Temperature increases faster than fish can adapt

Tiistai 29.12.2020 klo 16.28 - Mikko Nikinmaa

A temperature increase will affect fish populations everywhere. Depending on the species, the depth of the aquatic body and its accessibility the effects can be drastic – the most extreme outcome being  the total disappearance of the fish from the habitat. Because of this, the research on temperature biology of fish has become an important field of study in climate change research. The importance of fish studies is strengthened, as they can be an primary source of animal protein in food.

Fish can be either stenothermal or eurythermal. The definitions indicate the phenotypic plasticity of species with regard to temperature. Stenothermal species tolerate only small temperature changes, whereas eurythermal species can live in wide temperature range. It should be noted that most of the preferred fisheries species have narrow genotypic temperature tolerance. If they live in environments with different temperatures, their genotypes are different, each still having narrow temperature tolerance so that the cold-temperature genotype would not be able to tolerate the temperatures that the warm-temperature genotype lives in and vise versa. Although a temperature increase may actually increase the amount of fish flesh produced per unit time, the species accounting for the increased productivity are not preferred catch or food.

The roles of phenotypic plasticity and the speed of heritable genetic adaptation to temperature changes has been surprisingly little studied. 

Further, it is almost completely unknown, if the temperature tolerance is affected by environmental contaminants. One important recent study with zebrafish (Morgan et al. PNAS 2020: https://www.pnas.org/cgi/doi/10.1073/pnas.2011419117) suggests that the genetic adaptation to increased temperature is not fast enough to keep pace with the temperature increase that is currently occurring. It also appears that the plasticity of tolerated temperatures decreases, when the population adapts to increased maximal temperature.

So, this is bad news throughout. The fish that we like to eat are stenothermal. The eurythermal species could substitute for them, but even they have problems in genetic adaptation. Furthermore, it seems that tolerance to reduced temperature evolves faster than that to increased temperature. All of these points make the case for markedly slowing down and stopping the current temperature increase stronger. If we want to eat fish, climate change must be stopped.

 

Rising temperature affects fish more than previously thought

Lauantai 15.8.2020 klo 21.02 - Mikko Nikinmaa

A recent study in Science (Dahlke et al., Science 369, 65–70, 3 July 2020) has evaluated, how fishes are affected by temperature increase associated with climate change. Fish are an increasingly important food source for humankind, so their success in warming waters is of primary importance for feeding human population. Consequently, the ability of fish to tolerate warming waters has been studied intensively. Earlier, it has been estimated that only 5 % of fish populations would be adversely affected by temperature increase predicted to occur by 2100. A lot of fisheries experts have sucked of relief about this, as overfishing

is a major threat presently, and it is thought that overfishing may decrease fish populations by half before 2050. In fact, it has been estimated that temperature increase would make population sizes of fishes larger in some areas.

The limitation of earlier estimations has been that the possibility that possible differences between temperature tolerances of age groups have not been estimated. This was done in the study by Dahlke et al. The results show that temperature tolerance of different age groups of fish is markedly different. The embryos (developing fish within egg cases) and spawning adults (blue and black lines in the figure) appear to have up to 20^oC smaller tolerated temperature range than free-swimming larvae or non-reproducing adults (red and orange lines). The difference is greatest at mid latitudes, and decreases both (and especially) in the arctic and near equator.

The reason for decreased temperature tolerance is probably due to mismatch between oxygen uptake and consumption. Oxygen uptake is limiting in the embryos enclosed within eggs, whereas the oxygen transport of free-living larvae and juvenile and non-reproducing adults becomes more effective. In spawning adults the oxygen consumption increases without improvement of oxygen transport. Physiological studies about the interaction between temperature, oxygen transport and consumption are needed in different life stages of fish to enable conclusive evaluation of what causes life stage-dependent variation of temperature tolerance.

Cod - a component of fish'n chips disappearing because of climate change?

