5.0
Fisheries Studies in the Lower Cape Fear River System,
June
2002 - June 2003
Center
for Marine Science
University of North Carolina at Wilmington
5.1
Introduction
The sampling period June 2002-June 2003 represented the
sixth consecutive year of a comprehensive survey of fish populations in the
lower portion of the Cape Fear River basin.
This project represents one component of the University of North Carolina
at Wilmington’s Lower Cape Fear River Program. The
fisheries component has focused on obtaining baseline data on fish community
structure, seasonal and spatial trends in abundance, disease incidence, and
non-native fish populations. This
monitoring program has also provided valuable data on the response of fish
populations to hurricanes. Immediately
prior to the first year of sampling, Hurricanes Bertha and Fran made landfall
over the Cape Fear River basin. We
were able to document impacts to, and short-term recovery of, the fish community
following these events in the spring and summer of 1997 (Mallin et al. 1997;
1998). The landfall of Hurricanes
Bonnie in August 1998 and Floyd in September 1999 provided additional
opportunities to examine the immediate effects of these large-scale disturbances
on fish community structure, this time with the benefit of baseline data
collected before the storms. The lack of hurricanes during the 2000, 2001, and
2002 sampling periods gave us the opportunity to begin documenting the long-term
effects and potential recoveries of fish communities after these large-scale
disturbances. Throughout the
2001/2002 year of sampling, the Cape Fear River basin experienced a prolonged
and severe drought. This event has
provided the opportunity to investigate potential impacts of drought conditions
on the fish community in the lower Cape Fear River system. Large rain events in
the spring of 2003 resulted in a recovery from the drought and gave us the
opportunity to document drought recovery changes in the fish community (Figure
5-56). The specific objectives of this year's study were to document seasonal
and spatial patterns in 1) fish species composition, 2) fish abundance, 3) fish
disease incidence, and 4) non-native fish populations.
Our objectives also included studying the long-term effects of prior
hurricanes on fishes of both the Cape Fear and Northeast Cape Fear Rivers.
We will also be documenting changes in fish community structure within
our sampling area due to the drought of 2002 and the recovery from the drought
in 2003. We used three gear types,
gillnets, trawls, and a boat electroshocker, to sample a broad segment of the
fish population. The fisheries
monitoring component remains a cooperative effort between the Lower Cape Fear
River Program (Dr. Thomas Lankford and Michael Williams, gillnets and
electroshocking), and the North Carolina Division of Marine Fisheries (NCDMF,
Wilmington office, trawl).
5.2
Methods
Study
Sites
Fish monitoring was conducted at each of nine fixed
sites in tidal regions of the lower watershed (Figure 5-57).
Five sites were selected in the Cape Fear River mainstem: approximately
1.5 km above the NC11 bridge (NC11 = H11), the lower limb of the oxbow
downstream from Sykes landing near Acme (AC = WL), the mouth of the Black River
below Lyon Thoroughfare (BBT = BLK), and the mouth of Indian Creek (IC). One
site was selected in the Brunswick River between the Belleville boat ramp and
the Highway 74/76 bridge (BRR). The
remaining locations were in the Northeast Cape Fear River: approximately 2 km
downstream of the NC117 bridge at Castle Hayne (NCF117 = 117), opposite the
Hoechst Celanese dock (NCF6 = GE), at the mouth of Smith Creek (Smith = SMT),
and in Horseshoe Bend (HB). Each
site was located near a water quality monitoring station.
Gillnets
Gillnets were used to sample large resident and
anadromous species that are less susceptible to electroshock and trawl
collection. Sinking, 50-meter, 5 ½
inch stretch, monofilament nets were deployed perpendicular to the current to
sample the lower half of the water column on the shoreline.
At the Horseshoe Bend and Smith Creek sites, 30-meter nets were used due
to the channel being too narrow at these locations is too narrow to set longer
nets. In each sampling month the
nets were set over a three-day period. This
resulted in two 24-hour soak times at each station, and allowed sampling both
during the day and night. After the
first 24-hour soak period, the nets were checked and redeployed to reduce fish
mortality. Due to the high
incidence of fish mortality in summer, soak times were reduced to less than four
hours during months that water temperatures exceeded 21oC.
Catches were standardized to reflect a 24-hour set in our
catch-per-unit-effort calculations to compensate for the reduced soak time.
All fish captured were identified, measured (nearest mm total length) and
examined for external evidence of disease (i.e. ulcerations, lesions, fin rot,
structural deformities, etc.). All
fish were released at the sampling site. The
number of species collected, catch per unit effort (CPUE = number fish caught
/24 hour/50 meter net), % diseased fish (number of diseased fish divided by the
total catch), and % non-native fish (number of non-native fish divided by the
total catch) was determined for each site during each sampling month.
Trawl
North Carolina Division of Marine Fisheries (NCDMF)
personnel conducted monthly trawl sampling at each station following primary
nursery trawl sampling protocol. This
sampling method targets small, bottom-oriented fishes that are generally not
collected with either of the other sampling methods.
For each sample, a 3.2 meter flat otter trawl with 0.64 cm mesh in the
body, a 0.32 cm mesh bag, and a tickler chain was towed with the current for one
minute. All fish were identified,
measured (nearest mm total length, TL), examined for external evidence of
disease, and released at the study site. The
number of species collected, catch per unit effort (CPUE = number of fish /
tow), % diseased fish (number diseased fish / total catch), and % non-native
fish (number of non-native fish divided by the total catch) were determined for
each site and sampling month.
Boat
electroshocker
We conducted boat-electroshocking surveys monthly at 8
of the 9 sampling locations (water conductivity at the Brunswick River site is
typically too high to permit electroshocking).
