Abstract
As a top predator, California sea lions (Zalophus californianus) can be used as sentinels to record ecosystem conditions because of the trace metals that bioaccumulate in their tissues and are biomagnified in the trophic webs. The concentration of 11 trace elements (Al, As, Cd, Co, Cu, Fe, Hg, Ni, Pb, Se, and Zn) was measured in California sea lion skulls from four regions of the Gulf of California (Mexico): Northern Gulf, Ángel de la Guarda, Central Gulf, and Southern Gulf. The aims of this study were (1) to determine and compare the mean concentration of trace elements among the four regions, and (2) to estimate the pollution situation of each region using the more toxic trace elements. The elements found in higher concentration in sea lion bone were Al (overall mean of 73.70 µg g–1) and Zn (60.78 µg g–1). Only the concentration of As and Hg showed significant differences among regions: As was higher in the Central Gulf than in Ángel de la Guarda and the Northern Gulf, while Hg was higher in the Northern Gulf and Ángel de la Guarda than in the Central and Southern Gulf. The comparative analysis of the pollution situation indicated that the Central Gulf was the most affected by As and Cd, and the Northern Gulf and Ángel de la Guarda by Hg. Regions with different trace element concentrations may reflect different feeding habits and oceanographic conditions, and are congruent with other regional patterns suggested for the Gulf of California.
Highlights
As top predators and due to their longevity, sea lions are appropriate species for recording ecosystem conditions as biomonitors of certain environmental conditions such as pollution, presence of particular prey species, and productivity (Aurioles-Gamboa and Zavala-González 1994, Fair and Becker 2000)
In this study we examined the concentration of 11 trace elements (Al, As, Cd, Co, Cu, Fe, Hg, Ni, Pb, Se, and Zn) accumulated throughout the lifespan in the skull of individuals from the four previously defined regions for sea lion rookeries in the Gulf of California
For this study we used a total of 66 skulls of California sea lions, collected between 1978 and 1994 at 10 rookeries located in four regions of the Gulf of California: Northern Gulf (San Jorge and Isla Lobos rookeries), Ángel de la Guarda (Granito, Los Cantiles, and Los Machos rookeries), Central Gulf (San Esteban, San Pedro Mártir, and Nolasco rookeries), and Southern Gulf (Farallón de San Ignacio and Los Islotes rookeries)
Summary
As top predators and due to their longevity, sea lions are appropriate species for recording ecosystem conditions as biomonitors of certain environmental conditions such as pollution, presence of particular prey species, and productivity (Aurioles-Gamboa and Zavala-González 1994, Fair and Becker 2000). They enable monitoring trace elements that biomagnify in the trophic webs They do not have any biological function and besides occurring naturally, they may reflect an environment polluted by anthropogenic activities (Thompson 1990)
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