(DRAFT) - Taxonomy
Species spot
Species Id M010007
Date 26 AUG 96
TAXONOMY
NAME - spot
OTHER COMMON NAMES - spot, flat croaker, golden croaker, silver gudgeon, goody, Lafayette, chub, roach, Jimmy, oldwife, spot croaker, post croaker, chopa blanca, Norfolk spot and Cape May goody
ELEMENT CODE -
CATEGORY - Fish
PHYLUM AND SUBPHYLUM - Chordata,
CLASS AND SUBCLASS - Osteichthyes,
ORDER AND SUBORDER - Perciformes,
FAMILY AND SUBFAMILY - Sciaenidae,
GENUS AND SUBGENUS - Leiostomus,
SPECIES AND SSP - xanthurus,
SCIENTIFIC NAME - Leiostomus xanthurus
AUTHORITY - Lacepede 1803
TAXONOMY REFERENCES - *15*
COMMENTS ON TAXONOMY -
Other common names include flat croaker, golden croaker, silver gudgeon,
goody, Lafayette, chub, roach, Jimmy, oldwife, spot croaker, post croaker,
chopa blanca, Norfolk spot, Cape May goody (Dawson 1958).*15*
Taxonomy - 1 (DRAFT) - Status
Species spot
Species Id M010007
Date 26 AUG 96
STATUS
Coded Status
Sport Fish
Game (Consumptive Recreational)
Commercial
Commercial/consumption
See Comments
REFERENCES FOR STATUS - *15* and 136
COMMENTS ON STATUS -
The spot is one of the most abundant demersal fishes in coastal waters of
the South Atlantic Region, and is both commercially and recreationally
important.*15*
Spot are harvested by sport and commercial fisheries *136*.
Status - 1 (DRAFT) - Distribution
Species spot
Species Id M010007
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - AQUATIC
REFERENCES FOR HABITAT - 136
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine AB3 5
Estuarine AB3 4
REFERENCES FOR NWI - *151*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Gamefish
REFERENCES FOR SPECIES ASSOCIATIONS - 136
COMMENTS ON SPECIES ASSOCIATIONS -
Spot are preyed upon by large gamefish *136*.
Habitat Associations - 1 (DRAFT) - Food Habits
Species spot
Species Id M010007
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 15 and 136
LIFESTAGE FOOD FOOD PART
Larva See Comments; Food See Comments
Larva Microorganisms See Comments
Juvenile Invertebrate Cordates See Comments
Adult Invertebrate Cordates See Comments
Juvenile Polychaetes Not Specified
Juvenile Crustaceans Not Specified
Juvenile Ostracods Not Specified
Juvenile Copepods Not Specified
General Polychaetes Not Specified
REFERENCES FOR GENERAL FOOD - 15 and 136
REFERENCES FOR JUVENILE FOOD - 136
COMMENTS ON FOOD -
Because spot commonly live over muddy bottoms (Parker 1971) in or near
aquatic vegetation, sediment type is assumed to provide an index of food
availability. Since Weinstein (1979) was unable to correlate spot abundance
with percentage of organic matter in the sediments, the HSI model for spot
includes only mean sediment grain size as an index of food availability.
Sediment type rather than benthos abundance has been selected for ease and
rapidity of assessment. Studies throughout spot habitat indicate that food
organisms of the proper sizes usually are available. *151*
Approximately 93% of the summer diet consists of polychaetes; most of the
remainder is Macoma spp. Spot represent a signficant link in the transfer of
energy from the detritivores and primary consumers eaten by spot in the Bay
to its predators in the waters of the adjacent continental shelf *136*.
COMMENTS ON ADULT FOOD -
Adults are predators on infaunal and epibenthic invertebrates.
Plant material and detritus noted in stomachs of juvenile and adult spot
probably provide little nutritional value because spot lack cellulase
activity in their gut (Stickney and Shumway 1974). However, the microbial
flora associated with this material may provide some nutritive value
This material is probably ingested incidentally, as juveniles and adults
occasionally feed by scooping up or diving into the substrate.
The prey of adults in estuarine or coastal waters of the South Atlantic
Region has not been reported, but adult spot probably feed much as they do
in other areas. Chao and Musick (1977) reported that adult spot in
Chesapeake Bay were nocturnal predators on zooplankton, benthic infauna, and
epifauna. Organisms most frequently consumed were polychaetes (mostly
Pectinaria gouldii, Glycinde solitaria, Amphitrite spp., Nereis succinea,
Food Habits - 1 (DRAFT) - Food Habits
Species spot
Species Id M010007
Date 26 AUG 96
and Nepthys spp.), amphipods (Gammarus spp.), cumaceans, gastropods,
pelecypods, nematodes, the mysid Neomysis americana, and several copepods.
