Precision of age determination of northern offshore spotted dolphins.

Reilly, Stephen B. and Hohn, Aleta A. and Myrick, Jr., Albert C. (1983) Precision of age determination of northern offshore spotted dolphins. La Jolla, CA, NOAA/National Marine Fisheries Service/Southwest Fisheries Science Center, (NOAA Technical Memorandum NMFS, SWFC-3)

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We investigated within- and between-reader precision in estimating age for northern offshore spotted dolphins and possible effects on precision from the sex and age-class of specimens. Age was estimated from patterns of growth layer groups i n the dentine and cementum of the dolphins' teeth. Each specimen was aged at least three times by each of two persons. Two data samples were studied. The first comprised 800 of each sex from animals collected during 1973-78. The second included 45 females collected during 1981. There were significant, generally downward trends through time in the estimates from multiple readings of the 1973-78 data. These trends were slight, and age distributions from last readings and mean estimates per specimen appeared to be homogeneous. The largest factor affecting precision in the 1973-78 data set was between-reader variation. In light of the relatively high within-reader precision (trends considered), the consistent between-reader differences suggest a problem of accuracy rather than precision for this series. Within-reader coefficients of variation averaged approximately 7% and 11%. Pooling the data resulted i n an average coefficient of variation near 16%. Within- and between-reader precision were higher for the 1981 sample, and the data homogeneous over both factors. CVs averaged near 5% and 6% for the two readers. These results point to further refinements in reading the 1981 series. Properties of the 1981 sample may be partly responsible for greater precision: by chance there were proportionately fewer older dolphins included, and preparation and selection criteria were probably more stringent. (PDF contains 35 pages.)

Item Type: Monograph or Serial Issue
Title: Precision of age determination of northern offshore spotted dolphins.
Personal Creator/Author:
Reilly, Stephen B.
Hohn, Aleta A.
Myrick, Jr., Albert C.
Refereed: Yes
Series Name: NOAA Technical Memorandum NMFS
Number: SWFC-3
Date: 1983
Publisher: NOAA/National Marine Fisheries Service/Southwest Fisheries Science Center
Place of Publication: La Jolla, CA
Issuing Agency: United States National Marine Fisheries Service
Subjects: Ecology
Item ID: 2458
Depositing User: Patti M. Marraro
Date Deposited: 21 Jul 2009 14:28
Last Modified: 29 Sep 2011 19:05

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