Linking Brook Trout Movement and Otolith Microchemistry in a Coastal Maine System

Brook trout movements were studied in Stanley Brook, a small, oligotrophic, and coastalstream on the southern end of Mount Desert Island, Maine.  Between 2006 and 2012, the stream was electro-fished in both spring and fall. Untagged fish were PIT tagged while recaptures were measured and returned to the system.  Passive PIT antennas were located within and just upstream of tidal influence.  From thousands of tagged fish,  31 fish were selected in spring of 2013 for terminal sampling based on  i) capture and tagging at age 1, ii) a high rate of recaptures and detections over multiple years and  iii) divergent patterns of movement into tidal habitat. Otoliths were extracted from these fish for trace element analysis using a high resolution ICP-MS coupled to laser ablation system. For each sample, ablated material along a transect extending from the core to the edge of the otolith provided data on  ²⁵Mg, ⁵⁵Mn, ⁸⁵Rb, ⁸⁸Sr, and ¹³⁸Ba and ⁴⁸Ca relative to otolith annuli.   We use these data, in conjunction with validated age, growth and movement data to characterize patterns of instream movements with respect to marine influence.