Fisheries

4.1 Introduction

    Anadromous fish populations have undergone significant declines in the Cape Fear River basin. In the late 1800's, sturgeon landings from the Cape Fear River were the largest in the southeastern United States, and sturgeon, shad, herring and striped bass supported valuable commercial fisheries (McDonald 1887). Striped bass and American shad are still fished in the Cape Fear River, but landings are very low (Sholar 1977, Moser and Ross 1993). Due to population declines, there is no longer a river herring or sturgeon fishery in the Cape Fear River. Poor water quality, overfishing, habitat degradation and limited access to historical spawning sites are all likely reasons for anadromous fish declines (Ross et al. 1988).
    In addition to population declines in anadromous fishes, recreational anglers complain that resident fish communities are dominated by only a few species and that fish disease incidence is high. A recent survey of anadromous fishes in the lower Cape Fear River also noted the proliferation of hardy non-native species: flathead catfish, hybrid striped bass, blue catfish, and common carp (Moser and Ross 1993). These species may be able to out-compete native fishes, particularly in areas that experience periods of poor water quality. While a recreational fishery for catfish and sunfish still exists in this drainage, there are strong indications that the resident fish population is stressed.
    Following the southeastern North Carolina landfall of Hurricane Fran in September 1996, dissolved oxygen levels in the Cape Fear River basin were depressed for an extended period (see Chapter 5). In the Northeast Cape Fear River drainage the entire water column went anoxic for over two weeks. In the main stem of the Cape Fear River, hypoxic conditions were recorded during this period, but anoxia was confined to the lower part of the drainage. A number of fish kills, primarily in the Northeast Cape Fear and its tributaries were reported, but the effect of acute anoxia on the entire fish population was not known. In addition to direct mortality resulting from low dissolved oxygen levels, fish populations were potentially indirectly affected by reductions in food resources (see Chapters 3 and 5) and restricted habitat.
    A comprehensive survey of anadromous and resident fishes in the tidal freshwater portion of the Cape Fear basin was initiated in January 1997. The objectives of this survey were to 1) document the incidence of fish disease, 2) characterize fish community structure, and 3) track the effects of Hurricane Fran in both the Cape Fear and Northeast Cape Fear rivers. The survey was a cooperative effort between the Cape Fear River Program (Dr. Mary Moser, gillnets), the North Carolina Division of Marine Fisheries (Wilmington Office, trawl) and the North Carolina Wildlife Resources Commission (Districts 2 and 4, electroshocking). Using three gear types we were able to sample a broader segment of the fish population than can be achieved with only one sampling technique.

4.2 Methods

Study Sites

    Nine study sites were selected for fisheries monitoring (Figure 4.1). 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 at 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 (N117), about 0.8 km upstream of NCF6, and at the mouth of Smith Creek (Smith). The locations were usually near water quality monitoring stations (see Chapter 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. 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.). Anadromous species and catfish were tagged to allow later identification of individuals. All fish were released at the sampling site. The number of species collected, catch per unit effort (CPUE = number of fish / net), % 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

    District 2 and 4 biologists with the N.C. Wildlife Resources Commission 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. Sampling at the Northeast Cape Fear River sites employed a 7500 watt electrofishing system with an 18 dropper anode array, while sampling at the Cape Fear River sites employed a 5000 W generator with a 12 dropper anode array. 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 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 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 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.

4.3 Results

Species Richness

    A total of 45 species were collected in this survey (Tables 4.1 - 4.15). Electroshocking collections had the highest number of species (n = 39) and the greatest range of fish sizes (Tables 4.11 - 4.15). Gillnetting contributed three additional species to the electroshocking species list: Atlantic sturgeon, silver redhorse, and flathead catfish (Tables 4.1 - 4.5). Trawling added three more species: spottail shiner, freshwater goby, and summer flounder (Tables 4.6 - 4.10). During the course of this survey, we collected three species not previously known to occur in the lower Cape Fear drainage: brook silverside, silver redhorse and grass carp. The gillnets generally collected very large fishes (> 400 mm TL) and trawling collected primarily the smallest size classes (< 100 mm TL).
    While fish diversity varied with sampling, method, time of year and location (Figures 4.2 - 4.10), some trends in species diversity emerge when the data are pooled by either month (Figure 4.11) or station (Figure 4.12). The number of species in electroshocking collections increased with time during the course of this survey, while trawl and gillnet collections had similar numbers of species among months (Figure 4.11). Electroshocking collections were also most diverse at upriver stations (N117, NC11) and had the fewest species in estuarine stations (Smith, HB, NCF6). Similarly, gillnet catches were most diverse in the upper Cape Fear and the number of species declined with distance downstream (Figure 4.12); however, all Northeast Cape Fear gillnet samples had low species richness (< 5).

Fish Abundance

    Fish abundance varied widely with sampling method, time and location of capture (Figures 4.2 - 4.10). Because of this variability, pooling results across months or stations is misleading. For example, fish abundance appears to increase with time (Figure 4.11), but this is due to two very large trawl collections in April (Brunswick River, Figure 4.7, and Smith Creek, Figure 4.8) and one large electroshocking collection from Horseshoe Bend (Figure 4.6). These collections were all of schooling estuarine species: bay anchovies and striped mullet (Tables 4.9 and 4.15). Both gillnet sampling and trawling captured more fish in the Cape Fear River sites than in the Northeast Cape Fear River sites in most months, while the number of fish captured using electroshocking was similar in the two rivers (Figure 4.13).

