Background Chelsea Sager, Caitlin Joosten, Molly Dieterich, & Dr. David Lonzarich University of Wisconsin-Eau Claire Biology Department Chelsea Sager, Caitlin Joosten, Molly Dieterich, & Dr. David Lonzarich University of Wisconsin-Eau Claire Biology Department Otoliths are calcium carbonate structures found in the inner ear of fish. Otoliths have been found to create daily growth rings and can therefore be used to establish fish age. In this study over 500 fish otoliths were counted by microscope and then Julian age was determined by back calculation. Results Introduction Objective 1: Comparison of Population Lengths in Wisconsin versus Washington Streams In May fish from Washington were larger than fish in Wisconsin. By September Wisconsin fish had caught up to and surpassed Washington fish in length. Objective 2: Comparison of Wisconsin and Washington Coho Salmon and How Birth Timing Affects Growth Fish born in Wisconsin showed no difference in growth depending on birth date. Size differences remained consistent through out the summer. Washington fish born later displayed significantly larger growth increases; allowing them to catch up to fish born earlier.  Growth rate and survivorship in coho salmon (Oncoryhnchus kisutch) are often significantly affected by birth date, stream conditions, predation, and competition for limited resources.  Being born early in the season can provide the advantage of securing limited territory space and experiencing a longer growing season. Being born late in the season can provide an advantage because there are more prey present, lowering the risk of predation.  The two streams studied here, Cranberry River in Wisconsin and Fork Creek in Washington, are exposed to different flow regimes. The Cranberry River has high flow events regularly in spring and summer, whereas Fork Creek, a lowland creek along the west coast, is exposed to high flow events during the winter months almost exclusively.  Our expectation in this study was that differences in the physical and biological conditions of the two study streams would manifest in different patterns of growth and survival for stream rearing coho salmon.. Objectives Objective 1 Compare the frequency of fish based on total length and how these frequencies changed from May to September between the two streams. Objective 2 Determine if birth date had an affect on growth and if the pattern of growth was consistent between the two streams. Objective 3 Estimate age-specific mortality in the two streams using cross-sectional frequency data. Summary Acknowledgments  It appears that growing conditions in the Wisconsin stream were more favorable than growing conditions in the Washington stream. There are several possible explanations for this pattern. It could be that the Wisconsin stream, although colder, is more productive. Higher salmon densities in the Washington stream also could have been a contributing factor, as could have been the summer flow regime in the Wisconsin stream. Summer flooding in Wisconsin Many students have participated in the project since it began nearly five years ago. In addition to the three involved in the production of this poster, they include Rachel Schoen, Matthew Brewer, Yaron Firezen, Tim Morschauser, David Koslov, Ernest Ruiz, Paulina Duarte, Rachel Haazert, Carissa Pannell, Patrick Murack, Bill Hintz, Kristine Funk, Rebecca Kitzman, Kristine Dahlheimer and Nalee Xiong. Mary Lonzarich and Dr. Steven Campana (Bedford Oceanographic Institute in Halifax, Canada) are owed special thanks. Mary for her extraordinary work in organizing and managing a large collection of specimens and data files and Dr. Campana for his generous support of time and expertise in training our lab group in the fine art of otolith analysis. We also wish to thank the UWEC Office of Research and Sponsored programs, which provided funds to support 12 students and the UWEC Diversity Mentoring program, which provided funds for two others. Funding for the printing of this poster was provided by UWEC Differential Tuition and the Office of Research and Sponsored Programs. The method used here for computing fitness based on birth dates of fish is discussed in an accompanying poster by Dieterich, Lonzarich, and Kraker. Strong selective mortality against fish born later in the season is seen in Washington fish, whereas in Wisconsin those fish born earlier in the season experience higher selective mortality. Objective 3: Estimating Age Selective Mortality of Wisconsin and Washington Coho Salmon WisconsinWashington n = 156 n = 86 n = 152 n = 120  Washington coho salmon were larger entering the summer months but Cranberry River coho salmon subsequently grew at a much faster rate so that by the fall they were significantly larger on average (73 vs 62 mm, total length)  Growth rates in Wisconsin coho salmon did not vary as a function of birth date; however, Washington coho salmon appeared to exhibit a strong pattern of compensatory growth (i.e., younger fish growing faster than older fish).  Patterns of juvenile coho salmon survival indicated sharp differences in age-specific selection for the two study streams. In Fork Creek, survival probabilities were highest for fish that hatched earliest in the spring months. In the Cranberry River, survival was greatest for individuals that hatched later in the season. Conclusions graphics/hatchery/alevin.jpg From our study we are able to draw the following conclusions. X = 42 mm X = 46 mm X = 72 mm X = 63 mm streams increases fish movement and upset feeding hierarchies. Feedinhg (or dominance) hierarchies lead to growth biased strongly in favor of large fish. No such bias would be expected in a stream where hierarchies are unstable. In fact, such a pattern of growth is suggested from our size-frequency graphs.  Differences in age-selective mortality of salmon in the two streams could be indicators of differences in the environmental factors regulating population size (predators, competitors, floods), but mortality risk might also be affected by differences in the behavior of coho salmon. Consider the compensatory growth pattern in the Washington population. Younger fish grew more rapidly than larger fish, but the behaviors that promoted such growth also appeared to have decreased their survivorship.