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A Comparison of Common Age Determination Methods for American Shad (Alosa sapidissima) from the Connecticut River
Başlık:
A Comparison of Common Age Determination Methods for American Shad (Alosa sapidissima) from the Connecticut River
Yazar:
Beres, Frank, author.
ISBN:
9780438007260
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (47 pages)
Genel Not:
Source: Masters Abstracts International, Volume: 57-06M(E).
Advisors: Steven K. Burian; NIcholas Edgington.
Özet:
American shad (Alosa sapidissima) populations along the Atlantic coast and in the Connecticut River are prone to fluctuations but have mostly been in decline for decades. Reliable and practical methods for determining population age structure are vital to management decisions that ensure geographically distinct populations remain viable. Results from scale-based and otolith-based ageing methods determined by a single reader were assessed via: (1) percent agreement and (2) coefficients of variation to assess precision between ages derived from otolith and scales for each individual fish, and (3) Bowker's test of symmetry and (4) age-bias plot to determine if conflicting ageing results were by chance or due to inherent differences in the structures. Structures examined were found to have a low agreement and coefficients of variation, suggesting systematic differences in ages derived from the two structures. Results from Bowker's test of symmetry and the age-bias plot both show reader bias in ageing results as age estimates increase.
Previous studies from other areas, such as the Merrimack and York Rivers, have shown similar differences in results of shad ageing techniques both between readers and structures, with otoliths showing the highest accuracy and reproducibility. However, scales and otoliths had not previously been compared for ageing American shad from the Connecticut River. This comes at an important time in American shad management for the Connecticut River system, as the population structure of Connecticut River stocks are being truncated into fewer and younger age-classes, increasing the potential for a life history shift from iteroparity to semelparity.
Notlar:
School code: 0928
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
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