Livingston (1984) reported similar findings for two populations of spot in
the Gulf of Mexico.*15*
COMMENTS ON JUVENILE FOOD -
Juveniles are predators on infaunal and epibenthic invertebrates. The
transformation from post-larvae to juveniles (at about 25 mm SL) marks a
change from a sight-feeding planktivore to a partly olfactory-dependent
benthic feeder. The bodies of transforming postlarvae become deeper, their
mouths and eyes smaller, and their sensory appendages more developed (Chao
and Musick 1977). The diet of large postlarvae and small juveniles reflects
this change; small juveniles prey on insect larvae, polychaetes,
harpacticoid copepods, and other crustaceans.
Juveniles seemingly switch to nocturnal feeding shortly after transformation,
which may be a strategy for predation avoidance (Hodson et al. 1981b).
Recent evidence attributes some distribution patterns to differential
mortality due to size-selective predation (Polhar 1982). Another possible
explanation for nocturnal feeding may involve avoidance of high daytime
temperatures in shallow marsh areas (Hodson et al. 1981b). Finally, prey
availability may be much greater at night than during the day because many
invertebrate prey species are nocturnal.
Plant material and detritus noted in stomachs of juvenile and adult spot
probably provide little nutritional value because spot lack cellulase
activity in their gut (Stickney and Shumway 1974). However, the microbial
flora associated with this material may provide some nutritive value (Cammen
et al. 1978). This material is probably ingested incidentally, as juveniles
and adults occasionally feed by scooping up or diving into the substrate
(Roelofs 1954; Ckhao and Musick 1977).
Diets of larger juveniles are variable. Studies within the South Atlantic
Region (Stickney et al. 1975, Hodson et al. 1981b) showed no pattern in the
diet of spot, and similar findings have been reported in other areas
(Sheridan 1979). Regional differences in the diets are probably due to
differences in the availability of prey in the variety of habitiats in which
spot live.*15*
Juvenile spot primarily consume benthic invertebrates including: ostracods,
copepods, and polychaetes *136*.
COMMENTS ON LARVAE FOOD -
There have been no studies to date of the feeding habits of larval spot in
the South Atlantic Region, but general patterns may be inferred from studies
in the northern Gulf of Mexico (Govoni et al. 1983).*15*
Regional differences in the diets of larval spot appear to reflect
prevailing hydrographic conditions. Larvae collected near river mouths had
fed on taxa representative of more oceanic areas (Govoni et al. 1983).
Regardless of geographic area, major prey categories remained fairly
similar.
Food Habits - 2 (DRAFT) - Food Habits
Species spot
Species Id M010007
Date 26 AUG 96
The zooplankton of the South Atlantic Region sometimes shows tremendous
geographic variation (Bowman 1971), due in part to the periodic intrusion of
cold-water upwellings onto the continental shelf. The diets of larval spot,
therefore, probably vary according to geographic distribution of the
zooplankton. Differences in diets associated with upwellings may affect the
survival of larval spot; however, the larvae have relatively high
assimilation efficiences, and dependence on zooplankton patches appears to
be less than that of some other abundant fishes (Govoni et al. 1982, 1985).
Postlarval spot entering the estuary apparently feed much like larvae.
Early accounts showed that individuals up to 25 mm SL fed primarily on
planktonic copepods and ostracods (mostly Harpacticoids, Centropages spp.,
Temora spp., and Acartia spp.) in the Newport River estuary (Kjelson et al.
1975; Peters and Kjelson 1975), but feeding rates are highest in late
morning (Kjelson and Johnson 1976). Field and laboratory data have
indicated that the size of prey increases with the size of the postlarvae
(Kjelson and Johnson 1976).*15*
Food Habits - 3 (DRAFT) - Environment Associations
Species spot
Species Id M010007
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
E Water Temperature: Specified in Comments
L Water Temperature: Specified in Comments
J Water Temperature: Specified in Comments
A Water Temperature: Unknown
G
G Dissolved Oxygen: Specified in Comments
J Water Depth Preference: Specified in Comments
J
L Estuarine habitat zone: specified in comments
L
J Estuarine habitat zone: specified in comments
J Aquatic Features: Specified in Comments
J Inland Wetlands: Specified in Comments
J Inland Wetlands: Inland shallow fresh marshes
G Bottom Type [Aquatic]: Rooted aquatic vegetation
G Bottom Type [Aquatic]: Mud or silt
G Bottom Type [Aquatic]: Specified in Comments
A
G Water Temperature: Specified in Comments
A Bottom Type [Aquatic]: Specified in Comments
A Water Depth Preference: 10-25 ft.
