PS 37-42 - Changes in trophic behavior of fish assemblages over a 100 year historical record

Abstract: We examined fish populations from Catatonk Creek, NY USA that have been collected approximately biannually since 1925 and preserved at the Cornell Museum of Vertebrates. Over this time period, we analyzed 43 time periods and 470 individual fish for morphological characteristics and stable isotope ratios. Using a combination of dissections and computerized tomography (CT) scanning we assessed mouth gape size, abdominal volume, digestive-track length and various other morphological characteristics. Additionally, we measured the stable isotope ratio of carbon, nitrogen and sulphur from fin clips and muscle tissue of all fish in the time series. The morphological data strongly suggested that multiple species in the record moved to a less predatory and more basal trophic behavior. This included a decrease in gape size, an increase in overall abdominal volume and an increase in the the length of the digestive system. The isotope ratios of nitrogen were consistent with the anatomical measures showing a depletion in the record suggesting feeding at a lower trophic position. Although we have no good record for the nitrogen baseline through time, the coincident observations of changing morphology and isotope ratio are suggestive of large changes in trophic behavior. The most rapid changes in both morphology and isotope ratio occurred in the record just after the introduction of a novel fish species into the Catatonk drainage. Beginning at this time, the novel species is found to consistently occupy higher isotope space while the two original native species decrease in trophic position and exhibit changes in morphology over the next 20-40 years. In addition to changes in tropism, we also see evidence of changing inputs to the river over time in the isotope records. Most notably, the ratios of sulphur change dramatically over the record and appear to be coincident with the decline in use of sulphur-containing coal use in the Northeastern United State.