Chinook salmon stock composition in Lake Huron: using otolith microchemistry as a natural marker of stream origin

Analysis of natural geochemical markers is a powerful, emerging approach for the study of natal origins and movement of animals. Our research will use otolith microchemistry to assign the rearing origin of Chinook salmon in Lake Huron. Our main hypothesis is that differences in elemental and isotopic concentrations among streams and hatcheries will be reflected in Chinook salmon otoliths. Our project objectives are to 1) test the hypotheses that differences exist in elemental concentrations of otoliths of wild Chinook salmon fry of known origin from Lake Huron and that differences in otolith microchemistry are related to differences in water chemistry; 2) test the hypothesis that otolith microchemistry can discriminate hatchery from wild Chinook salmon fry; and 3) develop and test a statistical model based on otolith microchemistry to discriminate the rearing origin of Chinook salmon from the recreational fishery. Water samples will be collected from Lake Huron tributaries and hatcheries that supply Chinook salmon and will be analyzed using inductively coupled plasma optical emission spectrometry/mass spectrometry (ICP-OES/MS) and multicollector ICP-MS (MC-ICP-MS). Chinook salmon fry will be collected from streams and hatcheries throughout the Lake Huron basin and otoliths will be removed. Otolith elemental and stable isotopic microchemistry will be determined by laser ablation ICP-MS and MC-ICP-MS. With these data, statistical models will be developed to discriminate stream and/or hatchery origin. The ability of otolith microchemistry to identify stock composition will be tested using adult Chinook salmon sampled from Lake Huron through existing OMNR and MiDNR sampling programs. Statistical models will be used to assign natal origin to adults and to test for spatial variation in catch composition.