Aaron Fordham and Dr. Dennis Shiozawa, Biology
The Mottled Sculpin Cottus bairdii is found in cool to cold streams, creeks and rivers of northern North America (Page and Burr 1991). Sculpin are a benthic fish, living on the bottoms of the streams and rivers that they occupy. They reach 125 to 200 mm in total length when mature and can grow to 31mm-36mm by autumn of their first year of life (Ludwig and Normen 1969). Very little research has been conducted on the age and growth of C. bairdii and no comparative studies have been done examining the influence of elevation in their growth rates.
Our research would develop an understanding of what elevations of fresh water streams are most favorable for sculpin growth. With rising water temperatures being forecast by the E.P.A (Eaton and Scheller 1996) in association with global warming, this information may become critical for predicting the future of the species.
Since mottled sculpin are cold water fish, they should grow faster in the lower water temperatures found at higher elevations. To test this hypothesis twenty populations of Cottus bairdii were examined. Many of these had been collected previously and were available from the Fish Collection of the Monte L. Bean Life Science Museum (Table 1). Over 1000 fish from varying streams elevations in Utah were collected using electrofishing equipment.
After collection, the sculpin are measured, otoliths removed for aging and then the fish is preserved in alcohol as a museum voucher. Otoliths are bones that are secreted in the inner ear of fish. They function in sound reception and balance. These bones do not articulate with other bones. They are located at the lower rear of the cranium. These are extracted from the sculpin and then mounted on microscope slides with superglue. Each otolith is then prepared for viewing by sanding with fine grit sandpaper. Once properly ground a digital image is taken using a camera mounted on a microscope. The magnification and scale of the image is also recorded. The image is then archived. Once the digital image of the otolith is captured the age can be determined by counting the annuli. The annuli, or ring, on the otolith are zones of slowed growth that are deposited in the winter. The interval between annuli represents one year’s growth.
The final processing of the otolith images is the measurement of the distance from the center of the otolith to each of the annuli and to the edge. Then by regressing fish length with its otolith total length from a population of fish a predictive equation can be generated. This equation allows the projection of the size of each fish at the time of annulus formation. This process, called back calculation, allows the estimation of the size of the fish at the end of each year of growth.
Since receiving the ORCA grant we have processed data on roughly 1700 sculpin otolith samples. These samples were analyzed to determine what relationship exists between age at growth, elevation and latitude. The analysis that we have conducted so far has shown that there is no definitive relationship between our variables. We presented our preliminary results in February 2008 at the Utah chapter of the American Fishing Society annual meeting in Moab, UT. Currently I am in the process of concluding our data analysis and writing our manuscript to publish.
Once the research is completed I will prepare an oral or poster presentation for an aquatic biology meeting, likely either the Desert Fishes Council or the North American Benthological Society. Ultimately I hope to publish this study in the Transactions of the American Fishery Society, Freshwater Biology, or the Journal of the North American Benthological Society. This paper would be of interest to these journals because very little is known about the age structure and growth of any of the freshwater cottids, and nothing has been done using elevation as a possible factor in inducing differential growth rates.
References
- Eaton, J. G., John, and R. M. Scheller. 1996. Effects of climate warming on fish thermal habitat in streams of the United States. American Society of Limnology and Oceanography 41(5): 1109-1115
- Ludwig, G.M., and C.R. Norden, 1969. Age, growth, reproduction of the northern mottled sculpin (Cottus bairdi) in Mt. Vernon creek, Wisconsin.- Milw. Public Mus. Occas Pap. Nat. Hist. 2:1-67
- Page, L.M., and B.M. Burr. 1991. A field guide to freshwater fishes: North America north of Mexico. Houghton Mifflin Company, Boston, Massachusetts. 432pp