Anchovies in the Bay of Biscay are smaller than 30 years ago


In a new study covering three decades of scientific data, AZTI technology centre has found evidence that proves that this species is now smaller. The study has been backed by European projects LIFE Urban Klima 2050 and SEAWISE.

Research findings suggest that the cause is a complex interaction of factors such as temperature and population abundance.

AZTI technology centre, which specialises in marine and food research, has found evidence in a new study covering three decades of scientific data (from 1990 to 2021) that proves that anchovies in the Bay of Biscay are now smaller. The findings of this study have been published in the prestigious Global Change Biology journal.

Specifically, AZTI’s expert staff have observed a clear decrease in the average size and weight of adult specimens of European anchovy (Engraulis encrasicolus L.). Analyses suggest that the specimens are not only smaller, but are also changing in shape and becoming more slender.

“The decrease in weight is slightly more pronounced than in total length, with reduction rates that have accelerated by up to 25% per decade over the last twenty years,” highlighted Fernando Taboada, one of the main authors of the AZTI study.

Although these changes are partly due to ocean warming, the researchers involved in the study suggest a complex interaction of environmental factors. They also rule out that fishing has had a significant influence.

“We found that the more abundant the anchovies, the smaller the specimens, but this relationship with population density is less clear in more advanced stages, where temperature has been revealed as the main cause of the decrease in size,” added Guillem Chust, another of the study’s authors.

Temperature-size rule

“In general, juvenile fish in warmer waters grow faster than their counterparts in colder waters; however, these warmer conditions slow down subsequent development, leading to a smaller adult body size, known as the temperature-size rule (TSR),” explained the experts.

Researchers have confirmed two ecogeographical hypotheses to assess on a large scale how fish size changes when water temperature changes: the first one states that, when comparing different fish species that are closely related (e.g. species of the genus Engraulis), fish generally tend to be larger in colder water. The second focuses on different populations of the same species. Observations made by the technology centre reveal that, in general, individuals from the different European anchovy populations tend to be larger in colder seas.

However, as AZTI points out, “it is crucial to be cautious, as the study is based on observations and has its limitations. Additional evidence suggests, however, that the decrease in anchovy size could be an indicator of the response to changes in climate and ecosystem functioning in the Bay of Biscay”.

The study has been backed by European projects LIFE Urban Klima 2050 and SEAWISE. It has also been funded by the Department of Agriculture, Fisheries and Food Policy of the Basque Government through the FEMPA projects; and by the General Secretariat for Fisheries of the Ministry of Agriculture, Fisheries and Food of the Spanish Government, through the Next Generation funds of the Recovery Plan.