A joint study by the University of La Laguna and the Spanish Institute of Oceanography has found that mercury levels in Canary mackerel have halved over the last 50 years. The research, led by Alba Jurado and Enrique Lozano and published in ‘The Conversation,’ compares historical specimens from 1973 with more recent catches from 2021 in Canary waters.
The authors attribute this positive change to environmental measures, such as the phased removal of lead from fuels and the Minamata Convention on Mercury, which have had “real effects.” The study highlights pelagic fish like sardines, jacks, and mackerel as valuable indicators of marine chemical health. They grow quickly, live relatively short lives, and exist in the middle of the food chain, allowing them to reflect environmental changes within months.
In their research, the team analysed up to twenty different chemical elements in the muscle of these fish, some of which are essential for life, while others, such as cadmium, lead, and mercury, can be toxic when accumulated excessively. It was noted that the concentrations of harmful elements in the mackerel usually fall below European legal limits but can vary by season, fish size and age, catching location, and even natural phenomena.
One significant factor affecting this variability is the upwelling of cold, nutrient-rich waters off Northwest Africa, which increases metal concentrations in species like mackerel and jacks during colder months. The study emphasises this is a natural oceanic process rather than pollution. Additionally, the phenomenon known as calima, which transports mineral particles from the Sahara Desert to the Atlantic, also affects fish composition. This dust brings iron, aluminium, copper, and zinc into the ocean, impacting phytoplankton and the marine food web.
Recent volcanic activity in the Canary Islands has further influenced marine chemistry, with studies showing increases in metal levels in mackerel caught near affected areas, especially following the eruption in La Palma.
The researchers point out that fish from different islands exhibit unique characteristics. Mackerel from Tenerife and Gran Canaria, known for higher human activity, tend to show slightly elevated concentrations of elements linked to urban and port activities. In contrast, fish from Lanzarote and Fuerteventura typically present higher levels of elements associated with African upwelling and Saharan dust. Biological factors, such as age, size, reproductive state, and dietary habits, also play a role in the accumulation patterns of these chemicals.
