8.0 Fisheries Studies in the Lower Cape Fear River System, 1998-1999
Mary L. Moser
8.1 Introduction
This represents the third year of a comprehensive survey of fish populations
in the tidal freshwater and upper estuarine portion of the Cape Fear River basin. Past
years of fish sampling have focussed on obtaining baseline data on fish community
structure, reporting seasonal and spatial trends in fish abundance and diversity,
documentation of disease incidence and monitoring of non-native fish populations. This
monitoring program has also provided valuable data on the response of fish populations to
acute hypoxia resulting from the passage of large storms. Immediately prior to the first
year of fish sampling, Hurricanes Bertha and Hurricane 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. 1998). The landfall of
Hurricane Bonnie in August 1998 provided yet another opportunity to examine the effect of
this stochastic process on fish community structure. However, this time we have the
benefit of baseline data collected before the storm. Therefore, objectives of this
year’s survey were to: 1) document trends in fish disease, 2) characterize fish
community structure, 3) monitor non-native fish populations, and 4) track the effects of
Hurricane Bonnie on fishes of both the Cape Fear and Northeast Cape Fear rivers. We used
three gear types, gillnets, trawls, and a boat electroshocker, to sample a broad segment
of the fish population. The work was a cooperative effort between the Cape Fear River
Program (Dr. Mary Moser, gillnets and electroshocking), and the North Carolina Division of
Marine Fisheries (NCDMF, Wilmington Office, trawl).
8.2 Methods
Study Sites
Fish monitoring was conducted at nine study sites in tidal regions of
the river main stem and estuary. Five sites were selected in the Cape Fear River:
approximately 1.5 km above the NC11 bridge (NC11), the lower limb of the oxbow downstream
from Syke's Landing near Acme (AC), the mouth of the Black River below Lyon Thoroughfare
(BBT), the mouth of Indian Creek (IC), and in Horseshoe Bend (HB). One site was selected
in the Brunswick River between the Belville 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), opposite the Hoechst Celanese
dock (NCF6), and at the mouth of Smith Creek (Smith). The locations were all near water
quality monitoring stations (see Section 2) and were limited to areas where all three gear
types (gillnets, trawls, and boat electroshocker) could be employed. A 183 m reach at each
site was marked off and sampling was conducted in the same reach each month.
Gillnets
Gillnet sampling was designed to sample very large resident and
anadromous fishes that are less susceptible to electroshock and trawl collection.
Monofilament nets with 11 cm stretched mesh were weighted to sink, thereby sampling the
lower half of the water column at each station. Nets were 50 m in length and were deployed
from the shoreline, perpendicular to the current. At the Horseshoe Bend and Smith Creek
sites, 30 m 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 h soak times at each station, and allowed sampling both during the day
and at night. After the first 24 hr soak, the nets were checked and re-deployed to reduce
fish mortality. Due to the high incidence of sturgeon mortality in summer months, we
reduced soak times when temperature exceeded 28oC. However, all catch data were
standardized to reflect a 24 h set. All fish captured were identified, measured (nearest
mm total length, TL), and examined for external evidence of disease (e.g., ulcers,
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 of fish / 50 m
net set for 24 h), % diseased fish (number of diseased fish divided by 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 sites
(the conductivity at the Brunswick River site was too high to allow reliable sampling with
this gear). This technique targets shoreline oriented species that are difficult to
capture with either trawls of gillnets. We used a 7500 watt electrofishing system with an
18 dropper anode array from an aluminum boat. At each site, a 183 m reach was sampled by
making a pass with the current down each shoreline and one pass down the middle of the
river. All stunned fish were dipnetted and placed in an aerated holding tank until the
entire reach had been sampled. Fish were then identified, measured (nearest mm total
length, TL), and examined for external evidence of disease (e.g., ulcers, 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 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) were determined for each site and
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 m flat otter
trawl with 0.64 cm mesh in the body, a 0.32 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 of diseased fish divided by total catch), and % non-native fish (number of
non-native fish divided by the total catch) were determined for each site and sampling
month.
8.3 Results and Discussion
Species Richness
A total of 72 species were collected in this survey (Tables
8.1 - 8.36). Electroshocking collections had the highest number of species (n = 60) and the
greatest range of fish sizes (Tables 8.25 -
8.36). Gillnetting collections were the least
speciose (n = 19 species) and trawl catches were intermediate in species richness (n = 40
species). The gillnets generally collected very large fishes (> 400 mm TL) and trawling
collected primarily the smallest size classes (< 100 mm TL).
