6.0 Fisheries Studies in the Lower Cape Fear
River System, June-December 1999.
Michael S. Williams and Mary L. Moser
Executive Summary
Fish diversity and abundance were decreased in the 1999 summer/fall
sampling period. An area of concern is the drop in post larval croaker this season. Loss
of nursery habitat in the Cape Fear could have negative impacts on recruitment of
commercially important marine species. Non-native abundance has increased in the gill net
catch this season. Through competition, hybrid striped bass may be depressing our native
striped bass (Morone saxatalis) population. Another area of concern is the increase
in the number of grass carp (Ctenopharyngodon idella) captured. This species feeds
on aquatic vegetation that aids in erosion control and is used as nursery habitat for
juvenile fish. An increasing population of this species could have negative impacts on
future recruitment of fisheries resources in the Cape Fear. Overall, external signs of
fish disease remain low in the Cape Fear (1.6%). Bowfin (Amia calva), however, are
exhibiting a 50% infection rate. That this resident species continues to exhibit an
abnormally high infection rate warrants concern and future tissue sampling for contaminant
loading.
6.1 Introduction
This was the third year of a comprehensive survey of fish populations
in the lower portion of the Cape Fear River basin. Past surveys have focused on obtaining
baseline data on fish community structure, seasonal and spatial trends in abundance,
monitoring 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
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 Hurricane Bonnie in August 1998 provided another opportunity
to examine the effects of these large-scale disturbances on fish community structure, this
time with the benefit of baseline data collected before the storm. Hurricane Floyd made
landfall in September 1999 giving us yet another opportunity to document fish community
response to these large storms. 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 effects of Hurricane Floyd 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). The data within
this chapter represent the period June-December 1999.
6.2 Methods
Study Sites
Fish monitoring was conducted at nine study sites in tidal regions
of the lower watershed. Five sites were selected in the Cape Fear River mainstem:
approximately 1.5 km above the NC11 bridge (NC11), the lower limb of the oxbow downstream
from Sykes 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 Bellville 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. An 18 meter reach at each site was marked off and sampling
was conducted in the same reach each month.
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
when the temperature exceeded 25oC. Data 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 /net day), % 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 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 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 (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 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 over 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), 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) was
determined for each site and sampling month.
6.3 Results
Species Richness
A total of 56 fish species were captured in the June – December
samples of 1999 (Tables 6.1-6.21). Electroshocking
produced the most diverse samples this year (n=45), as it did in 1997 and 1998. Trawling
produced 35 species and gillnetting produced 16. In general, trawling produced small
individuals (average 60 mm) and gillnetting produced large individuals (average 620 mm).
There was no discernable pattern to the differences in number of species between stations
or between months (Figures 6.1 –
6.9). Over the course of this four-year survey, 1997
was the only year without hurricane impacts. In our non-hurricane year, seasonal patterns
in diversity and abundance were documented (Mallin et al. 1998). Species richness peaked
in late summer/early fall and tended to be highest in up-river stations. This pattern was
obscured by Hurricane Bonnie in 1998 (Mallin et al. 1999) and was affected again by
Hurricane Floyd in 1999. Species richness showed no seasonal or spatial trend in 1999
(Figures 6.1-6.13). An alarming trend is the steady drop in species richness over the last
three fall seasons. The June-December samples have demonstrated declines from 70 species
in 1997, to 65 species in 1998, to 56 species in 1999. Cumulative effects from four
hurricanes in four years may be hampering the ability of the fish community to recover in
the Cape Fear River system.
Abundance
June-December abundance declined from 1998 by 43 % and catch-per-unit-effort
declined by 41%. An important portion of this abundance drop (43%) was due to reduced
post-larval Atlantic croaker abundance in the trawl samples. Atlantic croaker spawn over
the continental shelf and their larvae drift into estuaries to utilize them as nursery
areas (Norcross 1991). The influx of croaker larvae was most likely impeded by the large
fresh water discharge after Hurricane Floyd. Loss of the use of nursery areas in the Cape
Fear River system may negatively impact future recruitment of commercially important
marine species. Abundance fluctuations due to estuarine post larval species loss does not
account for all of the abundance drop. Decreases in freshwater resident species account
for 44 % of the abundance loss. This may be due to the compounding effects of four
hurricanes in four years. Not only does the oxygen drop from hurricanes cause fish kills,
but long term effects from pollution introduced from these storms can bioaccumulate in the
tissues of fishes. Accumulation of toxins in fish can lead to higher infection rates
(Macfarlane et al. 1986), a lower reproductive output (Gillespie 1986), behavior changes,
damage to internal organs, and even death (Coughlan 1989). There is clearly a need to
conduct tissue testing for toxins in local fish species. Information from this testing
will both allow us to ascertain if bioaccumulation of toxins is occurring in our
fisheries, and allow us to provide information that may protect the public from
potentially ingesting harmful toxins. Information gained from this work would also insure
that the abundance and diversity drop is the result of a disturbed system that has not had
a chance to recover and not a polluted system where the accumulated toxins are impeding
reproduction. There is a critical need for further fish surveys to document whether fish
populations are recovering in the Cape Fear River drainage.
