Like many commercial marine fish populations, the eastern Atlantic and Mediterranean population of Atlantic bluefin tuna (Thunnus thynnus) has experienced dramatic changes in abundance and complexity during the past 50 years due to overexploitation. Since 2014, this population has shown signs of recovery, yet we have a poor understanding of how it was composed prior to 1970, and thus how those more recent changes reflect long-term population dynamics when exploitation rates were lower and climate conditions were different. Improving this understanding would provide confidence in what the targets for recovery should be and help to predict responses to future anthropogenic and natural events.
A prerequisite for identifying long-term population dynamics is obtaining data from different time points to be compared. However, as with many ecological systems, long-term data for marine fishes are lacking. Usually, the best data available for historical eras (and in only the most-studied species), are catch reconstructions such as the tuna trap catch series (dating back to 1512, the longest catch reconstruction for any marine species). These reconstructions are vital yet are limited in the extent to which they can reveal past population states as they do not necessarily represent past abundance and cannot reveal past population complexity, i.e. in distribution, behavior and life history traits. Additionally, historical catch reconstructions are further limited in terms of which trends can be identified between more temporally distant and variable environmental and ecological conditions.
The latest Editor's Choice article in ICES Journal of Marine Science is a review of archaeological and historical information related to the eastern Atlantic and Mediterranean population of Atlantic bluefin tuna, and suggests that by 1970, which is the current management and conservation target for recovery, this population had already likely declined from historical levels. The authors suggest that novel multidisciplinary analyses on archaeological and archived tuna remains such as genomic, isotopic, and morphometric analyses can reveal past population dynamics and to what extent population abundance and complexity may have been lost throughout the long exploitation history of this population.
The authors assembled a database of tuna remains, i.e. tuna bones and scales, dug up in archaeological excavations, or archived in collections, which is free to access and update at tuna archaeology. They assessed the opportunities presented by these remains first in terms of investigating exploitation extent by comparing the number and location of archaeological remains in given periods together with the literature, and second by identifying ecological questions which could be addressed by studying the biomolecules preserved within these ancient bones, and their morphology.
Read Exploitation history of Atlantic bluefin tuna in the eastern Atlantic and Mediterranean—insights from ancient bones, the latest Editor's Choice article in ICES Journal of Marine Science. Editor's Choice articles are always free to read.
A 13th century depiction of fishing for Atlantic bluefin tuna (Thunnus thynnus) by tuna trap—in this case, the almadraba de tiro (beach seine) variation—at Zahara de los Atunes, Andalusia, Spain. Image: © Fundación Casa Medina Sidonia 2021.