A Water Depth Preference: Specified in Comments
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 15 and 136
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 136
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 136
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 136
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Spot occur throughout a wide range of physicochemical conditions; however,
relatively little is known about the effects of physicochemical conditions
on different stages of spot. In most studies, only the limits of tolerance
of a particular life stage to one or two environmental variables have been
determined; virtually nothing is known about interactive or chronic
effects.
Tolerance to thermal shock and other environmental extremes varies with
Environment Associations - 1 (DRAFT) - Environment Associations
Species spot
Species Id M010007
Date 26 AUG 96
developmental stage.
Hodson et al. (1981a) found that as acclimation temperature increased,
critical thermal maxima (CTM) of spot also increased. However, a
significant interaction effect was evident between temperature and
salinity, such that CTM values increased with decreased salinity at low
acclimation temperature (10 degrees C), but decreased with decreasing
salinity at high acclimation temperature (30 degrees C). Thus because
young spot are initially acclimated to cold ocean temperatures, the
decrease in salinity as they move into estuaries increases their CTM and
tolerance to higher temperatures that often occur there. In addition, spot
entrained in power plant cooling water may have an increased chance of
survival if that water is of low salinity (Hodson et al. 1981a).*15*
Although the metabolic rate of spot is relatively low, their oxygen
requirements (per unit body weight) may render them unfit to survive
hypoxia in shallow tidal pools.*15*
The spot is a demersal, marine spawning fish. Spot are commmon near grass
beds and over muddy substrates. Spot leave the Bay as water temperatures
decline in the fall. Fish in their second or third year of life do not
penetrate very far into the estuary, and are abundant only in the lower
Virginia portion of the Bay *136*.
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
In Chesapeake Bay, adults are found in mesohaline to polyhaline salinity
zones. Spot leave the Bay as water temperatures decline in the fall. Fish
in their second or third year of life do not penetrate very far into the
estuary, and are abundant only in the lower Virginia portion of the Bay.
Adult spot habitat in the Chesapeake is defined as mid-mesohaline to
polyhaline areas with depths to 6 m overlying soft sediment bottoms *136*.
COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
The spot is a demersal, marine spawning fish. Spawning activity on the
continental shelf adjacent to the Chesapeake Bay was reported to occur
during late fall and winter. Some adults may spawn twice a year. Adult spot
do not survive after they spawn *136*.
COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Juvenile spot spend much of their lives in estuaries. In the Maryland
portion of the Bay, spot juveniles congregate in the oligohaline zone,
although when population densities are high, some young move into tidal
freshwater, shallow marshes, and drainage ditches. In the lower Bay, young
juveniles are found in mesohaline and polyhaline tidal marshes *136*.
COMMENTS ON RESTING JUVENILE ENVIRONMENTAL ASSOC_ -
Early field observations suggested that juveniles may be more tolerant of
low temperatures than adults. However, the temperature tolerance of large
juvenile and adult spot is not known.
Burton (1979) reported that ventilation rates indicative of cold stress
occurred in juveniles held at 5 degrees C. The upper temperature tolerance
for small juvenile spot is about 35 degrees C, depending on the size of the
fish, its condition, and the acclimation temperature (Hodson et al.
Environment Associations - 2 (DRAFT) - Environment Associations
Species spot
Species Id M010007
Date 26 AUG 96
1981a).*15*
The tolerance of postlarval and juvenile spot to low oxygen concentrations
is intermediate in comparison with other estuarine species. Exposure of 90
mm TL spot to a dissolved oxygen concentration of 0.8 mg/l for 96 h at 27
degrees C resulted in 5% mortality; an oxygen concentration of 0.6 mg/l
resulted in 95% mortality. These results should not be interpreted as
indicating safe levels because the chronic effects of depressed oxygen
levels on growth and survival are unknown. Concentrations greater than
0.6-0.8 mg/l could be below the tolerance level under conditions of
increased activity, higher temperature, or other factors affecting
metabolism. Although the metabolic rate of spot is relatively low, their
oxygen requirements (per unit body weight) may render them unfit to survive
hypoxia in shallow tidal pools.*15*
COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Post-larval spot spend much of their lives in estuaries. Post-larval spot
inhabit Chesapeake Bay from early April through early November. In the
Maryland portion of the Bay, spot larvae congregate in the oligohaline
zone, although when population densities are high, some young move into
tidal freshwater, shallow marshes, and drainage ditches. In the lower Bay,
spot larvae are found in mesohaline and polyhaline tidal marshes *136*.
