Tracking signals of change in Mediterranean fish diversity based on local ecological knowledge

Abstract

One of the expected effects of global change is increased variability in the abundance and distribution of living organisms, but information at the appropriate temporal and geographical scales is often lacking to observe these patterns. Here we use local knowledge as an alternative information source to study some emerging changes in Mediterranean fish diversity. A pilot study of thirty-two fishermen was conducted in 2009 from four Mediterranean locations along a south-north gradient. Semi-quantitative survey information on changes in species abundance was recorded by year and suggests that 59 fish species belonging to 35 families have experienced changes in their abundance. We distinguished species that increased from species that decreased or fluctuated. Multivariate analysis revealed significant differences between these three groups of species, as well as significant variation between the study locations. A trend for thermophilic taxa to increase was recorded at all the study locations. The Carangidae and the Sphyraenidae families typically were found to increase over time, while Scombridae and Clupeidae were generally identified as decreasing and Fistularidae and Scaridae appeared to fluctuate in abundance. Our initial findings strongly suggest the northward expansion of termophilic species whose occurrence in the northern Mediterranean has only been noted previously by occasional records in the scientific literature.

Figure 1. Study locations in the Mediterranean Sea.

Figure 2. Percent distribution of fishing methods adopted by the respondents.

Interviewed (Tot N = 32) were both recreational (N = 8, 25%) and professional (N = 24, 75%) fishermen.

Figure 3. Non-metric Multi Dimensional Scaling (nMDS) ordination comparing interviews outputs across the different study locations.

The position of each dot is defined by the assemblage of species recorded in each interview. La = Lampedusa; Li = Linosa; Mi = Milazzo; Ps = Porto San Giorgio. I = Group ‘INCREASE’; D = Group ‘DECREASE’.

Figure 4. Dynamic of the abundance of ‘SIMPER species’, according to fisher's perceptions.

Trends of relative abundance on a scale from 0 to 5 (see text) of the species contributing mostly to the SIMPER analysis. Bold continuous line: mean relative abundance; dashed green line: null model of no temporal change in relative abundance; dashed blue lines: best fitting local regressions before and after break point; vertical dashed line: breakpoint or year of significant change in the temporal evolution of abundance, with 95% confidence intervals in red brackets.