277 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
n* established in 1881 
Spencer F. Baird 
First U S- Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Modeling the predation dynamics 
of invasive blue catfish (Ictalurus furcatus) 
in Chesapeake Bay 
Joseph D. Schmitt (contact author) 1 
Brandon K. Peoples 2 
Aaron J. Bunch 3 
Leandro Castello 1 
Donald J. Orth 1 
Email address for contact author: jschmitt@usgs.gov 
Abstract —Blue catfish (Ictalurus fur¬ 
catus) have been widely introduced 
throughout the United States and are 
invasive in Chesapeake Bay. Despite 
this proliferation, little is known about 
the diet of this large, predatory catfish. 
We used stratified random sampling to 
collect stomachs from 14,488 blue cat¬ 
fish in Chesapeake Bay. Canonical cor¬ 
respondence analysis (CCA) was used 
to identify key drivers of the diet of 
blue catfish, and generalized additive 
models (GAMs) were used to explore 
trends in rates of predation by blue 
catfish on depleted or commercially 
valuable native species, including 
American shad ( Alosa sapidissima), 
blueback herring (A. aestivalis), ale- 
wife (A. pseudoharengus), American eel 
(Anguilla rostrata ), and blue crab (Cal- 
linectes sapidus). Results of CCA reveal 
that diets were significantly correlated 
with season, salinity, and total length 
(TL) of blue catfish, and those from our 
GAMs reveal the circumstances asso¬ 
ciated with greater predation on these 
species. For example, we found that 
Alosa species were most susceptible to 
predation by large catfish (>600 mm 
TL) in freshwater areas during the 
month of April. This paper describes 
methods for identifying times, loca¬ 
tions, and other circumstances that 
are associated with maximal predation 
rates upon certain taxa. The informa¬ 
tion gained from these approaches can 
be used to inform management strate¬ 
gies, with the goal of reducing effects of 
predation on specific organisms. 
Manuscript submitted 8 February 2019. 
Manuscript accepted 9 September 2019. 
Fish. Bull. 117:277-290 (2019). 
Online publication date: 19 September 2019. 
doi: 10.7755/FB. 117.4.1 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Department of Fish and Wildlife 
Conservation 
Virginia Polytechnic Institute and State 
University 
106 Cheatham Hall 
Blacksburg, Virginia 24060 
Present address for contact author: 
Lake Erie Biological Station 
U.S. Geological Survey 
6100 Columbus Avenue 
Sandusky, Ohio 44870 
Invasive species are key drivers of the 
global biodiversity crisis (Vitousek et al., 
1997; Mack et al., 2000), can cause enor¬ 
mous economic losses (Pimentel, 2011), 
and can result in native species declines 
and extinctions (McGee et al., 2015). 
Invasive fish species have been a chronic 
problem at the global scale, yet there are 
considerable knowledge gaps pertaining 
to their impacts on recipient ecosys¬ 
tems (Cucherousset and Olden, 2011). 
Some introduced fish species appear to 
be benign, but others have deleterious 
ecological effects, restructuring native 
communities through competitive inter¬ 
actions or direct predation (Helfman, 
2007; Albins and Hixon, 2008). Because 
of these potential impacts, description 
of the diet is important in understand¬ 
ing how an invader may affect a given 
ecosystem (Brandner et al., 2013; Dick 
et al., 2014). 
The blue catfish (Ictalurus furcatus ) is 
the largest catfish species (Ictaluridae) 
in North America and is one of the most 
Department of Forestry and Environmental 
Conservation 
Clemson University 
256 Lehotsky Hall 
142 Jersey Lane 
Clemson, South Carolina 29634 
Region 1 Office 
Virginia Department of Game and Inland Fisheries 
3801 John Tyler Memorial Highway 
Charles City, Virginia 23030 
prolific invasive fish species in Atlan¬ 
tic slope drainages of the southeastern 
United States (Fuller and Neilson, 2018). 
Blue catfish have been widely stocked 
outside of their native range (Mississippi 
River basin) for recreational fishing pur¬ 
poses (Graham, 1999), and they were 
introduced to tidal rivers in Virginia 
during the 1970s (Greenlee and Lim, 
2011). Blue catfish populations grew 
rapidly during the late 1990s, prompting 
concern and subsequent management 
action (Fabrizio et al., 2018). Populations 
of blue catfish have since expanded from 
tidal freshwater areas into oligohaline 
and mesohaline portions of several tidal 
tributaries of Chesapeake Bay (Greenlee 
and Lim, 2011). This expansion is prob¬ 
lematic because these brackish areas 
serve as spawning and nursery habitat 
for many native marine and estuarine 
species (MacAvoy et al., 2009; Magoro 
et al., 2015). 
Over several decades, populations of 
native fish taxa, including the Atlantic 