No new species were added to the fish species list for this year.
However, dissection of American eels, Anguilla rostrata, we collected revealed the
presence of a parasite previously not known to occur in the Cape Fear River drainage. The
eel swimbladder nematode, Anguillicola crassus is capable of rapid range expansion,
and has spread from Japan through Europe and into North America (Barse and Secor 1999).
Before 1995, A. crassus was known only to infect Japanese and European eels (Anguilla
japonica and A. anguilla). During the early 1980’s infected eels were transmitted
from Asia to Europe where they rapidly became established. Then, in 1995, Fries et al.
(1996) found a single immature nematode in a wild American eel (A. rostrata)
collected from Winyah Bay, South Carolina. Since this initial discovery of A. crassus
on the East Coast of the United States, Barse and Secor (1999) have documented the
occurrence of this exotic parasite in American eels taken from Chesapeake Bay and Hudson
River drainages. Our discovery of this parasite is significant because it was not known to
occur in North Carolina previously and could negatively impact the native eel populations
in the Cape Fear River and adjacent drainages (see Non-native Species section).
Fish diversity did not vary widely among stations (Figures 8.1 –
8.9). Electroshocking collections at site NCF6 produced more species than any other
station sampled with any gear (Figure
8.10), particularly during the summer months (Figure
8.11). Due to the high numbers of species collected at NCF6, pooled data for the two
sub-basins (Figures 8.12 and
8.13) indicated that electrofishing collections in the
Northeast Cape Fear River were more diverse than Cape Fear River collections. A large
number of species were recorded from NCF6 because both estuarine fishes (e.g., speckled
trout, menhaden, summer flounder) and freshwater residents (e.g., bowfin, bluegill, golden
shiner) occur in this area. This is most evident in summer when the saltwater/freshwater
interface is displaced upstream. While estuarine species are also commonly collected at
Smith, BRR and HB, these sites do not support as many freshwater residents
Seasonal trends in species diversity were not as apparent this year as
in previous years of fisheries monitoring (Mallin et al. 1997, Mallin et al. 1998). This
is due to the relatively speciose collections made in winter months of this year. In
addition, the effects of Hurricane Bonnie may have impacted diversity, which typically
peaks in late summer - early fall (September-October). Hurricane Bonnie made landfall in
late August 1998. This storm produced anoxic conditions in the Cape Fear River drainage
(Section 9) which resulted in extensive fish kills immediately thereafter. This is
reflected in the lower than expected species diversity we recorded in September
collections using all gear types (Figure
8.11). Moreover, this depression in the species
diversity following the storm was more pronounced for Northeast Cape Fear sub-basin
stations (Figure 8.13) than for those in the Cape Fear River main stem
(Figure 8.12). This
is probably because hypoxic conditions in the Northeast Cape Fear River are more extreme
and prolonged than in the Cape Fear River following such storms (Section
9). It should be
noted that species diversity recovered quickly at all sites that we sampled, unlike the
protracted recovery period that we documented after the passage of Hurricane Fran in early
September 1996 (Mallin et al. 1998).
Fish Abundance
We collected almost 50% more fish in this year (n = 13,023) than in
1998 (n = 8,724). Seasonal patterns in fish abundance were similar to those reported in
previous years (Mallin et al. 1997, Mallin et al. 1998), with largest electroshocking and
gillnetting collections occurring in late spring and summer months. The trawl sample
abundance clearly reflected patterns of fish immigration, especially the recruitment of
post-larval Atlantic croaker. This species dominated the trawl catches in October,
November and December, as they moved into the estuary from offshore spawning sites. They
arrived in largest numbers in the Cape Fear River in September (Table
8.17) and were
captured most commonly in the Northeast Cape Fear River in November (Table
8.18). Juvenile
croaker, spot, and menhaden were all caught in large numbers in estuarine stations later
in the spring (Tables 8.22 –
8.24).
Trawling and electroshocking generally produced more individuals than
gillnetting (Figures 8.1- 8.9). As in previous years, electroshocking CPUE was higher in
the upper Cape Fear River stations than in more estuarine sites and lower in the upper
Northeast Cape Fear River stations than in sites farther downstream (Figure
8.10).
