• Help
  • Find
  • Facebook
  • Twitter
Blog - Bioenergetics for management and conservation
You are here:
    • Avoid predation or starvation: which strategy maximize rainbow trout juvenile survival?by Léa Bulon and Mylène Jury

      Published by Charlotte Recapet the September 9, 2019 on 7:12 AM

      Natural populations are increasingly exposed to a range of biotic stressors, such as predators, and abiotic environmental stressors such as environmental variations (seasonality -  Wingfield, 2013) or chemical pollution (Fisher et al., 2013). (We could think to grandma Margaret who throws away her bleach bucket directly into the river or grandpa George who loses all his plastic lures into the lack). The first year of life is complicated for all organisms because they are more sensitive to those kinds of stressors and their survival is highly impacted.

      In temperate zones, fry are subjected to high predation during the growing season and a nutritive resource deficit during winter. This is why juveniles need to find the best way to maximize their survival and make population viability durable through the time. Predators prefers a fry-up of little fish, it is why predation mortality is higher in small fish than large (Parkinson et al., 2004). However, growth itself may impose a significant energy mobilization which can drive trade-offs between growth and other metabolic processes. If you are really interested by the topic but not by fish, we recommend you to look at the article written by Mcleod et al., 2008, about birds.

      During winter, the metabolism needs some fuels like lipids and proteins to work because resources are often limited. Production of energy storage is energetically expensive, and energy contributes less to increasing their body-size.

      Is it better to allocate their energy into the growing season to avoid predators or into the lipid storage to survive during winter?

      Stephanie Morgensen and John R. Post, scientists from Canada, are been interested in this process. They led an experiment with juvenile rainbow trout (Oncorhynchus mykiss). They developed a mathematical model to determine the energy allocation strategy maximizing the first-year survival of rainbow trout.

      Rainbow trout juveniles are sampled from two sets of lakes in British Columbia in Canada. The first site is located on the Bonaparte Plateau and it corresponds to highly and cold lakes. The second site is located near the town of Merritt and it corresponds to low altitude and warm lakes. In warm lakes, the winter season is shorter than in cold lakes and there are more resources for juveniles.

      They found that juvenile growth is different between the two kinds of lakes: fish from the cold lakes growth more than fish from warm lakes. As we said before, production of lipid storage consumes more energy than growth and resources are more abundant in warm lakes. It is why, fish from warm lakes are more able to stock and fish from cold lakes, to growth. However, fish do not follow only one strategy. Indeed, they grow during the first part of the non-winter season and then they put their energy into the lipid storage to survive during winter. This switch between the strategies is controlled by environmental conditions and determined trout survival during winter.

      The juvenile survival trade-off influencing by environmental conditions such as temperature and resource availability would be important to understand population viability with the evolution of environmental conditions. Rainbow trout has been introduced into many streams and water bodies for recreational fishing because they are easy to catch and quite combative (fishing federation). They constitute an important economic interest it is why, it is one of the most studied species by biologists (INRA). This may lead to management measures to improve pisciculture conditions or to instore fishing quotas and a minimum size of capture. It could be also interesting to know if energy allocation strategies affect physiological processes like growth or reproduction.

      And you what would you choose to survive during winter?

      Cited study: Mogensen, S., & Post, J. R. (2011). Energy allocation strategy modifies growth–survival trade-offs in juvenile fish across ecological and environmental gradients. Oecologia, 168(4), 923–933. doi:10.1007/s00442-011-2164-0

      Creative Commons License
      This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

    • A damned energy loss for migratory fishes: dams!by Manon Salerno

      Published by Charlotte Recapet the June 10, 2019 on 9:42 AM

      Many species of fish grow in the sea and breed in rivers. These migratory fish are called anadromous. When a migratory fish is ready to breed, it leaves the sea and up a river to lay watershed upstream. It will find the optimum conditions to reproduce and allow the development of its offspring. But to do so, they spend a lot of energy on the upstream and sometimes, obstacles like dams in their path does not make it easy for them. This is the case of American Shad in the Connecticut River in the United States. Since the 1970s, 4 hydroelectric dams have been built in the river. Even if they are equipped with fish ladders, these obstacles require the Shad more energy to cross them than if they were not present. We know energy availability can be a limiting factor in migration. Thus, in 1999, scientists wanted to understand energy management in these fish, especially when it is modified by the presence of such.

      Any organism needs energy to perform the movements / migrations necessary for its life cycle. When they are heading into a period that will not allow them to feed (overwintering, migration), some species store energy, such as the bear before hibernating. For American Shad, this stock has to be created before migration because it will not feed during this move. First, scientists have found these are subcutaneous lipid reserves and skin constitute a special tissue for energy storage, which is rather unusual. Salmon, for example, usually mobilizes lipids from muscles and viscera. In contrast, for migration, somatic tissues (red and white muscles and skin) provide about 90% of the energy required in shad.

