Center
for Marine Science
University of North Carolina at Wilmington
The sampling
period June 2001-May 2002 represented the fifth 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 UNCW’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 and 2001
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 current (2001/2002) year of sampling, the state of North Carolina 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. 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, and documenting changes in fish community structure within our sampling area due to this year’s severe drought. 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).
Fish monitoring was conducted at each of nine fixed
sites in tidal regions of the lower watershed (Figure
32).
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), the mouth of Indian Creek (IC), and in
Horseshoe Bend (HB). 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), and at the mouth of Smith Creek (Smith = SMT).
Each site was located near water a 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, 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 because the channel 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 23oC.
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/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.
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.
We conducted boat electroshocking surveys monthly at 8
of the 9 sampling locations (water conductivity at the Brunswick River site was
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 the entire reach had been 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.
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.
1997 was a non-hurricane year that we have all twelve months of sampling
data. In this year a seasonal
pattern in species richness and abundance was documented (Mallin et al 1999).
The sampling period covered by this report was not impacted by a
hurricane, but did not show the seasonal pattern that was expected.
The electroshocking data typically contribute the highest species
richness of all gear types and it is likely that the lack of a discernable
pattern is due to the absence of electroshocking data from October 2001-June
2002. The trawling data have shown
a relatively stable winter/spring species richness with 25 species captured in
1998, 1999 and 2002. The
summer/fall trawling data produced 31 species, the second lowest number of
species captured during this season since 1997.
This was, however, a slight increase from last year and does not indicate
a decreasing trend. The
winter/spring gillnetting species richness data shows this was the second lowest
number of species captured at 13. The
winter/spring seasons do not show a pattern indicative of a decrease in species
richness. The summer/fall
gillnetting species richness decreased each year from 1997 (n=19 species
captured) to 2001 (n=14 species). This
trend of decreasing species richness (26% decline over four years) is a pattern
of concern. The observation that
species richness increased slightly in 2002 (n=15 species) is encouraging and
suggests that the downward trend may have reversed (Figures
1-12/18).
Future monitoring is necessary to document such a reversal.
The winter/spring trawling catch-per-unit-effort was
the highest seen to date. This was
over a forty percent increase from the previous high in the winter/spring of
1998. The spring trawling catch was dominated by the capture of
>5,000 spot (Leiostomus xanthurus) and 6,000 Atlantic croaker (Micropogonias
undulatus). The persistent
drought during 2001/2002 reduced river flow and led to higher salinities at most
of our sampling stations. This
upstream shift in the estuarine salinity distribution (Figure
2.1) may have led
to the increased abundance of these two estuarine-dependent species at our lower
riverine stations. The lack of
electroshocking data for much of the sampling period prevented us from
documenting whether declines in freshwater-resident species (e.g., redear
sunfish, Lepomis microlophis, and bluegill, Lepomis macrochirus)
occurred at salinity-impacted stations. If
such changes occurred, it would have reinforced the premise that the increase in
these estuarine dependent species was due to a change in local salinities due to
the current year’s drought. The
freshwater resident species that we do have information on (e.g., flathead
catfish (Pylodictus olivarius) and blue catfish (Ictalurus furcatus))
indicate no significant change compared to previous years.
The summer/fall 2001 data also showed the highest
catch-per-unit-effort recorded. Summer/fall
CPUE was 70% higher than the previous high recorded in the fall/winter season of
1999. The increase was driven
primarily by increases in estuarine-associated species such as bay anchovies (Anchoa
mitchilli), Atlantic croakers (Micropogonias undulatus), and
hogchokers (Trinectes maculatus) that use the lower Cape Fear River and
estuary as juvenile nursery habitat. It
should be emphasized that the lower Cape Fear River system is an important
nursery habitat for juvenile 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.
Gillnet CPUE during the winter/spring period declined
slightly this year but has varied widely over previous years with no discernible
trend. Dominant species during this period included blue catfish (Ictalurus
furcatus ), American
shad (Alosa sapidissima), and bowfin (Amia calva).
Gillnet CPUE for the summer/fall sampling period declined for the third
consecutive year (Figures 1-11/13/19). In
previous years, hurricanes were presumed to contribute to these declines.
