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    • Shad, those endangered travelersby Alicia Dragotta and Claire Valleteau

      Published by Charlotte Recapet the April 6, 2020 on 1:52 PM


      Photograph by MRM association

      Shad are migratory fish that travel great distances between sea and river in order to reproduce. These long journeys are the source of great energy expenditure, particularly to find the most favourable spawn environment. These species are considered bio-indicators of our waterways. Their presence or absence indicates the ecological state of the water. Migratory distance was governed by energetics, behaviors, maturation, and upstream delays at dams. Individual adult migrant American shad (Alosa sapidissima) ascend the Connecticut River and spawn, and survivors return to the marine environment. Theodore Castro-Santos and Benjamin H. Letcher presented a simulation model of these behaviors.

      The purpose of this model is to evaluate the effects of biological and physical variables on adult spawning success and survival. Only energy devoted to migration has been taken into account in the model. Physiology and energetics strongly affected distribution of spawning efforts and survival into the marine environment. Delays to both upstream and downstream movements had dramatic effects on spawning success. Other factors influencing migratory distance included entry date, body length, and initial energy content. Furthermore, dams alter reproductive success and have an impact on migration (delay).

      This model suggests shad that spend more time in the river have greater spawning success but are more likely to die of energy depletion.  Many important factors in the models presented here remain enigmatic. Perhaps the most important question is what causes shad to reverse direction and migrate downstream. Do both energetics and maturation play a role ?

      Answering this question could be difficult but may be possible using, say, a combination of physiological telemetry (e.g., Hinch et al. 1996) and data on reproductive status, especially of downstream migrants.  The purpose of this paper was to develop a management tool to evaluate the relative importance of biological and physical factors on shad reproduction and survival. Restoring access to spawning habitat by providing fish passage has been a central management strategy. Ecological continuum is very important to preserve species, including these migratory fish. Dams for example, were built for many reasons, at the origins in order to mill operations, and today for hydraulic energy exploitation. We have to reconsider the interest of these dams, remove those which are useless and adapt the others. This process has been under way for several years, opening the door to restoring access to the rivers.

      Read the full study: Castro-Santos, T. and Letcher, B.H. (2010) Modeling migratory energetics of Connecticut River American shad (Alosa sapidissima): implications for the conservation of an iteroparous anadromous fish. Canadian Journal of Fisheries and Aquatic Sciences. 67(5): 806-830. https://doi.org/10.1139/F10-026

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    • What does the future has in store for red salmon in a context of global climate change?by Camille Sestac and Amandine Tauzin

      Published by Charlotte Recapet the November 1, 2019 on 1:18 PM

      Pacific salmon have extremely complex life histories and may be threatened by global climate change, as Peter S. Rand and colleagues investigate in their recent study.


      Life cycle of Sockeye Salmon

      Among all species, fishes must adapt to face disruptions caused by global climate change. Sockeye salmon (Oncorhyncus nerka), an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it, has a complex life cycle. As a migratory species, their energetic demands are high during spawning migration. Climate change might have important impacts on populations and their migration via variation of river discharge, increase of water temperature and decline of growth conditions. Aiming to better understand the impacts of these disruptions on the migratory performance of this species of salmon, Peter S. Rand from Wild Salmon Center teamed up with researchers from British Columbia. Their goal is to evaluate the effects of past and future trends in river discharge and temperature on the migratory performance of Sockeye Salmon in the Fraser River.

      In a context of global climate change, it is crucial to understand the effects of disruptions on ecosystems and the populations living in them. Indeed, it is important to know the impacts of these disruptions on every stage of their life cycle (the juvenile freshwater period, the estuarine period, and the subadult marine period) so that we can maintain the populations stock. It’s especially important for fishery management because the fishing quota has greatly increased over the last decades and has threatened populations of Pacific salmon, particularly during their spawning migration. That’s why with three main objectives, these scientists used analysis to improve the understanding of how changes in river conditions can affect the energy use and the mortality rate in Sockeye salmon population. To do so, they used several models: one to search a link between energetic conditions of individuals and en route mortality, one to simulate the energy use during spawning migration and one to hindcast and forecast energy use by simulating fish’s behaviour and migration conditions (for more information, a tip, read the article!).