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Larvae can tolerate temperatures as low as 5 degrees C (Hettler and
Clements 1978). The rate of post-shock cooling also affected egg and
larval mortality; rapid cooling increased mortality. The upper temperature
tolerance for postlarval spot is about 35 degrees C.
Salinity may affect development of spot. Spot were reared successfully at
30-35 parts per thousand, and only minor differences were found (probably
temperature related) between laboratory-reared larvae and those collected
in the South Atlantic Region and the Gulf of Mexico. Low salinities do not
appear to be necessary for development and metamorphosis into juveniles;
however, the effects of salinity on survivorship of larvae and indirect
effects on later stages are not known. One study found that spot were more
active at a higher rate of salinity change (10 ppt/h) than at lower rates
(5 ppt/h, 1ppt/h) and suggested that spot may avoid areas with rapidly
changing salinity.*15*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Laboratory studies indicated that spot embryos do not develop at
temperatures below 14 degrees C. Tolerance of spot eggs to thermal shock
varies seasonally; the eggs are affected more by heat shock than are early
embryos and larvae (Hettler and Clements 1978). The rate of post-shock
cooling also affected egg mortality; rapid cooling increased mortality.*15*
Environment Associations - 3 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
LIFE HISTORY
PHYSICAL DESCRIPTION: The following general description of spot was
summarized from Johnson 1978. The body of the spot is rather deep and
compressed, with a strongly elevated back; the head is obtuse and short;
mouth is inferior and small, the maxillary extends posteriorly to about the
middle of the eye. The dorsal fin is continuous with a notch between the
anterior spinous portion (9-11 spines) and the posterior soft portion (29-35
rays); the anal fin has 2 spines and 12-13 rays. There are 72-77 lateral
line scales and 24-25 vertebrae. Spot are bluish-gray above and somewhat
golden below. They have 12-15 oblique dark streaks (these may be indistinct
in large specimens), a large black spot above the upper edge of the gill
cover, and fins are generally pale to yellowish. Adults are not likely to be
confused with other species of sciaenids, but juveniles superficially
resemble the juveniles of several other species, including the Atlantic
croaker, Micropogonias undulatus; the star drum, Stellifer lanceolatus; and
the silver perch, Bairdeilla chrysoura. The following characteristics
distinguish otherwise morphologically similar sciaenids from spot; the
Atlantic croaker has many barbels on the lower jaw and a strongly serrate
preopercle; the star drum has a strongly serrate preopercle, well-developed
dentition, and a lanceplate caudal fin; the silver perch has well-developed
dentition and a rounded caudal fin. Although eggs and larvae of most
sciaenids are not likely to occur with those of spot (Powles and Stender
1978), the eggs and larvae of silver seatrout, Cynoscion nothus, Equetus
spp., the banded drum, Larimus fasciatus, and the Atlantic croaker may
co-occur with spot. The eggs of most sciaenids have not been described, but
several characters are useful for distinguishing larval spot from other
species. The spot has fewer vertebrae (24-25) than the silver seatrout
(26-27), and for fish longer than 5 mm in standard length (SL), the spot has
fewer precaudal vertebrae (10) than any other species of Cynoscion. For
specimens at least 6 mm SL, spot have more anal fin pterygiophores (14-15)
than the banded drum (8-10); individuals shorter than 6 mm SL are not likely
to co-occur with small spot larvae. (Pterygiophores are the skeletal
elements of fin support.) The larvae of spot have fewer dorsal fin rays
(29-35) and more anal fin rays (12-13) than any of the described species of
Equetus (36-55 and 5-8 rays, respectively). AT about 4 mm SL, spot differ
from the Atlantic croaker only in pigmentation. The spot has a large
melanophore in the peritonuem anterior to the visceral mass between the
cleithra, a triangular or diamond-shaped pigment pattern on the ventral
abdomen, and continuous pigment row along the anal fin base. The
pigmentation differences between spot and Atlantic croaker are retained up
to about 20 mm SL. Larvae of spot differ from those of Atlantic croaker in a
number of other characteristics: 4.0 mm SL, the eye diameter of spot is
larger (>10% of SL); by 7.0 mm SL, spot have a shorter preanal length (<5%
of SL); by 20-30 mm SL in Atlantic croaker the mandibular barbels are
evident in some specimens, and by 50 mm SL they are present in all.*15*
REPRODUCTION: In the South Atlantic Region, spawning occurs from October to
March and peaks in December and January. This spawning period is later than
that in the Mid Atlantic Region and somewhat earlier than that in the
northern Gulf of Mexico, where spawning begins in December and peaks in
January and February. Spot typically migrate offshore to spawn in moderately
deep water along the South Atlantic Region. This behavior is similar to that
of the species in other parts of its range. A comparison of the frequency
Life History - 1 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
distributions of the lengths of spot larvae caught off Beaufort, North
Carolina, indicates that spawning occurs over the outer shelf throughout
most of the spawning season. Off North Carolina most spawning probably
occurs 75-90 km offshore. A limited amount of spawning has been documented
in inshore waters. Spawning apparently occurs at all latitudes throughout
the South Atlantic Region, at least as far south as Cape Canaveral, judging
from the occurrences of small larve. Spawning activity begins in fall, when
ripening adults collect off beaches and then begin to migrate southward
shortly before or during their offshore spawning migration. It was suggested
that spot migrating sourthward along South Carolina beaches were the primary
source of fish caught in the commercial haul-seine fishery. Spot from more
northern waters may use coastal waters of the South Atlantic Region during
winter as spawning or feeding grounds. Spot tagged in Chesapeake Bay and
Delaware Bay have been recaptured off North Carolina. There is little
published information on the fate of spot after they are spent. It was
suggested that few spot survive spawning; however, spent fish were
collected. After spawning, adult spot may remain offshore, but they are
rarely taken by bottom trawling in these areas. Although the spot spawns in
fall and winter, it appears to spawn only in relatively warm water. It was
reported that spot held in a laboratory spawned only at 17.5-25.0 Celsius.
