Analysis of demersal species assemblages from trawl surveys in the South Adriatic sea (original) (raw)
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Fish and fishery historical data since the 19th century in the Adriatic Sea, Mediterranean
Scientific Data
Historic data on biodiversity provide the context for present observations and allow studying long-term changes in marine populations. Here we present multiple datasets on fish and fisheries of the Adriatic Sea covering the last two centuries encompassing from qualitative observations to standardised scientific monitoring. The datasets consist of three groups: (1) early naturalists’ descriptions of fish fauna, including information (e.g., presence, perceived abundance, size) on 255 fish species for the period 1818–1936; (2) historical landings from major Northern Adriatic fish markets (Venice, Trieste, Rijeka) for the period 1902–1968, Italian official landings for the Northern and Central Adriatic (1953–2012) and landings from the Lagoon of Venice (1945–2001); (3) trawl-survey data from seven surveys spanning the period 1948–1991 and including Catch per Unit of Effort data (kgh−1 and/or nh−1) for 956 hauls performed at 301 stations. The integration of these datasets has already dem...
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.
2011
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Fisheries Research, 2001
Trawl surveys carried out in the Adriatic Sea in 1948 and 1998 provided information on the changes that occurred in the composition and distribution of demersal ®sh resources over the 50 years period. The main change was the decrease of elasmobranchs diversity and frequency, mostly referring to the Hypotremata group. Life history parameters appeared to be determining factors, since small sized species such as the smallspotted catshark (S. canicula) or the brown ray (R. miraletus) were frequently collected in both surveys, while bigger shark species and most other rays disappeared or were rarely found during the 1998 survey. Regarding bony ®shes, common species were collected with similar frequency in both surveys; some ®shery target species (e.g. the hake) have similar percentage values (biomass) in both surveys, while others (the silver scabbard®sh) have increased values, and some (mainly small sized species such as red mullet) replace elasmobranchs at the top of the catches. Despite the low number of observations (two surveys only) and some sampling differences, the data provide an interesting long-term comparison.
The MEDITS-99 sampling was performed along all the Iberian Peninsula coasts of the western Mediterranean (from the Alborán Sea to Cape Creus) in a space-scale of 1000 Km N-S, at depths ranging between 27-790 m. Fish and decapod crustaceans were dominant in the megafaunal compartment sampled by trawling. Based on both the fish and the decapod crustacean compositions, a comparison of trophic guilds has been attempted, with fish and decapods classified as: 1) migrator macroplankton feeders (mM), 2) non-migrator macroplankton feeders (nmM), 3) nektobenthos-suprabenthos feeders (NS), 4) epibenthos feeders (Epib), 5) large detritus-scavengers (Sca), 6) infaunal feeders (Inf), 7) deposit feeders (Dep) and 8) small detritivorous feeders (Det). Multivariate techniques showed the following differences in the trophodynamics of the megafaunal assemblages along the coasts of the Iberian Peninsula: 1) crustaceans (mainly decapods) have different trophic structures on the shelf and on the slope; 2) on the slope, fish exhibited more clear changes as a function of the geographical gradient than crustaceans; and 3) trophodynamics of bathyal fish showed some geographic variations between the Alborán Sea, the Catalano-Balearic Basin, and the Algerian Basin (Vera Gulf and Alicante sectors), with a progressive north-south increase in planktophagous species.
