Initial experimental research on the hydraulics of froth co-current column

Przeprowadzono wstępne badania doświadczalne hydrauliki współprądowej kolumny pianowej. Określono rzeczywisty czas przebywania cieczy i gazu w obrębie piany dynamicznej. Obliczono w sposób przybliżony wielkość powierzchni międzyfazowej. Wyznaczono spadki ciśnienia gazu na półce suchej, mokrej oraz w warstwie piany. Przedstawiona kolumna ze względu na swoje walory w postaci relatywnie dużej powierzchni międzyfazowej oraz stabilnej pracy przy wysokim obciążeniu cieczą powinna znaleźć zastosowanie w przemysłowych procesach wymiany masy.Experimental studies on hydraulics of froth co-current column were performed. Gas and liquid real residence time in the froth was determined. Gas and liquid interfacial area was approximately calculated. Gas pressure drop across the dry and wet shelf as well as in the froth layer were measured. The presented column due to its advantageous features, i.e. relatively large gas – liquid interfacial area and stable work under high wetting density should be applied in industrial mass transfer operations

Pêche et changement climatique au Saloum : entre sécheresse et exploitation du sel et avancée de la mer

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Pêche et changement climatique au Saloum : entre sécheresse et exploitation du sel et avancée de la mer

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Climate-driven shift of Sardinella aurita stock in Northwest Africa ecosystem as evidenced by robust spatial indicators [résumé]

ICAWA : International Conference AWA, Dakar, SEN, 13-/12/2016 - 15/12/2016In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and more landed by fishermen in Morocco, while the sardine has become a target by fishing vessels in Mauritania and Senegal. This indicates a modification in the distribution areas of pelagic resources. To verify this hypothesis, an outstanding database consisting in 14 acoustic surveys with a consistent and high sampling intensity (2263 trawl hauls) conducted by the RV Fridtjof Nansen from 1995 to 2015 was investigated in this study to identify trends in distribution shifts in pelagic fishes. A focus was made on sardinellas and the main species in the southern part of the region. Two strong spatial indicators are used in this study: the latitudinal extreme location and the barycentre of biomasses. Two clear trends can be observed from the data analysed. Firstly, in the southern and tropical part of this system the typical trend is that pelagic species show an increasing northward distribution. This applies to S. aurita, Trachurus trecae, Chloroscombrus chrysurus, Sphyraena guachancho and Brachydeuterus auritu. A second group is observed, those that do not show any clear trend in distributional shift, but where the distribution is stable over the period. The typical species observed here are S. maderensis and Decapterus rhonchus. Despite some variations in the upwelling intensity, we show that the sea surface temperature is by far the main parameter to explain this northern shift. We also discuss the likely - and largely unknown - influence of the under-estimation of the detections because of the absence of sampling in the shallow coastal zone. The impact of such displacements is also discussed in term of regional management of these shared stocks

IEEE/OES Acoustics in Underwater Geosciences Symposium (RIO Acoustics)

In this work we compare the result obtained by in situ echosounder measurements on eastern Venezuelan and south Sénégal coastal shelves where Sardinella aurita was the predominant species occurred in fish school structure. The both stocks are known as genetically independent. Persistent school typology was already described by Petitgas and Levenez (1996) analysing Senegalese echogram database. We compiled and analyzed an acoustic database (7 surveys) of Venezuelan fish school populations. The echo type typology encountered in the both countries is similar over the year. On the others hand, two standardized acoustics surveys have been carried out in 1999, with the same research vessel and echosounder (38 kHz) in Sénégal and Venezuela. The 'echointegration by shoal' method was performed on the data collected on both stocks. The observed fish school descriptors (energetic, morphologic and spatial) showed that the differentiation between day and night fish schools was mainly due to morphologic variables (fractal dimension). In Venezuela the echo types were different between day and night as in Sénégal, but on the entire diel cycle the quantitative and qualitative characteristics of fish schools were similar on both ecosystems. Both acoustic fish school populations are similar; they are constituted by a same dominant species Sardinella aurita. Observation of small pelagic fish school during the night is not unusual. The schooling behaviour and the diel aggregative dynamics of small pelagic fish around the world are discussed according our result and literature review. School morphology appears to be common to large number of species, and aggregative dynamics, species dependent