This technique targets shoreline oriented species that are difficult to
capture with trawls or gillnets. We
used a 7500-watt electrofishing system with an 18-dropper array from an aluminum
boat. At each site, a 183-meter
reach was sampled by making a pass along each shoreline, standardizing to a
power output of 5000 watts. All
stunned fish were captured using a dip net and placed in an aerated holding tank
until one side of the reach had been sampled.
Fish were then released down current of the sampling area and the
remaining side not shocked was then sampled.
Fish were identified, measured (nearest mm total length, TL), examined
for external evidence of disease (e.g., ulcers, lesions, fin rot, structural
deformities, etc.) and released at the sampling site.
The number of species collected, catch-per-unit-effort (CPUE = number of
fish / 183 m reach), % diseased fish (number of
diseased fish divided by total catch), and % non-native fish (number of
non-native fish divided by the total catch) was determined for each site and
sampling month.
A mechanical failure of the electroshocking boat generator in mid-October
of 2001 prevented electrofishing and necessitated the purchase and assembly of a
new boat and generator. Consequently,
the months of October 2001 to July 2002 were not sampled with this gear.
A new electroshocking boat and generator were obtained and electrofishing
was resumed in July 2002.
5.3
Results and Discussion
Community-Level
Species
Richness
Species richness is an important indicator of aquatic ecosystem health. The presence of many different species in a system generally indicates a healthy fish community with high productivity and resource availability. Declines in species richness may signal declines in ecosystem health due to the deterioration of water quality or biotic interactions such as predation, competition or disease. Because 1997 was a non-hurricane year, we were able to collect all twelve months of sampling data. In this year a seasonal pattern in species richness and abundance was documented (Mallin et al 1999). In general species richness tends to be higher in summer and fall than in spring and winter in the electroshocking surveys. Although this trend has been apparent every year since 1997, there has been a long-term decline in species richness in the samples obtained using this gear. The trend line shows the gradual decline of over 23% (Figure 5-44). Lack of funding caused a loss of data January through July 2000 and October through June of 2001. Both data gaps happened during the winter/spring seasons, which typically have lower species abundance. Therefore, this trend toward a decline becomes a cause for concern considering the trend line would show an even further decline if the lost data from the months not sampled had been incorporated into the analysis.
Species
richness in the trawling samples has remained fairly constant since 1997. The trend line shows a slight increase. Species richness tends to be lower during the spring/summer
months in the trawling survey just as it is in the electroshocking survey.
The data gap from January to July in 2000 would likely have lowered the
end of the trend line and show less of an increase.
It is noteworthy that the drought between May and August of 2002 also
showed the highest number of species captured in the trawling survey since 1997.
Only five of the sixty-four months of sampling before the drought
captured 18 or more species. June,
July, and August of the 2002 drought documented a catch of 19, 20, and 21
species respectively (Figure 5-45). During
a drought, low freshwater river flow allows the salt wedge to move further
upstream into normally freshwater habitat.
This creates a more estuarine habitat in our sampling area, allowing more
estuarine oriented species to utilize the area.
It should be emphasized again that the lower Cape Fear River system is an
important habitat for marine fishes, and particularly juvenile marine fishes.
The functional value of Cape Fear River nursery habitat depends largely
on its ability to provide biotic and abiotic conditions that are suitable for
growth and survival of juvenile fishes. Because
many resource species utilize the Cape Fear River system as a juvenile nursery,
it is important that environmental conditions be monitored closely and that
these habitats receive protection from anthropogenic or other impacts that
compromise their suitability as habitat.
Gillnetting
species richness has been highly variable.
Catches are still dominated by non-natives.
A difference in richness was documented between the low flow
winter/spring season of 2001 and the high flow winter/spring season of 2002.
This is contrary to species richness decreases documented after high flow
events in the spring flood of 1998 and the hurricane flood of 1999 (Figure
5-46). Future surveys should focus
on what influences species richness during flood and non-flood events.
Abundance
Catch-per-unit-effort
in electroshocking samples went up sharply in the 2001 samples.
Other than this increase, electroshocking CPUE has declined every year
since 1997 (Figure 5-47). No
seasonal trends have been documented.
The
trawling CPUE trend line shows an increase.
This increase was driven by unprecedented catches of Atlantic croaker,
spot, southern flounder and hogchokers during the springs of 2001 and 2002.
The 2003 spring trawling CPUE is well above the 1997-1999 spring seasons
but over 50% less than the 2001 spring season (5-48).
Observation of flow rates during this time of year do not suggest a
correlation between flow rate and the above average trawling catches (Figure
5-56).
Gillnetting
catch-per-unit-effort trends remain relatively constant since 1997 (Figure
5-49). The trend line shows an
increase due to the exceptionally large catches of blue catfish during June and
July of 2002. An effort of only 1.5
net days in June captured 31 blue catfish along with 7 other fish, and in July
2.1 net days netted 24 blue catfish and 18 other fish.
It appears the drought of 2002 increased blue catfish
catch-per-unit-effort. It will be
important in future surveys to investigate whether the drought caused the
increase in CPUE or if there were actually more blue catfish in our sampling
area. Catch-per-unit-effort is used
to indicate a population size. If
environmental conditions are affecting non-native fishes susceptibility to
gillnets, however, then the data may show a change in population size when
environmental conditions actually caused the change. Whether the low flows caused the catfish to become more
susceptible to gillnets or more catfish were in the area, future surveys should
investigate how droughts affect the catch of blue catfish in the Cape Fear
River.