However, consistently high catches of juvenile spot, croaker, and menhaden in the
Brunswick River and large catches of croaker at NC117 obscured this pattern for trawl
collections. In early 1997, we observed that fish abundance was lower in the Northeast
Cape Fear River than in the Cape Fear River (Mallin et al. 1997); but in 1998 fish
abundance was the same or higher in the Northeast Cape Fear than in the Cape Fear in most
months (Mallin et al. 1998). This difference between years was attributed to the recovery
of fish populations in the Northeast Cape Fear River following Hurricane Fran. Similarly,
in this year fish abundance was generally lower in the Northeast Cape Fear River than in
the Cape Fear River main stem in the months after passage of Hurricane Bonnie in August
1998.
Disease Incidence
Of the 13,023 fish we captured, 166 exhibited external evidence of
disease (1.3%). This is very similar to disease incidence levels we reported for 1998 of
1.5% (Mallin et al. 1998). As in previous years, 0 - 100% of the fish collected in an
individual sample were diseased (Figures 8.1 -
8.9), and most of the disease evidence was
in the form of fin rot or ulcerated red sores. No disease was noted in any of the trawl
collections. This was probably due to the fact that the trawl collected small juveniles
and transient species that would not have experienced prolonged exposure to degraded water
quality. Disease incidence was highest in fish collected using electroshocking (3.8%), as
in our 1997 electroshocking collections where disease incidence was 3.3% (Mallin et al.
1997). Most of the disease incidence in electroshocking collections was noted in resident
freshwater species (bowfin, Amia calva; largemouth bass, Micropterus salmoides; and
sunfish Lepomis sp.), with nearly all bowfin exhibiting reddened sores or lateral
lesions. Because these species reside in the same area for extended periods, they are more
likely to be exposed to extreme or prolonged doses of low quality water than transient
species. For gillnet collections, disease incidence was 2.1% and catfish had the highest
incidence of disease. This is a lower disease incidence for gillnet collections than the
4.0% incidence reported in 1998 (Mallin et al. 1998).
There was no clear seasonal pattern of disease incidence in either
sub-basin (Figure 8.12 and
8.13). In contrast, diseased fish were more common in the
warmer months of 1998 than in winter (Mallin et al. 1998). None of the fish we collected
from the Brunswick River or NCF6 had any evidence of disease. The lack of disease in
estuarine stations was also noted in previous years (Mallin et al. 1997, Mallin et al.
1998) and may be attributed to the higher numbers of transient species collected in these
areas. As in the other years of study, we found that disease incidence was higher in Cape
Fear River stations than in the Northeast Cape Fear drainage. This is a persistent
pattern, and may indicate that there are toxicants or other environmental stressors in the
Cape Fear River mainstem that are not as prevalent in the Northeast Cape Fear River.
Non-native Species
Non-native fishes made up over 50% of the gillnet catch this year.
These species are not naturally indigenous to the area and may be detrimental to native
fishes. Moser and Roberts (in press) documented the extirpation of native catfish by
introduced catfish in the Cape Fear River drainage. They also documented the rapid
proliferation of blue catfish since their introduction in 1966 and hypothesized that the
growth in blue catfish populations in recent years may be attributed to their ability to
feed on the introduced Asiatic clam, Corbicula fluminea. Blue catfish were the most
common species in our gillnet collections. It should also be noted that they were common
in the trawl catches in upper Cape Fear stations where juveniles are regularly captured.
In addition, non-native species were nearly as abundant in the Northeast Cape Fear River
as they were in the Cape Fear main stem (Figure 8.12 and
8.13), while in other years the
Northeast Cape Fear has not had as many non-indigenous fishes (Mallin et al. 1998). This
may signal the colonization of other parts of the drainage by these invasive species. As
in 1998, we collected a few (n=3) adult grass carp (Ctenopharyngodon idella) in the
upper Cape Fear River. Capture of grass carp is significant because they have only
recently been introduced into the drainage and they are potentially very destructive
herbivores. It is encouraging that abundance of this fish remains low.