The continued decline in summer gillnet catches during the past year when
no hurricanes occurred warrants close examination in future surveys. Gizzard
shad, flathead catfish, and Atlantic sturgeon dominated the summer/fall season
of 2001.
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. 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.
For this reason, the trawling data is not considered to be a good
indicator of disease percentages. The
gillnet survey captures large resident fish that can yield disease incidence
information. Unfortunately, when captured in the gill nets fish can have
external marks and scales missing that may obscure external signs of disease.
Due to the inherent problems using these gear types to observe external
signs of infection, this program relies heavily on the electroshocking data for
disease information. Due to the
lack of electroshocking data for much of this year, interannual comparisons of
disease incidence for resident fishes are unavailable.
The new electroshocking boat is currently in use and the interannual
comparisons and trend investigations will be updated in next year’s report.
The gillnet data showed that only four species captured during the winter/spring and summer/fall seasons exhibited definitive external signs of disease. The bowfin (Amia calva) exhibited a 67% infection rate, the channel catfish (Ictalurus punctatus) exhibited a 50% infection rate, the hybrid-striped bass (Morone saxatalis X Morone chrysops) showed a 20% infection rate, and the blue catfish (Ictalurus furcatus ) exhibited a 3% infection rate (Figures 1-11/15/16).
The relative abundance of non-native fishes (expressed as a percentage of native
fishes) in the trawling survey was the second lowest winter/spring percentage
since 1999. The summer/fall survey
showed a slight decrease in non-native percentage from last year.
The summer/fall trawling survey has fluctuated interannually and shows no
discernable trend (Figures 1-11/14/17). The
most abundant non-native fishes collected in the trawling and gillnetting
surveys during 2001-2002 were blue catfish (Ictalurus
furcatus), channel catfish (Ictalurus
punctatus) and flathead catfish (Pylodictis olivaris).
No new species of non-native fishes were encountered.
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 (Hackney 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 recent 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).
Trends
in Abundance of Important Species
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 five seasons of sampling, but no distinct trends have been observed (Figure
20).
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 an 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.
With American sturgeon caviar currently selling for $192.00 a pound and
smoked sturgeon selling for $14.00 a pound, a directed fishery for them will
likely be lucrative and attract considerable fishing pressure. Due to their slow growth, late age at maturity, and high
monetary value, Atlantic sturgeon are highly susceptible to overfishing.
Although catch per unit effort from this survey shows a small stable
juvenile population, the available data does not indicate that the Cape Fear
Atlantic sturgeon population could support a directed fishery (Williams and
Moser 2000). Future surveys should
closely monitor this species to determine if increases in water quality and the
construction of canals around dams that block their spawning migration can
increase their abundance to a level that a sustainable directed fishery can be
maintained. Catch-per-unit-effort from this survey shows a fluctuating
but stable juvenile population in the Cape Fear River system (Figure
21).
The blue catfish (Ictalurus
furcatus) was introduced into 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). The success of the blue
catfish in the Cape Fear River system is likely due to it's 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 surprisingly 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. 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 continue to be the dominant catch in the gillnet survey (Figure
22).
Bowfin
Although much maligned by many fishermen, 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 (Hendrick, et al
1994). This permits bowfin to utilize hypoxic areas in the water
where other predators are excluded. Disease
percentages ranged from 48% in the fall of 2000 to less than 27% in the spring
of 2001. 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 2000/2001 sampling period but has since declined in
the 2001/2002 sampling period (Figure 23).
Channel catfish were introduced into the Cape Fear in
the early 1900's. 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 (Figure
24).
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. No significant
changes in catch-per-unit-effort have been observed during this sampling period
(Figure 25).
Grass carp (Ctenopharyngodon idella)
catch-per-unit-effort remains low and sporadic in the Cape Fear River system (Figure
26). In 1997 a number of
these fish were captured in several locations, possible as a result of escapes
into the system from flooding associated with Hurricane Fran. The
flooding from Hurricane Floyd in late 1999 does not seem to have led to a major
increase in catches of this non-native species.
Hybrid striped bass are a hybrid of striped bass (Morone
saxatilis) 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 bass are not converted into reproduction.
