Collapse of a bivalve fishery documented by historical records and paleontological data

Archival data sources can bridge the gap between the paleoecological and ecological time-series and provide a socio-economic context for the understanding of long-term changes in populations of exploited marine species. Detailed fishery statistics from the eastern Adriatic Sea extend back to the early 1870s when the Austro-Hungarian maritime administration initiated a systematic and centralized reporting of annual landings. Here we combine these data with early naturalist accounts to track changes in the Ark shell (Arca noae) populations in that area over the last 150 years. Our results indicate that the collapse of the Ark shell fishery in the 1950s was preceded by at least 80 years of intensive exploitation. During that time A. noae fishery was one of the most important in the eastern Adriatic with the annual catch regularly exceeding 200 t and reaching as much as ~780 t in 1879. At the same time it was one of the cheapest marine products available on the market, consumed primarily by the poor. Historical testimonies indicate that by the late 19th century, fishery administrators and naturalists were well aware of the adverse effects of overexploatiation of marine populations and destructive fishing practices. However, A. noae was explicitly excluded from the regulations establishing legal size limits and no-catch periods that were introduced in the 1880s to protect the Mediterranean mussel (Mytilus galloprovincialis) and European flat oyster (Ostrea edulis), two bivalve species characterized by lower annual landings but much higher market value. Following a mass mortality event in the late 1940s, the annual catch of A. noae rapidly declined and has remained below ~30 t until today – an order of magnitude lower compared to the late 19th and early 20th century. Decades-long, intense harvesting of A. noae may be one the major drivers of the significant shift in its life history characteristics, which was previously documented by sclerochronological analyses of modern and fossil (middle to late Holocene) shells of this species.