Keskiviikko 8.7.2020 klo 14.27 - Mikko Nikinmaa

In an effort to introduce some physiological realism to stock assessments, Hänsel et al. (Ocean warming and acidification may drag down the commercial Arctic cod fishery by 2100; PLOS ONE, https://doi.org/10.1371/journal.pone.0231589 April 22, 2020) have modelled how some factors caused by temperature increase and ocean acidification affect traditional stock modelling of cod. Although at crude level (e.g. not taking into account any effects of aquatic pollution), the study gives sobering views. While up to the present an increase in temperature has been beneficial for recruitment, the future looks gloomier. Because of the improved recruitment until the bottom temperature reaches +5^oC, cod stocks have actually increased with temperature increase. However, now the bottom temperature in most cod fisheries areas is beginning to be above that temperature, whereby further temperature increase causes reduced recruitment. Also, ocean acidification reduces recruitment. The modelling suggests that because of temperature increase and ocean acidification, cod catches, which could at present be sustainable, lead to rapid loss of cod populations by 2100.

The predictions by Hänsel et al give a very strong reason, why understanding the physiology of fisheries species is imperative for planning sustainable fisheries.

Physiological studies add a predictive component to modelling fish stocks

Perjantai 3.7.2020 klo 18.00 - Mikko Nikinmaa

Mirella Kanerva, Kristiina Vuori and us others have recently published a study about the  fitness of salmon during their feeding migration in different parts of the Baltic Sea (Kanerva et al. Environmentally driven changes in Baltic salmon oxidative status during marine migration, Science of the Total Environment, in press, https://doi.org/10.1016/j.scitotenv.2020.140259). The study is extremely difficult, since it tried to evaluate, how the physiological status of a commercially important fish species in natural environment is affected by food, water temperature and environmental pollution. It is noteworthy that we were able to show that factors affecting the oxidative status of the fish affected the fitness and seawater survival of the salmon. It was also possible to show that increased toxicant load, elevated temperature and cyanobacterial blooms already in the present Baltic Sea induce changes, which are measurable with physiological parameters, and are likely to affect recruitment of salmon.

The point about physiological measurements being able to predict changes in fitness and recruitment is revolutionary for fisheries biology. This is because earlier one has based all the models for stock estimations on retrospective observations on catches and spawning success. The findings of our study indicate  that physiological expertise can add a predictive component to recruitment models.

Our results also indicate, which parts of the Baltic Sea are most contaminated affecting the oxidative status of salmon. It is no surprise that effects are observed in the Gulf of Finland. However, these findings show that similar parameters could be used elsewhere to evaluate, if environmental contamination is serious enough to affect preferred fisheries species. Again, this adds a predictive component to earlier estimations based on retrospective data.

Hitherto, fish physiology has remained a small field, but our results indicate that it could play a major role in modelling fish stocks, because it adds a predictive component to models and thereby gives possibilities for more rapid fisheries decisions than are currently possible.

State of the world - what has happened in 25 years

Lauantai 18.11.2017 klo 12.40 - Mikko Nikinmaa

Twenty five years ago the Union of Concerned Scientists wrote "World Scientists' Warning to Humanity" (with the major authors and 1700 scientists' signatures) where they were concerned about population growth, freshwater availability, climate change, extinctions etc. Now, scientists have looked at what has happened in the past 25 years, and concluded that "World Scientists' Warning to Humanity: Second Notice" was in order. This article was published on November 13 in Bioscience with William J. Ripple as the first author (in addition to the major authors the article had 15,364 scientist signatories from 184 countries). Apart from the ozone hole, which is now starting to shrink, all the environmental problems recognized in 1992 have become worse, and are still continuing to be more detrimental. For example, the amount of carbon dioxide emissions has increased in the last year after it had stabilized or even slightly decreased in the previous two years. In the past 25 years, the availability of fresh water has decreased by 25 %, mean global temperature increased by 0.5 degrees C, carbon dioxide emissions have almost doubled, the dead zones in marine areas increased by almost a third, forests decreased by about 5 % and vertebrate species number decreased by about 30 %. Although human population growth has stopped in the developed countries, the same thing has not happened in Africa and most Asian countries, whereby the total world population has increased by almost 40 % with no sign of increase rate to be slowing down. The number of extinctions in vertebrates is probably much smaller than that of invertebrates - for example insect biomass in certain protected areas in Germany has decreased by 75 %. A significant problem is also that despite increased catching effort, the marine fish catches have decreased by about 20 % from the best years. One final note of the gloomy statistics, we consider almost always only deforestration as causing a decrease in carbon dioxide removal. However, because of the prevalence of sea area, almost half of global photosynthetic activity takes place in marine algae. Marine pollution has decreased algal photosynthesis by approximately 10 % in the past 25 years.                                

