Anchovy is a commercial species that supports large fisheries in the Mediterranean Sea. In addition, anchovy is an essential element of the pelagic food web, playing a considerable role in connecting ...the lower and upper trophic levels. Comparisons made regarding length frequency distribution, demographic structure, growth during the first year inferred from otoliths, and the condition factor of anchovy inhabiting the Spanish Mediterranean Sea (General Fisheries Commission for the Mediterranean management units, GSA06-Ebro Delta and 01-Alboran Sea), based on five-year data, clearly showed significant growth differences between areas and evidenced the existence of two independent anchovy stocks in the Spanish Mediterranean Sea. The anchovies inhabiting the Alboran Sea had higher growth than the anchovies inhabiting the Ebro Delta for the same age (one year old). The dramatic decline of the Alboran Sea anchovy could be related to the current management legislation in the Spanish Mediterranean Sea, based mainly on a common minimum catch size (9 cm), which should be revised given that sustainable anchovy exploitation is crucial for the pelagic food web equilibrium.
The ingestion of microplastics and natural fibres (<5 mm) was assessed for two commercial fish species in the western Mediterranean Sea: Sardina pilchardus and Engraulis encrasicolus. ...Gastrointestinal tracts from 210 individuals from 14 stations were examined with 14.28–15.24% of the small pelagic fish S. pilchardus and E. encrasicolus having ingested microplastics and natural fibres. A latitudinal increase in condition index (Fulton's K) of S. pilchardus gave an indication that larger individuals with better physical condition are less likely to ingest microplastics and natural fibres. Fibres were the most frequent particle type (83%) and Fourier Transform Infrared spectroscopy (FT-IR) analysis indicated polyethylene terephthalate was the most common microplastics material (30%). Results from this study show that both microplastics and natural fibres of anthropogenic origin are common throughout the pelagic environment along the Spanish Mediterranean coast.
•Fifteen percent of sampled European pilchards and European anchovies ingested microplastics and natural fibres.•Condition index (Fulton's K) influences the ingestion of microplastics and natural fibres in the sampled European pilchard.•The ingestion of microplastics and natural fibres in these fish species is widespread along the Spanish Mediterranean coast.•Eighty-three percent of ingested anthropogenic particles were fibres.
The zooplankton composition of the Sound Scattering Layer (SSL) detected at multiples frequencies, 18, 38, 120 and 200 kHz, along the continental shelf of the Northern Alboran Sea (Mediterranean Sea) ...has been identified in July 2013 and 2014 by means of different plankton nets and the SSL dominant scatterers have been identified using zooplankton scattering models.
Three acoustic patterns, based on their distinctive relative frequency response (r(f)), have been detected along the continental shelf, matching with three zooplankton communities; in coastal areas (25–40 m bottom depth), a homogeneous community composed by Fluid-like zooplankton, mainly crustaceans, exhibiting a r(f) peak at 120 kHz, (ii) in intermediate areas (40–190 m) a heterogeneous community composed by Fluid-like (crustaceans, chaetognaths, larvaceans, doliolids, Calycophora siphonophores), Elastic-shelled (heteropods) and Gas-bearing (fish larvae) zooplankton, exhibiting a r(f) peak at 38 kHz (iii) in the continental shelf edge (180–250 m), a zooplankton community dominated by Maurolicus muelleri fish larvae, exhibiting a r(f) peak at 18 kHz. Scattering models results showed that stronger scatterers as fish larvae (Gas-bearing), although scarce in samples, dominated the backscattering energy at almost all frequencies and locations. Fluid-like zooplankton contribution was only significant in coastal areas at high frequencies (120 and 200 kHz).
The application of these findings to all echograms collected over the study area made it possible to obtain, the macro scale spatial distribution of the zooplankton communities as well as the SSL backscatter energy all over the continental shelf, highlighting the suitability of the use of acoustic data as an indicator of secondary production.
Display omitted
•The SSL relative frequency response change according to its zooplankton composition.•Strong scatterers as fish larvae mask the detection of weak scatterers as crustaceans.•The main SSL environmental forcing were the distance to the coast and the thermocline.•Acoustic data were verified as indicator of the secondary production.
•Malaga Bay constitutes the main anchovy schooling area in the Northern Alboran Sea.•Anchovy larvae (2–40 mm length) form a benthic scattering layer in Malaga Bay.•Anchovy recruitment success ...indicators can be derived from acoustic surveys.•Acoustic surveys contribute to the knowledge of anchovy behaviour and dynamic.
During the MEDiterranean International Acoustic Survey (MEDIAS) carried out in 2016 and 2017 in the Northern Alboran Sea in July, a benthic scattering layer located mainly in Malaga Bay was acoustically detected at multiple frequencies and biologically identified using different sampling devices (plankton net and pelagic trawl). This layer mainly corresponded to an anchovy larvae aggregation ranged 2 and 40 mm standard length. Our results pointed out that anchovy larvae massively migrate from the surface to the bottom near the coast, until the 70 m isobath, forming large aggregations acoustically detected as a scattering benthic layer, in which small schools form and emerge.