Disease
Whether from exposure to toxicants, environmental stressors, or resource limitation, high infection rates in a fish community indicate a deterioration of ecosystem health and function. Fishes captured in this survey that exhibit external signs of disease are closely examined. The capture site, the anatomical sites of diseases, and a description of the diseases are documented for each specimen. Disease percentages in the electroshocking samples have been highly variable since 1997. No seasonal or spatial patterns have been observed. Although there are data gaps for the periods January-July 2000 and November-June 2002, the long-term data suggest a decline in overall disease incidence (Figure 5-50). In fact, the July 2002-June 2003 season had the lowest disease incidence of any season other then the July-June 2000 season (for which six months of data were missing. For the current year, species with the highest disease percentage were bowfin (34%), striped bass (25%) and largemouth bass (10.6%).
The trawling survey typically captures small, young fishes which are difficult to observe for the small lesions and/or ulcerations that we use to document external signs of disease in this program. This is likely the reason that of the >50,000 fishes captured in the trawling survey, only two fish have been documented to have external signs of disease (Figure 5-51). For this reason, the trawling data are not considered to be a good indicator of disease percentages.
The gillnet
data showed a decline in disease percentage.
The trend line showed over a 50% drop from January of1997 to June of 2003
(Figure 5-52). The decline in the
percentage of diseased Bowfin was a major contributor to the drop in the overall
disease percentage. Of the 18
bowfin captured in the gillnets during the period June 2002-June 2003, none
showed external signs of disease. The
two species captured in gillnets with external signs of disease were striped
bass (7.8 %) and blue catfish (1.9%).
Non-natives
Trend lines for percent
non-native species captured in the electroshocking survey increased slightly
since 1997. Higher than average
catches in the fall of 2000, spring of 2001, and spring of 2003 caused the
increase in the trend line (Figure 5-53). Large catches of redear sunfish, common carp and blue catfish
led to the sharp increase of percent non-native during the 2002/2003 season.
Trawling trends show little
change in non-native percentages. Large catches of blue and channel catfish in the winter of
1997 and spring of 1998 have skewed the trend line to show a decreasing
non-native percentage in the most recent years of sampling (Figure 5-54).
The non-native catches are driven by blue catfish, channel catfish, and
redear sunfish.
Although
the gillnetting catch percentage continues to vary widely (0-100%) there is a
slight trend toward an increasing non-native percentage (Figure 5-55).
Catches continue to be dominated by blue catfish, flathead catfish, and
common carp. When all the samples
are combined from January 1997 to June 2003, the non-native percentage of
resident fish is just over 56%. Blue
catfish continue to dominate the gillnet catch (64%) as-well-as the non-native
gillnet catch (37%).
Non-natives
are species that have been introduced, either intentionally or by accident, to
systems and do not naturally occur there. Non-natives
often prey on and compete with native species for resources.
They are often tolerant of a wide range of environmental conditions and
may have fewer natural predators than native species.
This gives non-natives a competitive advantage that can lead to the
population suppression or extirpation of more desirable native species.
Dr. Mary Moser, for example, documented the extirpation of native catfish
from the Cape Fear River system by the non-native blue (Ictalurus
furcatus), flathead (Pylodictis
olivaris), and channel (Ictalurus
punctatus) catfishes (Moser and Roberts 1999).
The lower Cape Fear River Program has captured
just 3 native catfish since 1997 compared to >2,000 non-native catfishes.
Flathead catfish are
piscivorous at age 1 and are known to consume largemouth bass, catfish and
sunfishes (Ashley and Buff 1987, Hackney, P. A. 1965).
The state record blue catfish is 80 pounds, the state record flathead
catfish is 69 pounds and the state record channel catfish is 40 pounds.
In contrast the largest of the native catfish species reaches just 13
pounds. The large body sizes and
high abundance of these non-native catfishes are likely having dramatic impacts
on the native fish community.
Grass carp (Ctenopharyngodon
idella) are another non-native species of concern.
Grass carp have reached sizes of over 60 pounds in this state.
They are herbivores and have been introduced to reservoirs and ponds
throughout the Cape Fear River basin to control aquatic vegetation.
When they are introduced to the Cape Fear by flooding events, however,
they consume aquatic vegetation that functions in controlling erosion and as
nursery habitat for juvenile fishes. The
state of North Carolina recognized the potentially destructive habits of this
species and requires that all grass carp be certified as triploid before they
can be introduced to ponds and reservoirs. A study in the Chesapeake Bay found
that although stocking of non-sterile grass carp has been illegal since 1979,
18% of the feral grass carp collected in Chesapeake Bay tributaries were not
triploid. The researchers
speculated that the non-triploid carp originated from illegal stocking efforts
or had been introduced them before the regulations were put into place (Schultz
et. al. 2001). If a mistake has
been made and 100% of the grass carp introduced were not sterile, then there
could be a reproducing population of grass carp in the Cape Fear. If conditions
are favorable, it takes only a few individuals to populate a river system.
An example would be the flathead catfish.
Eleven individuals were introduced in 1966 and they are now one of the
dominant predators in the Cape Fear River system.
A reproducing population of non-native grass carp could thus severely
impact our fisheries resources (Raibley et al. 1995). Catch data provided from this program continues to document
low numbers of grass carp in the Lower Cape Fear River. It is also noteworthy that all individuals captured have been
between 633 mm (24 inches) and 1097 mm (43 inches). Captures of smaller sizes of grass carp (ie. <150mm / 6
inches) may indicate reproduction within the river system.
Due to the observations of low catch numbers (six between June 2002 and
June 2003) and size classes larger than that expected from the young-of-the-year
size class, there is no data to document grass carp reproduction in the lower
Cape Fear River. Future surveys should continue to document the sizes and
numbers of grass carp captured so that if reproduction becomes likely, then
appropriate management plans can be initiated.
