Small-Scale Coastal Fishing Shapes the Structure of Shallow Rocky Reef Fish in the Aegean Sea

Maria Sini,Zoi Thanopoulou,Christos Katsoupis,Irida Maina,Paraskevi K Karachle,Stefanos Kavadas,Stelios Katsanevakis,Konstantinos Vatikiotis

doi:10.3389/fmars.2019.00599

Abstract

Shallow rocky reef fish assemblages were studied in sites of low versus high fishing pressure (FP) across different parts of the Aegean Sea, in order to assess community structure at a large scale and investigate spatial variability in relation to FP, depth, and geographic location. A total of 15 pairs of high and low FP sites were selected (18 sites in North Aegean, 12 in South Aegean). The level of FP was defined based on a fishing pressure index specifically developed for coastal small-scale fisheries in the region. In each site, fish communities were investigated at two depth zones (5 and 15 m). Number of species, fish size (TL) and abundance were recorded along strip transects through underwater visual surveys. Abundance and TL were used to estimate biomass, and fish species were assigned to distinct trophic and commercial status groups. An 8-fold range in fish density and a 14-fold range in fish biomass were detected, while community structure was affected by all spatial variables considered (FP, depth, geographic location). The N Aegean sites scored higher in number of species and biomass of carnivorous fish, whereas the S Aegean had a higher biomass of several allochthonous and thermophilous species. Abundance and biomass estimates were higher in low FP sites, and primarily at the 15 m depth zone, where low FP sites had 2 times higher abundance and 2.8 times higher biomass. However, differences were mainly due to an increase of fish with low or no commercial value, whereas biomass of highly-priced fish was overall low. Given that sites of lower FP represent areas of lower conflicting interests for fisheries whilst providing enhanced biomass levels, they should be included in future marine conservation planning schemes, as they could contribute to the replenishment of fisheries and the boosting of conservation benefits provided by MPAs, once properly managed.

Highlights

Compared to the vast area covered by the open sea, shallow coastal environments are subjected to disproportionately higher pressures due to their dynamic interplay with the terrestrial realm and the direct effects of human activities
Of the three biodiversity indices considered (S, H’, and 1-D), statistical differences were only detected in S, where the number of species was significantly higher in the N Aegean sites and at the 15 m depth zone compared to the S Aegean sites and the 5 m depth zone, respectively (Table 2)
Across the 30 sites sampled at the shallow rocky reefs of the Aegean Sea, we found an 8-fold range in fish density and a 14fold range in fish biomass

Summary

Introduction

Compared to the vast area covered by the open sea, shallow coastal environments are subjected to disproportionately higher pressures due to their dynamic interplay with the terrestrial realm and the direct effects of human activities. Many important Mediterranean rocky reef benthic communities, such as canopy-forming macroalgal forests of the genus Cystoseira and Sargassum are vulnerable to such stressors and have suffered major losses and severe degradation in the recent decades (Thibaut et al, 2015). For this reason, they have been classified as endangered in the European Red List of Habitats (Gubbay et al, 2016). In Mediterranean rocky reefs, high predatory fish abundance has been observed to control sea urchin populations at low levels, substantially reducing grazing pressure over macroalgal beds (Sala et al, 1998). Reef fish have an intrinsic economic value for artisanal fisheries and underwater tourism, greatly supporting coastal economies (Badalamenti et al, 2000)

Objectives

Methods

Results

Conclusion