Fish are expected to shrink in size by 20 to 30 per cent if ocean temperatures continue to climb due to climate change

August 21, 2017 University of British Columbia read full ScienceDaily article here

…A new study by researchers at the University of British Columbia provides a deeper explanation of why fish are expected to decline in size. “Fish, as cold-blooded animals, cannot regulate their own body temperatures. When their waters get warmer, their metabolism accelerates and they need more oxygen to sustain their body functions….There is a point where the gills cannot supply enough oxygen for a larger body, so the fish just stops growing larger.”…

….as fish like cod increases its weight by 100 per cent, its gills only grow by 80 per cent or less. When understood in the context of climate change, this biological rule reinforces the prediction that fish will shrink and will be even smaller than thought in previous studies.

Warmer waters increase fish’s need for oxygen but climate change will result in less oxygen in the oceans. This means that gills have less oxygen to supply to a body that already grows faster than them. The researchers say this forces fish to stop growing at a smaller size to be able to fulfill their needs with the little oxygen available to them.

Some species may be more affected by this combination of factors. Tuna, which are fast moving and require more energy and oxygen, may shrink even more when temperatures increase. Smaller fish will have an impact on fisheries production as well as the interaction between organisms in the ecosystems.

Daniel Pauly, William W. L. Cheung. Sound physiological knowledge and principles in modeling shrinking of fishes under climate changeGlobal Change Biology, 2017; DOI: 10.1111/gcb.13831

From the paper’s discussion:

Lefevre et al. (2017) concede that “global warming may lead to reduction in average body size and size-at-age of fish (see Munday et al., 2008; Daufresne et al., 2009; Baudron et al., 2014)” , but suggest that “underlying mechanisms be investigated […] using sound physiological knowledge and principles”. Firstly, we demonstrated here that GOLT provides a parsimonious explanation for the manner that fish growth can be constrained by the physical geometry of the gill respiratory area, and consequently, its ability to take up oxygen from waters. Secondly, GOLT explains a wide range of phenomena and perceived anomalies of fish biology and ecology that are directly or indirectly related to fishes’ oxygen needs and growth without the need to invoke different ad hoc hypotheses. Thirdly, through the use of a mathematical model, we demonstrate that GOLT is able to predict the decrease in body size of marine fish under warming, which intensifies when realistic parameters are selected. All of this is also consistent with the evidence presented by physiologists (e.g., Pörtner et al., in press), who also demonstrated that fish exposed to high temperatures cannot meet their increased oxygen demand (see, e.g., Bozinovic & Pörtner, 2015; Pörtner & Knust, 2007; Pörtner et al., 2006).

It is often easier to develop ad hoc unconstrained hypotheses that are then used to explain individual cases than to develop generalizable theory capable of explaining perceived anomalies, e.g., the high value of dG in the common thresher shark reported in Wegner (2016) and Wootton et al. (2015). This is well illustrated by Lefevre et al. (2017), who suggest that it “is essential that the correct underlying mechanisms be investigated and identified, and that projection of the effects on fish populations be modeled using sound physiological knowledge and principles” and that “other mechanisms must be at play in French river fishes” in the context of a study that shows the decrease in body size of fishes in a French river. Thus, instead of developing a different explanation for each instance of these phenomena, for each species, we show that the GOLT can provide a unified explanation. With GOLT, we do not need to assume that the fish of French rivers use physiological mechanisms to respond to temperature increase that are different from those of other fish. In addition, GOLT could be used to predict similar phenomenon for fishes in Spanish rivers, or ot her European river fishes, without assuming that these fishes are physiologically constrained in a manner fundamentally different from one another.

Finally, it is true, as Lefevre et al. (2017) note, that GOLT is not mentioned in the physiology textbooks of Schmidt-Nielsen (1997) and Evans and Clairborne (2006). Similarly, what we now know as ‘plate tectonics’ were not mentioned in some geology textbooks until way in the 1970s (Oreskes, 1999). This is due to scientific progress, which requires textbooks to be updated when a new understanding of previously unexplained processes emerges.

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Measuring global biodiversity change: Essential Biodiversity Variables

  • Essential Biodiversity Variables constructed from various sources of data and are the underlying variables to assess changes in biodiversity through time can be produced to measure biodiversity change at a global scale.
  • EBVs can be used to measure progress toward key global policies to protect the world from further loss of biodiversity, support sustainable use of natural resources and enhance benefits from these.
  • harmonization of data collection and technical data management as well as legal complications and constraints are key bottlenecks

read full ScienceDaily article here

…EBVs are constructed from various sources of data and are the underlying variables to assess changes in biodiversity through time. They can be used to measure the achievement of targets like the Aichi targets set by the Convention for Biological Diversity (CBD) or the Sustainable Development Goals (SDGs) identified by the UN 2030 Agenda for Sustainable Development, to protect the world from further loss of biodiversity, support sustainable use of natural resources and enhance benefits from these…

The publication is an outcome of the first two workshops organized by the EU-funded Horizon 2020 project GLOBIS-B: GLOBal Infrastructures for Supporting Biodiversity research

…Measurements of changes in species distribution and abundance underpin policy indicators to quantify population trends and extinction risk for threat categorization, assessments of geographic range dynamics, spread of invasive species, and biodiversity responses to climate change and habitat conversion. The discussions during the two workshops showed that the harmonization of data collection and technical data management as well as legal complications and constraints are key bottlenecks for building global EBV data products on species distribution and abundance….

W. Daniel Kissling et al. Building essential biodiversity variables (EBVs) of species distribution and abundance at a global scaleBiological Reviews, 2017; DOI: 10.1111/brv.12359