MacAvory et al.: Anadromous fish as marine nutrient vectors 
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Table 2 
Isotope values for all fish used in this study seperated by Family. “A” indicates anadromous, * indicates euryhaline range. Guild 
assingments are based on diet as reported in Jenkins and Burkhead (1993). “C” indicates a group with some isotope data derived 
from MacAvoy et al. (2000). White perch ( Morone americana) shows elevated 13 C content is probably not marine protein given 
the low 6 34 S ratio; M. americana is a secondary carnivore and the high 6 13 C reflect this. Standard deviation is given after the ± 
and N is in parentheses. 
Family and Species 
Common name 
Guild: food types 
6 13 C 
6 15 N 
6 34 S 
Anguillidae 
Anguilla rostrata 
American eel 
generalist: insects, 
snails, fish, clams 
-24.7±0.7 (3) 
11.2±0.8 (3) 
0.9+2. 4 (3) 
Atherinidae 
Menidia beryllina 
inland sliverside 
planktivore 
-23.8±0.9 (3) 
15.5 + 0.2 (3) 
10.0±0.9 (3) 
Catostomidae 
Erimyzon oblongus c 
creek chubsucker 
planktivore: 
planktonic crustaceans 
-28.1 (1) 
10.9 (1) 
5.1 (1) 
Centrarchidae 
Micropterus salmoides 
smallmouth bass 
carnivore 
-23.0±1.9 (5) 
14.5±1.3 (5) 
7.6±3.2 (5) 
Lepomis gibbosus 
pumpkinseed 
carnivore: insects, worms 
-25.4±1.1 (8) 
13.1±1.3 (8) 
6.5+2. 3 (9) 
Lepomis macrochirus 
bluegill 
carnivore: insects, worms 
-23.7±2.2 (5) 
14.7+1.8(5) 
4.7±2.0 (5) 
Clupeidea 
Alosa pseudoharengus A ■ c 
alewife spawning 
anadromous: copepods, 
diatoms, ostracods, 
shrimp, fish 
— 17.4±1.1 (7) 
12.8±0.8 (7) 
17.9±0.8 (6) 
Alosa aestivalis A> c 
Alosa sapidissima A< c 
blueback herring 
spawning 
juvenile American 
anadromous: 
copepods, cladocerans 
anadromous: copepods. 
-19.0±0.6 (7) 
13.2±0.3 (7) 
17.5±0.4 (7) 
shadspawning 
small invertebrates 
-20.2±0.6 (4) 
12.6±0.4 (4) 
8.0±2.2 (4) 
Dorosoma cepedianum 
gizzard shad 
planktivore: filter feeder 
-20.2±2.1 (7) 
14.0±0.9 (7) 
7.8±2.5 (7) 
Cyprinidae 
Hybognathus regius 
eastern silvery 
minnowcarnivore: diatoms, 
algae, ooze detritus 
-23.0±2.1 (6) 
12.4±3.4 (6) 
6.5±2.5 (6) 
Notemigonus crysoleucas 
golden shiner 
carnivore: microcrustaceans 
insects 
-24.8±1.1 (5) 
13.1±1.6 (5) 
2.5±1.7 (5) 
Ictaluridae 
lctalurus furcatus c 
blue catfish 
carnivore/piscivore 
-21.6±1.9 (43) 
15.4±2.0 (43) 
9.2±3.0 (43) 
Ictalurus punctatus 
channel catfish 
opportunistic generalist 
-20.5±2.0 (3) 
13.4±1.2 (3) 
8.5±3.2 (3) 
Ameirus nebulosus 
brown bullhead 
generalist/omnivorous 
-24.0±0.8 (3) 
13.2±0.5 (5) 
5.3±1.6 (5) 
Ameirus catus 
white catfish 
generalist/omnivorous 
-21.2±2.7 (10) 
15.8±2.3 (10) 
8.7±4.7 (10) 
Lepisosteidae 
Lepisosteus osseus 
longnose gar 
predator, piscivore 
-23.1 
16.8 
8.34 
Moronidae 
Morone saxatilis A 
Morone americana A * 
striped bass 
white perch 
generalist, piscivorous 
carnivorous: worms, 
shrimp, fish 
-25.0±2.3 (2) 
-20.7±1.2 (5) 
13.3±2.4 (2) 
16.7 ±1.4 (5) 
3.4±4.3 (2) 
7.5±3.9 (5) 
Percidae 
Perea flavescens c 
yellow perch 
carnivore: insects small fish 
-25.1±2.1 (6) 
14.3±2.2 (6) 
6.9±1.6 (6) 
The second objective was to test whether the different 
guilds of fish showed the incorporation of the marine 
isotope signal brought to the tidal freshwater by the 
anadromous fishes. This was observed, but largely lim- 
ited to the predator guild. 
Of the groups examined, the anadromous fish were 
the most 13 C-enriched, with mean values of approxi- 
mately -19%e, followed by predators and planktivores 
(means -21.8%c and -22.0%e, respectively), which were 
not significantly different from each other. This sug- 
gests that, of the remaining two guilds, carnivores were 
significantly 13 C -depleted relative to generalists (mean 
-24.1%c and -23.5%c, respectively; Table 2). There was 
approximately a 10%c range in 6 13 C among the exclu- 
sively freshwater guilds (Table 2, Fig. 2). 
Anadromous fish have elevated d 15 N values relative to 
freshwater fish with similar feeding strategies. However, 
the trophic enrichment and diet-tissue discrimination 
associated with <5 15 N signatures make using nitrogen a 
less effective tracer for source than carbon or sulfur. In 
this study there was less variability within the guilds 
5 15 N signatures, relative to r> 13 C, although the range (%c) 
