Tracking the world's fisheries

There's been quite an important development in the analysis of fisheries in the last few days. A collaboration between Oceana, Google and SkyTruth has led to the release of a prototype platform called Global Fishing Watch (more on this here). The software uses satellite data to track global commercial fisheries activity, and once the public version is released it will allow ordinary citizens the opportunity to track and view global fisheries dynamics as well as the ability to update and contribute with their own information.

We've seen in previous posts that at present, fisheries are considerably lacking in assessment and analysis. This lack of information has led to much of the uncertainty. Pereira et al. 2010 highlight that not only is this absence of information detrimental for understanding of present phenomena, it severely limits the quality of modelling that scientists construct in an effort to predict future changes.

While it is too early to say for certain, this new development might be able to remedy some of these problems. Satellite data will be able to provide large-scale views of fish migrations and stocks, and local data contributed by citizens may be able to provide more detailed, specific information. It's also a great idea to involve 'normal people' in this project, as the workload is too vast for a single governing body to do on its own. Furthermore, by getting involved local people could take an interest in issues and perhaps shift to more sustainable practices. They might also have superior knowledge and understanding of the local geography and fisheries dynamics.

I think this project is definitely something to keep an eye on and hopefully it will provide much needed data once the public version has been released.

Aquaculture

When you think about it, the global fish industry is peculiar in one aspect. Whereas the majority of food production has progressed to human controlled cultivation, or farms, over the last several thousand years, it would seem that fish catch is the last remaining example of mass-scale hunter gathering. After all, the mobile nature of fish means that the logical action is to gear up your boat, set sail and hope for a good catch. Increasingly however this seems to be changing.

Recent decades have seen expansion in aquaculture, an attempt to replicate terrestrial agricultural practice in the form of 'fish farms'. Typically, this is achieved through setting up nets in the sea not too far from the coast, populating them with a particular fish species and then providing required conditions and nutrients to raise them in much the way pastoral farmers have farmed livestock for millennia.

The figure below shows that at present, over half of seafood is still wild caught while 45% is sourced from farms. It is predicted that by 2030, aquaculture will dominate production with a 62% share. Many have hailed aquaculture as the solution to many existing problems with global fish harvesting, including overexploitation by humans.

Figure 1 - Global seafood consumption (Source: World Bank).

The extent to which aquaculture can be seen as the long desired fix to fisheries problems is highly contestable. One thing that is quite certain however is that aquacultural practices are likely to be affected by climate change.

A recent IPCC report (2014) pointed out that despite their seeming independence from the larger ocean ecosystem, fish farms will still experience difficulties. The food stocks for many farmed fish species are anchoveta. Declines in this pelagic fish stock will have the result of a reduced food source for aquaculture, leading to declines in output and possible price spikes.

However, unlike many advanced aquaculture technologies found in the global north, many poorer regions of the planet are reliant on ecosystem services to raise their stock. So any changes to the ecosystem at large, which have been mentioned in previous posts, will have an impact on their farms (IFAD).

Additionally, extreme weather events resulting from climate change are likely to inflict damage on coastal aquaculture projects, making it an increasingly infeasible business endeavour fraught with uncertainty and instability.

There have been attempts in recent years to carry out fish farming on land with the aid of vast tanks. However, in many cases this has proved to be too costly and the resulting waste can lead to severe eutrophication in nearby freshwater systems if disposed off improperly.

If you've been following the blog regularly, it might seem like quite a bleak forecast so far. Predictions of so many large scale disruptions in the future can seem a bit overwhelming, but from next week we'll be looking at what measures and actions can be taken to reverse or minimise climate impacts. So cheer up!

Cry me a river - Part Two

Last week we saw how climate can impact the hydrological cycle, and how this can in turn have disruptive implications for freshwater fisheries. Today we will see how climate change can directly affect ecosystems by influencing nutrient dynamics.

Eutrophication is the process by which a lake or fluvial ecosystem is overwhelmed by an unprecedented influx of nutrients. This can lead to the formation of dense algal blooms on the surface of the water which prevent photosynthesis from occurring in the deeper strata of the water column. In turn, there fewer bottom-dwelling plants can grown, leading to a shortage of food supply for smaller fish, and the effect cascades through the food web right the way to the top predator, often leading to disastrous fish kills.

 Additionally, dense algal blooms can deplete the dissolved oxygen in the water. This can lead to an environment that is unsuitable for fish species, both large and small, that previously populated the ecosystem.

The main cause of eutrophication is the massive influx of nutrients due to human activity. The widespread use of fertilisers and the discharge of industrial and domestic waste in watercourses can lead to increased inputs of nitrates and phosphates. However, scientists are beginning to examine how, if at all, climate change will impact eutrophication processes in terrestrial freshwater environments.

Figure 1 - Potomac River, USA, with dense green cyanobacterial bloom typical of eutrophication

A paper by Ficke et al. (2007) suggests a possible mechanism by which increased global temperatures could augment the process of eutrophication. Warmer temperatures have the potential to increase algal growth and bacterial metabolism. Enhanced growth and metabolic rates provide an opportunity for algal and bacterial populations to explode, leading to scenes like the one above.

Heino et al. (2009) draws attention to the fact that temperature increase will intensify precipitation events (discussed in the last post), which leads to a more intense process of nutrient leeching from fertilised soil and a greater input of nitrates and phosphates into lakes and rivers.

If these predictions are true the implications for freshwater fish stocks are quite severe, with a limited source of food for many established fish species and the increased likelihood of fish kills due to oxygen depletion.