As a result of competition with hybrids, striped bass may not be as
healthy and may not produce as many offspring.
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 appears to have decreased
since 1999, future surveys should examine whether this trend continues (Figure
27). It is interesting to note that
highest CPUE values for hybrid striped bass have been associated with hurricane
years. This suggests that
individuals are introduced to the lower Cape Fear River system by flooding
events upstream. Decreases in CPUE
during non-hurricane years suggest that individuals introduced into the system
may have a short residency, perhaps due to high fishing mortality.
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 fishermen.
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. Although this fall’s
sampling period showed a low catch-per-unit-effort, CPUE from this period has
proven to be highly variable and no trends are apparent.
The spring sampling CPUE has averaged over 0.43 longnose gar captured in
a fifty-meter gill net in a 24 hr period. Analysis
of this spring’s sampling period showed a CPUE of less than 0.04.
This is a significant drop and future studies should monitor this
closely. It will be important to
determine if this drop was simply an outlier or if it was representative of a
negative trend in their relative abundance (Figure
28).
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 southern flounder (Paralichthys lethostigma). While
summer flounder tend to inhabit more saline waters, southern flounder are found
throughout our entire survey area. Large catches of juveniles during spring months 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
29).
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.
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 (Micropogonias
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). 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 30). 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. 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
30).
Striped bass (Morone
saxatilis) are one of 7 anadromous species found in the Cape Fear River
system. Due to dramatic declines 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). Although declines
in water quality and the introduction and possible predation by nonnative
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 declined by 50%
between 1990-1992 and 1996-1999.
Catch-per-unit-effort of hybrid striped bass during the same time period
more than doubled (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. Despite a significant increase in the 1999 spring shocking and
trawling catch-per-unit-effort, overall striped bass abundance remains low in
the Cape Fear River system (Figure 31).
The loss of the electroshocking data from this years
survey has hampered our ability to closely monitor species richness and disease
incidence. Despite this, trawling
catches of over five-thousand Spots (Leiostomus xanthrus ), and
six-thousand Atlantic croakers (Micropogonias undulatus), created the
largest trawling catch-per-unit-effort in the history of the survey. The large
catches of estuarine dependent species further reinforces the important role the
Cape Fear River system plays as nursery habitat.
With the data that is available, the drought has had little effect on
overall fish community structure, non-native percentages, or disease incidence.
Relative abundance, however, has been impacted by the large
catch-per-unit-effort increases in the trawling survey.
Whether the increase was due to interannual variability, a large
year-class, or simply due to the increased salinity caused by the severe
drought, is a question that future surveys should investigate.
Although most of the trend analyses showed no discernable patterns for
most species, a trend toward decreasing gillnetting catch-per-unit-effort and
species richness in the summer/fall season may be developing and should be
closely monitored in future surveys.
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, and to assess
their potential predatory impacts on other native species.
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 initiated,
with testing focused on resource species that are harvested for human
consumption.
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.
We thank the Division of Marine Fisheries, Wilmington office for conducting the trawling portion of this survey, and for continued technical, logistical and funding support. Field assistance was provided by Aaron Baugh, Roger Keeter, Anna Scherer, Anthony Santos, Andrea Quattrini, Susie Holst, Doug Parsons, Matthew McIver, Gene Conway, Coult Markovsky, Rob Keller, Rebecca Feres, Kelly Mellette, and Sarah Aimone.
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 Southeastern 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 Southeastern 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. R. McIver, S. H. Ensign, T. D. Alphin, M. S. Williams, T.
E. Lankford, 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.
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,
M.L. and S. 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
Patrick,
W. L. and M. L. Moser. 2001. Potential Competition between Hybrid Striped Bass (Morone
saxatilis x M. americana)
and Striped Bass (M. saxatilis) in the Cape Fear River
Estuary, North Carolina. Estuaries
24:425-429.
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
Williams,
M.S. and M.L. Moser. 2000. Spawning of the Atlantic sturgeon (Acipenser oxyrhynchus)
in the Cape Fear River system, North Carolina.
Report to the North Carolina Fisheries Resource Grant Program, North
Carolina Sea Grant Program, Raleigh, N.C.
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