Quantifying Ingress Patterns of Atlantic Menhaden Using Spectral Analysis

Success of fish recruitment is set in the early life history stages.  During this time, environmental conditions greatly affect survivorship. Because of the environmental changes that are occurring globally, we must understand the sources of our fisheries’ recruits in order to successfully manage and conserve them. One powerful tracer of fish origin is otolith chemistry. By conducting life history scans of otoliths, we can reconstruct environmental records of individual fish.  Advances in technical methods have led to obtaining these data with increasing accuracy. The analysis of scan data, however,  has been largely qualitative to date.  We present a quantitative approach to analyzing life history scan data by applying spectral analyses to the time series obtained from laser ablation ICPMS scans. This method allows us to make use of the full spatial and temporal aspects of our data, without making assumptions about their independence.  We demonstrate the use of spectral analysis of life history scans of juvenile Atlantic menhaden (Brevoortia tyrannus) to identify varying patterns of ingress into Chesapeake Bay. By quantitatively evaluating life history scan data, we reveal the additional information contained in the records, as well as highlight the necessity of applying appropriate statistical tests to ecological time series.