Krill spatial distribution in the Spanish Mediterranean Sea in summer time

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.

Anthropogenic particles in the zooplankton aggregation layer and ingestion in fish species along the Catalan continental shelf

“…This gives an indication of the potential fate of fibres as they have previously been reported on the sea floor in coastal sediments (Alomar et al, 2016;Mathalon and Hill, 2014), however this type of AP is not often observed in sea surface trawls (van Sebille et al, 2015). In the western Mediterranean, zooplankton and krill aggregations, which are fundamental in marine food webs and contribute to the diet of all kinds of fish species, including pelagic species, are mainly found between 25 and 160 m depth in the water column (Ventero et al, 2019(Ventero et al, , 2020. When modelling the 3D vertical distribution of non-buoyant particles, Soto-Navarro et al ( 2020) highlighted that the average depth for aggregation across the Mediterranean Sea was 35 m; however, for the Western Mediterranean Sea, the average depth in this model rarely exceeds 60 m. Recent authors suggest that given the small size of fibres, these may be more easily entrained in the upper-or lower-turbulent motions and often do not settle for long periods of time, or, if settled, they resuspend (Bagaev et al, 2017), which could be explaining their prevalence in the water column in comparison to fragment-type particles, as pointed out by results from our investigation.…”

“…In the western Mediterranean Sea, numerical models have found the highest concentrations along the Catalan coast and most abundant across this region between 20 and 30 m depth (Soto-Navarro et al, 2020). Taking this into account, it is essential to quantify these items, mainly because zooplankton aggregation layers and krill-like aggregation areas constitute the main feeding grounds for pelagic fish inhabiting the continental shelf of the Mediterranean Sea, which can be clearly detected during the day by echo sounders (Ventero et al, 2019(Ventero et al, , 2020 and diurnal vertical migrations of pelagic fish may play a crucial factor in vertical transport and mixing processes, which is a current knowledge gap (Van Sebille et al, 2020).…”

Understanding the oceanographic dynamics of the Isla Chañaral baleen whale feeding ground, (Humboldt Archipelago, Northern Chile) to extend habitat protection

“…(1) So, to correctly associate the received echo to its source, the acoustic signal was first refined by eliminating background noise, estimated according to the following equation (de Robertis and Higginbottom, 2007;Ventero et al, 2019) (Equation 2): Where a is the absorption coefficient, R is the frequency range respective (m) and offset is the logarithmic form of sv (Equation 3): offset = 10loɡ 10 * (sv)…”

Automatic classification of acoustically detected krill aggregations: A case study from Southern Ocean

“…In the last decades, marine fishery science widely used acoustic-based techniques to obtain information about the spatial distribution and abundance of economically and ecologically important pelagic (i.e. inhabiting the water column) organisms ( [2], [7], [8], [6], [25], [38], [52]). Several specific characteristics make acoustic methods an effective tool in monitoring pelagic populations.…”