      Long-range forecasts of lower Fraser river temperature during the summer of 2018

      Using these friendly models, Rand and his colleagues proved that energy reserves and energy depletion of early Stuart Sockeye salmon are major factors that can affect their ability to reach their spawning grounds. They also stated that energy depletion is a function of both river temperature and discharge. Therefore, this population is structured by condition-dependant mortality. Nevertheless, this group of researchers brought to light a mechanism that allows fishes to cope with some environmental variability, providing a certain degree of resilience over time. Therefore, even if energetic demands and migration mortality increase as a result of exposure to warmer temperatures, it will be compensated by reduced time travel to the spawning ground as the river flow will be lower.

      However, increase of temperature means increase of diseases appearing and developing and that stress added may be a direct cause of increased mortality during migration. Finally, as if it wasn’t already bad enough for our salmons, ocean productivity can be affected by climate change and thus affect their river migration success. In fact, this can lead to a decrease of body size and body energy content. It implies that individuals will start their migration with lower energy densities and will be more likely to exhaust their energy stock before even reaching the spawning grounds.


      Salmon jumping over a weir
      According to the US-Canada Commission, a 21° C temperature spike was measured on the Fraser River in 2009. However, sockeye salmon show signs of physiological stress and migratory difficulties above 19°C and from 20°C, the first signs of illness and death appear. But migration of Sockeye salmon is not only threatened by climate change. In fact, migration of salmon specially is impacted by humans or natural obstacles. Dams and weirs form large obstacles for this migratory species and can be very difficult to cross. Many studies have already proved that this kind of obstacles, even when equipped with crossing devices, delay their migration and thus jeopardize their reproduction. This can lead to a decline of the population and in some cases to its extinction, as it happened in Belgium.

      So, whilst some questions have been answered, it seems that more studies need to be carried out to improve our knowledge about the impact of global change which seems to be another sword of Damocles hanging over the head of Sockeye salmon.

      Cited paper: Rand, P.S. et al. (2011) Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon. Trans. Am. Fish. Soc. 135(3), 655-667. https://doi.org/10.1577/T05-023.1

      Featured images: Life cycle of Sockeye salmon by Camille Sestac, graph from https://www.pac.dfo-mpo.gc.ca/science/habitat/frw-rfo/index-eng.html , Sockeye Salmon from www.ryanvolberg.com

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    • Zinc pollution of our rivers: shrimp on alertby Lucille Baron and Macha Joanin

      Published by Charlotte Recapet the August 12, 2019 on 10:03 AM

      No, we will not make an exhaustive catalog of the pollutants that affect our streams and boredom will not settle in your heads by reading us. Instead, we have chosen to discuss the effect of one of the very present emerging pollutants zinc on Gammarus pulex, through the study of Maltby and Naylor (1990).

      At present, world zinc production is over 13,000 kilotons (2018). Zinc is commonly used in metal corrosion coatings and for the manufacture of fertilizers and pesticides (European Commission, 2008b). Thanks to its physico-chemical properties, zinc melts particularly in fresh water, and it is absorbed on suspended solids and sediments (INERIS, 2014). All organisms living in these ecosystems are therefore exposed to this pollution and therefore, indirectly, we too, human.

      Thus, it is important to measure the risks of this exposure on organisms and especially to know the effects of zinc on populations in the long term. For this, researchers have studied, experimentally, the energy deployed in the reproductive mechanisms by aquatic organisms exposed to zinc at different concentrations. In additions, they sought to know if exposing females during a first brood (called current) could have an effect on their second brood unexposed (called subsequent).

      Gammarus pulex is a sentinel species, not only because this shrimp is abundant in fresh waters of England, but in addition it is fed with particulate matter which constitutes, in the natural environment, a large zinc stock. To measure the risks of maintaining the species and the genetic heritage of each individual under the effect of zinc, it is sufficient to study the offspring of females exposed to this compound at different concentrations. The number of individuals which hatched, and the size of each one give some indication of the energy allocated to reproduction. That's what researchers at the British Ecological Society did. If you haven’t understood anything about our attempt to explain the methods used to carry out the study experience, here is a summary diagram that you may be clearer!

