Whole otolith elemental analysis reveals feeding migration patterns causing growth rate differences in anadromous whitefish from the Baltic Sea

Impact of feeding migration pattern on growth rate of whitefish (Coregonus lavaretus L.) from River Kemijoki was investigated. River Kemijoki is located in the northernmost Gulf of Bothnia (Baltic Sea). Whitefish ascending the river to spawn show major growth rate variations. To study whether these variations are related to different feeding areas (migratory connectivity), whole otoliths from fast-growing (FAST^G) whitefish (n = 9, age 4 years, average weight 790 g) and slowly growing (SLOWLY^G) whitefish (n = 9, age 8 years, average weight 600 g) were analysed for elemental (Ba, Sr, Mg, Zn, Mn, Ca) concentrations by inductively coupled plasma-optical emission spectrometry. Results showed that the FAST^G whitefish had much lower otolith Ba concentration (~45%, p ≤ .01) than SLOWLY^G whitefish, revealing that FAST^G whitefish have spent more time in water of higher salinity/lower latitude, that is at feeding grounds in the southern Gulf of Bothnia. Otoliths of the FAST^G whitefish had also higher Mg (~25%, p ≤ .001) and Zn (~20%, p ≤ .05) concentrations, but lower Ca (~5%, p ≤ .01) concentrations, than the otoliths from SLOWLY^G whitefish. These results further reveal that FAST^G and SLOWLY^G whitefish have been spatially separated. In conclusion, bulk otolith elemental analysis revealed spatial separation and migration differences in river-spawning whitefish subpopulations in the Gulf of Bothnia, which apparently lead to differences in fish growth rate. Our results increase the understanding of river-spawning whitefish biology and its population structure and dynamics and may contribute to a sustainable management of river-spawning whitefish stocks.