However, the mechanisms are not yet fully understood, and there is much discussion as to whether climate change can actually ameliorate the disruptive process. Research by Schindler (1997) found that climate change coincided with declines in phosphorus levels in certain Canadian lakes. Ficke et al. (2007) suggest that the increased stratification of the water column in response to warmer temperatures could lead to a sequestration of nutrients in the hypolimnion, where they are inaccessible to algae and bacteria that may try to grow on the surface of the water.

Now while this might seem inconclusive, present knowledge suggests that we really cannot give any definitive answers as to how climate change will impact eutrophication processes. The articles looked at in this post suggest that increased temperatures work alongside other factors to determine the outcome. So for the best results we'd best examine lakes and rivers on a case by case basis. Hopefully further research will shed more light on the topic, but the present lack of consensus is testament to the complexity of the matter at hand.

Cry me a river - Part One

So far we've focused on the implications of climate change on marine fisheries. In today's post we will look at the problems faced by freshwater environments, mainly rivers and lakes, and their ecological assemblage.

It's important to recognise that the effects of climate change on freshwater environments are not exactly the same as those acting on marine fisheries. As discussed in previous posts, changes in chemical dynamics are responsible for damage to coral reefs and fish stocks. Rivers and lakes on the other hand are susceptible to changes in the hydrological cycle. This is a very broad topic in itself, and there is a great blog you can visit to find out more if you're interested.

First of all, increased inland temperatures can have a direct effect on lakes and rivers. Obviously, it can intensify aridity and therefore lead to a higher dry season mortality of fish and other important species in ecosystem. Additionally, many species have a particular acceptable range of temperature (known as their temperature niche) and any change in temperature can drive fish species out of their habitats. Worse still, it can lead to the succession of more competitive invasive species, parasites and pathogens which threaten 'native' species.

Furthermore, increased temperatures can lead to changes in the mixing of lake water. Mixing regimes are highly important due to the internal circulation of nutrients. Lake Tanganyika, occupying territory in the Democratic Republic of Congo, Tanzania, Burundi and Zambia, has experienced a slowdown in the mixing of water strata. This has meant that nutrients are no longer resuspended as much, leading to a decline in plankton species assemblages and a 30% decrease in the yield of planktivorous fish.

Figure 1 - Lake Tanganyika

The complexity of the hydrological cycle means that it is quite difficult to predict with certainty how it will respond in the face of future temperature increases. A policy briefing by the WorldFish Center suggests that continued climate change is likely to lead to increased seasonal and annual variability in precipitation patterns. In turn, this is likely to unpredictable flood and drought extremes that can potentially have severe impacts on inland fisheries. These changes mean that Bangladesh, a country that relies on fisheries for 80% of its protein intake, is likely to see an increase of 23-39% of areas prone to flooding. Flooding is a particular issue as the high wet season discharge and low dry season flows can lead to a disruption of the spawning season of various species.

An extensive analysis of historical data of salmon ecology in the Thames, the Severn, the Wye, the Lune and the Dee suggests that the increase in frequency of summer droughts and winter floods due to climate change are likely to lead to lower survival rates and a diminished abundance of the species.

The importance of the climate on hydrological processes is therefore quite obvious.

Plenty more fish in the sea? - Part Two

Figure 1 - The Carbon Cycle (source: WBGU 2006)

As mentioned last week, ocean acidification is another problem faced by many of the world's fisheries. Central to understanding this phenomenon is the carbon cycle, represented here in the image. The numbers in bold represent carbon reservoirs in gigatonnes (Gt), while the other numbers represent carbon fluxes in gigatonnes per year. We can see that together, the intermediate/deep ocean and the surface layer lock up about 38,000 Gt and that the largest annual influx to the oceanic store comes from the atmosphere. The flux dynamic between the surface and ocean is driven by different partial pressures of CO2 between the atmosphere and seawater, leading to an annual uptake of 2 Gt of carbon by the ocean each year - a figure that amounts to about 30% of annual anthropogenic emissions.

When it has been exchanged and passed into the ocean, CO2 is able to react with other chemicals. The ocean establishes a reversible equilibrium reaction involving CO2:

Figure 2 - Carbon in the ocean

 Carbon dioxide reacts with carbonate ions and water in the ocean to form acidic bicarbonate ions. With a continuous influx of CO2 into the equation due to anthropogenic carbon emissions, the partial pressure of CO2 increases and the equation equilibrium shifts towards bicarbonate, producing more of the acidic ions

Now while slight changes in ocean pH would not have direct impacts on fish, it is important to consider the implications elsewhere in the ecosystem. Increased acidity is predicted to disrupt planktonic crustacean communities, which would have a knock-on effect on the juvenile fish and fish larvae that rely on them for food. Likewise, bivalve molluscs and echinoderms are forecast to decline in the face of changing acidity. They provide a source of food for a variety of adult fish species. With both juvenile and adult populations at risk, it's clear that ocean acidification puts significant pressure on fish populations. It is believed that to date acidity has gone from 8.2 to 8.1 - an increase of 30%.

Additionally, ocean acidification leads to problems with coral reefs too. The process of calcification, which is instrumental in the construction of coral skeletons, is impaired by the increased CO2 concentrations. This happens because higher CO2 concentrations shift the equilibrium in the above equation towards the right, in favour of bicarbonate and at the expense of carbonate. Consequently, coral reefs are less able to expand, and we know from the last post how important reefs are in marine ecology.

So far, we've looked primarily at the implications of climate change for marine fisheries. Next time we'll consider the impacts on fluvial fish stocks - that's salmon to look forward to.