collected young larvae (< 16 days old) only at water temperatures higher
than 19.3 Celsius. Larvae were collected in waters with surface temperatures
of 7.4-17.3 Celsius. The distributions of masses of warm water across the
continental shelf may affect the spawning locations of spot during the
course of the spawning season. There are no published accounts of the
fecundity of spot in the South Atlantic Region. In one study 77,000 and
84,000 potential ova in two females (unspecified size and state of maturity)
were found. It was reported that several different sizes of ova in ripening
spot and suggested that individual fish may spawn repeatedly over a period
of several weeks. The fecundity of spot in other parts of its range is also
poorly known.*15* BEHAVIOR: Eggs of the spot are pelagic. At 20 Celsius they
hatch in about 48 h and the yolk sac and oil globule are absorbed within the
next 5 days. There are no published accounts of the distribution of eggs
from any part of the spot's range. This lack of data is related to lack of
adequate taxonomic descriptions of eggs of spot and other sympatric species
of sciaenids. The larvae of spot are widely distributed along the South
Atlantic Region during late fall and early winter; however, the size
distribution and relative abundance vary across the continental shelf.
Although size generally increases (and relative abundance decreases) in
nearshore areas, small larvae have been collected in nearshore waters early
and late in the spawning season. The mechanisms by which spot larvae are
transported to estuarine nursery areas from the offshore spawning grounds
are not known; however, both active behavior and passive transport
mechanisms have been demonstrated in other species of fishes. Because the
eggs and larvae of spot are buoyant and usually near the surface of the
water, the offshore distributions of early life history stages may be
affected by Ekman transport, tides, and temperature. Wind-induced Ekman
transport may initially affect the abundance of larvae in offshore waters;
however, larvae become more demersal during later stages. As later larval
stages settle out of the upper water column, they probably become less
affected by Ekman transport and are more affected by other forces (inertia
and Coriolis) that occur at greater depths. The limited swimming ability of
small sciaenid larvae (0.25-1.0 m/s for brief periods;) suggests that spot
Life History - 2 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
larvae move into estuaries primarily by drifting. Larvae 10-24 mm SL first
appear in coastal estuaries in January, but movement into estuaries probably
peaks in February and March. Because of the extended spawning season, larval
and juvenile spot continue to enter many estuaries throughout the first half
of the calendar year. This prolonged spawning and recruitment period may
provide a buffering effect against unusual climatic conditions. It was found
that larvae and postlarvae (fish that have not completed metamorphosis to
the juvenile stage, and are still planktonic) entered North Carolina
estuaries at ages of 40-74 days (mean = 59 days). They observed little
within-sample variation in age, and hypothesized that spot entered the
estuary in somewhat distinct age cohorts. In addition, small individuals
arrived at the estuary near both the beginning and end of the recruitment
period; this occurrence probably is a result of nearshore spawning at both
the beginning and end of the spawning season or from more rapid transport
mechanisms at these times. Postlarval spot entering Chesapeake Bay appear to
be somewhat older than spot migrating into estuaries in North Carolina. This
observation provides additional evidence that populations in the Mid
Atlantic Region may use the South Atlantic Region for spawning. Temperature
may affect the ingress of larvae and postlarvae to estuaries; however, the
roles of temperature and other environmental factors are not well known.