We documented the occurrence of a non-native parasitic nematode, Anguillicola
crassus, in American eels we examined from both the Cape Fear and Northeast Cape Fear
stations. As is the case for many invasive exotic species, the proliferation of A.
crassus is facilitated by its rapid life cycle and its ability to tolerate a variety
of conditions (Kennedy and Fitch 1990). This nematode is highly fecund and capable of
completing an entire life cycle in less than two months under laboratory conditions
(DeCharleroy et al. 1990). The parasite reproduces in the swimbladder of the eel host. The
eggs are released into the water and are subsequently ingested by in an intermediate
crustacean host, which is needed for larval development. Frequently a paratenic fish host
feeds on the intermediate host. The definitive host, the eel, ingests either crustaceans
or fish bearing the infective stages of the parasite. After the initial introduction of A.
crassus in Europe, the incidence and intensity of infection in European eels quickly
increased (up to 100% in some cases, Kennedy and Fitch 1990). While death of wild eel
hosts is usually uncommon, heavy infections by A. crassus can lead to hemorrhagic
lesions, swimbladder fibriosis or collapse, skin ulceration, decreased appetite and
reduced swimming performance (reviewed be Barse and Secor 1999). Therefore, the
documentation of this exotic parasite in the Cape Fear River is very important and further
monitoring of its presence and its effects on the eel population are warranted.
8.4 Acknowledgments
We thank the N.C. Division of Marine Fisheries, Wilmington Office, for their
cooperation in collecting and transmitting the data used in this report. Brad Hammers of
the N.C. Wildlife Resources Commission also helped us to complete electrofishing samples
when our electrofishing equipment was being repaired. Cape Fear Community College kindly
provided dock space during periods when we were unable to trailer our boats. Field
assistance was provided by M. Williams, W. Patrick, S. Roberts, J. Conway, E. Johnston, J.
Bichy, and T. Thorpe. Confirmation of rare fish identification was provided by F. Rohde.
M. Williams produced the figures used in this report. The N.C. Estuarine Research Reserve
provided office support and the vessel used to conduct gillnet sampling.
8.5 Executive Summary
Comparing fish monitoring results in this year to those of previous years
resulted in some interesting differences, and similarities. The effects of Hurricane
Bonnie (August 1998) on the fish community were less pronounced than those we documented
in the aftermath of Hurricane Fran in 1997. However, fish populations in the Northeast
Cape Fear River were impacted more than those in the Cape Fear River by both storms.
Northeast Cape Fear River fish populations did not fully recover for almost a year
following Hurricane Fran, but fish diversity and abundance rebounded in just a few months
following the passage of Hurricane Bonnie. The history of storm events and the less
widespread hypoxia following Hurricane Bonnie probably both contributed to the relatively
rapid recovery of the fish community. Although overall disease incidence remained low
(1.3%), there has been a persistent trend toward higher incidence of disease among fish
collected in the upper Cape Fear River stations, as compared to upper Northeast Cape Fear
or estuarine stations. This may indicate degraded water quality or environmental stressors
in the upper Cape Fear River. Non-native species continue to
dominate the gillnet collections. In addition, we documented the occurrence of a parasitic
nematode in the swim bladder of American eels we collected throughout the drainage. This
is the first time that this non-indigenous parasite has been found in North Carolina and
it may have significant adverse effects on the eel population in this drainage.
8.6 Literature Cited
Barse, A. M., and D. H. Secor. 1999. An exotic nematode parasite of the American eel. Fisheries 24:6-10.
De Charleroy, D., L. Grisez, K. Thomas, C. Belpaire, and F. Ollevier. 1990. The life cycle of Anguillicola crassus. Diseases of Aquatic Organisms 8:77-84.
Fries, L. T., D. J. Williams, and S. K. Johnson. 1996. Occurrence of Anguillicola crassus, an exotic parasitic swim bladder nematode of eels, in the southeastern United States. Transactions of the American Fisheries Society 125:794-797.
Kennedy, C. R., and D. J. Fitch. 1990. Colonization, larval survival, and epidemiology of the nematode Anguillicola crassus, parasitic in the eel, Anguilla anguilla, in Great Britain. Journal of Fish Biology 36:117-131.
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.
Moser, M.L., and S.B. Roberts. in press. Effects of non-indigenous ictalurid introductions and recreational electrofishing on native ictalurids of the Cape Fear River drainage, North Carolina. First International Ictalurid Symposium, American Fisheries Society Special Publication.
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