Impacts de l'oxgène dissous sur la distribution spatiale, l'abondance et la croissance du flétan du Groenland (Reinhardtius hippoglossoides) dans l'estuaire et le golfe du Saint-Laurent

RÉSUMÉ: L’estuaire et le golfe du Saint-Laurent comptent parmi les écosystèmes mondiaux touchés par la problématique de l’hypoxie (faibles niveaux d’oxygène dissous). Dans l’estuaire, une importante détérioration des conditions d’oxygène dissous dans les couches d’eaux profondes (> 200 m) est survenue entre 1930 et 1980 suite à un mélange de causes naturelles et anthropiques. Malgré cette situation, la population du flétan du Groenland (Reinhardtius hippoglossoides) demeure abondante dans l’estuaire et le golfe du Saint-Laurent, notamment au niveau des chenaux Laurentien, Esquiman et Anticosti où, paradoxalement, les conditions d’oxygène sont les plus faibles. Comme cette espèce est l’une des principales espèces de poissons exploitées par la pêche commerciale dans l’estuaire et le golfe du Saint-Laurent, sa distribution en relation avec ces zones à faibles concentrations en oxygène dissous soulève plusieurs questions d’importance tant sur le plan biologique que sur le plan de l’exploitation de cette ressource marine. Les travaux de recherche menés dans le cadre de cette thèse avaient pour objectif de déterminer l’impact de l’hypoxie sur la distribution spatiale, l’abondance et la croissance du flétan du Groenland dans différentes régions de l’estuaire et du golfe du Saint-Laurent. Le premier objectif était d’une part, de décrire les associations entre la distribution spatiale des poissons, leur densité et les caractéristiques physiques jugées importantes (position géographique, profondeur, température et oxygène dissous) en relation avec la taille des poissons et, d’autre part, d’évaluer l’importance de l’oxygène dissous dans la sélection de l’habitat par le flétan du Groenland. Un second objectif consistait à déterminer l’importance relative de l’oxygène dissous sur la croissance des flétans juvéniles. Plus précisément, nous avons examiné les tailles moyennes aux âges 1 et 2 chez les juvéniles et les taux de croissance dans les différentes régions de l’estuaire et du golfe du Saint-Laurent en relation avec l’oxygène dissous, la profondeur, la température et la densité des juvéniles. Finalement un troisième objectif était d'identifier des proxies qui permettraient d’évaluer la condition des poissons et de mieux qualifier le niveau des réserves d’énergie présentes chez le flétan du Groenland en milieu naturel. Dans le premier chapitre, j'ai observé que les fortes densités de flétans se trouvaient dans les habitats caractérisés par de faibles teneurs en oxygène (c'est-à-dire l'estuaire du Saint-Laurent; 49 ºN et à l'ouest de 64 ºW). Ceci est particulièrement vrai pour les juvéniles, que l’on soit en période de faible ou de forte abondance. La forte association entre densités élevées et faibles concentrations en oxygène dissous indique une grande tolérance de l’espèce aux conditions hypoxiques et suggère également que les effets physiologiques négatifs potentiellement causés par les conditions hypoxiques pourraient être compensés par d’autres facteurs tels la disponibilité de nourriture ou une moindre pression de prédation. Les résultats obtenus dans ce chapitre ont également permis de définir clairement l’estuaire du Saint-Laurent comme principale nourricerie pour les flétans du Groenland de l’estuaire et du golfe du Saint-Laurent. Dans le deuxième chapitre, j'ai démontré que globalement les faibles niveaux d’oxygène affectent la croissance des juvéniles, mais que, les effets négatifs de ces faibles niveaux d’oxygène ne sont pas assez importants pour provoquer un déplacement des juvéniles. Les résultats de ce chapitre nous ont permis de démontrer que les tailles moyennes aux âges 1 (17 ± 0,83 cm) et 2 (27 ± 1,08 cm) ainsi que le taux d’accroissement entre les âges 1 et 2 dans les différentes zones de l’estuaire et du golfe du Saint-Laurent étaient largement supérieures à celles observées dans d’autres populations du flétan du Groenland. Le taux d’accroissement entre l’âge 1 et 2 variait entre 8 et 12 cm pour des températures comprises entre 3,7°C et 5,5°C. Nous avons également démontré qu'il variait inversement avec le niveau d’oxygène dissous, et diminuait de façon significative à partir d’un seuil situé sous les 80 μmol/L (~25 % saturation). L'examen de la croissance saisonnière des juvéniles pour la période allant de 2006 à 2010 démontre une croissance continue de ceux-ci, suggérant qu'ils se concentrent dans des zones productives avec un accès permanent à la nourriture. Ces résultats suggèrent également que les caractéristiques biologiques de l'habitat occupé par les juvéniles favoriseraient leur maintien dans cette zone malgré les faibles concentrations en oxygène dissous. Dans le troisième chapitre, j'ai observé que la teneur en eau du muscle et du foie est inversement proportionnelle à leur teneur en énergie. De ce fait, la mesure de la teneur en eau du muscle et du foie du flétan pourrait fournir un moyen précis pour estimer les réserves d’énergie disponibles chez le flétan. Les flétans juvéniles présentaient un facteur de condition variant entre 0,81 au printemps et 0,80 à la fin de l'été. L'indice de condition est similaire entre les deux saisons. Le coefficient de Fulton K et l'indice hépato-somatique l’IHS sont associés de façon significative au contenu énergétique spécifique du muscle et du foie. Ainsi, la mesure du facteur de condition et de l'indice hépato-somatique fournit un moyen simple et adéquat pour estimer le contenu en réserves énergétiques chez le flétan. Au cours de cette thèse, nous avons pu démontrer que le flétan du Groenland est une espèce résistante à l’hypoxie, ce qui explique sa présence dans les habitats situés dans les zones les plus hypoxiques de l’écosystème de l’estuaire et du golfe du Saint-Laurent. Nos résultats suggèrent également que les faibles niveaux en oxygène dissous actuels n'ont pas