Swimming speeds of spot larvae and juveniles have been positively correlated
with temperature. In addition, some early workers observed mass mortality of
spot during periods of low water temperatures (5-10 Celsius), although it
has been suggested that larvae and postlarvae may be more tolerant than
older fish to such temperatures. The relative importance of passive and
behaviorally mediated transport of larvae within estuaries is poorly
understood. Because peak recruitment for winter-spawned larvae in most
Atlantic coast estuaries occurs at a time when estuarine thermal
stratification and tidal exchange ratios are at a yearly maximum, active
migration and use of tidal water movements are believed important in the
dispersal of spot and other estuarine species. During migration in the Cape
Fear River (North Carolina) estuary, postlarval and juvenile spot occur in
the middle and lower layers of the water column during the day and
concentrate near the surface at night. This behavior may enable spot to use
tidal currents to augment their lateral movement into the shallow areas of
estuaries. In another study, it was found that abundance of small spot in
ichthyoplankton collections was much lower near the mouths of tidal creeks
than in areas closer to the headwaters in the Cape Fear estuary. Spot, thus,
appeared to congregate in the shallow-water portions of estuaries.
Unfortunately, behavioral mechanisms that augment movement in some estuaries
do not always apply in other estuaries having different hydrographic
characterisitics. Postlarval spot have been collected in large numbers
throughout estuaries and apparently are tolernat of a wide range of
physical, chemical, and biotic factors. Similar numbers of spot have
commonly been collected during the period of peak recruitment in estuarine
areas having very different physicochemical conditions. Some studies have
suggested that other habitat features such as substrate and sea grass beds
are important in determining the distribution of spot in localized areas.
Several investigators have studied the effects of river discharge
(especially high water conditions) on the recruitment of spot and estuarine
community structure. It was reported that, although postlarvae were absent
in sections of the main channel of the Cape Fear River during high water,
the fish recovered rather rapidly to pre-high water densities. The
Life History - 3 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
structural patterns of the shallow-water fish assemblages in the Cape Fear
River estuary were not affected by annual differences in river discharge. It
was concluded that recruitment of spot and other fishes may be inhibited
during discharge peaks of the Ogeechee River in Georgia, but that
upper-estuary nursery areas were used during high water. No correlation was
found between the abundance of spot and annual variation in river discharge
in Apalachicola Bay, Florida. Juvenile spot that have congregated in the
shallow water of tidal creeks tend to disperse as they increase in size;
this emigration into deeper waters after growth appears to occur throughout
estuaries, and results in the size-specific use of shallow estuarine
habitats Differences in gear bias, sampling methods, and experimental design
have probably contributed to reports that various size classes of spot are
ubiquitous in estuarine areas. Juvenile spot live in different habitats for
different periods of time. Tagged individuals remained in tidal creeks of
the York River estuary for an average of 91 days, and the population
remained there as long as 6 months. This observation suggests that the
exchange of juvenile spot between marsh habitats is relatively minor during
the first summer. In another study, Rozas and Hackney (1984) concluded that
the period of residency is much shorter in oligohaline marches of the Cape
Fear River. It is not known whether these differences are related to the
productivity or structural complexity of the habitat. Older fish may be
"tracking" their epibenthic and infaunal food supply in the estuary, or they
may be moving to avoid increased predation by wading birds and crabs in
shallow water (Weinstein and Brooks 1983). Large juveniles apparently move
into deeper portions of estuaries. Trawling in South Carolina (Shealy et al.