      The results they obtained are surprising and show that exposure to zinc (even at low concentrations) significantly increases the number of broods aborted. This result is related to the decline of foods assimilated by females when they are exposed to zinc. The total energy drawn from food is no longer sufficient to sustain metabolic needs while maintaining the mechanisms of maturation and reproduction. Nevertheless, when exposed females carry her brood to term, the number of offspring of each does not seem to vary, despite of the difference in duration of exposure. So, a small criticism of the Figure which represent the percentage of broods aborted in function of the concentration of zinc (Figure 3) can be realize : we found in the control situation (not exposed to zinc), a great variability between the two categories tested. So, in science when the" control "already has significant variability, the results should be interpreted with caution thus it is difficult to conclude to a difference between the current and the subsequent.

      The results concerning the size variation of the descendants, bring a complementarity to this analysis because the researchers observe a reduction of the size in the generations following the exposure. It is the reduction of the available energy (females stopping feedings) which as a consequence the reduction of the size of the individuals of the next brood. Also, on this point, it is unfortunate that the study does not take into account the size of the female that could have an impact on the size of the offspring (Taïr-Abbaci K., 2016).

      The increase of the number of broods aborted and the decrease of the size can have a negative impact on the fitness of populations as exposure to zinc increases abortion. Also, the smallest offspring will take longer time to mature and under stress conditions, this phenomenon may be aggravated over generations and the snowball effect may strongly decreased fitness of individuals. Ultimately, these effects can have a profound impact on the entire population.

      The study seems relatively far from reality since it remains experimental, in the laboratory, and is not carried out in a natural environment and therefore with real conditions of experimentation and exposure to zinc. Thus, the adaptations set up or not by the organisms and the cocktail effects (potential combined effect of different compounds) are not taken into account.

      Nevertheless, the study above begins to be old, the latter dating back to 1990.Today, techniques allow to observe the embryonic development precisely and it turns out that during the different embryonic stages aberrations can appear (Bach et al., 2010). Then, it is difficult to think that abortion is the only response implemented by females when exposed to these chemical compounds. 

      In addition, reproductive success does not depend solely on embryonic development. It is important to consider the energy allocated to ovocyte development and the search for sexual partners to define the impact of zinc on the Gammarus pulex cohorts.

      It’s possible to reduce the production of zinc with recycling it.  However, the recycling of metals can sometimes be too expensive for small industries or privates companies. So, there are other ways than the installation of water decontamination mechanisms. Thus, bio-decontamination can be considered for these companies or industry but can also be useful to large industry in addition to their mechanisms for an exhaustive decontaminations and better water quality. Agriculture is also a source of metal pollution, so it is important to carry out hedgerows planting campaigns near fresh water since they have the function of absorbing a large part of the contaminants resulting from the leaching of flooded soils.

      Cited study: Maltby L. and Naylor C. (1990) Preliminary observations on the ecological relevance of the Gammarus ‘scope for growth’ assay: effect of zinc on reproduction, Functional Ecology. 4, 393-397.

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    • Are vulture restaurants needed to sustain the densest breeding population of the African white-backed vulture?by Mikel Cherbero and Tom Laffleur

      Published by Charlotte Recapet the August 3, 2018 on 10:00 AM

      As obligate scavengers, vultures are entirely dependent on carrion. These last decades, carrion abundance has decreased in many areas. The two main causes of this trend are clearly identified. Natural habitat destruction reduces wild animal carrion abundance, which is the natural resource of scavengers. At the same time, the modification of agricultural practices, essentially the generalization of carcass rendering, has reduced the availability of cattle carrion. These factors have led to a negative trend on scavenger populations. This is especially the case in Africa, where most of avian scavenger species are now endangered. African savanna ecosystems were originally rich in avian scavengers, but most of the species are actually endangered.


      White-backed vultures feeding on zebra carrion - Bernard Dupont - CC BY-SA 2.0

      In this study, authors model the carrion ecology of an ecosystem in Swaziland which is home to the densest breeding population of the African white-backed vulture (Gyps africanus), a critically endangered species. They also study other threatened scavenger species of Swaziland: white-headed vulture (Trigonoceps occipitalis), Nubian vulture (Torgos tracheliotos), marabou stork (Leptoptilos crumenifer), tawny eagle (Aquila rapax) and bateleur (Terathopius ecaudatus). The purpose of this work is to better understand the feeding activity of the white backed vulture and to modelize population trends for these six species (using life-history traits and modelization of carrion availability), and based on these results authors discuss if the establishment of vulture restaurants would be beneficious.

