always distinctive in small shrimp, but blue-spotted shrimp are easily
recognized (in life) by a prominent dark circular spot with a blue center
surrounded by a black and then a yellow ring on each side of the sixth
abdominal segment.*257*
The sexes of mature crangonid shrimp are easily distinguished. Sexes of
shrimp can be separated at 22-24 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 blue-spotted shrimp can be found year-round on
California coasts.
Ovigerous blue-spotted shrimp are usually most abundant in nearshore coastal
areas, peaking in winter.*257*
Eggs hatch directly into late zoea-stage larvae, which swim dorsal sides up
and with abdomens hanging vertically.*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
Life History - 1 (DRAFT) - Life History
Species shrimp, blue-spotted
Species Id M070014
Date 26 AUG 96
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.
Juveniles of blue-spotted shrimp generally have abundance peaks in
spring but live in higher-salinity regions. Juvenile blue-spotted shrimp
are uncommon in coastal embayments because they prefer the higher-salinity
water offshore; they are rare in waters of <25 ppt salinity.*257*
MIGRATIONS:
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*
ADULTS: 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
has more than one brood.*257*
GROWTH: In all crangonids, males and females grow at different rates.
The maximum size of blue-spotted shrimp is believed to be 59 mm (male) and
64 mm (female).*257*
Offshore populations of crangonids may reach much larger lengths.
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 attributable to the physiological
effects of salinity, reduced food availability, or a combination of these
and other factors.*257*
Life History - 2 (DRAFT) - Life History
Species shrimp, blue-spotted
Species Id M070014
Date 26 AUG 96
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.*257*
MORTALITY: Annual abundance of crangonid shrimp varies widely. Annual
abundance indices for blue-spotted shrimp in San Francisco Bay varied by
more than tenfold 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
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.*257*
Life History - 3 (DRAFT) - Management Practices
Species shrimp, blue-spotted
Species Id M070014
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, blue-spotted
Species Id M070014
Date 26 AUG 96
References
References - 1