This work has highlighted the potential of acoustic surveys such as MEDIAS to generate anchovy recruitment success indicators complementary and simultaneously to the traditional ones (biomass of the reproductive stock) and their great utility as a fisheries management tool in areas such as the Alboran Sea where the fishing resource is scarce.
Our knowledge for the distribution of Atlantic mackerel (Scomber scombrus) in the Mediterranean Sea is very limited and fragmented. In the current work habitat suitability modelling was applied to ...summer acoustic surveys data of Atlantic mackerel juveniles derived from the north part of the Mediterranean (i.e. acoustic data from the Gulf of Lions, pelagic trawls held during acoustic surveys in Spanish Mediterranean waters, south Adriatic Sea, Strait of Sicily and North Aegean Sea) using generalized additive models along with satellite environmental and bathymetry data. Bathymetry along with sea surface temperature and circulation patterns, expressed through sea level anomaly and the zonal component of the absolute geostrophic velocity, were the variables found important. The selected model was used to produce maps presenting the potential nursery grounds of Atlantic mackerel throughout the Mediterranean Sea as a measure of habitat adequacy. However, the assessed potential nursery grounds were generally marked as “occasional”, implying that although there are areas presenting high probability to encounter Atlantic mackerel, this picture can largely vary from year to year stressing the high susceptibility of the species to environmental conditions. In a further step and towards a spatial management perspective, we have estimated and visualized the overlap between Atlantic mackerel and anchovy/ sardine juvenile grounds throughout the basin. Results showed that although the degree of overlapping was generally low, not exceeding 15 % in general, this varied at a regional level going up to 30%. The potential of the output of this work for management purposes like the implementation of spatially-explicit management tools is discussed.
In this study, we examine anthropogenic particles (APs) in the zooplankton aggregation layer and in fish species along the continental Catalan shelf. APs in the zooplankton aggregation layer were ...found in 100% of the net tows. Fibres of textile origin dominated the types of AP found in the zooplankton aggregation layer (96%). APs were found ingested in all species of fish at each sampling site, with an overall ingestion occurrence of 21%, with the most abundant fragments (62%). Significant differences in ingestion occurrence were found between species and hierarchal cluster analysis identified two feeding groups, S. pilchardus, T. trachurus and P. erythrinus almost exclusively ingested fibres while T. mediterraneus, S. colias and S. cantharus almost exclusively ingested fragments. The results indicate that the ingestion of APs in the first group of species occurs through indirect ingestion, whereas, in contrast, the second group is composed of more predatory and selective feeders, possibly through accidental predation. In general, our findings indicate that the fate of APs in fish on the Catalan continental shelf depends on the combination of feeding ecology and the availability of APs in the water column.
Display omitted
•The zooplankton aggregation layer was between 25 and 64 m depth.•Fibers (96%) were dominant in the zooplankton aggregation layer.•A 5–69% occurrence of anthropogenic particles (fibers and fragments) was found in 7 pelagic fish species.•The prevalence of fragments was more common in predatory feeders and fibers in filter and generalist feeders.
The abundance of microplastics (plastic particles of less than 5 mm) along the sea surface and in seafloor sediments have been extensively documented worldwide; however, little is known in terms of ...the vertical distribution of microplastics in the water column, especially in the epipelagic zone. Considering the biological importance of this area, the quantification of microplastics available here is essential to identify potential impacts for marine organisms. This study reports the vertical distribution of microplastic abundances throughout the water column in two Marine Strategy Framework Directive (MSFD) demarcations from the western Mediterranean Sea during July 2019. Three concatenated 5-L Niskin bottles were used for sampling at 5, 15 and 25 m from the sea surface in stations with a total depth smaller than 50 m and at 5, 25 and 50 m from the sea surface in stations with a total depth greater than 50 m. This study demonstrates the ubiquitous abundance of microfibers, 96% of the microplastic items identified in the upper epipelagic layer of the western Mediterranean Sea. Microplastics exhibit a heterogeneous vertical and horizontal spatial distribution. Fragments had a very low representation (4% of the items) but showed a similar frequency of occurrence along all sampling depths. In terms of size, 68% of the microplastics were less than 2 mm in length. Microplastics quantified within the study area were mainly composed of low-density polyethylene (LDPE) and polypropylene (PP) (20% each) followed by cellulose acetate (CA) (16%) and polyestyrene (PS) (14%). Regarding the spatial distribution of microplastics, higher abundances were found at intermediate distances (5–10 km from the coast) with mean values of 2.41 ± 1.90 items L−1 and further away (>20 km) from the coast, with mean values of 2.11 ± 1.80 items L−1. A slight decreasing trend in the abundances of microplastics from the sub-surface to deeper waters was also observed. Stations within MPAs waters showed no significant differences in microplastic abundances when compared to non-MPAs stations. Overall, the results of this study highlight the ubiquitous presence of microplastics, primarily microfibers, along the epipelagic layer of the Spanish Mediterranean continental shelf.
