Concentrations of strontium in the pectoral fin rays of the white sturgeon(Acipenser transmontanus) by laser ablation sampling - inductively coupledplasma - mass spectrometry as an indicator of marine migrations

Laser ablation sampling - inductively coupled plasma - mass spectrometry (L AS-ICP-MS) was an effective technique for the comparison of relative Sr con centrations in the opaque growth zones (annuli) in the fin rays of white st urgeon (Acipenser transmontanus). Three of 29 Fraser River white sturgeon ( 10.3% of the sample) showed significantly higher Sr fin ray concentrations in at least one annulus compared with the remainder of the fin ray, and thi s was interpreted as evidence of marine migrations. Eleven other individual fish had significantly higher mean Sr concentrations in their first 15 ann uli compared with annuli 16-30 but lower than the concentrations of the thr ee putative diadromous fish, and this was interpreted as evidence of time s pent in the estuary. Eight Fraser River fish greater than 15 years old show ed no significant increase in fin ray Sr concentations in the first 15 annu li, and Sr concentrations remained below 350 ppm throughout their lives. Th ese individuals were considered likely to have spent most of their lives in a freshwater environment. Based on the evidence in this study, it is proba ble that the majority of white sturgeon in the lower Fraser River are not d iadromous, but many spend extended periods of time in the Fraser River estu ary as juveniles.