A sea elephant rarely deceives
It is the story of a large seal, the unwitting witness to the carelessness of human beings. This is because Mirounga angustirostris (the northern elephant seal) is a cruel reminder of the old adage: “after us the deluge”. The pollutants that we dump into the environment find their way into the marine food chain, and they contaminate all levels of this pyramid with the risk that they may find their way onto the plate of a super predator: mankind itself. The northern elephant seal is therefore this “great witness” which is observed by two researchers from Liège, Sarah Habran and Krishna Das, of the Oceanology Laboratory of the University of Liège, in an article published by the international journal Environmental Pollution (1). This article, which is a prelude to the doctoral thesis of Sarah Habran, is in line with an extensive Belgian and international study on the effect of pollutants on marine mammals (2).
As carnivorous marine mammals, the elephant seals are the largest representatives of the seal family phocidae or true seals. Their name, which evokes the land elephants endowed with trunk and defences, has been given to them because of two physical characteristics that differentiate them from other phocidae. Firstly, there is their imposing mass: while an ordinary seal of male sex measures 1m70 for an equivalent weight of 100 kilos, the northern elephant seal can reach three tonnes in the case of an adult male! Secondly, there is this kind of rough trunk (called proboscis) that develops in the males. This curious appendage enables them to amplify the eructations and roars they make when they enter into competition with rivals of the same species.
This family counts two separate species which don’t meet each other: the southern elephant seal (Mirounga leonina), which inhabits the Subantarctic region and come to breed on the region’s coasts (Patagonia, The Falkland Islands, The Kerguelen Islands), and the northern elephant seal (Mirounga angustirostris), which frequents the Northern Pacific Ocean and comes to breed and moult on the American coasts, in California or in Baja California to the north of Mexico. Only this latter species is concerned by the present study, which is being carried out at the same time as a study on the grey seals of the North Atlantic.
There is a great sexual dimorphism in the northern elephant seal: the males, who can measure as much as five metres in length, are much heavier than the females who measure a maximum of three metres in length. These animals have a very polygamous system of reproduction: the larger dominant males preside over large groups of females known as a ‘’harem”. A single dominant male can therefore “seduce” and fertilize more than fifty females in one season!
(1) Sarah Habran, Cathy Debier, Daniel E. Crocker, Dorian S. Houser, Krishna Das, Blood dynamics of mercury and selenium in northern elephant seals during the lactation period, in Environmental Pollution 159 (2011) 2523-2529, éd. Elsevier
(2) Sarah Habran’s thesis is in line with a larger framework which is interested in the levels and effects of organic and inorganic pollutants in marine mammals. This research convention is financed by the Fundamental collective Research Fund (Funds associated with the F.R.S. – FNRS) and finances two teams at the University of Louvain-la-Neuve (Prof. Cathy Debier) and the University of Liège (Dr Krishna Das and Prof. Jean-Marie Bouquegneau). Other collaborators both Belgian and foreign brought their help and expertise to the table for the acquisition of samples, veterinary monitoring and the analysis of the different organic pollutants: Sonoma State University (California, United States), Sea Mammal Research Unit (University of St Andrews (Scotland, United Kingdom), Dr Ursula Siebert (University of Veterinary Medicine Hannover, Foundation, Institute of Terrestrial and Aquatic Wildlife Research –ITAW–, Germany), Prof. Jean-Pierre Thomé (CART, ULg), Prof. Adrian Covaci (Toxicological Center, Université d’Anvers).