165 
Abstract — The tidal freshwater of 
Virginia supports anadromous her- 
ring ( Alosa spp.) spawning runs in 
the spring; however, their importance 
as nutrient delivery vectors to the 
freshwater fish food web remains 
unknown. The stable isotope sig- 
natures of fishes from 21 species 
and four different guilds (predators, 
carnivores, generalists, and plankti- 
vores) were examined in this study 
to test the hypothesis that marine 
derived nutrients (MDNs) brought by 
anadromous fish would be traced into 
the guilds that incorporated them. 
Spawning anadromous fish were 13 C 
and 34 S-enriched (6 13 C and 6 34 S of 
approximately 18%c and 17.7%», respec- 
tively) relative to resident freshwater 
fish. Of the guilds examined, only 
predators showed 13 C and 34 S-enrich- 
ment similar to the anadromous fish; 
however, some generalist catfish also 
showed enriched signatures. Specific 
fatty acid 6 13 C signatures for gizzard 
shad (Dorosoma cepedianum), blue 
catfish ( Ictalurus furcatus), and ale- 
wife (Alosa pseudoharengus), show 
a 10 %c range among fishes, clearly 
reflecting isotopically distinct dietary 
sources. The 6 13 C and <5 34 S distribu- 
tion and range among the freshwater 
fishes suggest that both autochtho- 
nous and allochthonous (terrestrial C3 
photosynthetic production and MDN) 
nutrient sources are important to the 
tidal freshwater fish community. 
Manuscript submitted 25 June 2008. 
Manuscript accepted 20 October 2008. 
Fish. Bull. 107:165-174(2009). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Anadromous fish as marine nutrient vectors 
Stephen E. MacAvoy (contact author ) 1 
Greg C. Garman 2 
Stephen A. Macko 3 4 
Email address for contact author: macavoy@american.edu 
1 Department of Environmental Science 
American University 
4400 Massachusetts Ave. NW 
Washington, DC 20016 
2 Center for Environmental Studies 
Virginia Commonwealth University 
1000 W. Cary St., Suite 111 
Richmond, Virginia 23284 
3 Environmental Science Department 
University of Virginia 
291 McCormick Rd. 
Charlottesville, Virginia 22903 
4 Program in Geobiology and Low Temperature Geochemistry 
U.S. National Science Foundation 
4201 Wilson Boulevard 
Arlington, Virginia 22230 
Streams in which anadromous fish 
spawn are often nutrient poor and 
the spawning anadromous fish may 
be an important source of nutrients 
to them (Kline et al., 1993; Wipfli 
et al., 2003). Sometimes spawning 
anadromous fish even fertilize near- 
stream terrestrial environments 
(Ben-David et al., 1998; Koyama et 
al., 2005). The spawning fish are 
frequently semelparous and deliver 
marine derived nutrients (MDN) to 
the freshwater as moribund biomass, 
excreted ammonium ion (NH 4 + ), or 
through gamete release (Cederholm et 
al., 1989; Browder and Garman, 1994; 
Wipfli et al., 2003). Several studies 
in Alaska and the Pacific Northwest 
of North America have demonstrated 
the importance of marine nutrients 
brought to freshwater streams by 
anadromous salmonids (Bilby et al., 
2003; Kline et al., 1993; Francis et 
al., 2006). In the Gulf of Mexico, 
migrating Gulf menhaden (Brevoor- 
tia patronus) transported estuarine 
nutrients into inshore environments 
(Deegan, 1993), and returning salmon 
contributed to the productivity of 
Lake Ontario tributaries (Rand et al., 
2002). However, less work has been 
done on the East Coast of the United 
States where coastal development 
has been much more intense and the 
dominant anadromous species ( Alosa 
spp.; herring (A. aestivalis), American 
shad (A. sapidissima), and alewife (A. 
pseudoharengus )) are often not highly 
abundant (Deegan, 1993; Garman and 
Macko, 1998). Although the Alosa 
spp. on the east coast tend towards 
an iteroparous life cycle rather than 
a semelparous one, they do experi- 
ence heavy postspawning mortality 
(alewife postspawning mortality has 
been measured as 41% (Havey, 1961) 
and between 39% and 57% (Durbin et 
al., 1979)). Because tidal freshwater 
streams receive nutrients from marine 
and freshwater primary productiv- 
ity at different times, the incorpora- 
tion of these nutrients by consumers 
may be different depending on feeding 
guilds. Fish found in the same area in 
a stream may derive nutrition from 
local or translocated productivity. In 
nutrient poor systems, such as East 
Coast United States tidal freshwater 
areas, it is important to understand 
nutrient sources to different feeding 
guilds (e.g., predators, carnivores, 
generalists, and planktivores). 
For more than 20 years now, car- 
bon and nitrogen stable isotopes (re- 