      They first calculated the foraging radius (r) of the white-backed vulture, based on the Foraging radius concept theory. The foraging radius represents the radial distance from the nest in which the energy inputs are greater than the costs of feeding and needs of the vulture and its litter. This theory is adapted to this species, because vulture always comes back to the nest after feeding. They compiled available bibliography and collected data on metabolism and life-history parameters of the species. Using this data, they applied a model created with the same purpose by Ruxton & Houston in 2002 for the Ruppell’s vulture (Gyps rueppellii), which is phylogenetically and ecologically close to the white backed vulture.

      The results shows that the foraging radius is 260 km in the main part of the year. This radius is large, vultures can feed in neighboring countries (South Africa, Mozambique), it implies an international cooperation in the management of these endangered populations. A positive aspect is that individuals can spread over large area, so the studied population can form or sustain other populations. On the other hand this radius is much greater than the natural reserve surface, thus vultures can be exposed to several risks, like poisoning, when they are feeding. When vulture have to feed a chick, energy needs are logically greater so the foraging radius is reduced to 40 km. Carrion availability is more problematic during this period, which should therefore be targeted if vulture restaurants are setted up.

      Using novel Population Dynamics P-Systems, they show that carrion provided by wild ungulates biomass is currently enough to sustain this vulture species. According to the model, white-backed vulture population will continue increasing in Swaziland, and will pass from approximately 300 pairs to more than 500 in twenty years. The other studied avian scavenger populations will follow the same trend, but are far less abundant than white-backed vulture. The model shows also that three main species are composing vultures’ food: the Impala (Aepyceros melampus), the blue wildebeest (Connochaetes taurinus) and the plains zebra (Equus burchelli) represent 55 % of total carrion.

      However, in light of the forecasted population increases, food will become a limiting factor. This is particularly true for the period from November to April, for which the model show a carrion deficit. During this period African vultures are not breeding so they can go far away to feed themselves. But the model also shows a carrion deficit during the breeding season after five to thirteen years of simulation. This lack of food resources can be considered as a natural limiting factor. According to the model, the area has probably reach its maximum carrying capacity after twenty years.

      To conclude, authors suggest that setting up supplementary feeding stations in Swaziland should be seriously considered, especially during the breeding season. Good managed restaurants would have several advantages : secure the viability of the population and thus increase its capacity to act as a source population, avoid poisoning risks and create the opportunity to capture and tag vultures. This last point would allow to improve knowledge about the avian scavenger species, necessary for a more effective conservatory management.

      Cited study: Kane A., Jackson A.L., Monadjem A., Colomer M. A., Margalida A., 2015. Carrion ecology modelling for vulture conservation : are vulture restaurants needed to sustain the densest breeding population of the African white-backed vulture? Animal Conservation (18) 279-286.

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    • Temperature-dependent body size effects determine population responses to climate warmingby Alison Arraud and Laura Duran

      Published by Charlotte Recapet the July 5, 2018 on 1:55 PM

      Up to now, neither the size nor the stage of the individual were considered to studying the population responses to climate warming. On 2014, a scientific group proposed another way to understand the temperature effects on fish populations. They improved the interaction effects of temperature-dependence with the size and the stage of fish on their energetic thresholds responses. Energetic thresholds themselves act on the dynamic of stade-structured population (e.g. parr, smolt, adult).


      Flathead mullet (Mugil cephalus) - Roberto Pillon - CC BY 3.0 Unported

      Finally, this study found that increasing temperature could redistribute biomass across life stages and modify the regulation of the population by reworking the intra-specific competition. Other studies have shown that high temperature during ontogenesis can accelerate the development and growth of individuals or, give individuals of smaller sizes early maturation.

      This study points out the importance of taking into account the interactions between temperature and size-specific (maturing, reproduction, etc.) that will lead to a set of behavioral responses that have consequences on the structuring of a population. This is all the more important in the context of global warming.

      Cited study: Lindmark, M., et al. (2018). Temperature-dependent body size effects determine population responses to climate warming. Ecology Letters 21(2), 181-189.

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