DOI: 10.5061/dryad.9s4mw6mkv
title: Stable landings mask irreversible community reorganizations in an overexploited Mediterranean ecosystem

description: 1. Background. Cumulative human pressures can induce non-linear
 discontinuous dynamics in ecosystems, known as regime shifts. Regime
 shifts typically imply hysteresis, a lacking or delayed system response
 when pressures are reverted, which can frustrate restoration efforts. 2.
 The goal of the study. Here we investigate whether the northern Adriatic
 Sea fish and macroinvertebrate community, depicted by commercial fishery
 landings, has undergone irreversible regime shifts over the last 40 years.
 3. What was done. We use a stochastic cusp model to show that, under the
 interactive effect of fishing and warming, the community reorganized
 through discontinuous changes. 4. What was found. Part of the community
 has now reached a new stable state, implying that a recovery towards
 previous baselines might be impossible. Interestingly, total landings
 remained constant across decades, masking the low resilience of the
 community. 5. The relevance. Our study reveals the importance of carefully
 assessing regime shifts and resilience in marine ecosystems and advocates
 for their inclusion into management.
description: The database includes landings
 data and only seafood products caught by the Chioggia’s fishing fleet,
 operating in the Northern Adriatic Sea. Landing categories represent
 single or multiple species/taxa and were recorded monthly
 (Barausse et al., 2011;
 Mazzoldi et al., 2014).
 Some categories were removed since they include freshwater or lagoon
 species, species coming mainly from local extensive aquaculture and/or
 species whose fishery is regulated (e.g., eel, tunas), and therefore
 variation in landing is not expected to represent variation in abundance
 (for a discussion on this matter regarding the Clodia database, see
 (Barausse et al., 2011;
 Mazzoldi et al., 2014)).
 To analyze community changes over time, monthly data were summed to annual
 totals. Species which were occasionally recorded, with more than 15 zero
 annual landings, were removed. In total 37 categories, including 92
 species, were used to analyze the dynamics of the Northern Adriatic Sea
 community. Since the time
 series are fishery-dependent data and span many years in which the fishing
 capacity differed, landings were divided by fishing capacity (the gross
 tonnage of the fleet, a proxy for fishing pressure) to make them better
 indicators of relative biomass. Fishing capacity data were built using two
 datasets. The first one, including ISTAT (Italian National Institute of
 Statistics) and unpublished data, spanned from 1951 to 1993 and was
 reported in Gross Register Tonnage (GRT) (Barausse et al., 2011). The second one, obtained from the EU Fleet
 Register (https://ec.europe.eu//fisheries/cfp
 fishing_rules/fishing_fleet_en), contained data since 1991 reported in
 Gross Tonnage (GT). Since these two units of measurement cannot be
 directly converted one to another, the data provided in GRT were converted
 into GT using a conversion factor of 1.076 calculated based on the
 overlapping values of the two time series. Yearly landings in tonnes were
 thus divided by yearly Gross Tonnage. This choice reduced the period
 spanned by the dataset to 1951-2018.