Identifying the natal origin of fish is important to understand connectivity among populations. Capelin, Mallotus villosus, is a key forage fish species that spawns at beach and deep-water habitats along the Newfoundland coast. I investigated the ability to identify the natal habitat of larval capelin using otolith chemical signatures quantified via LA ICP-MS. Otolith signatures of larvae reared under identical conditions were highly variable and classification into treatments was low (~50%). To investigate whether maternal investment was responsible for this variability, artificially fertilized eggs were reared under controlled treatments. Otolith signatures reliably classified individuals into families with high success (83.4%), suggesting maternal investment may confound our ability to identify natal origin. Eggs incubated in water enriched with 137Ba revealed trace elements from the environment are being incorporated into developing otoliths. These findings suggest moderate-high differences in water chemistry and environmental conditions are required to identify the natal origin of capelin. / October 2016

Increased knowledge of stock mixing and migration patterns of Atlantic bluefin tuna (Thunnus thynnus) is required to appropriately manage and conserve declining populations. The nursery origin of giant bluefin tuna present in the Gulf of St. Lawrence was identified using stable carbon (δ13C) and oxygen (δ18O) isotopes in sagittal otoliths. Anthropogenic and natural processes are capable of impacting atmospheric and oceanic concentrations of δ13C and δ18O, affecting otolith concentrations. Therefore, inter-decadal variation of δ13C and δ18O in the otolith cores (corresponding to the first year of life) of bluefin tuna was examined prior to stock predictions and temporal variability was detected in both isotope ratios. Significant changes in both δ13C and δ18O were recorded in the otolith cores of individuals with birthdates between 1947 and 2003. Both δ13C and δ18O varied significantly as a function of year of birth, with δ13C decreasing and δ18O increasing over the time period investigated (-2.39×10-2 and 5.78×10-3 per year, respectively). The rate of change in otolith δ13C was nearly identical to the reported rates of atmospheric δ13C depletion, recently attributed to the burning of fossil fuels (referred to as the Suess effect). Observed shifts in otolith δ18O were less pronounced and likely linked to changing physicochemical conditions (i.e. salinity) in oceanic reservoirs over the time period investigated. The results show that otolith cores of bluefin tuna effectively track inter-decadal trends and record past oceanic δ13C and δ18O levels. After adjusting for inter-decadal trends, the isotopic composition of milled otolith cores of giants from three decades (1970s, 1980s, 2000s) and three regions were compared to otolith δ13C and δ18O values of yearling bluefin tuna collected from eastern and western nurseries. Maximum likelihood estimates indicated that 99% of bluefin tuna caught in the Gulf of St. Lawrence fishery originated from the western nursery, with no significant differences among the decades and regions examined. Results suggest that little to no mixing of eastern and western populations of adult bluefin tuna occurs in the Gulf of St. Lawrence, making it important for the management and conservation of the declining western population.

Increased knowledge of stock mixing and migration patterns of Atlantic bluefin tuna (Thunnus thynnus) is required to appropriately manage and conserve declining populations. The nursery origin of giant bluefin tuna present in the Gulf of St. Lawrence was identified using stable carbon (δ13C) and oxygen (δ18O) isotopes in sagittal otoliths. Anthropogenic and natural processes are capable of impacting atmospheric and oceanic concentrations of δ13C and δ18O, affecting otolith concentrations. Therefore, inter-decadal variation of δ13C and δ18O in the otolith cores (corresponding to the first year of life) of bluefin tuna was examined prior to stock predictions and temporal variability was detected in both isotope ratios. Significant changes in both δ13C and δ18O were recorded in the otolith cores of individuals with birthdates between 1947 and 2003. Both δ13C and δ18O varied significantly as a function of year of birth, with δ13C decreasing and δ18O increasing over the time period investigated (-2.39×10-2 and 5.78×10-3 per year, respectively). The rate of change in otolith δ13C was nearly identical to the reported rates of atmospheric δ13C depletion, recently attributed to the burning of fossil fuels (referred to as the Suess effect). Observed shifts in otolith δ18O were less pronounced and likely linked to changing physicochemical conditions (i.e. salinity) in oceanic reservoirs over the time period investigated. The results show that otolith cores of bluefin tuna effectively track inter-decadal trends and record past oceanic δ13C and δ18O levels. After adjusting for inter-decadal trends, the isotopic composition of milled otolith cores of giants from three decades (1970s, 1980s, 2000s) and three regions were compared to otolith δ13C and δ18O values of yearling bluefin tuna collected from eastern and western nurseries. Maximum likelihood estimates indicated that 99% of bluefin tuna caught in the Gulf of St. Lawrence fishery originated from the western nursery, with no significant differences among the decades and regions examined. Results suggest that little to no mixing of eastern and western populations of adult bluefin tuna occurs in the Gulf of St. Lawrence, making it important for the management and conservation of the declining western population.

Asian carp have rapidly expanded their range through much of the Mississippi River Drainage over the past 10 to 15 years. Silver and bighead carp are now the dominant fish species present along several reaches of the Illinois River. The upper Illinois River and shipping canals entering Lake Michigan are of great concern as pathways for Asian carp to enter the Great Lakes. Knowledge of reproductive habitats and dispersal pathways for these species may be valuable for ongoing and future efforts to control these exotic invasives. Previous studies have successfully identified spawning areas of native riverine species via otolith microchemistry, but this technique has not yet been applied to Asian carps. Both stable isotope and trace element ratios have been found to differ significantly among the large rivers of the Mississippi River drainage, enabling identification of natal environment for individual fish. The primary objective of this study was to identify differences in natal river origin and floodplain habitat use through the incorporation of trace elements (Sr:Ca) and stable isotopes (δ18O and δ13C). Silver and bighead carp were collected via electrofishing and trammel netting along four reaches of the Illinois River from the Mississippi-Illinois River confluence at Grafton, IL to the upper segment of the Illinois River upstream of Starved Rock State Park. Sagittal otoliths were removed from both silver and bighead carp collected from each of the four reaches of the Illinois River for analysis of stable isotope ratios and trace element concentrations. Water samples were collected seasonally from the four reaches of the Illinois River and several of its associated floodplain lakes in addition to the Missouri, Upper Mississippi and Middle Mississippi Rivers to validate water signatures of the various river reaches. Results indicated the majority of adult Asian carp caught in the Illinois River originated from the Illinois. However, there was strong evidence indicating roughly twenty percent of captured adults were in fact immigrants from other sources; primarily the Middle Mississippi river and, to a lesser extent, the Missouri River. Stable isotope results indicated that Asian carps primarily used river channel rather than floodplain lake habitats during early life. The findings of this study suggest current Asian carp removal efforts should continue to be primarily directed within the Illinois River, however, the evidence of immigrant silver carp indicate expanding the control efforts into other rivers (Middle Mississippi River and Missouri River) will further support the control of Asian carp within the Illinois River.