Effect of fishing on community structure of demersal fish assemblages (original) (raw)
Related papers
2001
The average size and the size structure of some fish and decapod species (Helicolenus dactylopterus, Hoplostethus mediterraneus, Galeus melastomus, Aristaeomorpha foliacea, Aristeus antennatus, Plesionika martia and Polycheles typhlops), dwelling the deep waters of the Ionian Sea (eastern-central Mediterranean), were analysed in two areas of different fishing activity. One of the areas is offshore the south-eastern Italian coast, where trawl fishing is carried out intensively between 300 and 700 m. The other is offshore the north-western Greek coast, where fishing is carried out down to 400 m depth. Data were collected during August-September 2000 by means of an experimental trawl survey. The mean size and the size frequency distribution were compared between the two areas using non-parametric statistical tests. H. dactylopterus, A. foliacea and P. typhlops showed highly significant larger mean size and higher percentages of larger specimens in the unexploited area (Greece) than in ...
Assessment of demersal distribution between two fishing areas in North and Central Greece
The site specific CPUE and biomass of the demersal fauna were assessed in two sampling areas situated in Pieria (north Greece, lower Thermaikos) and Argolikos bay (central Greece). In total 22 hauls were conducted 12 of which in Pieria and 10 in Argolikos between January and August of 2009. The demersal fauna showed differences between number of taxa, number of individuals, abundance and biomass between the sampling sites. Mullus barbatus, Trachurus mediterraneus and Diplodus annularιs were the most dominant species in the area of Pieria (40% of the total abundance), whilst the most dominant species in Argolikos were Mullus barbatus, Lepidopus caudatus and Diplodus annularιs (60% of the total abundance). Species richness, diversity, evenness and numerical abundance were higher in Pieria. Cluster analysis and multidimensional scaling indicated differences between the two sites. Abundance biomass curves suggested that both sites are moderately disturbed, whereas K-dominance curves suggested that Pieria was slightly more impacted but not statistically significant compared to Argolikos.
Univariate diversity indices and multivariate analyses (cluster and multidimensional scaling (MDS) were performed in order to evaluate biodiversity in two neighbouring areas of the Eastern Mediterranean with different fishing intensity. Data were collected from two trawl surveys (July and August 2000) in two areas of the Ionian Sea. In the area off the South-eastern Italian coast, there is a trawl fishery at depths between 300 and 700 m that targets the deep-sea shrimps Aristeus antennatus and Aristaeomorpha foliacea. In the other area off Northern Greece, fishing is only carried out down to 400 m depth.
Bottom trawl impacts on Mediterranean demersal fish diversity: Not so obvious or are we too late?
Continental Shelf Research, 2017
Measures of biodiversity change may be useful as indicators if they are responsive to manageable drivers of biodiversity loss. However, there are many candidate indicators that are considered to be robust to survey artifacts and sensitive to manageable impacts. Using extensive survey data on demersal fish assemblages around the Balearic Islands (western Mediterranean) we analyze relationships among 'traditional', taxonomic and functional diversity indices, to identify a minimum set of indices that provide a good representation of the different aspects of diversity. Secondly we model the responses of the demersal fish community diversity to bottom trawl fishing pressure. To do so, we used two different approaches: i) considering fishing effort and depth as continuous explanatory variables; and ii) grouping samples according to bathymetric sampling strata and contrasting levels of fishing effort. The results show that diversity can be described using different complementary aspects such as species richness, evenness, and the taxonomic and functional breadth of the species present in a given community, displaying different responses to fishing pressure. However, the changes in diversity in response to fishing may only be detectable in those communities where the levels of fishing pressure have remained relatively low. When communities have been exposed to high levels of fishing pressure for a long period, the relevant changes in diversity may have happened long before the onset of monitoring of the fishery, and hence it may be too late to detect differences between levels of fishing effort. This seems to be the case on the middle slope of the Balearic Islands, where vulnerable species have disappeared or are very infrequent, and have been replaced by species better-adapted to fishing impacts.
Klaoudatos D, Vardali S, Apostologamvrou C, Lolas A, Neofitou N, Conides A, Gkafas GA, Sarantopoulou J, Kolindrini D, Roditi K, Exadactylos A, Vafidis D, 2023
A fishery-independent survey with a commercial bottom otter trawl was conducted in the Pagasitikos Gulf, a semi-enclosed, trawl-restricted gulf in Greece. The study aimed to ecologically assess the fishery communities that are experiencing a decline in fishery landings. Twelve hauls of 30 min duration each were conducted in the eastern, western, and central parts of the gulf at depths between 62 and 97 m. In total, 57 species were captured, with the highest species number recorded in the west (35 species), followed by the center (32 species) and east (29 species). The highest numerical abundance was recorded at the center, followed by the east and west, with an opposing trend exhibited for biomass; however, GLM detected no significant spatial differences (in area or depth) or interaction. Ecological indices exhibited significantly lower values in the west–east area comparison. Linear Discriminant Analysis, mMDS, and hierarchical clustering indicated the presence of two main groups (east and west), with PERMANOVA showing a significant difference in the demersal communities among the identified groups. The results indicated moderately disturbed demersal communities and an increasing level of disturbance from east to west. Considering the economic value of Pagasitikos to the local fishing community, additional fishery management measures are deemed necessary to protect the fishery resources and mitigate the potential risks of overexploitation.
Fisheries Research, 2006
The effect of trawling on demersal fish assemblages was measured in an experiment involving repeated trawling in the Strait of Sicily. Three areas were chosen according to their exploitation level by commercial trawl fishery: practically unexploited by the commercial fishery (area C), subject to light and recent fishing pressure (area L) and heavily exploited by commercial trawl fishery (area H). Data were collected during two scientific surveys carried out in autumn 1997 and 1998; temporal replication was used to confirm the observed spatial pattern. The status of the demersal fish communities in the three areas was compared using a variety of approaches and a number of community metrics (cluster analysis, similarity percentage analysis, ANOSIM pairwise test, size spectra, diversity indices). Results indicate that abundance, species composition and size-structure of the fish community in area H are different from the other two areas. Differences between area C and area L are small and concern mainly the relative abundance of some species. Eventually, the results show how fishing can substantially shape the fish communities in the three areas.
Small-Scale Coastal Fishing Shapes the Structure of Shallow Rocky Reef Fish in the Aegean Sea
Frontiers in Marine Science
Shallow rocky reef fish assemblages were studied in sites of low versus high fishing pressure (FP) across 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 (Total Length; 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 8fold range in fish density and a 14-fold range in fish biomass were detected, while community structure was affected by all 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 the double abundance and 2.8 times higher biomass. Biomass of carnivores was generally very low, except at deep sites of low FP. 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.