Domesticating the wild through escapees of two iconic mediterranean farmed fish species

Abstract

Extractive fisheries and marine aquaculture share space and target species. Several regional-scale examples exist of escapees entering wild fisheries landings, yet no study has assessed the influence of aquaculture on landings at an ecosystem scale. We examined the effects of farmed fish escapes on fisheries using FAO data and published escape rates for Gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). Seabream landings were significantly correlated with the estimated biomass of escaped seabream entering the wild. There was a similar pattern for seabass until 2005, but the overall relationship between landings and escapes was not significant due to the dramatic drop in catches in recent years. We argue that seabass escapees' relatively high mortality, lower capturability, and minor 'leaking' from farms may obscure their influence on landings. Significant positive fisheries regime shifts were detected for both species, matching the onset of aquaculture in the Mediterranean and the period when escapees from aquaculture surpassed landings. Our results suggest that fish escapes of these two iconic species may mask wild stock overexploitation, confound stock assessments, alter genetic diversity, increase the risk of spreading pathogens and parasites, and compete with wild conspecifics while boosting fisheries landings.

Keywords: European seabass; Gilthead Seabream; Escape events; Fisheries landings; Small-scale fisheries; Stock assessments.

Fig. 1

Temporal trends in fisheries landings (blue lines) and aquaculture production (red lines) in the Mediterranean and Black Sea area for seabass (Dicentrarchus labrax, left panel) and seabream (Sparus aurata, right panel). Data source FAO 2022.

Fig. 2

Temporal trends in (a) fisheries landings (red lines), (b) landings-per-unit-of-effort (LPUE) vs. estimated fish escapes biomass from aquaculture farms (blue lines) in the Mediterranean Sea and Black Sea for seabass (Dicentrarchus labrax, left panels) and seabream (Sparus aurata, right panels). F and P-values for Granger’s causality tests are shown in the respective panel. Note that panel b has two y-axes with different units. On the left-hand side of the left panel, the y-axis represents escapes in tonnes. On the right-hand side of the right panel, the y-axis shows LPUE in tonnes per vessel.

Fig. 3

Regime shift index (dotted lines) for the standardised fisheries landings anomalies (solid blue lines) and standardised landings-per-unit-of-effort (LPUE, solid red lines) for seabass (Dicentrarchus labrax, left panels) and seabream (Sparus aurata, right panels) in the Mediterranean Sea and Black Sea.