Research at Stetson University:
My research at Stetson University, located in DeLand, central Florida, focused on understanding fish community structure in freshwater springs. Focusing on Blue Springs in Volusia County, I used stable isotopes to:
- Examine food web structure in relation to seasonal fluxes in allochthonous nutrients. This research will focus on nutrient transport mediated by migratory species, such as Florida manatees (Trichechus manatus latirostris) and striped mullet (Mugil cephalus). I hypothesize that these nutrient fluxes provide important subsidies to the resident fish community of Blue Springs.
- Investigate both the direct and indirect impacts of invasive species on native fishes at the population and community levels. There are several species of nonnative fish that have become established in Blue Springs, including sailfin suckermouth catfish (Pterygoplichthys disjunctivus) and blue tilapia (Oreochromis aurea). My goal is to determine the ecological role that these species play in the overall fish community, and deduce their impact on native species.
- Examine physiological adaptations of spring-dwelling fishes to low-oxygen conditions that are often prevalent in these environments. Cosmopolitan species such as eastern mosquitofish (Gambusia holbrooki), Sailfin Molly (Poecilia latipinna), and Bluefin Killifish (Lucania goodei) are found in a range of habitats, including oxygen-poor water near spring boils. I will therefore be conducting experiments to examine the physiological and behavioural adaptations of these species to a range of oxygen levels.
My collaborators at Stetson University are Dr. Missy Gibbs and Dr. Kirsten Work, and several undergraduate students have gained valuable research experience working with us.
Postdoctoral Research:
During my postdoctoral time at the Illinois Natural History Survey, I investigated the interactions of non-native and native species in freshwater ecosystems in Illinois. The primary focus of this research was on invasive Asian carp in the Illinois River system. As Asian carp have the potential to alter food web structure and fisheries throughout the Great Lakes, I worked closely with university, state, and federal biologists and administrators to determine the distribution of Asian carp in the Illinois River, including initiatives to test and develop sampling, control, and removal protocols. Much of this research involved examining the effects of Asian carp on native fishes, including using stable isotope analysis of museum fish collections to reconstruct historical food webs and contrasting them with post-invasion food web structure. Initial results have shown that Asian carp appear to have depressed trophic structure and caused shifts in nutrient use relative to historic conditions. This research will therefore aid not only in preventing Asian carp ingress to the Great Lakes, but also in forecasting and mitigating their impacts.
Some of my other research projects included: analyzing existing data sets to determine how native predators affect survival of stocked fish, and how detritivores influence macroinvertebrate and zooplankton communities; modeling relative capture efficiency of multiple gears for sampling large-river fish communities; and investigating longitudinal changes in fish communities and nutrient dynamics of the Illinois River.
Publications:
Freedman, J.A., R.J.H. Hoxmeier, L.M. Einfalt, R.C. Brooks, & D.H. Wahl. 2012. Largemouth bass predation effect on stocked walleye survival in Illinois impoundments. North American Journal of Fisheries Management. 32: 1039-1045. DOI: 10.1080/02755947.2012.716014. or Download PDF
Wahl, D.H., M.D. Wolfe, V.J. Santucci, & J.A. Freedman. 2011. Invasive carp and prey community composition disrupt trophic cascades in eutrophic ponds. Hydrobiologia. 678: 49-63. DOI: 10.1007/s10750-011-0820-3. or Email PDF
Ph.D. Dissertation Research:
Ecology of large-river fishes
My Ph.D. research focused on the ecology of fishes in the Allegheny, Monongahela, and Ohio rivers of Pennsylvania. Specifically, I investigated the habitat use and trophic structure of fish assemblages, focusing on small lithophilic species such as darters. The overall project goals were to investigate any potential effects of gravel dredging on fish communities. Within that framework, I looked at distribution and biogeography of Ohio River fishes; effects of perturbations on trophic dynamics and food web structure in the Allegheny River; and the effects of anthropogenic manipulation of the rivers on darter ecomorphology.
