4 | RESULTS
From each period we were able to obtain tissue for δ13C and δ15N analysis from six San Juan River fishes. Sample sizes for each species were smaller for the historical (n range = 6 – 13) compared to the contemporary period (n range = 23 – 385) but the size range of each species sampled was similar (Table 1). Overall, the global mean δ15N of fishes increased from 9.36‰ (SD = 1.35) to 12.76‰ (SD = 1.43) between periods (Figure 2). Mean δ13C of fishes demonstrated less change with the historical mean of -22.67‰ (SD = 1.33) compared to the contemporary mean of -22.74‰ (SD = 0.96).