Trends in Abundance of Important Species
American
Shad
Throughout the history of settlement on the Cape Fear
River, the spring spawning run of the American shad (Alosa
sapidissima) has supported a very important commercial and recreational
fishery. Commercial landings of
this species have shown a gradual decline since the early 1970's, indicating a
decrease in their population size. To
stem any further decline in their numbers, the North Carolina Division of Marine
Fisheries enacted a Fisheries Management Plan for the American shad.
In 1998 an amendment to the Interstate Management Plan for American Shad
included a phase out of the offshore shad fishery over a five-year period
beginning in 1999. American shad migrate from Canada to Florida.
The offshore fishery intercepts shad that are migrating south to spawn in
the rivers and streams they originated from.
If North Carolina shad are being captured in Massachusetts, resource
managers here cannot regulate the shad fishery properly.
With the offshore phase out, the Cape Fear River shad fishery will become
even more important. Catch-Per-Unit-Effort
data have shown large fluctuations over the six seasons of sampling, but no
distinct trends have been observed. This
spring’s flow rates were the second highest recorded since 1997 and had the
third largest catch-per-unit-effort of American shad.
Last spring, however, had the lowest flow observed during this survey and
the highest April CPUE of the survey. Thus,
our data do not indicate a strong relationship between river flow during spring
months and the abundance of adult American Shad (Figure 5-20).
Atlantic
Sturgeon
Historically, North Carolina supported a large sturgeon
fishery. Due to overfishing,
habitat degradation, and dam construction, the Atlantic sturgeon (Acipenser
oxyrhynchus) is currently classified as a threatened species in North
Carolina and their possession has been banned since 1991. The shortnose sturgeon
(Acipenser brevirostrum) also occurs
in this drainage (Moser and Ross 1995) and has undergone such a dramatic
population decline that it has been federally listed as a endangered species.
Both species of sturgeon can live over 60 years.
While the shortnose reaches it's maximum size at around 100 cm (3.33
feet) the Atlantic sturgeon can attain sizes exceeding 300 cm (9.8 feet) and 270
kg (>600 pounds). Sturgeon are harvested for the meat, insinglass made from
the swim bladders, emulsifiers and thickeners from the cartilagenous backbone,
leather products made from their thick skin, and most importantly, the roe,
which can be made into high quality caviar (Williams and Moser 1999). With
American sturgeon caviar currently selling for $192.00 a pound and smoked
sturgeon selling for $14.00 a pound, overfishing can quickly become a problem.
Recent catches of ripe sturgeon during the spring spawning season and the
regular catches of juveniles in this survey indicate a reproducing population in
this drainage. Although previous years have documented relatively similar
catch-per-unit-efforts, the summer of 2002 yielded twice the CPUE of any season
since 1997. This also happens to be
the lowest flow conditions experienced during this survey.
Although catch-per-unit-effort increased greatly during these low flows
conditions, previous years with low flow summers did not have the same resulting
increases in CPUE. Future surveys should investigate river flow and other
environmental conditions that may impact the Atlantic sturgeon’s use of the
Lower Cape Fear River (Figure 5-21).
Blue
Catfish
The blue catfish (Ictalurus
furcatus) was introduced to the Cape Fear River by the Wildlife Resources
Commission in the attempt to create a trophy fishery (Moser and Roberts 1998). Although blue catfish were uncommon in the 1970's, they are
currently the most abundant species captured in our gillnet survey (Mallin et.
al. 1998,1999,2000,2001,2002). The
success of the blue catfish in the Cape Fear River system is likely due to its
generalist feeding behavior. Gut
content analyses have shown this species to feed on a wide range of prey
including snakes, birds, fish, shrimp, worms, eels, grapes, other fish, and
suprisingly clams. Over 75% of the
stomachs examined contained an Asian fresh water clam (Corbicula fluminia) that was introduced by a bilge discharge in the
Wilmington harbor in 1975 (Williams and Moser, in prep). Although
thought to have aided in the demise of our native catfish population through
competition, blue catfish are a popular sport fish and support a small
commercial fishery in the Cape Fear River.
Blue Catfish CPUE in the trawling survey continue to be highly variable,
but maintain a trend that doesn’t increase or decrease to any appreciable
degree. Blue catfish gillnetting
CPUE, however, increased last summer during the drought to over four times
higher than previously documented by this survey.
This species continues to be the dominant catch in the gillnet survey,
comprising thirty-seven percent of the total catch and sixty-four percent of the
non-native catch. Catch-Per-Unit-Effort
shows a slight increase in the trawling trend lines.
This is due to an extremely large catch of blue catfish in March of 2003
(Figure 5-24). It is interesting to
note that there was a large catch of adults during June and July of 2002 and a
large catch of juveniles in March and April of 2003.
Future surveys should investigate if large summer catches of adults can
lead to increases in juvenile abundance the following spring.
Bowfin
Although much maligned by many fisherman, bowfin (Amia
calva) are an important predator in the Cape Fear River system (Mallin et.
al. 1998,1999,2000). This native
species not only assists in keeping the forage base balanced, it can be used as
a valuable indicator of the quality of water that it inhabits. This species can
use a modified swim bladder to absorb oxygen from the air (Guier, et al 1994).
This permits bowfin to utilize hypoxic areas in the water where other
predators are excluded. Although
disease incidence is still high (>25%), this seasons sample showed one of the
lowest disease percentages documented by the survey.
A high incidence of diseased bowfin may indicate poor water quality. The
most common external sign of disease was termed scale hemorrhage. The term was used to describe areas on the fish where
multiple scales were missing and the underlying skin appeared red or inflamed.
