Abstract
The understanding of fish communities' changes over the past centuries has important implications for conservation policy and marine resource management. However, reconstructing these changes is difficult because information on marine communities before the second half of the 20th century is, in most cases, anecdotal and merely qualitative. Therefore, historical qualitative records and modern quantitative data are not directly comparable, and their integration for long-term analyses is not straightforward. We developed a methodology that allows the coding of qualitative information provided by early naturalists into semi-quantitative information through an intercalibration with landing proportions. This approach allowed us to reconstruct and quantitatively analyze a 200-year-long time series of fish community structure indicators in the Northern Adriatic Sea (Mediterranean Sea). Our analysis provides evidence of long-term changes in fish community structure, including the decline of Chondrichthyes, large-sized and late-maturing species. This work highlights the importance of broadening the time-frame through which we look at marine ecosystem changes and provides a methodology to exploit, in a quantitative framework, historical qualitative sources. To the purpose, naturalists' eyewitness accounts proved to be useful for extending the analysis on fish community back in the past, well before the onset of field-based monitoring programs.
Highlights
Natural fluctuations and human-induced modifications have caused long-term changes of marine fauna [1,2]
The full appreciation of these changes and eventually their relation with driving forces, need a broadening of the time horizon through which we look quantitatively at ecosystem dynamics
We performed the analysis of temporal trends using a linear regression of the median values of the fish community structure indicators, where we considered a = 0.1 as an appropriate threshold of significance for these inherently noisy data
Summary
Natural fluctuations and human-induced modifications have caused long-term changes of marine fauna [1,2]. The rescue and analysis of past records, which encompass literary, archival and scientific sources, for reconstructing a picture of what lived in the oceans in the past, is an important task [1,6,7,8,9]. While historical quantitative data for some species may be available [5], information on marine communities before the second half of the 20th century is, in most cases, anecdotal and merely qualitative [10,11]. Quantitative analysis of long-term changes at the community level, as well as integration of historical qualitative information with modern data, is not straightforward
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