Nonnative Fishes of the 

Cape Fear River System

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 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 (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.



Flathead catfish

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. 


Channel catfish

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.

Grass carp

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.


Common Carp


Redear Sunfish

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.