Investigations into the cause of these infections may shed light on
potential bioaccumulation of toxins by this species or attacks by toxic alga in
the Cape Fear River system. Catch-per-unit-effort
increased slightly in the gillnetting samples but dropped impressively in the
electroshocking samples since 1997. Throughout
this survey, bowfin exhibited the highest infection rate of any species
captured. Drops in abundance
coupled with drops in disease percentages may indicate a problem.
It may be that exposure to toxicants, environmental stressors, resource
limitation, or unknown sources for their high infection rates are reaching
critical levels and the infected individuals are being eliminated from the
population. Future surveys should focus on the decreases in CPUE of bowfin
(Figure 5-26).
Channel
catfish
Channel
catfish were introduced into the Cape Fear in the early 1900's (Smith 1907).
A small but stable population was established that persisted through the
1970's. In recent years, however,
this species has shown "reductions in relative abundance since the
introduction of the blue and flathead catfishes."(Moser and Roberts 1998).
The decline is likely due to competition with blue catfish.
This survey shows no significant trends in catch-per-unit-effort but did
have the highest gillnetting CPUE of the survey in July of 2002 and a trawling
catch that was four times higher than any channel catfish CPUE since 1997.
As with the blue catfish, there was a large catch of adults in the summer
of 2002 and a large catch of juveniles in the winter/spring of 2003.
Future surveys should investigate if large summer catches of adults can
lead to increases in juvenile abundance the following spring.
(Figure 5-28).
Atlantic
croaker and spot
In 2000 there were over 2.8 million pounds of spot (Leiostomus xanthurus) and over 10 million pounds of Atlantic croaker (Micropogias
undulatus) sold in North Carolina. As
with many marine species, croaker and
spot spawn offshore and their larvae migrate into estuarine nursery habitat
(Norcross 1991). The Cape
Fear River system is used as nursery habitat by these species (Mallin et. al.
1998,1999,2000,2001). Catch-per-unit-effort
can exceed hundreds per trip. Atlantic
croaker populations can fluctuate widely, and have shown this pattern in the
Cape Fear. In 1998 croaker had a statistically significant higher
catch-per-unit-effort in our fall samples, but no other changes have been
documented (Figure 29). Spot showed
no major fluctuations in abundance until the spring of 2001 when
catch-per-unit-effort was 10 times higher than previously documented by this
survey. The spring of 2002 showed a
seventeen-percent larger CPUE than the 2001 catch. Both of these species are important to recreational and
commercial fisheries here in North Carolina.
It is important that water quality and aquatic vegetation be protected in
the Cape Fear. This way the
critical nursery habitat is available and important commercial fisheries are not
negatively affected (Figure 5-38).
Flathead
catfish
In 1966 the North Carolina Wildlife Resources
Commission introduced the flathead catfish (Pylodictis
olivaris) to the Cape Fear River in an attempt to create a trophy fishery
(Moser and Roberts 1998). Within
15 years of their introduction, the flathead catfish was found to be the most
abundant catfish by weight and considered to be the new dominant predator in the
Cape Fear (Guier et. al. 1981). Guier's
study in the late 1970's showed that fish (99.4% by weight ) were the principle
prey of P. olivaris. Catfishes
were the dominant fish found in the flathead's diet (Guier et al. 1981, Ashley
et al. 1989). This is a strong
indication that the introduction of this species has led to the severe decline
of our native catfish populations.
The lower Cape Fear River Program has captured
3 native catfish since 1997 compared to over two-thousand non-native catfishes.
Thus less than 0.1% of our catfish captures are native species.
Future studies should reexamine the diet of flatheads to determine which
prey species are currently being exploited as a food source.
When all samples from this program are combined there is a slight trend
toward an increasing CPUE but no significant patterns have been observed.
(Figure 5-30).
Hybrid-striped
bass
Hybrid striped bass are a hybrid of striped bass (Morone
saxatalis) and white bass (Morone
chrysops). They have been
stocked as a put and take fishery in Lake Jordon nearly every year since 1983.
The hybrids are introduced to the Cape Fear River by flooding events.
Through competition, hybrids utilize the resources normally available to
striped bass (Patrick and Moser 2001). Hybrids do not reproduce and so the
resources they keep from striped are not converted into reproduction.
As a result of competition with hybrids, striped bass may not be as
healthy and in turn, not produce as many juveniles.
Tag and recapture data from studies conducted in this drainage suggested
that hybrids conduct a spawning run with true striped bass as has been
documented in other systems (Patrick and Moser 2001).
Due to competition with true striped bass for food resources and spawning
habitat, hybrid striped bass are likely having a negative impact on the striped
bass population in the Cape Fear River system.
While commercial landings of striped bass in North Carolina have shown a
gradual increase since 1990, landings in the Cape Fear System remain low and
this is the only river in North Carolina that stocks hybrid striped bass.
Although the hybrid striped bass population appeared to have decreased
since 1997, we have had an increase in the fall of 2002.
(Figure 5-34). Due to gradual decreases in CPUE during non-hurricane years,
it was suggested in last years report that individuals were likely introduced to
the lower Cape Fear River system by flooding events upstream.
The increase in the fall CPUE of 2002 however, followed a severe drought
during the summer of 2002. Future surveys should focus on the conditions that impact the
population size of hybrid striped bass in the Lower Cape Fear River system.
Longnose
gar
Longnose gar (Lepisosteus
osseus) are freshwater piscivores that can reach six feet in length and
weigh over fifty pounds. These predators not only consume game fishes but also
compete with more desirable species such as striped and largemouth bass.
This makes these non-game fish unpopular with local fisherman.
