Physical Disturbance by Bottom Trawling Suspends Particulate Matter and Alters Biogeochemical Processes on and Near the Seafloor

Bottom trawling is known to affect benthic faunal communities but its effects on sediment suspension and seabed biogeochemistry are less well described. In addition, few studies have been carried out in the Baltic Sea, despite decades of trawling in this unique brackish environment and the frequent occurrence of trawling in areas where hypoxia and low and variable salinity already act as ecosystem stressors. We measured the physical and biogeochemical impacts of an otter trawl on a muddy Baltic seabed. Multibeam bathymetry revealed a 36 m-wide trawl track, comprising parallel furrows and sediment piles caused by the trawl doors and shallower grooves from the groundgear, that displaced 1,000 m3 (500 t) sediment and suspended 9.5 t sediment per km of track. The trawl doors had less effect than the rest of the gear in terms of total sediment mass but per m2 the doors had 5× the displacement and 2× the suspension effect, due to their greater penetration and hydrodynamic drag. The suspended sediment spread >1 km away over the following 3–4 days, creating a 5–10 m thick layer of turbid bottom water. Turbidity reached 4.3 NTU (7 mgDW L–1), 550 m from the track, 20 h post-trawling. Particulate Al, Ti, Fe, P, and Mn were correlated with the spatio-temporal pattern of suspension. There was a pulse of dissolved N, P, and Mn to a height of 10 m above the seabed within a few hundred meters of the track, 2 h post-trawling. Dissolved methane concentrations were elevated in the water for at least 20 h. Sediment biogeochemistry in the door track was still perturbed after 48 h, with a decreased oxygen penetration depth and nutrient and oxygen fluxes across the sediment-water interface. These results clearly show the physical effects of bottom trawling, both on seabed topography (on the scale of km and years) and on sediment and particle suspension (on the scale of km and days-weeks). Alterations to biogeochemical processes suggest that, where bottom trawling is frequent, sediment biogeochemistry may not have time to recover between disturbance events and elevated turbidity may persist, even outside the trawled area.

Lockdown: How the COVID-19 Pandemic Affected the Fishing Activities in the Adriatic Sea (Central Mediterranean Sea)

The coronavirus disease 2019 (COVID-19) has brought a global socio-economic crisis to almost all sectors including the fishery. To limit the infection, governments adopted several containment measures. In Italy, Croatia, and Slovenia, a lockdown period was imposed from March to May 2020, during which many activities, including restaurants had to close or limit their business. All of this caused a strong reduction in seafood requests and consequently, a decrease in fishing activities. The aim of this study is to investigate the effects of the COVID-19 in the Northern and Central Adriatic fleet, by comparing the fishing activities in three periods (before, during, and after the lockdown) of 2019 and 2020. The use of the Automatic Identification System (AIS) data allowed us to highlight the redistribution of the fishing grounds of the trawlers, mainly located near the coasts during the 2020 lockdown period, as well as a reduction of about 50% of fishing effort. This reduction resulted higher for the Chioggia trawlers (−80%) and, in terms of fishing effort decrease, the large bottom otter trawl was the fishing segment mainly affected by the COVID-19 event. Moreover, by analysing the landings of the Chioggia fleet and the Venice lagoon fleets, it was possible to point out a strong reduction both in landings and profits ranging from −30%, for the small-scale fishery operating at sea, to −85%, for the small bottom otter trawl.

Spatiotemporal and ecological distribution of megabenthic crustaceans on the shelf-shelf break of Antalya Gulf, the eastern Mediterranean Sea

The spatiotemporal distribution and ecology of the suprabenthic and benthic mega-crustaceans were studied in the shelf-shelf break of Turkish waters of the eastern Mediterranean Sea (Antalya Gulf). Sampling was conducted seasonally in May 2014, August, October, and February 2015 using an otter trawl at depths of 10, 25, 75, 125 and 200 m along three transects. A total of 59 species were identified comprising 53 decapods (Eumalacostraca: Eucarida), 3 isopods (Eumalacostraca: Peracarida), and 3 stomatopods (Hoplocarida). Eighteen of the total identifiable species were invasive, and some of them significantly influenced the crustacean community structure. Parapenaeus longirostris, Pagurus prideaux, Charybdis (Goniohellenus) longicollis and Medorippe lanata were the most common species. Parasquilla ferussaci was reported for the first time in Turkish water of the Levantine Sea. Community structure showed seasonal patterns and differed along the depth gradient of habitat heterogeneity. The megabenthic crustacean assemblage was driven mainly by seafloor depth and was related to the fishing disturbance in the area (fishing/no-fishing zones). Environmental parameters were measured for each sample and tested in relationship to crustacean abundance by multivariate analysis CCA (canonical correspondence analysis). The results revealed significant differences in community structure related to substrate and the fine fraction of the bioseston.

