Isotopic effects of different preservation methods on scales of olive ridley sea turtles (Lepidochelys olivacea) from the Mexican Central Pacific.
BACKGROUND
Stable isotope analysis can be used to obtain information on olive ridley sea turtles in the Mexican Central Pacific (MCP). Tissue samples such as scale, muscle, and blood are usually not analyzed immediately and are preserved in different substances such as ethanol, formalin, sodium chloride, the ideal being liquid nitrogen. Due to logistical reasons, the latter preservation method cannot always be used. The objective of the present study was to evaluate the efficiency of dimethyl sulfoxide (DMSO) as a preservation agent for later stable isotope analysis.


METHODS
Forty-eight paired scale samples of olive ridley were collected in MCP waters and preserved in DMSO and liquid nitrogen. We determined their δ13C and δ15N values using a Carlo Erba 1108 elemental analyzer coupled to a ThermoFinnigan Delta Plus XP isotope ratio mass spectrometer (precision ±0.2‰ for each stable isotope). The mean isotopic ratios of each preservation method were compared.


RESULTS
Significant differences were observed between the isotopic ratios of samples in the two preservatives. Samples preserved in DMSO resulted in more negative isotopic values than those in liquid nitrogen, and a correction factor was calculated. The correction factors were 2.1‰ for δ13C values and 0.8‰ for δ15N values.


CONCLUSIONS
DMSO is not equivalent to liquid nitrogen for the preservation of olive ridley scales to be used for isotopic analysis. If DMSO has to be used for logistical reasons a replicate sample should also be collected to be able to estimate a correction factor. Copyright © 2016 John Wiley & Sons, Ltd.
Facultad de Ciencias Marinas, Universidad de Colima, Km 20 Carr. Manzanillo-Barra de Navidad. C.P., 28860, Manzanillo, Colima, México.
Carla
C
Carpena-Catoira
Facultad de Ciencias Marinas, Universidad de Colima, Km 20 Carr. Manzanillo-Barra de Navidad. C.P., 28860, Manzanillo, Colima, México.
Christian D
CD
Ortega-Ortiz
Departamento de Pesquerías y Biología Marina. Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Ave. IPN s/n Colonia Playa Palo de Santa Rita C.P., 23096, La Paz, Baja California Sur, México.
Fernando R
FR
Elorriaga-Verplancken