      According to this study, crossing dams is expensive in energy, especially for females. In fact, American Shad is a species able to reproduce itself several times in its life, but if migration requires too much energy, it will only happen once. It is therefore easy to understand a multitude of dams can have an influence on the reproduction of these fish and therefore on population size, even if they are equipped with systems allowing fish to pass. Not to mention some fish do not even find the fish ladder. These are more likely to be stressed, eaten by predators such as birds, or competing with other fish and unlikely to breed.

      Although fish ladders are quite efficient at the upstream for the American Shad, it is sometimes not suitable for other species. In addition, the outmigration can also present risks of mortality (water retention, drop height etc ...). It is therefore essential to remove the dams for which their function is not provided anymore. But in the United States, the erasure of small dams often meets opposition from local communities. Even though many dams have been removed, they represent a strong historical or landscape value for the inhabitants, creating tensions between the supporters of the restoration and the local communities. This situation reminds the context existing in France, where the aesthetic and historical arguments are very powerful. Many dams are attached to mills and water plants of olden times are therefore seen as a "living historical landscape" very characteristic of their landscape. Because of the local character of each operation, an opposition not necessarily collective but influential and well directed, is enough to block some sites.

      Cited study: J. B. K. Leonard and S. D. McCormick (1999) Effects of migration distance on whole-body and tissue-specific energy use in American shad (Alosa sapidissima). Canadian Journal of Fisheries and Aquatic Sciences 56(7), 1159-1171

      Creative Commons License
      This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

    • 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.

      Creative Commons License
      This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

    • Can bioenergetic models help the re-introduction of the native Rio Grande cutthroat trout in a Southwestern headwater stream?by Emmanuel Bourgoin and Aurélien Callens.

      Published by Charlotte Recapet the May 16, 2018 on 1:47 PM

      Re-introduction of native species is far from being simple: many parameters must be accounted for! To illustrate that, we are going to take a closer look at a study made by Kalb and Huntsman (2017) on a stream in southcentral New Mexico which was deemed suitable for re-introduction of the native Rio Grande cutthroat trout (Oncorhynchus clarkii virginalis). Before re-introducing this species, researchers wanted to know if the habitat was able to sustain it. Thus, they evaluated habitat using resource selection functions with a mechanistic drift-foraging model to explain rainbow trout distributions. They studied rainbow trouts because they are present on the stream and are close relative to the Rio grande cutthroat trout, consequently all the results of this study can be extended to this native species.

      Rainbow trout - Timothy Knepp/U.S. Fish and Wildlife Service - Public domain

      Each month, the available habitat and foraging locations were evaluated along the stream. Foraging locations were defined as the location where they could observe a foraging fish. For each foraging site, the length of the fish was estimated and physical characteristics such as discharge, focal velocity (current velocity at the head of the fish), depth, cover distance and temperature were measured on the exact fish location. These parameters were also measured on the available sites. Macroinvertebrate drift was estimated on all the locations (available and foraging). All these parameters were used in bioenergetic models which allow the researchers to estimate all the intakes of the fish (net energy intake, energy assimilated…) and all the costs associated with foraging (capturing a prey, swimming…).

      First, they observed that macroinvertebrate drift was strongly season- and temperature-dependant with high values in summer and fall and low values in winter and spring. Moreover, as we must expect it, water temperature, depth and discharge were found to be seasonal parameters too. Secondly, models identified the depth as the most limiting factor for habitat selection: trout of all ages preferred habitat location with a greater depth.  The most interesting thing about the models is that they can show the characteristics of the chosen habitat according to the age of the trout and the season. In fact, they showed that during the winter the smaller size-classes were more likely to choose a position closer to cover. Additionally, they highlighted that spring was the season with the greater energy intake for all the size-classes expect the 4+. Finally, drift-foraging models identified that 81% of observed trout selected positions could meet maintenance levels throughout the year and 40% of selected habitats could sustain maximum growth. Despite these last observations, the larger size-classes were energetically more limited throughout the year.

      This study showed that trout population prefers deep pool habitats with slow moving water and that this stream was able to sustain a great population of rainbow trout and could consequently sustain a great native population of Rio grande cutthroat trout. However, authors warn us about the risk of hybridization and interspecific competition and suggest removing the non-native fishes first.

      To answer the question in the title: yes, bioenergetic models can help to re-introduce a native species in a given environment. Nonetheless, this example is really specific: author had the chance to find and study a close relative to the native trout in the stream! The main thing to remember is that bioenergetic models give a lot of useful information on how a species uses an habitat and must be taken into account (if applicable) in the management of species.

      Cited study : Kalb, B. W., Huntsman, B. M., Caldwell, C. A., & Bozek, M. A. (2018). A mechanistic assessment of seasonal microhabitat selection by drift-feeding rainbow trout Oncorhynchus mykiss in a Southwestern headwater stream. Environmental Biology of Fishes, 101(2), 257-273.


      Creative Commons License
      This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.