Reference no: EM132392492
Assignment : Static size spectrum model practical
In this practical, we will implement a simplified version of the size spectrum model of Jennings et al. (2008). This is a simple static model, so does not involve differential equations. We do not explicitly have different groups in the model.
We have several questions we want to answer:
1. What is the biomass of fish in the world?
2. How might this change with climate change?
3. Can we understand the changes and what will it mean for human livelihoods?
How much fish is in the world is clearly related to how much food they have to eat. It is also related to temperature because at warmer temperatures phytoplankton, the primary producers, grow quicker and thus can support more fish. So, I have given you data on primary production (how fast the phytoplankton are growing) and temperature. There are no fish data needed as inputs, as our aim is to calculate how much fish there are.
To investigate how the biomass of fish might change in the future, I have provided data on how the ocean temperature and primary production is predicted to change. These data are global at 1º, and monthly from January 2006 to December 2100. These data are from one
GCM (General Circulation Model) and one (high) RCP(Representative Concentration Pathway, which are scenarios for the future).
We will be deriving the abundance spectrum (not normalised by bin width), which is:
log10(Abundance) vs log10(Mass). And it can be written as:
N(W) = aWb
And the biomass spectrum is then:
∫N(W)dW = (a/(b+1))Wb+1
Questions
1. Plot sea surface temperature and primary production globally for December 2006 and December 2100. What do you notice in each?
2. How does our estimate of total fish biomass in the world now compare with that of Jennings et al. (2008) who found 7.91 * 108 tonnes of fish? Take "now" as being in 2020. Why might ours be different?
3. Run a sensitivity analysis of the model (vary one parameter while keeping others constant). Plot a graph of Total Global Fish biomass vs Parameter values (different levels). Show the graph and explain what is happening:
a. Alpha = trophic transfer efficiency (default=0.125: Vary it between 0.05 and 0.2 in steps of 0.125)
b. Beta = Predator Prey Mass Ratio (PPMR, default=1000). Vary PPMR as 10, 100, 1000, 10000
c. E = Activation energy of metabolism (default=0.63). Vary as 0.6, 0.63, 0.66, 0.69
4. What is likely to happen to fish biomass in the future? Plot a global time series and a map and interpret your results
5. Consider that countries have control of their fisheries in their Exclusive Economic Zones (out to 200 nautical miles). Which countries/regions fishing could be most affected by climate change? What will this mean for livelihoods?
6. What is the global rate of decline in fish - per ºC of warming?
7. Outline what the model is doing, in your own words.