Revista Chilena de Historia Natural 81 (4): 561-574, 2008
RESEARCH ARTICLE
Fish scale preservation and abundance in sediments from the continental margin off Chile (21-
36º S)
The relationship between fish scale preservation and variations in the sediment redox
conditions on Chile’s continental shelf are evaluated herein through fish scale counts and normalized concentrations of redox sensitive
elements (Mo/Al, S/Al, Fe/Al) using eight sediment cores taken from sites under the influence of the oxygen minimum zone off Chile
(Iquique: 20º15’ S, Mejillones Bay: 23º S, Concepción: 36º S). Off northern Chile (Iquique and Mejillones), fish scales from anchovy
(Engraulis ringens) and the Myctophidae family are dominant (mean = 90 and 120 scales 1,000 cm<sup>-
3</sup>, respectively), wheras off central southern Chile (Concepción), jack mackerel (Trachurus murphy) scales
are the most abundant (mean = 140 scales 1,000 cm<sup>-3</sup>). The abundance of hake (Merluccius gayi
gayi) and sardine (Sardinops sagax) scales is approximately one order of magnitude lower than that of anchovy or
jack mackerel. In general, the highest values and widest ranges of variation in the Mo/Al, S/Al, and Fe/Al ratios are found in Mejillones
(Mo/Al ~ 0.8-12 mg g <sup>-1</sup>, S/Al 0.2-4.6 g g<sup>-1</sup>, Fe/Al 0.3-0.7 g g<sup>-1</sup>),
followed by Iquique (Mo/Al ~ 0.2-1.8, S/Al 0.2 0.7, Fe/Al 0.5-0.8); Concepción has lower, less variable values (Mo/Al ~ 0.07, S/Al ~ 0.15,
Fe/Al ~ 0.5). According to the Mo/Al ratio, used as an indicator of paleo-oxygenation, reducing conditions in the Mejillones Bay and
Iquique sediments are relatively more intense than in those off Concepción. At all three sampling sites, the relationship between the
abundance of anchovy scales and the logarithm of the Mo/Al ratio is statistically significant (r<sup>2</sup> = 0.46, P <
0.0001), indicating a dependence between these two variables. In particular, for Mo/Al < 1 mg g<sup>-1</sup>, small
changes in the redox conditions can affect considerably scale preservation in the sediment, whereas this dependence decreases with
Mo/Al ≥ 1 mg g<sup>-1</sup>.
Key words:
fish scales, Humboldt
Current System, sediments, redox-sensitive elements, molybdenum
