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600 and 800 mm TL. Most of the American eel consumed 
were yellow-phase (sexually immature adults), although 
phase determination was often difficult because of tis¬ 
sue degradation from digestion. Month was a significant 
factor in the model for American eel, and maximal pre¬ 
dation rates occurred during spring and fall, especially 
in April and October. This observation may be related to 
eel migration patterns driven by seasonal changes in tem¬ 
perature (Welsh et al., 2016; Aldinger and Welsh, 2017). 
For example, silver-phase American eel (sexually mature 
adults) make long spawning migrations in autumn, and 
yellow-phase American eel are known to make punctuated 
upstream movements as waters warm in spring (Welsh 
and Liller, 2013). Overall, predation by blue catfish on 
American eel was rare (predicted percent occurrence was 
<5% in all circumstances). 
Populations of eel species, including the American eel, 
have declined across the northern hemisphere (Bonhom- 
meau et al., 2008); therefore, blue catfish are unlikely to 
be drivers of these declines. Population declines may be 
attributed to many factors, although climate change and 
the proliferation of an invasive parasitic nematode are 
likely culprits (Shepard, 2015). Climate change may affect 
spawning and recruitment success of American eel because 
of their complex life history (Knights, 2003). Silver-phase 
eel undergo long spawning migrations to the Sargasso Sea, 
after which ocean currents transport larvae to nurseries 
on the continental slope (Wang and Tzeng, 2000). Warm¬ 
ing temperatures have been associated with changes in 
physical oceanographic processes in the North Atlantic 
Ocean, changes that may negatively affect the survival 
and transport of eel larvae (Knights, 2003). Furthermore, 
an exotic parasitic nematode, Anguillicoloid.es crassus, 
has expanded its distribution across the western Atlantic 
Ocean. Although this parasite does not cause immediate 
mortality, it damages the swim bladder and may increase 
mortality rates as silver-phase eel undergo long-distance 
spawning migrations (Fazio et al., 2012; Barry et al., 2014). 
Several conclusions can be drawn from the results of 
this study. First, our models revealed that American shad, 
river herring, and American eel are rarely consumed by 
blue catfish; however, large catfish (500-1000 mm TL) 
consume disproportionately more of these taxa. This may 
explain why results from all models indicate that overall 
predation on species of concern is highest in the James 
River, where large blue catfish are most abundant (Green¬ 
lee and Lim, 2011; Hilling et al., 2018). Predation on 
these taxa declines as blue catfish approach trophy size 
(>1072 mm TL; Gabelhouse, 1984), and reports from previ¬ 
ous work indicate that many trophy-sized blue catfish are 
cannibalistic or feed on gizzard shad (Schmitt et al., 2019). 
Although American shad, river herring, and American eel 
are rarely consumed, blue crab are frequently consumed 
by large catfish in brackish areas. 
These length-based feeding patterns have important 
implications for management of blue catfish in Atlantic 
drainages of the United States. In the James River, fish¬ 
ing for large blue catfish is quite popular (Greenlee and 
Lim, 2011), and many fishing guide services and tackle 
shops rely on this resource. For individuals involved in 
these businesses, the status of blue catfish as invasive is 
controversial because several other nonindigenous fish 
species are not considered invasive in this river, for exam¬ 
ple, the smallmouth bass and muskellunge (Esox masqui- 
nongy) in the non-tidal James River and the largemouth 
bass ( Micropterus salmoides) and channel catfish ( Ictal - 
urus punctatus ) in the tidal James River. This argument 
is valid; however, these species exist at much lower densi¬ 
ties and are far more spatially restricted than blue catfish. 
Blue catfish have spread to every major tributary of Ches¬ 
apeake Bay (Schloesser et al., 2011) and are abundant in 
brackish areas (Fabrizio et al., 2018). Moreover, population 
densities in the tidal James River have been estimated to 
be as high as 70,800 blue catfish/km 2 (Bunch et al., 2018). 
Although the results of our study indicate that trophy¬ 
sized blue catfish (>1072 mm TL; Gabelhouse, 1984) do not 
routinely consume imperiled species, it is likely that these 
large fish produce disproportionately more offspring than 
smaller fish (Hixon et al., 2014). Therefore, current regula¬ 
tions that require mandatory release of large blue catfish 
(e.g., in Virginia, anglers can only keep one blue catfish 
>813 mm TL per day) could potentially contribute to 
increases in population densities and further range expan¬ 
sion for this species. Mandatory release regulations may 
not be ideal; however, high contaminant burdens in large 
blue catfish can render them unfit for human consump¬ 
tion, particularly in the James and Potomac Rivers (Luel- 
len et al., 2018). Ultimately, it is probable that all future 
management of blue catfish in Chesapeake Bay will be 
controversial because differing opinions exist among var¬ 
ious user groups and management agencies (Orth et al. 4 ). 
Eradication programs for invasive species often fail 
in large, open systems (Britton et al., 2011; Franssen 
et al., 2014) and are unlikely to succeed for blue catfish 
in the Chesapeake Bay region (Orth et al. 4 ). Nonetheless, 
increased commercial harvest of large blue catfish (500- 
1000 mm TL) could reduce their predation on depleted 
alosines, American eel, and blue crab. In the James and 
Rappahannock Rivers, size structure of blue catfish is 
already shifting toward smaller sizes, as growth rates 
decline and large fish become rarer (Hilling et al., 2018). 
Currently, harvest of large catfish is limited because of 
concerns about contaminant burdens (Hale et al. 5 ); how¬ 
ever, it may be time to consider uses other than as human 
food for the harvest of these large catfish, including uses 
for pet foods and fertilizers (Orth et al. 4 ). Because blue 
crab are consumed most commonly in brackish segments 
of these rivers, managers may want to explore options to 
incentivize more harvest of blue catfish in these areas. 
4 Orth, D. J., Y. Jiao, J. D. Schmitt, C. D. Hilling, J. A. Emmel, 
and M. C. Fabrizio. 2017. Dynamics and role of non-native blue 
catfish Ictalurus furcatus in Virginia’s tidal rivers, 102 p. Final 
Report. Va. Dep. Game Inland Fish., Henrico, VA. 
5 Hale, R. C., T. D. Tuckey, and M. C. Fabrizio. 2016. Risks of 
expanding the blue catfish fishery as a population control strat¬ 
egy: influence of ecological factors on fish contaminant burdens, 
48 p. [Available from Va. Inst. Mar. Sci., Coll. William Mary, 1375 
Greate Rd., Gloucester Point, VA 23062.] 