1974) and Georgia (Music 1974) resulted in the capture of large numbers of
advanced juveniles in late summer and fall. Young-of-the-year spot
overwinter in the deeper portions of most estuaries (Music 1974; Chao and
Musick 1977). Relatively little is known about the importance of
environmental factors, habitat features, and biological processes in
determining the distribution and movements of juveniles. The distribution
patterns of some estuarine fishes have recently been ascribed to differing
mortality rates in various parts of estuaries (Polgar 1982). Weinstein and
Walters (1981) suggested that a similar phenomenon may explain the
distribution of young spot in the Cape Fear estuary. Mortality was higher in
polyhaline tidal creeks than in less saline creeks due to the presence of
seasonally abundant marine predators.*15* LIMITING FACTORS: Tolerance to
thermal shock and other environmental extremes varies with developmental
stage. Laboratory studies indicated that spot embryos do not develop at
temperatures below 14 degrees C, but the larvae can tolerate temperatures as
low as 5 degrees C. Studies have found that ventilation rates indicative of
cold stress occurred in juveniles held at 5 degrees C. Tolerance of spot
eggs to thermal shock varies seasonally; the eggs are affected more by heat
shock than are early embryos and larvae. The rate of post-shock cooling also
affected egg and larval mortality; rapid cooling increased mortality.*15*
Early field observations suggested that juveniles may be more tolerant of
low temperatures than adults. "Cold shock" has been reported in larval fish
returned to acclimation temperatures following thermal shock. However, the
temperature tolerance of large juvenile and adult spot is not known. The
upper temperature tolerance and the thermal shock tolerance of early life
history stages also vary with acclimation temperature. As acclimation
temperatures increase, tolerance to heat shock decreases. The upper
temperature tolerance for postlarval and small juvenile spot is about 35
Life History - 4 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
degrees C, depending on the size of the fish, its condition, and the
acclimation temperature.*15* Salinity. Low salinities do not appear to be
necessary for development and metamophosis into juveniles; however, the
effects of salinity on survivorship of larvae and indirect effects on later
stages are not known. Researchers have found that spot were more active at a
higher rate of salinity change (10 ppt/h) than at lower rates (5 ppt/h, 1
ppt/h) and suggested that spot may avoid areas with rapidly changing
salinity.*15* Dissolved Oxygen. The chronic effects of depressed oxygen
levels on growth and survival are unknown. Concentrations greater than
0.6-0.8 mg/l could be below the tolerance level under conditions of
increased activity, higher temperature, or other factors affecting
metabolism. Although the metabolic rate of spot is relatively low, their
oxygen requirements (per unit body weight) may render them unfit to survive
hypoxia in shallow tidal pools.*15* Contaminants. Many pesticides,
herbicides, heavy metals, and chlorination by-products have been found to
have significant lethal or sublethal effects on all stages of the life
histoy of spot. Developing eggs and larvae may be especially sensitive to
environmental contaminants. Furthermore, because of their relatively long
residence period in a particular tidal creek and the adjacent marsh,
postlarval and juvenile stages may be repeatedly exposed to various
contaminants.*15* Spot have significantly slower swimming speeds than other
abundant estuarine fishes (Hettler 1979). Small spot (<2.7 cm SL) cannot
maintain their orientation in currents exceeding 15 cm/s (Rulifson 1977;
Hettler 1979). These low swimming speeds and endurance levels could result
in significant mortality of spot caught in intake structures at industrial
or power generating plants.*15* Predation and Parasitism. There is little
published information about predation on spot. Because of their abundance
and wide distribution they are probably preyed upon by a large number of
other fishes. Researchers have reported that silversides (Menidia spp.)
preyed heavily on postlarvae in estuaries; their data suggested that
]predation affects distribution patterns of postlarvae. Juvenile and adult
spot are eaten by many other fishes, including striped bass, Morone
saxatilis; silky shark, Carcharhinus falciformis; seatrout, Cynoscion spp.;
bluefish, Pomatomus saltatrix; mackerels, Scomberomorus spp.; longnose gar,
Lepisosteus ossues; and flounders, Paralichthys spp.. Few external parasites
of spot have been reported. The parasitic copepods Lernaeenicus radiatus and
Ergasilus lizae have been reported from spot collected off South Carolina
and in the Gulf of Mexico, respectively. The marine leech Myzobdella
lugubris has been reported from spot. The spot serves as host to many
different types of internal parasites, including a microsporidean,
Ichthyosporidium sp.; the monogenetic trematodes Tagis bairdiella,
Pedocotyle minima, and Diclidophora caudalis; the digenetic trematode
Aphanurus sp.; and the acanthocephalan Telosentis tenuicornis.*15* Growth
Characteristics: One study counted daily growth increments on otoliths
(sagitta) to determine the age and growth history of larvae and post-larvae
collected off Beaufort Inlet, North Carolina, during fall and winter. Growth
of young spot was biphasic; it was rapid in the ocean and appeared to
coincide with a winter peak of plankton productivity, slowed during the
early months of estuarine residence (until about April), and then
accelerated after metamorphosis of larvae to the juvenile stage, at lengths
of about 25 mm SL. No significant differences in growth rates between years
was found. Size-selective mortality seemed to favor survival of faster
growing larvae. The same researchers found that growth rates of postlarvae
Life History - 5 (DRAFT) - Life History
Species spot
Species Id M010007
Date 26 AUG 96
in the estuary were slow in late winter and early spring. Studies have found
that spot reach 115-130 mm SL in their first year of growth and 150-175 mm
SL in their second year. Growth rates show seasonal and annual variation.
Growth in young juveniles is rapid in late spring and early summer, but
juvenile and adult spot grow very slowly during winter. Ultimate sizes
achieved by spot at the end of a growning season may be comparatively small
if high temperatures reduce feeding and retard growth. Size and Age at
Maturity: The smallest size at which advanced gonadal development was
observed was 170-175 mm TL. Other researchers indicated that spot reach
sexual maturity at sizes of 185-210 mm TL. Males may mature at a slightly
smaller size. Most spot reach sexual maturity in 2 years; but some may
require 3 years. Some adults are captured in estuaries throughout the year.