Disease
Of the 4,577 fish caught in June-December sampling period of 1999, 1.6%
exhibited external signs of disease (Figs.
6.1-6.13). That is an increase of 14% from the
June-december period of 1998. Most external signs of disease were in the form of fin rot
and/or ulcerated red sores. Bowfin (Amia calva), blue catfish (Ictalurus
punctatus), and bluegill (Lepomis macochirus) had the highest disease
incidence. No seasonal pattern of disease was observed this fall. The only spatial pattern
noted was the continually high disease percentage in the Cape Fear River stations as
opposed to the Northeast Cape Fear River stations. This is a pattern that has been
documented in all three years of sampling. It was brought to our attention in Mallin et
al. (1999) that there may be toxicants or environmental stressors in the Cape Fear that
may be causing the higher disease percentage in the Cape Fear drainage that are not in the
Northeast. Further investigations using fish tissue sampling may shed light into the
potential toxicant problems in the Cape Fear.
Of the diseased fish that were caught, 40% were bowfin (Amia calva).
This species can use a modified swim bladder to absorb oxygen from the air (Hendrick, et
al 1994). This unusual ability gives this species the ability to utilize hypoxic areas in
the water where other predators are excluded. Fifty percent of the bowfin caught exhibited
external signs of disease. A high number of diseased bowfin in a system could be an
indicator of degraded water quality.
Non-native species
Non-natives are species that have been introduced to a system by humans and
do not naturally occur there. Non-natives 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 natives. This gives non-natives a competitive advantage
that can lead to the population depression or extirpation of more desirable native
species. Moser and Roberts (1999) documented the extirpation of native catfish by the
non-native blue (Ictalurus furcatus) and flathead catfishes (Pylodictis olivaris)
in the Cape Fear drainage. Blue catfish were the most abundant species caught in gillnets
this fall (Tables 6.15-6.21). Flathead catfish are piscivorous at age-class 1 and are
known to consume juvenile striped bass, catfish and sunfishes, and current studies are
investigating their potential negative impacts on the shad population. Both of these
species have attained sizes of over 65 pounds. Their sheer
size and large population are likely having dramatic impacts on the riverine ecosystem.
Grass carp (Ctenopharyngodon idella) are another non-native
species of concern. They have reached sizes of over 60 pounds in this state. They are
herbivores and have been introduced to ponds and reservoirs to control aquatic vegetation.
When they are introduced to the Cape Fear by flooding events, however, they consume
aquatic vegetation that not only aids in controlling erosion but is also used as nursery
habitat by juvenile fish. The state of North Carolina recognized the potentially
destructive diet of this species and requires that all grass carp be certified as sterile
before they can be introduced to ponds and reservoirs. The number captured this season is
causing some concern. More have been captured this summer/fall sampling period (n = 8)
than in all the previous years of sampling combined. 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. A reproducing population of these non-natives
could have severe negative impacts on our fisheries resources (Raibley et al. 1995), and
monitoring of this species should be a priority of any future fish surveys.
Non-natives comprised 7.6% of our catch this year (Figs.
6.1-6.13).
They made up 65% of the gill net catch, up from 50% last year. The upper-most stations in
the Cape Fear and the Northeast had the highest percentage of non-natives, but no clear
pattern between stations or seasons was observed (Figs.
6.1-6.13). This is likely
explained by having less transient marine species in the freshwater upper-river stations.
Non-natives populations should be closely monitored in future surveys.
6.4 Acknowledgments
We thank the Division of Marine Fisheries,
Wilmington office for conducting the trawling portion of this survey and supplying the
data they collected for this report. We also thank Cape Fear Community College for
providing dock space during times we could not trailer our boat. Field assistance was
provided by John Bichy, Jean Conway, Wesley Patrick, Teresa Thorpe, and Kathryn Warne. The
N.C. Estuarine Research Reserve provided office support and the vessel used to conduct
gillnet sampling.
6.5 Literature Cited
Coughlan, D. J., and J. S. Velte. 1989. Dietary toxicity of
selenium-contaminated red shiners to striped bass. Transactions of the American Fisheries
Society 118:400-408.
Gillespie, R. B. and P. C. Baumann. 1986. Effects of high tissue
concentrations of selenium on reproduction by bluegills. Transactions of the American
Fisheries Society 115:208-213.
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.
Macfarlane, R. D., G. L. Bullock, J. J. A. McLaughlin. 1986. Effects
of five metals on susceptibility of striped bass to Flexeibacter columnaris.
Transactions of the American Fisheries Society 115:227-231.
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. 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.
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.