This species can tolerate a wide range of environmental conditions. Although the gar captured in this survey showed a high
occurrence of wounds, probably from motorboat propellers, no fish exhibited
external signs of disease. Knowing
their relative population levels allows us to track their potential impact on
other fish populations. There has
been a trend toward lower a lower catch-per-unit-effort but no patterns have
been documented in the electroshocking or gillnet surveys (Figure 5-36).
Southern flounder
The flounder fishery is the most lucrative finfish
fishery in North Carolina. In 2000
this fishery was valued at over 11.6 million dollars.
The vast majority of flounder caught in North Carolina are summer
flounder (Paralichthys dentatus) and
the southern flounder (Paralichthys
lethostigma). While the summer
flounder tend to inhabit more saline waters, southern flounder are found
throughout our more freshwater survey area.
Large catches (>100) of juveniles in the spring indicate that the Cape
Fear River system is an important nursery for P. lethostigma. Although
coast wide landings of southern flounder are declining, we observed a
statistically significant increase in the spring 2001 trawling and shocking
catch-per-unit-effort. The 2002
spring trawling catch-per-unit-effort was significantly lower than that of 2001,
but was still twice as high as any of the other years (Figure 5-42).
The spring season of 2002 showed an increase in CPUE from last year and
documented the second largest CPUE since 1997.
It is hoped that the large catch-per-unit-efforts of last the two years
is an indication of large year-classes that will soon enter the adult
population.
Striped
bass
Striped bass (Morone
saxitilis) are one of 7 anadromous species found in the Cape Fear River
system. Due to dramatic drops in
the population, a coast wide moratorium on striped bass fishing was imposed from
1985 to 1990. Although striped bass
populations in other N. C. drainages have rebounded, the Cape Fear River striped
bass population has not (Mallin et. al. 1998,1999,2000,2001,2002).
Declines in water quality and the introduction and possible predation by
non-native catfishes are probably contributing to the problem, one specific
culprit could be competition from hybrid striped bass.
Gillnet surveys showed the average catch-per-unit effort of striped bass
from 1990 to 1992 declined by 50% when compared to the catch-per-unit average
from 1996 to 1999. Unfortunately, the same survey showed a more than doubling of
the catch-per-unit-effort of hybrid striped bass during the same time period
(Patrick and Moser 2000). Tag and
recapture data and the capture of spent hybrid females also indicate that the
hybrid striped bass conduct a spawning run with the striped bass and may be
competing for mates and spawning habitat. The
true striped bass and the hybrids have a very high diet overlap.
If food resources, spawning habitat, or spawning partners are limited, it
is likely that the hybrids are depressing the true striped bass population in
the Cape Fear. Catch-Per-Unit-Effort was the higher during the 2002/2003 season
than any other season documented since 1997.
This increase comes after a major drought it is interesting, although low
flow conditions in previous years did not have the same resulting increases in
CPUE. Future surveys should investigate river flow and other
environmental conditions that may impact the spring anadromous run of striped
bass in the Lower Cape Fear River. (Figure 5-40).
5.4
Summary and Recommendations
The
reintroduction of electroshocking data from this years survey has given us the
ability to closely monitor species richness and disease incidence. Species richness in samples provided by this gear has shown
declines that give cause for concern. Trend
line analysis shows over a 23% drop and this is excluding a seven-month and a
nine-month data gap that would likely have lowered the trend line further due to
the time of year in which they occurred. Although
the drought had little, if any effect on overall fish community structure,
non-native percentages, or disease incidence, species richness reached record
levels in the trawling surveys. This
suggests the drought created a more estuarine environment in our sampling area
and more estuarine dependant species were therefore captured. The catches of
estuarine dependent species further reinforces the important role the Cape Fear
River system plays as habitat for not only resident species but estuarine and
marine species. Drops in disease
percentages in the electroshocking and gillnets surveys were mostly driven by
the drops in the disease percentage of bowfin.
Although most of the trend analysis showed no discernable patterns in a
positive or negative direction, a trend toward decreasing species richness and
catch-per-unit-effort in the electroshocking surveys may be developing and
should be closely monitored in future surveys.
At
the species-level,
It
is recommended that future monitoring efforts be expanded to address several
important issues
concerning Cape
Fear River fish communities.
1)
Diets of non-native catfishes (particularly blue catfish and flathead
catfish) should be
reexamined to determine whether these introduced predators continue to exploit
native
catfishes as prey. With such
substantial drops in the native catfish population, it will be
important to assess their potential predatory impacts on other native species
due to the
depletion of one of their prey items.
2)
Ploidy testing of feral grass carp should also be considered to assess
their potential
for reproduction and whether adults currently in the system are likely to
establish a
breeding population.
3)
Toxicant/contaminant testing should be incorporated as a parameter for
routine monitoring.
4)
Tagging of resource and indicator species should be conducted during
routine sampling.
This would enable mark/recapture studies to estimate important biological
parameters,
including population size, growth rate, home range, and migratory patterns.
5)
Finally, it is critical that future monitoring efforts continue without
interruption such that
additional data gaps do not further impede the survey’s ability to document
seasonal, spatial,
and interannual trends, as well as patterns of response to, and recovery from,
ecosystem disturbance.
5.5
Acknowledgements
We thank the Division of Marine Fisheries, Wilmington office for conducting the trawling portion of this survey, and for continued technical and logistical support. Field assistance was provided by, Melissa Anderson, Donald Burkhalter, Steve Hall, Susanna Holst, Roger Keeter, Matthew McIver, Bethany Noller, Robert Mires, Wiley Rimmer, Andrea Quattrini, Doug Parsons, Anthony Santoes, Joshua Slater, and Darrell Watson.