d'impacts majeurs sur la distribution, l’abondance et la croissance de cette espèce. Cependant, une diminution future des concentrations en oxygène dissous dans un contexte de changements climatiques pourrait affecter la distribution et la survie des juvéniles. Ces travaux sont donc d’importance pour anticiper et prédire les impacts potentiels d’une détérioration supplémentaire des concentrations en oxygène dissous sur l’abondance et la pérennité de cette ressource. -- Mot(s) clé(s) en français : hypoxie, flétan du Groenland, estuaire et golfe du Saint-Laurent, densité dépendance, distribution spatiale, choix de l'habitat, croissance, condition. -- ABSTRACT: The estuary and Gulf of St. Lawrence (EGSL) is one of the world’s ecosystems affected by hypoxia (low dissolved oxygen levels). In the estuary, a significant decrease in the dissolved oxygen conditions in the deepwater layers (> 200 m) occurred between 1930 and 1980 due to a combination of natural and anthropogenic causes. Despite this situation, Greenland halibut (Reinhardtius hippoglossoides) population is abundant in the EGSL, largely occuping the Laurentian, Esquiman, and Anticosti channels, where the lowest dissolved oxygen concentrations are found. Because Greenland halibut is an important commercial fish species in the EGSL, its distribution in relation to dissolved oxygen levels raises important biological issues regarding this species and its sustainable exploitation. The aim of this Ph.D. was to determine the effects of hypoxia on the spatial distribution, abundance, and growth of Greenland halibut in different regions of the EGSL. The first objective was to describe associations that may be present between fish spatial distribution, fish density, and physical characteristics deemed important in the EGSL (spatial location, depth, temperature, and dissolved oxygen) in relation to fish size. Another objective was to assess the importance of dissolved oxygen in habitat selection by Greenland halibut and to determine the relative importance of dissolved oxygen concentrations on juvenile growth. I examined mean lengths in 1- and 2-year-old juveniles as well as growth rates in different regions of the EGSL in relation to dissolved oxygen, depth, temperature, and juvenile density. A last objective was to look at possible proxies for the determination of general condition and the level of energy reserves in individuals captured in their natural environment. The results reported in Chapter 1 showed that high Greenland halibut densities were found in the St. Lawrence estuary habitats characterized by low oxygen levels (49ºN 64ºW); this was especially true for juveniles, whether periods of low or high abundance of the fish are considered. The strong association between high densities and low dissolved oxygen concentrations indicates a tolerance of this species to hypoxic conditions and suggests that if adverse physiological effects caused by hypoxic conditions are present, they are offset by other factors such as food availability or low predation pressure. The results have also clearly identified the St. Lawrence estuary as the main nursery for the EGSL Greenland halibut population. The results reported in Chapter II indicate that low oxygen levels affect juvenile growth, but that these effects are not pronounced enough to result in the displacement of juveniles. We showed that mean lengths of 1- and 2-year-old animals (17 ± 0.83 and 27 ± 1.08 cm, respectively) as well as the length increment between ages 1 and 2 in the different areas of the EGSL were much higher than those observed in other populations of Greenland halibut, even though oxygen levels were low and fish density was high. The length increment from ages 1 and 2 ranged between 8 and 12 cm for temperatures varying from 3.7 to 5.5°C. Growth rate varied inversely with the dissolved oxygen and significantly decreased when oxygen levels dropped below 80 μmol / L (~ 25% saturation). Estimates of juvenile seasonal growth for the 2006 to 2010 period show continuous seasonal growth, possibly because juveniles are concentrated in highly productive areas with permanent access to food. Again, the results emphasize that the negative effects of low dissolved oxygen concentrations are offset by other physical or biological environmental characteristics, such as food abundance, food availability, and/or predator density. In Chapter III, I demonstrated that muscle and liver water content are inversely proportional to their respective energy content. Therefore, measuring the water content of these two tissues could provide accurate tools to estimate Greenland halibut energy reserves. Condition factor ranged between 0.81 in spring and 0.80 at the end of summer. Condition factor was similar between the two seasons. Fulton's condition factor and hepatosomatic index were significantly associated with the specific energy content in both muscle and liver. Thus, Fulton's condition factor and hepatosomatic index provide simple and adequate means for estimating energy reserves in this species. Overall, we showed that Greenland halibut is resistant to hypoxia, explaining its prominent use of habitats in the most hypoxic areas of the EGSL ecosystem. Our results also suggest that the current low levels of dissolved oxygen have no major impact on the distribution, abundance, or growth of this species. However, if oxygen levels decrease further due to global changes the distribution and survival of this species may be affected. This work is therefore important to anticipate and predict potential impacts of a further deterioration of dissolved oxygen concentrations on the abundance and sustainability of this resource. Keywords : hypoxia, Greenland halibut, Estuary and Gulf of St. Lawrence, density dependence, spatial distribution, habitat selection, growth, condition. -- Mot(s) clé(s) en anglais : hypoxia, Greenland halibut, Estuary and Gulf of St. Lawrence, density dependence, spatial distribution, habitat selection, growth, condition