•Fibers were the predominant type found in the water column.•Sampling depth and station depth were significant factors in the vertical profile.•Higher microdebris abundances found at intermediate distances to the coast.•A heterogenic latitudinal distribution was found.•MPAs had similar microdebris abundances than non-MPAs stations.
Horse mackerel is a semi-pelagic fish widely distributed in the eastern Atlantic, where it represents a species of interest for fisheries and is subject to intense exploitation, leading to its global ...classification as a vulnerable species by IUCN. In the Northwestern (NW) Mediterranean Sea, the knowledge of their distribution, abundance and main biological parameters is fundamental to achieve their sustainable exploitation and contribute to the ecosystem approach to fisheries management. The time series (2009–2020) data set analyzed in this study came from two geographical subareas (GSAs) defined by the General Fisheries Commission for the Mediterranean (GFCM), Northern Spain (GSA06) and Northern Alboran Sea (GSA01) sampled in July during the MEDiterranean International Acoustic Survey (MEDIAS). Our results suggest that in summer, a higher concentration and aggregation of fish exists in GSA01, with a density ten times greater than in GSA06. Possible life history changes can be inferred through the analysis of the biological parameters of
Trachurus trachurus
in the NW Mediterranean Sea. In both GSAs, the annual decline of the size at first maturity (
L
50
) and condition factor (Kn) was prominent. Moreover, the population structure lacked adult modes that could guarantee a successful recuperation of future stocks. Nonetheless, fish inhabiting GSA01 seem to have a better adaptive response to the events responsible for these alterations. In comparison, GSA01 is under less fishing pressure and the upwelling occurring in this area contributes to a higher availability of food, in addition to reducing the increases in sea surface temperature due to climate change during the study period.
Abstract
We documented krill distribution in the Spanish Mediterranean Sea for the first time using acoustic methods, highlighting the method’s suitability to study marine communities restricted to ...specific areas with patchy aggregation behavior. The 2009–2017 acoustic time series analysis revealed that krill distribution, mainly located on the continental shelf edge, was driven by the presence of fronts and submarine canyons. On the other hand, areas of persistent krill distribution included from Cape La Nao to the eastern part of Almeria Bay, although an interannual northwards increase of krill presence had been detected in 2015–2017 likely related to the position of the Balearic front. We provide information on the aggregation characteristics and biological parameters of three krill species, Nyctiphanes couchii, Nematoscelis megalops and Meganyctiphanes norvegica. N. couchii and N. megalops formed patchy pelagic aggregations in the neritic and oceanic zone, respectively, and they were the most common species in the net tows. By contrast, M. norvegica formed a large demersal aggregation on the continental shelf edge and was only found in 2017; nevertheless, its 861-kg catch represented a unique milestone in the Mediterranean. Finally, krill species shared distribution area with Maurolicus muelleri; thus, coexistence between them are also described.
Trachurus mediterraneus is captured as by catch by the fishing fleet in the Spanish Mediterranean and usually landed as the global category of Trachurus spp., consequently there is a prominent lack ...of biological data on this species. The knowledge of the spatial and temporal evolution of its distribution, abundance and main biological parameters is essential to achieve a proper management and sustainable exploitation. Data collected in the MEDiterranean International Acoustic Survey (MEDIAS) 2009–2020 time series, carried out in July, has been analyzed to determine the evolution of the main ecological aspects of T. mediterraneus in two GFCM management units: Northern Spain (GSA06) and Northern Alboran Sea (GSA01). The results suggest a possible neritic distribution of T. mediterraneus, mainly concentrated at depths less than 60 m in GSA01 and up to 105 m in GSA06, as well as the existence of significant differences in abundance and length frequency distributions among GSAs. Furthermore, preliminary results regarding T. mediterraneus age and growth seemed to indicate a faster growth during the first two years in GSA01 than in GSA06. In both areas, potential changes in the life history traits of this species were evidenced, with a decreasing trend in the size at first maturity and condition factor over the years. Finally, five persistent distribution areas were located along the study area, highlighting Málaga Bay as a possible recruitment ground. The relevance of this study lies in the growing need for robust and current biological data of intermediate species in the marine food web and it contributes to the global purpose of achieving an integrated management of fishery resources.
•The GSA01 exhibited a higher abundance and biomass density of Trachurus mediterraneus compared with the GSA06.•For the 2009–2020 period, changes in life history traits were evidenced, with a decreasing trend in the size at first maturity and condition factor of T. mediterraneus over the years in the Spanish Mediterranean region.•Possible differences between GSAs were detected in the growth of T. mediterraneus during the first two years of age.
PDF
