5.0
Fisheries Studies in the Lower Cape Fear
River System, August 2000 – May 2001
Center
for Marine Science
University
of North Carolina at Wilmington
This was the fourth year of a comprehensive survey of fish populations in the lower portion of the Cape Fear River basin. Monitoring efforts continued to focus 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 the 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 more 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 fall 2000 sampling period has given us the opportunity to begin documenting the long-term effects and potential recoveries of fish communities after these large-scale disturbances.
The 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 include studying the long-term effects of Hurricanes on fishes of both the Cape Fear and Northeast Cape Fear Rivers. In addition, this years report includes a statistical analysis of abundance trends for 17 important resource and / or indicator species that occur in the drainage. 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 38). 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 was 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 four hours
during months that water
temperatures exceeded 25oC.
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.
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 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.
Statistical
analysis of interannual trends in abundance for 17 resource and/or indicator
species was performed for the period 1997 – 2001.
The analysis was conducted using a one-way analysis of variance and
tested for significant (p < 0.05) differences in mean CPUE among years.
Stations were treated as replicates in the analysis.
Due to fisheries sampling not being conducted during January – July
2000, the analysis was restricted to the periods August – December 2000 and
January – May 2001.
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. To date, 1997 remains the only non-hurricane year that
we have all twelve months of sampling data.
In our non-hurricane year a seasonal pattern in species richness and
abundance was documented (Mallin et al 1999).
This year species richness peaked in late summer / early fall and was
lowest in late winter / early spring (Figure 2).
In both the Northeast and Cape Fear River sub-basins, upper stations
(e.g., H11, 117) exhibited higher species richness than lower stations.
The Northeast Cape Fear samples showed a trend toward decreasing species
richness going downstream but this trend was not observed in the Cape Fear main
stem. Interannual comparisons
suggest a trend toward increasing species richness (Figure 3).
A total of forty-nine species were captured during spring 2001 compared
to 43 species in spring 1999 and 36 species in the spring 1998.
Compared to previous years,
fall 2000 sampling produced lower catch-per-unit-effort of fishes in trawling,
gillnetting, and electroshocking (Figure 17).
This observation was surprising given that the fall of 2000 was not
impacted by a hurricane and it was expected that catch-per-unit-effort would be
higher than the previous years when hurricanes occurred.
In the spring 2001, however, all three gear types documented the highest
catch-per-unit-effort of all the spring seasons sampled (Figure 17).
This increase was driven by increased catches of spot, striped mullet,
and southern flounder. These three
estuarine dependent species spawn offshore and their larvae migrate into
estuarine nursery habitat (Norcross 1991).
The Cape Fear River system is used heavily by these species as nursery
habitat. The functional value of
Cape Fear River nursery habitats depends largely on their ability to provide
biotic and abiotic conditions suitable for growth and survival of juvenile
fishes. Because many of our 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 for juvenile fishes.
Disease
Whether from exposure to
toxicants, environmental stressors, or resource limitation, high infection rates
indicate a deterioration of ecosystem health and function.
Of the 1776 fish captured this fall season, 52 (2.93%) exhibited external
signs of disease. This represents
the highest recorded infection rate during any fall season to date. When the
spring and fall samples are combined bowfin (Amia
calva) and the highest infection rate, with largemouth bass (Micropterus
salmoides) coming in second and warmouth (Lepomis gulosus) coming in third.
The spring 2001 samples, however, showed a disease percentage of 1.2 %,
the lowest value documented in any season (Figure 3). Reasons for these
fluctuations are unclear. One
contributor to the drop in the spring disease percentage was the bowfin (Amia
calva). In years past the infection rate for bowfin ranged from 40% to
slightly over 50%. During the spring
2001 sampling their infection rate dropped to 26.9%.
It does not appear that this trend is due to the selective mortality of
diseased bowfin. In fact,
catch-per-unit-effort data show a trend toward increasing numbers of bowfin. The
recent drop in infection rates is therefore encouraging and will be monitored
closely in future surveys.
The relative abundance of non-native fishes (expressed as a percentage of native fishes) declined slightly from the fall of 1997 (17%) through the fall of 1998 (8%), but has increased since 1998 and reached 13.5% during spring 2001. The most abundant non-native fishes collected during 2000-2001 were blue catfish (Ictalurus furcatus), redear sunfish (Lepomis macrochiris), and channel catfish (Ictalurus punctatus). 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 3 native catfish since 1997 compared to 1,618 blue catfish, 193 channel catfish, and 198 flathead catfish. Flathead catfish are piscivorous at age 1 and are known to consume juvenile 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 native catfish is 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). There was no statistically significant difference in catch-per-unit-effort between years. Although more were captured in the fall of 1999 than all previous years combined, there is a trend toward decreasing catches of grass carp since that time. Although the documented trend is encouraging, monitoring of this species should remain a priority of this survey to examine changes in population levels and determine if they indicate reproduction in this river system.
The American eel (Anguilla
rostrata) is the only catadromous species (lives in fresh water but returns
to marine waters to spawn) in the Cape Fear River system.
There is a small but valuable fishery for American eels in North
Carolina. A population decline has
been documented for this species in other states.
The decline has been attributed to overfishing and water quality
problems, but recently it was found that American eels have acquired a European
parasitic nematode that affects its swim bladder (Moser et. al. 2000). What
effect this new parasite might have on American eels coupled with high fishing
pressure is causing concern for the future of this species.
