SS1.02 Geochemical Tracers in Calcified Structures: Implications for Fisheries Research
Date: Tuesday, June 11, 2002
Time: 3:00:00 PM
Location: Carson A
WeberPK, University of California, Berkeley, USA,
Ingram, B, L, University of California, Berkeley, USA, 
Hutcheon, I, D, Lawrence Livermore National Laboratory, Livermore, USA, 
McKeegan, K, D, University of California, Los Angeles, USA, 
Important salmon spawning rivers within the Sacramento-San Joaquin river system have distinct and seasonally stable strontium isotopic composition (87Sr/86Sr) as a result of differences in basin geology from north to south along the western slope of the Sierra Nevada. Otolith 87Sr/86Sr is strongly related to water 87Sr/86Sr, but hatchery fish incorporate marine Sr from hatchery feed, systematically offsetting the otolith 87Sr/86Sr values relative to the watershed signal. Therefore, it is necessary to be able to distinguish hatchery from wild fish to correctly interpret the otolith 87Sr/86Sr value. In California, only 10 to 20 percent of hatchery salmon are tagged. We use otolith sulfur isotopic composition (34S/32S, expressed as delta-34S) to distinguish hatchery and wild fish. The difference in dietary delta-34S is large between the two (~13‰), and the difference is reflected in the otolith, providing a permanent record of whether a salmon is hatchery-raised or wild, and of dietary history in general. Combined, 87Sr/86Sr and delta-34S should allow the fish to be assigned to one of five hatcheries or one of seven regions in the Sacramento-San Joaquin river system.