Dynamic visual servoing from sequential regions of interest acquisition.: On behalf of: Multimedia Archives Dynamic visual servoing from sequential regions of interest acquisition.

International audienceOne of the main drawbacks of vision-based control that remains unsolved is the poor dynamic performances caused by the low acquisition frequency of the vision systems and the time latency due to processing. We propose in this paper to face the challenge of designing a high-performance dynamic visual servo control scheme. Two versatile control laws are developed in this paper: a position-based dynamic visual servoing and an image-based dynamic visual servoing. Both control laws are designed to compute the control torques exclusively from a sequential acquisition of regions of interest containing the visual features to achieve an accurate trajectory tracking. The presented experiments on vision-based dynamic control of a high-speed parallel robot show that the proposed control schemes can perform better than joint-based computed torque control

Učinak dodatka hrani (zakiseljivača i sredstva za vezivanje toksina) u proizvodnji mlijeka u mliječnih krava

Dairy cow feeding plays an important role in milk production. The present study was conducted to evaluate the effect of a feed additive (association of acidifier and mycotoxin binder) on milk production in dairy cattle. For this purpose, 22 cows belonging to three breeds (Montbeliard, Holstein, and Flekveih) were used. The cows were divided into two groups; a control group with seven cows and an experimental group with 15 animals. The results showed that the additive had a positive effect on milk production (23.14±5.87 litres for the experimental group vs 18.00±6.90 litres for the control). The additive also had a good effect on the percentage of sub-clinical mastitis: the Californian Mastitis Test (CMT) carried out at monthly intervals showed a clear improvement in the udder health of females in the experiment with 13 positive samples in the first test for nine cows (with four affected teats) and 10 positive samples for the second test in three cows (with three affected teats). Moreover, statistical tests revealed a significant difference in the mean fat content (35 g/L vs 23.86 g/L, respectively) while the average Faeces Consistency Score and Dornic acidity was lower in the experimental group compared to the control (2.23 vs 3.21 and 13.83 vs 16.14, respectively). These results show the importance of incorporating the feed additive into the diet of dairy cows and the need to implement an extension programme and zootechnical supervision of all actors in the sector to ensure the quality of milk production and the performance of dairy cows.Hranidba mliječnih krava je vrlo važna u njihovoj proizvodnji. Ova studija je provedena za procjenu učinka dodatka hrani (kombinacije zakiseljivača i sredstva za vezivanje mikotoksina) na proizvodnju mlijeka u mliječnih krava. U tu su svrhu praćeme 22 krave: 3 pasmine (montbeliard, holstein i flekveih). Krave su podijeljene u 2 skupine: kontrolnu skupinu sa 7 krava i eksperimentalnu skupinu s 15 životinja. Dobiveni rezultati pokazali su da organska kiselina ima pozitivan učinak na proizvodnju mlijeka (23,14±5,87 litara za eksperimentalnu skupinu u usporedbi s 18,00±6,90 litara za kontrolnu skupinu). Uz to, aditiv je imao i pozitivan učinak na postotak subkliničkog mastitisa. Kalifornijski mastitis test (CMT) proveden u razmaku od 1 mjeseca za životinje pokazao je jasno poboljšanje zdravlja vimena krava podvrgnutih istraživanju s 13 pozitivnih uzoraka u prvom testu za 9 krava (s 4 zahvaćene sise) i 10 drugih pozitivnih uzoraka za drugi test u 3 krave (s 3 zahvaćene sise). Statistički testovi su otkrili značajnu razliku između prosječnog udjela masnoća (35 g/L u usporedbi s 23,86 g/L) dok je prosječno bodovanje konzistencije izmeta i kiselost po Dornicu bilo niže u istoj skupini u usporedbi s kontrolnom skupinom (2,23 u usporedbi s 3,21 i 13,83 u usporedbi s 16,14). Podatci su pokazali važnost i potrebu dodatka hrani u hranidbu mliječnih krava i potrebu za provedbom programa proširenja i zootehničkog nadzora svih aktera u sektoru da bi se osigurala kvaliteta proizvodnje mlijeka i učinkovitost mliječnih krava