Disease Incidence

    Disease incidence ranged from 0 - 100% of the fish collected in an individual sample (Figures 4.2 - 4.10). Of the 2823 fish captured in the five months of this survey, 60 exhibited external evidence of disease (2.1%). No disease was noted in any of the trawl collections. Of the 243 large fishes collected using gillnets, 5 exhibited disease (hemorrhagic scale disease or fin rot). Most disease was noted among fishes collected in electroshocking surveys (4.3% of fish collected). A wider variety of disease manifestations was noted in these samples, including: spinal deformation, pug-headedness, skin ulceration, hemorrhagic scale disease (in bowfin), and fin rot. While disease was regularly encountered in the electroshocking surveys, fish collected using the gillnets exhibited a higher incidence of disease in the last months of the survey (Figure 4.11). All diseased fish caught in gillnets were from the Cape Fear River stations and no diseased fish were captured in the Northeast Cape Fear gillnet stations (Figure 4.13). Electroshocking collections of diseased fish occurred in all of the stations sampled. Disease incidence in these collections was highest at the mouth of the Black River due to a large number of bowfin with hemorrhagic scale disease. Disease incidence was lowest above the Highway NC11 bridge and in the estuarine stations: Horseshoe Bend, Smith Creek and Brunswick River (Figure 4.12).

Non-native Species

    Non-native species are species that have been either accidentally or purposefully introduced into a system by man and are not naturally indigenous to the area. In this survey, non-native fishes were most commonly caught with the gillnets and were infrequently captured with the electroshocker and trawl (Figures 4.2 - 4.10). These species dominated the catch in 5 of the 9 gillnet stations and were often the only fish collected. The most abundant non-native species were: common carp, blue catfish, hybrid striped bass, and flathead catfish. We also collected two grass carp: a 620 mm TL fish at the mouth of the Black River in February, and an 860 mm TL fish at Indian Creek. Both fish were killed and one specimen was frozen for later reference. While non-native fishes represented a higher percentage of the catch in the Northeast Cape Fear River gillnet sites (Figure 4.13), large numbers of these species were also caught in the upper Cape Fear (NC11 and AC). Common carp, blue catfish, threadfin shad, hybrid striped bass, redear sunfish, and grass carp were non-indigenous species captured with the electroshocker, and blue catfish were the only non-indigenous fish caught in the trawl sampling.

4.4 Discussion

    While the fisheries monitoring has only been conducted for a short time, several general conclusions can be made from the data collected to date. In spite of the high variability among stations and sampling months, both gillnet and trawl sampling indicated that species diversity and fish abundance was higher in the Cape Fear River stations than in the Northeast Cape Fear stations. It is possible that this may be in response to the anoxia that the Northeast Cape Fear stations experienced in the weeks following Hurricane Fran (September 1996). The composition of the catch also indicated that the Northeast Cape Fear River fish community is still recovering from the effects of prolonged anoxia. Fish collected from the upper Northeast Cape Fear early in the sampling period were primarily estuarine species (mummichog, hogchoker, mullet) and anadromous fishes that move through the area to reach upriver spawning areas. In contrast, early samples from the upper Cape Fear River contained more freshwater residents (catfish, bowfin, sunfish). These fish may have been able to survive the less extreme hypoxia that occurred in these locations following Hurricane Fran.
    Disease incidence was highest in adult, freshwater resident species and was relatively rare among juvenile fishes, anadromous species and estuarine fishes. Diseases are most likely to occur in fish that are exposed to degraded water quality for a prolonged time. Therefore, it is not surprising that disease incidence was highest in this survey among adult fish that reside in freshwater throughout their lives. No clear spatial pattern of disease incidence is evident from data collected so far, except that disease incidence in gillnet captures was only recorded in the Cape Fear River. The gillnet data also indicated an increase in disease incidence with time, which may have resulted from increasing water temperatures during the study period.
    Non-native fishes were common in the gillnet collections and often made up over 50% of the fish caught using this gear. These species prey on and compete with native species, and can have profound effects on the entire ecosystem. In addition, they are often hardy, opportunistic fish that can thrive in stressed systems. The apparent success of these species in the Cape Fear River drainage is therefore of concern because it may signal both degraded habitat and the decline of native fish. For example, although only two grass carp were collected in this survey, these fish are significant because: 1) they have never been caught in this system before, and 2) this species is a voracious herbivore and in large numbers could significantly alter the biota in this drainage. Grass carp are introduced into farm ponds, reservoirs and lakes to control aquatic weeds. Due to the potential dangers of grass carp proliferation, laws currently require that only sterilized grass carp can be introduced in North Carolina waters. The large size of the fish we caught indicates that they were introduced fish that escaped from nearby water bodies and are not the product of grass carp reproduction. It is likely that flooding which occurred following Hurricane Fran allowed these fish to enter the drainage. While small numbers of sterilized grass carp are probably not a serious problem, it is critical that grass carp (and all non-native species) abundance continue to be monitored to detect any increases in their population size.

 

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