ICHTHYOFAUNA IN THE INNER CONTINENTAL SHELF NEXT TO THE PARANAGUÁ ESTUARINE COMPLEX, SOUTHERN BRAZIL

The composition and structure of fish assemblages in the inner continental shelf of the Paraná State are affected by cold fronts and the rainfall regime. Data from fishing activities in this region, as well as the analysis of environmental characteristics, are the main tools available for understanding fish dynamics, under influence of increasing human activities. In order to better understand patterns and temporal variations in fish assemblages in the inner continental shelf of the Paraná State, a total of 24 double trawls were performed with an otter trawl between August 2000 and July 2001, in two sampling areas, the North area in front of the northern mouth of the Paranaguá Estuary Complex, and the South area, in front of the Leste beach. A total of 45,277 fish specimens belonging to 35 families and 97 species were caught. Sciaenidae was the most abundant family, with 37.1% of the total number of individuals caught, and with the highest richness (18 species). Statistical analyses evidenced significant differences in environmental characteristics and in fish fauna, and that both areas disturbances were observed in the fish assemblages during the dry and wet season, being more intense in the Southern area, disturbances that would be related to the shrimp fishing present in the two areas sampled in this study.

ENVIRONMENTAL DRIVERS OF FISH ASSEMBLAGES FROM THE SHALLOW INFRALITTORAL AREAS OF THE PARANAGUÁ BAY, SOUTHERN BRAZIL

The composition of estuarine fish fauna is dynamic and complex. Despite the variation in fish fauna in estuaries, it is possible to observe some species associated with microhabitats. The assemblage composition of these communities is apparently derived from habitat selection. The aim of this study was to assess the structure of the demersal fish fauna of the Paranaguá Bay and its relationship with biotic and abiotic factors. To this end, monthly collections were conducted using an otter trawl, from October 1999 to September 2000, at five sites in the shallow infralittoral. Biotic (organic matter, and invertebrates) and abiotic factors (salinity, temperature, pH, dissolved oxygen, seston, and nutrients) were recorded during sampling. A total of 6,623 individuals were captured, belonging to 2 species of Chondrichthyes and 53 species of Actinopterygii (26 families). Sciaenidae was the most representative in terms of richness, with 11 species, and Ariidae was the most representative in terms of abundance. The catfish Cathorops spixii was the most abundant species, representing 21 % of the entire catch. There were significant differences in the composition and abundance of the fish fauna among the studied areas, as evidenced by the Shannon-Wiener diversity index. Such differences seem to be related to the complexity of habitats, which occur due to different types of bottom cover found at each sampling site. The abiotic variables indicated little influence on the structure of the fish assembly. These results contribute to a better understanding of the fish fauna from the shallow infralittoral areas of the Paranaguá Bay, and provide data to decision makers for better implementation of management and conservation measures.

Juvenile fish assemblage recruitment dynamics in a mid-Atlantic estuary: before and after Hurricane Sandy

Hurricanes can have long-term effects on estuarine fauna. Understanding these effects is important as climate change may influence the severity and frequency of these storms. On 29 October 2012, Hurricane Sandy, a large storm spanning roughly 1850 km in diameter, made landfall in Brigantine, New Jersey (USA), approximately 20 km south of Barnegat Bay, during an ongoing study of the bay’s ichthyofauna, providing an opportunity to observe fish recruitment dynamics coincident with hurricane passage. The objective of this study was to measure variance in the Barnegat Bay pre-Sandy fish assemblage relative to that of 1 and 2 yr after the storm. Barnegat Bay fishes were surveyed with an extensive otter trawl study in April, June, August, and October of 2012 (pre-Sandy), 2013 (1 yr post-Sandy), and 2014 (2 yr post-Sandy). Species composition of the fish assemblage was similar across years. Analyzed structural characteristics (abundance, diversity, richness) of the fish assemblage were occasionally more likely to occur or were larger pre-Sandy and 2 yr post-Sandy relative to 1 yr post-Sandy, but this trend was inconsistent across seasons and between structural characteristics. Furthermore, odds of occurrence and length frequency distributions for many resident species and sentinel fall/winter spawners did not indicate that variance could be definitively explained as a hurricane effect. The capability of fish to relocate from areas of temporarily unsuitable habitat and annual new recruitment of larvae and juveniles to the bay likely contributed to the observed stability in the fish assemblage.