Publikationsdatum:
2022-05-25
Beschreibung:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2007
Beschreibung:
Geochemical signatures in the otoliths of diadromous fishes may allow for
retrospective analyses of natal origins. In an assessment of river-specific signatures in
American shad (Alosa sapidissima), an anadromous clupeid native to the Atlantic coast
of North America, stable isotope and elemental ratios in otoliths of juvenile American
shad produced accurate natal tags from 12 rivers. Significant inter-annual variability in
geochemical signatures from several rivers was detected, due largely to differences in
δ18O values among years. The database was further expanded to include 20 rivers from
Florida to Quebec, encompassing all major spawning populations. This task was
accomplished by collecting juvenile otoliths along with water samples from rivers where
juveniles were not sampled. Regressions between otolith and water chemistry for those
rivers where both were collected showed significant relationships for Sr:Ca, Ba:Ca, δ18O,
and 87Sr:86Sr ratios but not for Mg:Ca or Mn:Ca. Despite reducing the combined
signature to only four chemical ratios, cross-validated classification accuracies of knownorigin
juveniles averaged 93%. Ground-truthed signatures were used to classify migrants
of unknown origins. Adults returning to spawn in the York River were classified
according to their otolith composition. Only 6% of spawners originated from rivers other
than the York, supporting the hypothesis that most American shad spawn in their natal
river. Of remaining spawners, 79% originated from the Mattaponi River and 21% from
the Pamunkey River. The results suggested that while most American shad home to their
natal river there is less fidelity to individual tributaries, allowing subsidies to
subpopulations with persistent recruitment failure. Otolith signatures were also used in
mixed-stock analyses of immature migrants along the coast of Maine in the spring and
Minas Basin in the summer. Mixed-stock compositions showed remarkably low diversity
and were dominated by fish from the Shubenacadie and Hudson rivers, with an increasing
proportion of Potomac River fish over time. In contrast to results from adult tagging
studies, southern stocks were virtually absent. These data suggest ontogenetic shifts in
migratory behavior. The thesis concludes with a report that water contributed 83% of Sr
and 98% of Ba in the otoliths of a marine fish.
Beschreibung:
Support was given by National
Science Foundation grants to Dr. Thorrold (OCE-0215905 and OCE-0134998). I
received additional support from the Woods Hole Oceanographic Institution (WHOI)
Academic Programs Office, the American Museum of Natural History Lerner-Gray Fund
for Marine Research, a SEASPACE, Inc. Research Scholarship, and a WHOI Ocean Life
Institute Research Grant.
Schlagwort(e):
American shad
;
Fishes
;
Migration
Repository-Name:
Woods Hole Open Access Server
Materialart:
Thesis
Format:
application/pdf
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