Population Dynamics: Population levels of spot fluctuate tremendously; such
changes are typical of species with short life spans. Year-class strength is
probably determined during the larval and postlarval stages. Rates of
mortality in postlarval and juvenile spot vary among years and among
areas.*15*
SPAWNING AND RANGE: The spot is a demersal, marine spawning fish. Spawning
activity on the continental shelf adjacent to the Chesapeake Bay was
reported to occur during late fall and winter. Some adults may spawn twice
a year. Adult spot do not survive after they spawn. Post-larval and
juvenile spot spend much of their lives in estuaries. Post-larval spot
inhabit Chesapeake Bay from early April through early November. In the
Maryland portion of the Bay, spot larvae and young juveniles congregate in
the oligohaline zone, although when population densities are high, some
young move into tidal freshwater, shallow marshes, and drainage ditches. In
the lower Bay, spot larvae and young juveniles are found in mesohaline and
polyhaline tidal marshes. Spot are commmon near grass beds and over muddy
substrates. In Chesapeake Bay, adults are found in mesohaline to polyhaline
salinity zones. Spot leave the Bay as water temperatures decline in the
fall. Fish in their second or third year of life do not penetrate very far
into the estuary, and are abundant only in the lower Virginia portion of the
Bay. Adult spot habitat in the Chesapeake is defined as mid-mesohaline to
polyhaline areas with depths to 6 m overlying soft sediment bottoms *136*.
LIFE HISTORY CODES -
Hybrid
Reintroduced Native
Stocked
Number of Broods/Litters (Reproductive Efforts) Per Ye
REFERENCES FOR LIFE HISTORY- 15 and 136
Life History - 6 (DRAFT) - Management Practices
Species spot
Species Id M010007
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Existing Other management practices [specified in comments]
Beneficial Controlling pollution [thermal, chemical, physical]
Beneficial Changing tidal cycle/ current patterns
Adverse Applying herbicides
Adverse Salinity alteration
Adverse Applying other toxicants
Adverse Applying pesticides
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 15
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 15
REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 15
COMMENTS ON MANAGEMENT PRACTICES -
There are no current state or federal restrictions on the commercial or
recreational catch of spot *15*.
Spot have significantly slower swimming speeds than other abundant estuarine
fishes (Hettler 1979). Small spot (<2.7 cm SL) cannot maintain their
orientation in currents exceeding 15 cm/s (Rulifson 1977; Hettler 1979).
These low swimming speeds and endurance levels could result in significant
mortality of spot caught in intake structures at industrial or power
generating plants.*15*
Swimming and orientation behavior of spot vary with size. Spot <5cm SL
orient into weak currents (<15 cm/s), whereas larger spot drift with them.
Thus, despite their increased swimming capabilities, the larger spot are
also vulnerable to impingement on intake structures (Rulifson 1977).
Alterations in the design or careful placement of intake structures may
reduce impingment and entrainment of spot.*15*
Commercial catch of spot has fluctuated widely since 1939 and was too
sporadic to support a well-developed fishery in most states along the
Atlantic seaboard. The commercial catch has been consistently high only in
the Carolinas and Virginia, where nearly 75% of the total annual catch is
made.
Spot are taken in large numbers in fall by haul-seine fishermen along the
beaches of North and South Carolina. Catches consist predominantly of
maturing adults that are beginnning to migrate offshore to spawn. Spot are
also taken by shrimp trawlers, but the fish are usually small and useful
only for pet food or fish meal; sometimes they are discarded. Spot are
sought by sport fishermen because they take bait readily and can be caught
near bridges, piers, and wharves. Small-scale commercial gillnetters also
catch substantial numbers of spot in fall in South Carolina.
Management Practices - 1 (DRAFT) - References
Species spot
Species Id M010007
Date 26 AUG 96
References
15* Hales, L., M. Van Den Avyle. 1989. Species Profiles: Life
Histories and Environmental Requirements of Coastal Fishes and
Invertebrates (South Atlantic)--Spot. U.S. Fish and Wildlife
Service Biol. Rep. 82(11.91) pp 24.
136 * Chesapeake Bay Program. 1988. Habitat Requirements for
Chesapeake Bay Living Resources. Chesapeake Executive
Council pp 86.
151* Stickney, R. R., M. L. Cuenco. 1982. Habitat Suitability Index
Models: Juvenile Spot. U.S. Fish and Wildlife Service Biol. Rep.
82(10.20) pp 12.
References - 1