Introduction

During the last few decades, seals and other fish-consuming marine mammals have received attention as indicators of environmental pollution (Holden, 1970; 1975; 1978; Olsson et al., 1992) as they can reflect contaminant concentrations in their prey species as well (Law et al., 1992; Marcovecchio, 1994).

Mediterranean monk seals, Monachus monachus, occupy a high trophic level in the food web. Therefore they may be considered useful as an indicator species for investigating the biomagnification of heavy metals in the Greek waters and in the East Mediterranean in general. The IUCN/UNEP (1988) Action Plan for the Mediterranean monk seal has considers that pollution from chemical compounds may be an important limiting factor for the species’ welfare but its potential impact has not been assessed up until now. Studies on the incidence of metals on the Eastern Mediterranean subpopulations of the species, as well as from the whole Mediterranean region in general, are confined to one study of mercury concentrations in body hair of Monachus monachus (Yediler et al., 1993).


Objectives of the study

Given the endangered status of Monk seals and the potential for heavy metals to have detrimental effects upon marine vertebrates (Rawson et al., 1993), there is a clear need to augment the almost inexistent amount of data regarding heavy metal burdens in marine mammals from the Mediterranean Sea. This study is an initial investigation of heavy metal concentrations in this species and its aim is to form a baseline reference for future work.


Materials and Methods

	Map 1. Locations from where samples were collected (click to enlarge)

Tissues used in this study were derived from 17 different Mediterranean Monk Seal individuals. Samples were obtained from seals either found dead or that died during their treatment in the Seal Treatment and Rehabilitation Centre, Alonnisos. Information on the animals and the samples is provided in Table 1 locations of collection in Map 1. Localities were divided into six main geographic divisions (Table 1). Samples were analysed in the School of Ocean Sciences, Bangor, North Wales. Porcelain crucibles, previously washed with 10 % hydrochloric acid, were weighed and adequately labelled. Crucibles plus thawed sample tissues were weighed and placed in the oven at 60°C to desiccate. Samples were afterwards placed in a muffle furnace at a temperature of 540°C for five hours, until all the organic content was removed. Crucibles with samples were weighed again in order for ash weight to be calculated. 1% nitric acid was used to dissolve the ash and each sample was made up to 25ml solution in acid washed 25ml glass bottles sealed with polythene caps. Solutions were stored in acid washed plastic bottles until their analysis by Inductively Coupled Plasma–Atomic Emission Spectrometry (ICP-AES).

Table 1. Information of the Monk Seals’ samples used

Acknowledgements

Part of this study was submitted by A. Dosi for the fulfilment of the requirements of the M.Sc. Degree in Marine Biology at the University of Bangor, N. Whales. We would like to express our gratitude to Dr. Andy B. Yule for his advice and guidance throughout the completion of this thesis. We would also like to thank all authorities and individuals that contributed to this study, by reporting the strandings from where the samples were collected.