Historically, the Mediterranean Sea supported a rich shark fauna. Presently, however, populations of most shark species have significantly declined, largely due to intense fishing pressure.
...Interviews with crew members of bottom trawlers, drifting longliners and bottom longliners operating off the Costa Brava (Catalonia, NE Spain) were conducted between October 2016 and July 2017 in order to gather information on the current bycatch rate of several shark species.
Interviews covered 41.2% of the fleet and respondents were asked for the bycatch of selected shark species—Alopias vulpinus, Cetorhinus maximus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Mustelus spp., Prionace glauca, and Squalus acanthias—in two distinct time periods.
Bottom trawlers captured the highest diversity of species (eight) followed by bottom longliners (seven), and drifting longliners (three). Most respondents (89.7%) declared having captured at least one shark from 2006 to 2016 but only 56.4% declared having captured at least one shark from 2016 to 2017.
From 2016 to 2017, the whole fleet captured 89 specimens of H. griseus (95% confidence interval (CI) = 145, 34), 14 of G. galeus (95% CI = 30, 0), 3 of A. vulpinus (95% CI = 8, 0), 3 of I. oxyrinchus (95% CI = 8, 0), 3 of C. maximus (95% CI = 6, 0), and no Mustelus spp. The total bycatch of P. glauca and S. acanthias was uncertain due to extremely loose confidence intervals.
A significant decline was perceived by fishermen in the bycatch of C. maximus and S. acanthias, whereas the bycatch of H. griseus was considered to have remained stable.
This study suggests a dramatic reduction in the abundance of most of the medium‐sized and large sharks of the Costa Brava and the likely disappearance of Mustelus spp. from the area. Only H. griseus, S. acanthias, and P. glauca are still being bycaught frequently.
The Mediterranean Sea is considered a biodiversity hotspot and hosts a broad diversity of shark species. Unfortunately, many shark populations have suffered a long story of overexploitation and their ...abundance has strongly declined over the last decades. A few studies have addressed the trophic role of sharks in the northwestern Mediterranean Sea, yet little is known about their isotopic niches. In this study, the isotopic niches of six shark species (Alopias vulpinus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Prionace glauca and Squalus acanthias) from the northwestern Mediterranean Sea were determined and compared with those of sympatric predatory teleosts and marine mammals. Overall, δ13C and δ15N values were similar amongst all the shark species except for the three individuals of G. galeus, whose high δ15N values indicate recent immigration from a distinct area with a different isotopic baseline and hence were excluded from further analysis. The mixing models identified cephalopods as the dominant prey of the other five shark species and revealed that the medium-sized and large shark species studied here filled unique isotopic niches. Their trophic positions were similar to those of predatory teleosts and small dolphins but lower than those of larger dolphins, pilot whales and beaked whales. The high contribution of cephalopods to the diet of sharks in the northwestern Mediterranean Sea might be indicative of fish scarcity and deserves further research in the context of potential ontogenetic diet changes.
•The isotopic niche of six medium-sized and large sharks was assessed.•Their trophic positions suggested they act as high-level mesopredators.•Cephalopods were the dominant prey group in the diet of five sharks.•The position of sharks in the δ13C-δ15N biplot revealed a unique isotopic niche compared to teleosts and cetaceans.
Fishermen from 9 countries distributed throughout the Mediterranean Sea were interviewed between May and December 2019 with the aim of compiling information about the current impact of fisheries on a ...large deep-water shark species, the bluntnose sixgill shark (Hexanchus griseus). A total of 382 professional fishermen belonging to 6 different gears (bottom trawling, bottom longline, drifting longline, trammel nets, gillnets and polyvalent) took part in the study. Bottom trawlers were the most interviewed fishermen (n = 148) and the best fleet coverage was obtained for bottom longline (38.89%). Results showed most captures of H. griseus occur in the Western and Central Mediterranean Sea, particularly during the warm months of the year and most commonly by bottom trawlers and bottom longliners. At-vessel mortality (AVM) was rather low in all gears but a slightly higher degree of individual mortality is suggested in trammel and gillnets. The population trend of H. griseus in the Mediterranean Sea could not be inferred from the interviews as answers were highly variable, but the overall trend in some countries may suggest this species is showing signs of population decrease. The results of this study are mostly aligned with the latest IUCN assessment but also recommend reviewing the current status of H. griseus in the Mediterranean basin. Further empirical research on post-release mortality would also be advisable to implement measures that help reduce this source of mortality.