American eels have shown no statistically significant changes in
catch-per-unit-effort in this survey (Figure 22), but future surveys should
monitor their population levels closely.
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 four seasons of sampling, but no
distinct trends or statistically significant changes (Figure 23).
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 (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 and the regular catches of juveniles in
this survey indicate a reproducing population in this drainage.
Catch-per-unit-effort from this survey shows a fluctuating but stable
juvenile population in the Cape Fear River system (Figure 24).
Bluegill
The
bluegill sunfish (Lepomis macrochirus)
is an abundant resident species that supports an important recreational fishery.
This species was the 8th most abundant fish captured in the
survey and was 2nd most abundant in the electroshocking.
Catch-per-unit-effort of bluegills was stable during the springs of 1997
through 1999, but increased significantly during the spring of 2001 (Figure 25).
It is thought that the increase may represent a recovery from hurricane
impacts to the Cape Fear River system between 1996 and 1999.
Disease incidence for bluegills tends to be highly variable with no
discernable trend.
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). 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 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. Disease percentages ranged from 28%
in the fall of 1999 to less than 1% in the spring of 2001 (Mallin et all 2000).
Although there have been no significant changes in catch-per-unit-effort
(Figure 26), this species will be monitored closely for information on the cause
of the disease percentage fluctuations.
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 (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. Future
surveys should monitor the bowfin population closely and investigate the cause
of these infections. Although this
species has exhibited a high infection rate, catch-per-unit-effort has not
changed significantly during this survey (Figure 27).
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 statistically significant changes in
catch-per-unit-effort (Figure 28) and a low incidence of disease since 1997.
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 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. 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.
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. Since 1997 only 2 native
catfish have been captured while 1618 blue catfish, 193 channel catfish, and 198
flathead catfish have been captured. 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.
Flathead catfish exhibited a statistically significant decrease in the
fall 2000 but exhibited a statistically significant increase in spring 2001
gillnet catch-per-unit-effort (Figure 30). Reasons
for these changes are yet unknown but will be addressed in future surveys.
Hybrid-striped
bass
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 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, Bishop 1967).
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.
Catch-per-unit-effort data showed a statistically significant drop in the
fall gill net samples (Figure 32). 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 be decreasing, future surveys
should examine whether this trend continues.
Largemouth bass (Micropterus
salmoides) support one of the top recreational fisheries in the Cape Fear
River system. As one of the top-level predators in this river system, M.
salmoides are not only important in keeping the forage base balanced, but
their population levels and disease percentage can indicate the health of the
river system they inhabit. Largemouth
bass showed no significant difference in catch-per-unit-effort between years
(Figure 33). The disease percentage
showed an increasing trend from the spring of 1997 to the fall of 1998.
The percentage then dropped to 0 in the spring of 1999, but has steadily
increased since that time and has now reached the highest infection rate
documented during this survey of 20 percent.
Disease percentages for this species should be monitored closely in
future surveys.
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 nongame fish unpopular with local fisherman.
Knowing their relative population levels allows us to track their
potential impact on other fish populations.
The spring 2001 samples have shown an interesting pattern (Figure 34).
There was a statistically significant increase in the 1998
electroshocking samples. In the
spring samples since that time there has been an increase in the gillnetting
catch-per-unit-effort. This trend
indicates that the individuals from the 1998 year class are now becoming large
enough in size that they are being caught in the gillnets.
Although the gar captured in this survey showed a high occurrence of
wounds, probably from motorboat propellers, no fish exhibited external signs of
disease
Redear sunfish (Lepomis
macrochiris) are another introduced species in the Cape Fear.
In this survey they are the second most abundant sunfish captured after
bluegill. They are an important pert of the forage base and support a popular
recreational fishery. Although not statistically significant, there has been a
trend toward increased catch-per-unit-effort in the spring electroshocking
samples (Figure 36). Disease
percentage average continues to average approximately 4 percent with no
significant trends.
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). 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
from 1990 to 1992 was cut in half 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. 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 37).
In summary, monitoring efforts
during 2000-2001 revealed several encouraging trends evident at both the
community and species level. Overall
species richness and total abundance (indexed as CPUE) increased during spring
2001 to levels exceeding those for previous years.
A total of 49 species were captured during spring 2001 compared to 43
species in spring 1999 and 36 species in the spring 1998.
Total CPUE was also higher for all gear types during spring 2001 than for
any previous spring period. Increased
abundance was driven by increased catches of spot, striped mullet, and southern
flounder in 2001. The incidence of
disease during spring 2001 (1.2%) was also lower than observed during previous
spring periods. Collectively,
increases in richness and abundance combined with slightly lower disease rates
suggest that fish communities in the Cape Fear River are recovering from
hurricane impacts experienced during 1996, 1998 and 1999.
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 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.
We thank the Division of Marine Fisheries, Wilmington office for conducting the trawling portion of this survey, and for continued technical and logistical support. We also thank Cape Fear Community College for providing dock space during times we could not trailer our boat. Field assistance was provided by Bryan Bishop, Andrea Quattrini, Susie Holst, Scott Ensign, Elizabeth Tharpe, Shelly Miller, Jackie Cornett, Wiley Rimmer, Doug Parsons, Allison Sill, Beth Cummins and Barbara Bach. We thank the N.C. Estuarine Research Reserve for the use of their vessel to conduct gillnet sampling while ours was not available.
Guier
C. R., L. E. Nichols, and R. T. Rachels. 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
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
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