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Norfolk, VA, United States

Hoover R.R.,Center for Quantitative Fisheries Ecology | Jones C.M.,Center for Quantitative Fisheries Ecology
Marine Ecology Progress Series | Year: 2013

Life history scans of fish otoliths are bringing new insight into the structure, connectivity, and movement of fish populations. Data obtained from such scans, however, possess in-herent limitations that have not yet been fully addressed or understood. For example, several investigators have noted delays in otolith elemental uptake that do not appear to reflect habitat exposure. We hypothesized that the 3-dimensional structure of otoliths may produce sampling artifacts in the results obtained from laser ablation scans. To test this hypothesis, we sampled sagittal otoliths from juvenile Atlantic croaker Micropogonias undulatus with laser ablation inductively coupled plasma mass spectrometry to obtain elemental molar ratios of a common environmental marker (barium). We ablated 2 trenches of different depths on each otolith and performed spectral analyses on the data to investigate the effects of ablation depth, including differences in the periodicities and temporal variability between trenches. The mean barium concentration between the 2 trenches was significantly different (t = 114.25, p < 0.0001). From shallow to deep trenches, variance decreased; the standard error about the means was reduced from 0.609 to 0.086. Peaks in spectral density, which estimate the ingress timing for this species, were shifted in absolute value an average of 32 d. Our results highlight the necessity of considering depth of laser ablation when conducting life history scans. © Inter-Research 2013. Source


Hoover R.R.,Center for Quantitative Fisheries Ecology | Jones C.M.,Center for Quantitative Fisheries Ecology | Grosch C.E.,Center for Coastal Physical Oceanography
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2012

The ability to accurately measure the timing of migration is fundamental in testing hypotheses in marine ecology that deal with migration and movement of fish populations. Timing and patterns of movement in larval and juvenile fish have been estimated using life history scans of the chemical signatures encoded in their otoliths. We provide a quantitative approach to analyzing life history scan data using spectral analysis, which retrospectively measures the timing of ingress for individual fish. Saggital otoliths from juvenile Atlantic croaker (Micropogonias undulatus) were sampled using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Spectral analyses on these data estimate the timing of ingress at 68 days on average using strontium and 85 days using barium. Based on the inflection points of their nonlinear mixing curves, these data reveal entry and subsequent movement up-estuary. Moreover, we use these spectrally derived estimates to show that growth rates did not drive ingress timing for our samples. These data thus lend no support to the critical-size hypothesis in this instance. Source

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