5.6
Literature Cited
Ashley
K.W., and B. Buff. 1987.
Food Habits of flathead catfish in the Cape Fear River,
North Carolina.
Proceedings of the Annual Conference of the Southeast Association of
Fish and Wildlife Agencies, 41:93-99.
Guier
C. R., L. E. Nichols, and R. T. Rachels. 1981.
Biological investigation of flathead catfish
in the Cape Fear River.
Proceedings of the Annual Conference of the Southeast Association
of Fish and Wildlife Agencies, 35:607-621.
Hendrick,
M. S., S. L. Katz, D. R. Jones. 1994.
Periodic air-breathing in a primitive fish revealed
by spectral analysis. Journal of Experimental Biology 197:429-436.
Hackney,
P. A. 1965. Predator-prey
relationships of the flathead catfish in ponds under selected
forage fish conditions.
Proc. Ann. Conf. S.E. Assoc. Game and Fish Comm, 19:217-222.
Mallin,
M.A., M.H. Posey, M.L. Moser, G.C. Shank, M.R..
McIver, T.D. Alphin, S. H. Ensign, and
J. F. Merritt. 1997.
Environmental Assessment of the Lower Cape Fear River System,
1996-1997.
CMSR Report No. 97-01. Center
for Marine Science Research, University of
North Carolina at Wilmington, Wilmington,
N.C.
Mallin,
M.A., M.H. Posey, M.L. Moser, G.C. Shank, M.R.
McIver, T.D. Alphin, S. H. Ensign, and
J. F. Merritt. 1998.
Environmental Assessment of the
Lower Cape Fear River System,
1997-1998.
CMSR Report No. 98-02. Center
for Marine Science Research, University
of North Carolina at Wilmington,
Wilmington, N.C.
Mallin,
M.A., M.H. Posey, M.L. Moser, L.A. Leonard, T.D. Alphin, S. H. Ensign, M.R.
McIver,
G. C. Shank, and J. F. Merritt. 1999.
Environmental Assessment of the Lower Cape Fear
River System, 1998-1999. CMSR
Report No. 99-01. Center for Marine
Science Research,
University of North Carolina at
Wilmington, Wilmington, N.C.
Mallin,
M. A., M. H. Posey, M. R. McIver, S. H. Ensign, T. D. Alphin, M. S. Williams, T.
E. Lankford,
M. L. Moser, and J. F. Merritt.
2000. Environmental Assessment of
the Lower Cape Fear River
System, 1999-2000. CMSR Report No. 00-01. Center
for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin,
M. A., M. H. Posey, T. E. Lankford, M. R. McIver, S. H. Ensign, T. D. Alphin, M.
S. Williams,
M. L. Moser, and J. F. Merritt. 2001. Environmental
Assessment of the Lower Cape Fear River
System, 2000-2001.
CMSR Report No. 01-01. Center
for Marine Science, University of North
Carolina at Wilmington, Wilmington, N.C.
Mallin,
M. A., M. H. Posey, T. E. Lankford, H.A. CoVan, M.R. McIver, T. D. Alphin, M. S.
Williams, and
J. F. Merritt.
2002. Environmental Assessment of
the Lower Cape Fear River System, 2001-2002.
CMSR Report No. 02-01.
Center for Marine Science, University of North Carolina at Wilmington,
Wilmington, N.C.
Moser,
M.L., and S.B. Roberts. 1999.
Effects of non-indigenous ictalurid introductions and recreational
electrofishing on native ictalurids of the
Cape Fear River drainage, North Carolina. Pages 479 – 486
in E. R. Irwin,
W. A. Hubert, C. F. Rabeni, H. L. Schramm, Jr., and T. Coon, editors. Catfish
2000:
proceedings of the international ictalurid
symposium, American Fisheries Society, Symposium 24,
Bethesda, Maryland.
Moser
and Ross. 1995.
Habitat use and movements of shortnose and Atlantic sturgeons in the Cape
Fear River, North Carolina.
Transactions of the American Fishery Society.
124:225-234
Norcross,
B. L. 1991. Estuarine recruitment mechanisms of larval Atlantic croakers.
Transactions of the
American Fisheries Society.
120:673-683
Raibley,
P. T., D. Blodgett, R. E. Sparks. 1995.
Evidence of grass carp (Ctenopharyngodon idella)
reproduction in the Illinois and upper
Mississippi Rivers. Journal of
Freshwater Ecology. 10:65-74.
Schultz,
S. L. W., E. L. Steinkoenig, and B. L. Brown.
2001. Ploidy of feral grass
carp
(Ctenopharyngodon
idella) in the Chesapeake Bay Watershed.
North American Journal of
Fisheries Management.
21:96-101
List
of Figures
Figure
5-1. Fish
Collections: Cape Fear River at H11
(NC11), 2003
Figure
5-2. Fish Collections: Cape
Fear River at Syke's Landing, 2003
Figure
5-3. Fish Collections: Cape
Fear River at Black River, 2003
Figure
5-4. Fish Collections: Cape
Fear River at Indian Creek, 2003
Figure
5-5. Fish Collections: Cape
Fear River at Brunswick River, 2003
Figure
5-6. Fish Collections: Northeast
Cape Fear River at Castle Hayne (NCF117), 2003
Figure
5-7. Fish Collections: Northeast
Cape Fear River at GE (NCF6), 2003
Figure
5-8. Fish Collections: Northeast
Cape Fear River at Smith Creek (Smith), 2003
Figure
5-9 . Fish Collections: Cape
Fear River at HorseshoeBend (HB), 2003
Figure
5-10 .
Fish collections pooled by station (all months), 2003. Error bars
Figure
5-11 .