Publications:
Freedman, J.A., B.D. Lorson, R.B. Taylor, R.F. Carline, & J.R. Stauffer Jr. Published Online First. River of the dammed: longitudinal changes in fish assemblages in response to dams. Hydrobiologia. DOI: 10.1007/s10750-013-1780-6 or Email PDF
Freedman, J.A., R.F. Carline, & J.R. Stauffer Jr. 2013. Gravel dredging alters diversity and structure of riverine fish assemblages. Freshwater Biology. 58: 261-274. DOI: 10.1111/fwb.12056. or Email PDF
Freedman, J.A., T.D. Stecko, B.D. Lorson, & J.R. Stauffer Jr. 2009. Development and efficacy of an electrified benthic trawl for sampling riverine fishes. North American Journal of Fisheries Management. 29: 1001-1005. DOI :10.1577/M08-219.1. or Download PDF
Freedman, J.A., T.D. Stecko, R.W. Criswell, & J.R. Stauffer Jr. 2009. Extensions of the Known Ranges of Percina shumardi Girard and Three Species of Etheostoma (subgenus Nothonotus) in Pennsylvania. Journal of the Pennsylvania Academy of Science. 83: 42-44. Download PDF
Other Research Projects:
Little Salt Spring Fishes
Fish community & behaviour, trophic interactions of fishes in Little Salt Spring, Florida
Collaborators: Tim White, Ben Lorson, Jay Stauffer, John Gifford, Steve Koski
Lake Xiloa Cichlids
Trophic interactions and possible incipient speciation among cichlid species flock in Lake Xiloa, Nicaragua
Collaborators: Jay Stauffer, Jeff McCrary, Mathias Geiger
Spruce Creek Trout & Crayfishes
Use stable isotopes as support for stomach content (X-ray) data of the importance of crayfish in diets of trout, role of crayfishes in a stream food web, trophic ontogeny of crayfishes
Collaborator: David Lieb
M.Sc. Research:
Movement patterns and trophic structure of a reservoir fish community assessed using stable isotope analysis
Pulp mill and municipal sewage effluents can affect fishes in many ways and environmental programs, often using a sentinel-species approach, have been developed to assess these effects. With applications to environmental monitoring studies in mind, the goals of my thesis were to use stable isotope analysis to determine fish community structure in the presence of pulp mill and sewage treatment plant effluents, and to assess the movements and site-fidelity of common fish species in this area of Mactaquac Lake at Nackawic, New Brunswick. My results indicate that pulp mill- and sewage effluent-exposed sites have lower species richness, abundance, and diversity. Fishes that are present show marked differences in trophic position and dietary sources than those at non-exposed reference sites. Yellow perch and white sucker showed high site-fidelity while white perch showed high inter-site movements. Brown bullhead and banded killifish showed intermediate or uncertain degrees of movement. These results suggest that the pulp mill effluent and municipal wastewater effluent do affect the fish communities, while yellow perch and white sucker would make the best sentinel species. The use of local reference sites is also supported for future studies at the pulp mill in Nackawic NB.
This research has been published as:
Freedman, J.A., R.A. Curry, & K.R. Munkittrick. 2012. Stable Isotope Analysis Reveals Anthropogenic Effects on Fish Assemblages in a Temperate Reservoir. River Research and Applications. 28: 1804–1819. DOI: 10.1002/rra.1576. or Email PDF
Undergraduate thesis:
Why are there no really, really big bony fishes?
The largest teleost (bony fish) that is ever known to have existed is the ocean sunfish (Mola mola) reaches is up to 1 500 kg in mass. The largest extant elasmobranch (cartilaginous fish) is the whale shark, Rhincodon typus, which can reach 15 000 kg, and several other sharks also grow larger than Mola mola. This ten-fold difference (one order of magnitude) is very biologically significant. Some extinct sharks and marine reptiles, as well as living whales also grow much larger than this. Since there are certain advantages to large size, it seems probable that some teleost would have grown to larger size, if it were able. It therefore seems likely that there is some constraint preventing teleosts from growing to such size. I investigated possible reasons for this large size discrepancy in this literature-review based study. While no definite conclusions could be reached, life-history traits and growth rates were examined in more detail as they appeared to be the most likely constraints on maximum teleost size, as they limit the growth rate of fishes.
My undergraduate thesis was published as:
Freedman, J.A. & D.L.G Noakes. 2002. Why are there no really big bony fishes? A point-of-view on maximum body size in teleosts and elasmobranchs. Reviews in Fish Biology and Fisheries. 12: 403-416. DOI: 10.1023/A:1025365210414. or Email PDF
We must not forget that when radium was discovered no one knew that it would prove useful in hospitals. The work was one of pure science. And this is a proof that scientific work must not be considered from the point of view of the direct usefulness of it. It must be done for itself, for the beauty of science, and then there is always the chance that a scientific discovery may become like the radium a benefit for humanity.
– Marie Curie