We investigate long-term changes in the Mediterranean marine resources driving the trawl fisheries by analysing fishers’ perceptions (Traditional Ecological Knowledge, TEK) throughout the Mediterranean Sea during the last 80 years. To this end, we conducted an extended set of interviews with experienced fishers that enabled us to classify species (or taxa) as ‘decreasing’ or ‘increasing’ both in terms of abundance, as well as average size in the catch. The aspect that most clearly emerged in all the investigated areas over time was the notable increase of fishing capacity indicators, such as engine power and fishing depth range. Atlantic mackerel, poor cod, scorpionfishes, striped seabream, and John Dory demonstrated a decreasing trend in the fishers’ perceived abundance, while Mediterranean parrotfish, common pandora, cuttlefish, blue and red shrimp, and mullets gave indications of an increasing temporal trend. Although, as a rule, trawler captains did not report any cataclysmic changes (e.g. extinctions), when they were invited to estimate total catches, a clear decreasing pattern emerged; this being a notable finding taking into account the steep escalation of fishing efficiency during the past century. The overall deteriorating status of stocks in most Mediterranean regions calls for responsible management and design of rebuilding plans. This should include historical information accounting for past exploitation patterns that could help defining a baseline of fish abundance prior to heavy industrial fisheries exploitation.

Climate change (CC) can alter the configuration of marine ecosystems; however, ecosystem response and resilience to change are usually case‐specific. The effect of CC on the demersal resources of the Aegean Sea (east Mediterranean Sea) was investigated during the past six decades applying a combination of multivariate analysis, non‐additive modeling and the Integrated Resilience Assessment (IRA) framework. We focused on the study of: (i) the biological “system” complex, using proxies of biomass (landings per unit of capacity) for 12 demersal taxa, and (ii) the environmental “stressor” complex, described by 12 abiotic variables. Pronounced changes have occurred in both the environmental and biological system over the studied period. The majority of the environmental stressors exhibited strikingly increasing trends (temperature, salinity, primary production indices) with values started exceeding the global historical means during late 1980s‐early 1990s. It is suggested that the biological system exhibited a discontinuous response to CC, with two apparently climate‐induced regime shifts occurring in the past 25 years. There is evidence for two‐fold bifurcations and four tipping points in the system, forming a folded stability landscape with three basins of attraction. The shape of the stability landscape for the Aegean Sea's biological system suggests that while the initial state (1966–1991) was rather resilient to CC, absorbing two environmental step‐changes, this was not the case for the two subsequent ones (intermediate: 1992–2002; recent: 2003–2016). Given the current trajectory of environmental change, it is highly unlikely that the biological system will ever return to its pre‐1990s state, as it is entering areas of unprecedented climatic conditions and there is some evidence that the system may be even shifting toward a new state. Our approach and findings may be relevant to other marine areas of the Mediterranean and beyond, undergoing climate‐driven regime shifts, and can assist to their adaptive management.

Since the first introduction of the landing obligation (a.k.a. Discard ban) in 2015, the EU Mediterranean fisheries are facing some unforeseen challenges. The demersal bottom trawl fisheries, being the most significant contributors to the so-called 'discard problem', are confronted with the greatest challenges. Data from the Italian and the Greek fleet, spanning over two decades (1995–2015), were analysed with the intention of revealing the diversity and heterogeneity of the discard problem, especially for regulated species. Species composition of discards, as well as discarding rates, were shown to be irregular, fluctuating among areas, depth strata, seasons and years. Although fish dominated the discarded gross catch in weight, benthic invertebrates (other than commercial cephalopods and crustaceans) were the taxa discarded almost exclusively. The established minimum conservation reference size was largely ignored by fishers. From a management point of view, the present investigation suggests that the recently established Discard Management Plans lack scientific evidence (given the high intrinsic variability of the parameters and confusion regarding the rules) and provide exemptions from the landing obligation that will in practice allow the average Mediterranean bottom trawl vessel to continue business as usual. Moreover, detecting if these rules are actually respected is an almost impossible task for the Mediterranean control and enforcement authorities. Incentivizing the adoption of fishing technologies and practices that reduce pre-harvest mortality and post-harvest discards, while avoiding damage to sensitive marine species and habitats, seems the only way to move forward, rather than dealing with the problem after it has occurred.

European hake, Merluccius merluccius L. 1758, is a highly valuable demersal fish species exploited in both the east Atlantic and the Mediterranean Sea. Changes in the size-at-maturity of this species have been reported in various geographic areas. Size-at-maturity is a key parameter in fishery management. Our main goal was to study the trend of the size-at-maturity of European hake in the eastern Ionian Sea (Central Mediterranean) over the last five decades. Utilizing a multi-decadal series of data for various environmental variables, we employed multivariate analyses and non-additive modeling in an attempt to identify shifts in the climatic environment of the eastern Ionian Sea and whether the maturation of the hake population could be affected by these changes. The analyses used suggest a plausible environmental regime shift in the study area in the late 1990s/early 2000s. The decrease in size-at-maturity that was detected in the last two decades may, thus, be associated with environmental changes. However, as many fish stocks already experience fishery-induced evolution, further investigation is necessary to determine whether this environmental effect is an additional stressor on a possibly already fishery-impacted population. The outcomes of this study highlight the importance of investigating the relationship between fish reproductive traits and altered environmental conditions, as the latter are generally ignored during assessments, affecting the robustness of fishery management.