Fish collections pooled by month (all stations), 2003. Error bars
Figure
5-12 .
Number of Species at all Stations by Month, 2003.
Error bars represent standard error
Figure
5-13. Catch-Per-Unit-Effort at all Stations by Month, 2003.
Error bars represent standard error
Figure
5-14.
Percent Diseased Non-transients Captured at all Stations by Month, 2003
Figure
5-15.
Percent Non-natives captured at all Stations by Month, 2003
Figure
5-16.
Number of Species Captured at all Stations by Gear Type 1997-2003
Figure
5-17.
Catch-Per-Unit-Effort of Each Gear Type by Month 1997 – 2003
Figure
5-18.
Percentage of all Resident Diseased Fish by Season 1997 –
Figure
5-19. Non-native Percentage of Resident Fish by Season 1997 –
2003
Figure
5-20. Catch-Per-Unit-Effort of American Shad (Alosa sapidissima)
Figure
5-21. Catch-Per-Unit-Effort of American Shad (Alosa sapidissima) by Station 1/1997- 5/2003
Figure
5-22. Catch-Per-Unit-Effort
of Atlantic Sturgeon (Acipenser
Figure
5-23. Catch-Per-Unit-Effort
of Atlantic Sturgeon (Acipenser
Figure
5-24. Catch-Per-Unit-Effort of Blue
Catfish (Ictalurus furcatus)
Figure
5-25. Catch-Per-Unit-Effort
of Blue
Catfish (Ictalurus furcatus) by
Station 1/1997 - 5/2003
Figure
5-26. Catch-Per-Unit Effort of Bowfin (Amia calva) 1/1997 –
Figure
5-27. Catch-Per-Unit Effort of Bowfin (Amia calva) by Station 1/1997 –
Figure
5-28. Catch-Per-Unit-Effort of Channel Catfish (Ictalurus
Figure
5-29. Catch-Per-Unit-Effort of Channel Catfish (Ictalurus
Figure
5-30. Catch-Per-Unit-Effort
of Flathead Catfish (Pylodictus
Figure
5-31.
Catch-Per-Unit-Effort of Flathead Catfish (Pylodictus
Figure
5-32.
Catch-Per-Unit-Effort of Grass Carp
(Ctenopharyngodon idella) by Station 1/1997 - 5/2003
Figure
5-33.
Catch-Per-Unit-Effort of Grass Carp
(Ctenopharyngodon idella) by Station by Station by Station 1/1997 - 5/2003
Figure
5-34. Catch-Per-Unit-Effort of Hybrid Striped Bass (Morone saxatilis
X Morone chrysops) 1/1997 - 5/2003
Figure
5-35. Catch-Per-Unit-Effort of Hybrid Striped Bass (Morone saxatilis
X Morone chrysops) by Station 1/1997 - 5/2003
Figure 5-36.
Catch-Per-Unit-Effort of Longnose Gar (Lepisosteus osseus) 1/1997 - 5/2003
Figure
5-37.
Catch-Per-Unit-Effort of Longnose Gar (Lepisosteus
osseus) by Station 1/1997 - 5/2003
Figure
5-38. Catch-Per-Unit-Effort of Spot (Leiostomus xanthurus) 1/1997 - 5/2003
Figure
5-39. Catch-Per-Unit-Effort of Spot (Leiostomus xanthurus) by Station 1/1997 - 5/2003
Figure
5-40. Catch-Per-Unit-Effort of Striped Bass (Morone saxatilis) 1/1997 - 5/2003
Figure
5-41. Catch-Per-Unit-Effort of Striped Bass (Morone saxatilis) 1/1997 - 5/2003
Figure
5-42. Catch-Per-Unit-Effort of Southern Flounder (Paralichthys lethostigma) 1/1997- 5/2003
Figure
5-43. Catch-Per-Unit-Effort of Southern Flounder (Paralichthys lethostigma) 1/1997- 5/2003
Figure
5-44. Number of Species Captured in the Electroshocking survey
1/1997- 5/2003
Figure
5-45. Number of Species Captured in the Trawling survey 1/1997-
5/2003
Figure
5-46. Number of Species Captured in the Gillnetting survey 1/1997-
5/2003
Figure
5-47. Average Monthly Catch-Per-Unit-Effort in the Electroshocking
survey 1/1997- 5/2003
Figure
5-48. Average Monthly Catch-Per-Unit-Effort in the Trawling survey
1/1997- 5/2003
Figure
5-49. Average Monthly Catch-Per-Unit-Effort in the Gillnetting
survey 1/1997- 5/2003
Figure
5-50. Average Monthly Disease Percentage of Resident Fish Captured
in the Electroshocking survey 1/1997- 5/2003
Figure
5-51. Average Monthly Disease Percentage of Resident Fish Captured
in the Trawling survey 1/1997- 5/2003
Figure
5-52. Average Monthly Disease Percentage of Diseased Resident Fish
Captured in the Gillnetting survey 1/1997- 5/2003
Figure
5-53. Average Monthly Non-native Percentage of Resident Fish
Captured in the Electroshocking survey 1/1997- 5/2003
Figure
5-54. Average Monthly Non-native Percentage of Resident Fish
Captured in the Trawling survey 1/1997- 5/2003
Figure
5-55. Average
Monthly Non-native Percentage of Resident Fish Captured in the Gillnetting
survey 1/1997- 5/2003
Figure
5-56. Average Monthly Non-native Percentage of Resident Fish
Captured in the Gillnetting survey 1/1997- 5/2003
Figure
5-57. Map of sampling locations in the Lower Cape Fear River.
Figure
5-57. Map of Fisheries Sampling Locations in the Lower Cape Fear River.
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