•Most captures of H. griseus in bottom trawling and bottom longline.•Higher number of captures reported in the Western and Central Mediterranean Sea.•The frequency of capturing H. griseus was higher during warm months.•At-vessel mortality was overall low. Research on post-release mortality is encouraged.•No clear population trend was inferred from the interviews with fishermen.
The equatorial retroflection of the North Brazil Current (NBC) into the Equatorial Undercurrent (EUC) and its posterior tropical recirculation is a major regulator for the returning limb of the ...Atlantic Meridional Overturning Circulation. Indeed, most surface and thermocline NBC waters retroflect at the equator all the way into the central and eastern Atlantic Ocean, before they recirculate back through the tropics to the western boundary. Here, we use cruise data in the western equatorial Atlantic during April 2010 and reanalysis time series for the equatorial and tropical waters in both hemispheres in order to explore the recirculation pathways and transport variability. During the 1998–2016 period, the annual‐mean EUC transports 15.1 ± 1.3 Sv at 32°W, with 2.8 ± 0.4 Sv from the North Atlantic and 11.4 ± 1.3 Sv from the South Atlantic. At 32°W most of the total EUC transport comes from the western boundary retroflection south of 3°N (7.2 ± 0.9 Sv), a substantial fraction retroflects north of 3°N (5.6 ± 0.4 Sv), and the remaining flow (2.3 Sv) joins through the interior basin. The South Atlantic subtropical waters feed the EUC at all thermocline depths while the North Atlantic and South Atlantic tropical waters do so at the surface and upper‐thermocline levels. The EUC transport at 32°W has a pronounced seasonality, with spring and fall maxima and a range of 8.8 Sv. The 18 yr of reanalysis data shows a weak yet significant correlation with an Atlantic Niño index, and also suggests an enhanced contribution from the South Atlantic tropical waters during 2008–2016 as compared with 1997–2007.
Plain Language Summary
In the western margin of the tropical Atlantic Ocean, the North Brazil Current (NBC) carries warm and salty waters across the equator northward into the Caribbean Sea. However, an important fraction turns eastward in the equatorial region, retroflecting into the Equatorial Undercurrent (EUC). We find that indeed most of the NBC‐EUC retroflection water comes from the tropical and subtropical South Atlantic Ocean, but we observe that the EUC is also fed by North Atlantic waters, mostly from the north‐eastern tropical Atlantic. Remarkably, these northern and southern water sources follow different retroflection pathways at different latitudinal bands and density layers. Subtropical water from the South Atlantic is present in all density layers while other sources reach the EUC at shallower layers. We also observe that the water transport associated with the NBC‐EUC retroflection changes along the year, with maxima in spring and fall. Further, from 2008 to 2016 the EUC has increased slightly, associated with a greater contribution of South Atlantic tropical waters. This interannual variability is a result of local and remote changes of the trade wind system of the tropical Atlantic combined with climatic modes of variability such as the Atlantic Niño.
Key Points
A Lagrangian analysis identifies four water sources that feed the Equatorial Undercurrent (EUC) through the North Brazil Current retroflection
The main water source contributions change with density, each density class being dominated by a distinct retroflection latitudinal pathway
Reanalysis data shows an increase of tropical waters from the South Atlantic Ocean into the EUC from 2008 onwards
Given the hydrophilic structure of lysophospholipids (LPLs), their dietary inclusion translates into a better emulsifying capacity of the dietary components. The present study aimed to understand the ...mechanisms underlying the growth-promoting effect of LPL supplementation by undertaking deep analyses of the proximal intestine and liver interactomes. The Atlantic salmon (
) was selected as the main aquaculture species model. The animals were divided into two groups: one was fed a control diet (C-diet) and the other a feed (LPL-diet) supplemented with an LPL-based digestive enhancer (0.1% AQUALYSO
, Adisseo). The LPL-diet had a positive effect on the fish by increasing the final weight by 5% and reducing total serum lipids, mainly due to a decrease in the plasma phospholipid (
< 0.05). In the intestine, the upregulated interactome suggests a more robust digestive capacity, improving vesicle-trafficking-related proteins, complex sugar hydrolysis, and lipid metabolism. In the liver, the LPL-diet promotes better nutrients, increasing several metabolic pathways. The downregulation of the responses to stress and stimuli could be related to a reduced proinflammatory state. This study on the benefits and modes of action of dietary LPLs opens a new window into fish nutrition and could be extended to other productive species.
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