Fish vertebrae as archeological biomarkers of past marine ecological conditions: Comparison of mercury levels in Chilean swordfish between the Middle Holocene and the modern period

Abstract

The ocean has always been a source of inspiration for past and present civilizations, especially for those involved in fishing activities. The regular fishing of large pelagic fish by past societies using harpoons has been demonstrated, with several studies reporting the discovery of an important fishery of large pelagic fish (including swordfish) dating from as early as the sixth millennium BCE on the North Chilean Pacific Coast. The swordfish (Xiphias gladius) is a cosmopolitan, highly migratory species found in all warm and temperate oceans and seas, and mercury is known to bioamplify along food webs, increasing with the trophic level of organisms up to these top predators. This study, therefore, analyzes and compares the mercury levels of archeological and modern vertebrae in swordfish. The archeological fish remains were recovered during excavation of the Zapatero archeological site on the northern coast of Chile, and the modern vertebrae were collected from specimens caught in the Pacific Ocean. The archeological vertebrae showed lower levels of mercury in comparison with those of current individuals, despite their larger size. However, the elevated Hg levels in archeological vertebrae proved the presence of naturally occurring mercury in the mid‐Holocene. Analyses on modern vertebrae confirmed the anthropic origin of mercury in the marine food web. Mercury biomagnifies through the marine food chain to swordfish (and humans) and did so even during the Holocene (bioaccumulation phenomenon). This study evidences that vertebrae and bones are potentially good biomarkers of mercury, including for archeological fish remains, and that the possible harmful effects on the health of past human communities can be analyzed and explained by the high consumption of fish.

Insights into swordfish (Xiphias gladius) movement patterns and habitat utilization off the coast of northern Chile

“…Similar to findings in the ENP (Carey & Robison 1981, Dewar et al 2011, the swordfish tagged off the coast of northern Chile revealed daytime depths that were much shallower than those documented for offshore waters (Abascal et al 2010). The daily depth records also showed considerable basking activity, a behavior that has supported the use of harpoon methods in this region since the sixth millennium BCE (Béarez et al 2016, Biton-Porsmoguer et al 2022. The relatively shallow daytime existence aligns with areas of low DO levels.…”

Patologías congénitas y defectos del desarrollo en poblaciones arqueológicas en la costa desértica de Antofagasta: reflexiones sobre su origen a partir de casos de estudio

“…Lamentablemente, el estado de esta investigación nos limita en establecer efectivamente si la ingesta y/o inhalación de arsénico son los causantes de estas patologías, o si todos los miembros de las comunidades participaron activamente en el sistema de parentesco propuesto. Por otro lado, tampoco podemos descartar que la ingesta de otros metales pueda estar causando las enfermedades aquí mencionadas, como se ha sugerido en recientes trabajos, los cuales han detectado la presencia elevada de cadmio y cobre en restos humanos (Huerta, 2019), y de mercurio en recursos marinos consumidos en tiempos prehistóricos (Biton-Porsmoguer et al, 2022). Todos estos metales tienen el potencial de generar enfermedades congénitas (Winter, 1982;da Rocha et al, 2011;Taboada et al, 2017;Bjorklund et al, 2019).…”

A study of trophic structure, physiological condition and mercury biomagnification in swordfish (Xiphias gladius): Evidence of unfavourable conditions for the swordfish population in the Western Mediterranean

“…Atmospheric inputs represent the main source of mercury in the Mediterranean Sea, representing annual fluxes of about 37.7 Mg y -1 THg and 0.4 Mg y -1 MeHg, with higher THg and MeHg concentrations being recorded in the Western basin compared to the Eastern basin, both in seawater and sediments (Cossa et al, in press). The origin of Hg in the oceans is natural, ancient and anthropogenic (Biton-Porsmoguer et al, 2021).…”