Climate forecasts in disaster management: Red Cross flood operations in West Africa, 2018

In 2008, the International Federation of Red Cross and Red Crescent Societies (IFRC) used a seasonal forecast for West Africa for the first time to implement an Early Warning, Early Action strategy for enhanced flood preparedness and response. Interviews with disaster managers suggest that this approach improved their capacity and response. Relief supplies reached flood victims within days, as opposed to weeks in previous years, thereby preventing further loss of life, illness, and setbacks to livelihoods, as well as augmenting the efficiency of resource use. This case demonstrates the potential benefits to be realised from the use of medium-to-long-range forecasts in disaster management, especially in the context of potential increases in extreme weather and climate-related events due to climate variability and change. However, harnessing the full potential of these forecasts will require continued effort and collaboration among disaster managers, climate service providers, and major humanitarian donors

Using seasonal climate forecasts to guide disaster management: the Red Cross experience during the 2008 West Africa floods

In 2008, the seasonal forecast issued at the Seasonal Climate Outlook Forum for West Africa (PRESAO) announced a high risk of above-normal rainfall for the July–September rainy season. With probabilities for above-normal rainfall of 0.45, this forecast indicated noteworthy increases in the risk of heavy rainfall. When this information reached the International Federation of Red Cross and Red Crescent Societies (IFRC) West and Central Africa Office, it led to significant changes in the organization’s flood response operations. The IFRC regional office requested funds in advance of anticipated floods, prepositioned disaster relief items in strategic locations across West Africa to benefit up to 9,500 families, updated its flood contingency plans, and alerted vulnerable communities and decision-makers across the region. This forecast-based preparedness resulted in a decrease in the number of lives, property, and livelihoods lost to floods, compared to just one year prior in 2007 when similar floods claimed above 300 lives in the region. This article demonstrates how a science-based early warning informed decisions and saved lives by triggering action in anticipation of forecast events. It analyses what it took to move decision-makers to action, based on seasonal climate information, and to overcome traditional barriers to the uptake of seasonal climate information in the region, providing evidence that these barriers can be overcome. While some institutional, communication and technical barriers were addressed in 2008, many challenges remain. Scientists and humanitarians need to build more common ground

Experimental and Numerical Cavitation Flow Analysis of an Industrial Inducer

In the present study, a CFD model for cavitation simulation have been investigated and compared to experimental results in the case of 3-bladed industrial inducer. The model uses a multiphase approach, based on multiphase mixture assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The model allows a good prediction of the cavitation inception as well as the main cavity dimensions. The threshold corresponding to the head drop is also well predicted by the model. It was found that the cavitation induced head drop is mainly due to an increase of energy losses and a decrease of the supplied energy. The hydrodynamic mechanism of head drop is investigated through a global and local analysis of the flow field