Mediterranean marine demersal resources: the MEDITS international trawl survey (1994-1999)
2002
The MEDITS-99 sampling was performed along all the Iberian Peninsula coasts of the western Mediterranean (from the Alborán Sea to Cape Creus) in a space-scale of 1000 Km N-S, at depths ranging between 27-790 m. Fish and decapod crustaceans were dominant in the megafaunal compartment sampled by trawling. Based on both the fish and the decapod crustacean compositions, a comparison of trophic guilds has been attempted, with fish and decapods classified as: 1) migrator macroplankton feeders (mM), 2) non-migrator macroplankton feeders (nmM), 3) nektobenthos-suprabenthos feeders (NS), 4) epibenthos feeders (Epib), 5) large detritus-scavengers (Sca), 6) infaunal feeders (Inf), 7) deposit feeders (Dep) and 8) small detritivorous feeders (Det). Multivariate techniques showed the following differences in the trophodynamics of the megafaunal assemblages along the coasts of the Iberian Peninsula: 1) crustaceans (mainly decapods) have different trophic structures on the shelf and on the slope; 2) on the slope, fish exhibited more clear changes as a function of the geographical gradient than crustaceans; and 3) trophodynamics of bathyal fish showed some geographic variations between the Alborán Sea, the Catalano-Balearic Basin, and the Algerian Basin (Vera Gulf and Alicante sectors), with a progressive north-south increase in planktophagous species.
Hydrobiologia, 2011
The bottom trawl fishery developed on the slope off Balearic Islands (western Mediterranean) has been analysed from different sources of information: (i) data obtained during experimental bottom trawl surveys developed annually since 2001; (ii) daily sale bills from the bottom trawl fleet, available since 2000. Considering both hydrographical and geomorphologic conditions, the study area was divided in four geographical sectors. Multivariate techniques were applied to identify assemblages and their main species, and to investigate the influence of environmental variables in the slope communities. Fishery-independent and fisherydependent indicators were calculated, both at specific and community level, for the assemblages identified. In all cases, they were summarised using the Traffic Light approach. Three assemblages have been identified in the slope trawl fishing grounds off the Balearic Islands: (1) the almost unexploited shelf break, where teleosts predominate; (2) the upper slope, where teleosts still predominate but crustaceans are also very important (with Nephrops norvegicus as target species); (3) and the middle slope, where crustaceans predominate (with Aristeus antennatus as target species). Depth was the main factor affecting the species composition of the assemblages, although other factors such as area, year and effort level also affect. Indicators estimated from both sets of data suggested an improvement in the state of N. norvegicus, although the results suggest the influence of other factors than fishing impact in the state of this resource. For A. antennatus, marked differences have been found depending on the data source. In the upper slope, indicators suggested an improvement in the state of this assemblage, which can be related to a decreasing trend found in the fishing effort exerted in this depth range. Indicators from the middle slope showed differences for both sets of data. The characteristics of both data sources and of the species analysed are discussed as responsible of these differences.
Effects of commercial trawl fishing in the Strait of Sicily on the diversity of demersal resources
ICES CM, 2000
The effects produced by commercial trawl fishing on the diversity of demersal resources in two zones of the Straits of Sicily subject to different fishing effort were analysed. Data were available from a total of 79 hauls, carried out annually in autumn 1997 and 1998 between 200 and 400 meter depth and pertained to the bathyal muddy bottoms biocenosis (Perès and Picard, 1964) on the whole. Data on fishing effort, recorded since 1995, come from the Harbour Office and have been verified from interviews to crews and captains of Mazara del Vallo trawl fisheries.
Journal of Marine Systems, 2007
A trophic mass-balance model was developed to characterise the food web structure and functioning of the Northern and Central Adriatic Sea and to quantify the ecosystem impacts of fishing during the 1990s. Forty functional groups were described, including target and non-target fish and invertebrate groups, and three detritus groups (natural detritus, discards and by-catch of cetaceans and marine turtles). Results highlighted that there was an important coupling between pelagic-benthic production of plankton, benthic invertebrates and detritus. Organisms located at low and medium trophic levels, (i.e. benthic invertebrates, zooplankton and anchovy), as well as dolphins, were identified as keystone groups of the ecosystem. Jellyfish were an important element in terms of consumption and production of trophic flows within the ecosystem. The analysis of trophic flows of zooplankton and detritus groups indirectly underlined the importance of the microbial food web in the Adriatic Sea.