Although most of the indices show radical worsening in the state of global environment, the situation with ozone hole indicates that if mankind heeds the warnings, we are able to make the changes required to keep the environment in satisfactory state. The stratospheric ozone layer above Antarctica is now strongest since 1988. If similar united actions were done for the other questions pinpointed by the authors of the Bioscience article, they could also be solved in reasonable fashion. Changes of diet, schooling, improvement of women's situation, discontinuation of fossil fuel use could all be done if we so decided.

Fishing quotas - strict ones are needed to protect fish

Torstai 20.7.2017 klo 13.53 - Mikko Nikinmaa

Fishermen always complain that they are allowed to fish too little and fish biologists have alerted people to the fact that politically decided fishing quotas are too big. If fishing cannot be reduced, several preferred species will become extinct in the next hundred years. The lobbying groups for fishing industry have hitherto been able to convince politicians that putting money in new and effective fishing vessels and having fishing quotas enabling overfishing are good ways of preserving employment - one need not care if preferred fish disappear from nearby areas. With new vessels obtained, e.g. with European Union support, one can have longer fishing journeys than earlier.

It appears that a significant problem with fishing is that the identification of fish by fishermen is poor. If one is approaching the maximum allowed quota for one species, the fish are just marked to be of species, where quotas are not near filling. Giving this type of misinformation varies a lot depending on which country the fisherman is from.

However, even in the interests of fishermen, the fishing quotas should be set on scientific, and not political grounds. Further, the quotas should be followed. And actually, increasing the use of aquacultured fish with land-based feed and effective removal of wastes, is the way forward. All these points are important in order to have fish diversity also for future generations.

Blue Economies - The Seas Affect Our Lives in Many Ways

Keskiviikko 14.6.2017 klo 10.21 - Mikko Nikinmaa

Blue economies are another recent catchword, which indicates economical activity associated mainly with marine environments. From the environmental point of view there are a couple of things that need to be realized.

First, marine pollution is a huge problem. It is probably the biggest single factor behind climate change. Because of the large sea area, algae, largely unicellular microalgae, contribute 40-50 % of the total photosynthesis of the earth. Although in certain areas microalgal growth has increased, it has been estimated that owing to marine pollution the overall amount of carbon dioxide fixed by algae has decreased 10-20 %. This decrease of carbon dioxide sink is greater than that caused by recent rainforest cuts. An important component of marine pollution which has recently got much attention is plastic pollution. A lot has been talked about microplastics, but the weathering of plastics generates even smaller components, nanoplastics, which affect phyto and zooplankton. Their effects can be direct, but additionally they can result in hydrophobic environmental pollutants to become concentrated and available to organisms.

Second, world's seas are overfished. Environmentally, the use of cultured fish would be better than supporting fishing that can cause extinction of the most popular food species within 100 years. However, the problems with aquaculture are the present marked use of antibiotics and pesticides. Both should be diminished. Also, at present the feed is mainly fish flour, which means that overexploitation of natural fish is not reduced by aquaculturing, only changed to species with less human consumption. So, environmentally friendly aquaculture would require development of feeds that are not based on fish flour.

These are two things that need to be considered when developing blue economies.