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GRANT
NUMBER:
NA86FD0110
NMFS NUMBER: 98-NER-037
REPORT
TITLE:
Inter-Laboratory Investigation on the Feasibility of Otolith
Microconstituent Analysis to Characterize Atlantic Bluefin
Tuna Structure
AUTHOR:
David
H. Secor
PUBLISH
DATE:
March 16, 2001
AVAILABLE
FROM:
National Marine Fisheries Service, Northeast Region, One
Blackburn Drive, Gloucester, MA 01930-2298. PHONE:
(978) 281-9267
ABSTRACT
Protocols used
to collect and prepare otoliths for chemical analysis
may result in either contamination or loss of elements,
thus biasing population studies in unknown ways. We evaluated
precision and bias associated with collection and cleaning
procedures for three Atlantic tuna species: Atlantic bluefin
tuna (Thunnus thynnus), yellowfin tuna (T.albacares)
and blackfin tuna (T.atlanticus). Elemental concentrations
were measured using solution-based inductively coupled
plasma mass spectromentry (ICPMS) and atomic absorption
spectrophotometry (AAS). Seven elements were present above
detection limits in all samples (Na, Mg, K, Ca, Mn, Sr,
Ba). Mean concentrations of all seven elements were statistically
indistinguishable in fresh pairs of otoliths of T.
thynnus ( mean error 5%, range 2-8%) and T. albacares
(mean error 5%, range 3-7%); no indication of a left versus
right otolith effect was observed. Otolith elemental concentrations
were size-dependent, and significant inverse relationships
were observed for Mg, Na, and K. Deliberate contamination
of previously cleaned samples using a 10-ppm solution
of a mixture of elements demonstrated that otoliths easily
acquire surface contamination. Recleaning contaminated
otoliths restored elemental concentrations to levels similar
to control otoliths. Precision of paired comparisons between
cleaned otoliths and those exposed to contamination and
recleaned was high (mean error 6%). The effects of storage
at two temperatures (7 d at -20 C; 3 d at 1 C) were investigated.
For K, Ca, Sr, Mn, and Ba, variation between control (removed
immediately) and treatment otoliths (in situ freezing
or chilling) was similar to variation observed within
fresh otolith pairs (mean error: fresh vs. frozen 5% iced
5%).
Statistically
significant but small (<10%) post-mortem storage effects
were observed for Na and Mg. Estimates of error indexed
to natural ranges in otolith chemistry of T. thynnus
and T. albacares from different geographic regions
in the Atlantic and Pacific showed that error values of
several elements (Mg, Ba, Na, K) accounted for a small
proportion of the natural range, suggesting levels of
precision achieved in this study are suitable for the
purpose of stock delineation.
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