Natural variation in elemental composition of sagittae from red drum

Concentrations of calcium, strontium, sodium, and potassium were measured along chronological transects of sectioned sagittae from adult red drum (Sciaenops ocellatus), using a wavelength-dispersive electron microprobe. Coarse sampling involved triplicate measurements at the centre of each opaque (winter) and translucent (summer) zone. Fine sampling was performed in duplicate at equidistant points (15 mu m apart) spanning four opaque zones (3 years of life). Concentrations of strontium generally increased with distance from the core (age). Other elements showed no consistent long-term trends. Sodium and potassium showed consistent differences between winter and summer otolith zones for ages 6 to 15, but calcium and strontium did not show this seasonal difference. Sampling through these zones on a finer spatial scale confirmed the winter/summer differences as cyclic trends. There was general concordance between annual variation in sodium and potassium concentrations in otoliths and concurrent trends in sea temperature, but significant departures in agreement suggested that temperature was not the immediate determinant of sodium and potassium incorporation. It is suggested that the roughly seasonal patterns of variation in otolith sodium and potassium concentrations may be a result of reproductive activity. (C) 1995 The Fisheries society of the British Isles