Local, Seasonal, and Yearly Condition of Juvenile Greenland Halibut Revealed by the Le Cren Condition Index

An understanding of biological characteristics, such as growth patterns, condition, and energy reserves, is important for better understanding the environmental constraints exerted on fish populations. This is especially true for exploited fish stocks in the current context of climate change. Using biological data collected from 2006 to 2009 during bottom trawl research surveys by Fisheries and Oceans Canada in the estuary and Gulf of St. Lawrence (EGSL) as well as data from 2000 to 2018 in the northwest Atlantic, we sought to improve our knowledge on the seasonal condition of Greenland Halibut Reinhardtius hippoglossoides juveniles and to better understand the divergence in some life history traits between juveniles captured in these two regions. We validated the use of the Le Cren condition index and evaluated its relationship with energetic status in juvenile (20–32-cm TL) Greenland Halibut. In the EGSL, juvenile condition was higher in winter and spring compared to summer and fall. Such variations may result from this species’ pelagic predation activity and prey availability. Juveniles captured in the EGSL during 2016–2017 were larger but had a lower condition index than those captured in the northwest Atlantic, but we found no indication of earlier sexual maturation in the EGSL that could explain the sex ratio differences we observed in catches from these two areas

Kármán vortex shedding in the wake of a 2D hydrofoil: Measurement and numerical simulation

The present study deals with the shedding process of the Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds numbers. Investigations are performed in order to evaluate the ability of an unsteady numerical simulation to accurately reproduce the vortex shedding frequency. The vortex shedding frequency, derived from flow induced vibrations measurements, is found to follow the Strouhal law as long as none of the resonance frequencies of the hydrofoil is excited. For such lock-off conditions, the Kármán vortices exhibit a strong spanwise 3D instability. For Reynolds numbers ranging from 35’000 to 40’000, the torsion mode of the hydrofoil is excited with a substantial increase of the vibration level. In this case, the shedding frequency is locked onto the vibration frequency. The vortex roll-up, shedding and advection are well predicted by the computations as well as the 3D instability. Nevertheless, the numerical simulations underestimate the vortex shedding frequency of about 20%. No significant influence of the turbulence models, the incoming flow turbulence intensity and the mesh size is observed on the computed values. To investigate the issue of discrepancy between absolute values of measured and computed shedding frequency, we intend to address the sensitivity of the vortex shedding frequency to the boundary layer. It is indeed know that the boundary layer transition point to turbulence for this profile geometry is located slightly downstream of the midchord for an incidence angle of 0°. In contrast, the numerical simulation, as it solves the RANS equations, models the whole flow as being turbulent. Consequently, rough stripes are placed just behind the hydrofoil leading edge. For such a configuration, the boundary layer is turbulent from the leading edge in a similar way to the computations. Notable influence of the roughness is observed: The vortex shedding frequencies are significantly decreased in comparison to the smooth leading edge. The average Strouhal number St decreases from 0.24 to 0.18 and is nearly equal to the computational one, St=0.19. Kármán vortices being very sensitive to the boundary layer, differences in the transition points between experiments and computations have to be minimized in order to aspire good agreement

A Review of the In-Network Computing and Its Role in the Edge-Cloud Continuum

Future networks are anticipated to enable exciting applications and industrial services ranging from Multisensory Extended Reality to Holographic and Haptic communication. These services are accompanied by high bandwidth requirements and/or require low latency and low reliability, which leads to the need for scarce and expensive resources. Cloud and edge computing offer different functionalities to these applications that require communication, computing, and caching (3C) resources working collectively. Hence, a paradigm shift is necessary to enable the joint management of the 3Cs in the edge-cloud continuum. We argue that In-Network Computing (INC) is the missing element that completes the edge-cloud continuum. This paper provides a detailed analysis of the driving use-cases, explores the synergy between INC and 3C, and emphasizes the crucial role of INC. A discussion on the opportunities and challenges posed by INC is held from various perspectives, including hardware implementation, architectural design, and regulatory and commercial aspects

Preparation of anti-vicinal amino alcohols: asymmetric synthesis of D-erythro-Sphinganine, (+)-spisulosine and D-ribo-phytosphingosine

Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM-ether directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor D-erythro-sphinganine and the antitumor agent (+)-spisulosine, while the Overman rearrangement of chiral allylic trichloroacetimidates generated by asymmetric reduction of an alpha,beta-unsaturated methyl ketone allowed rapid access to both D-ribo-phytosphingosine and L-arabino-phytosphingosine