On the resiliency of an eastern boundary upwelling ecosystem exposed to multiple stressors : an acoustic approach [résumé de poster]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022The resistance of an east border upwelling system was investigated using relative index of ma-rine pelagic biomass estimates under a changing environment spanning 20-years in the strongly exploited southern Canary Current Large marine Ecosystem (sCCLME). We divided the sCCLME in two parts (north and south of Cap Blanc), based on oceanographic regimes. We de-lineated two size-based groups ('plankton' and 'pelagic fish') corresponding to lower and higher trophic levels, respectively. Over the 20-year period, all spatial remote sensing environ-mental variables increased significantly, except in the area south of Cap Blanc where sea surface Chlorophyll-a concentrations declined and the upwelling favorable wind was stable. Relative index of marine pelagic abundance was higher in the south area compared to the north area of Cap Blanc. No significant latitudinal shift to the mass center was detected, regardless of trophic level. Relative pelagic abundance did not change, suggesting sCCLME pelagic organisms were able to adapt to changing environmental conditions. Despite strong annual variability and the presence of major stressors (overfishing, climate change), the marine pelagic ressources, mainly fish and plankton remained relatively stable over the two decades, advancing our understanding on the resistance of this east border upwelling system

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

In Northwest Africa, the small pelagic fish are in abundance and play a crucial role for the food safety of populations. The pelagic resources are exploited both by small-scale artisanal and industrial fleets. The landing structure of the countries in the region has been in perpetual change during the last years. The sardinella has been more and more landed by fishermen in Morocco, while the sardine has become a target by fishing vessels in Mauritania and Senegal. This indicates a modification in the distribution areas of pelagic resources. To verify this hypothesis, an outstanding database consisting in 14 acoustic surveys with a consistent and high sampling intensity (2263 trawl hauls) conducted by the RV Fridtjof Nansen from 1995 to 2015 was investigated in this study to identify trends in distribution shifts in pelagic fishes. A focus was made on sardinellas and the main species in the southern part of the region. Two strong spatial indicators are used in this study: the latitudinal extreme location and the barycentre of biomasses. Two clear trends can be observed from the data analysed. Firstly, in the southern and tropical part of this system the typical trend is that pelagic species show an increasing northward distribution. This applies to S. aurita, Trachurus trecae, Chloroscombrus chrysurus, Sphyraena guachancho and Brachydeuterus auritu. A second group is observed, those that do not show any clear trend in distributional shift, but where the distribution is stable over the period. The typical species observed here are S. maderensis and Decapterus rhonchus. Despite some variations in the upwelling intensity, we show that the sea surface temperature is by far the main parameter to explain this northern shift. We also discuss the likely - and largely unknown - influence of the under-estimation of the detections because of the absence of sampling in the shallow coastal zone. The impact of such displacements is also discussed in term of regional management of these shared stocks

International conference ICAWA 2017 and 2018 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

Factors influencing landed prices and those of processed products (fish and processed) are mainly landed quantities and product quality. The latter are in turn influenced by the seasonality of sardinella conditioned by the temperature of the water. It is usually in cooroon periods (April to June) that sardinella landings are more important and it is at this time also that the prices of fresh fish and processed products are the lowest. On the other hand sardinella is rare in lolli most often (October to December) and it is at this period also that the prices are generally higher. Nevertheless, depending on whether one is on the Petite Côte or on the Grande Côte, fishermen's appreciations of the periods of abundance of sardinellas differ. However, from the analysis of fishermen's knowledge on sardinella migration and bioecological models, it appears that sardinella are present on Senegalese coasts during periods of low temperature. As the cold water periods are later and shorter, the sardinella will be increasingly rare on the coast in Senegal, its higher price, accessibility is more difficult and consequently the animal protein deficit of the populations more accentuated