PROGRAM ASPECTS

Chapter 7. Computer simulation program FOOD CHAIN (VIJVER) and PERCH (BAARS)

The figures - as referenced in the text - are not ready yet. See the textbook itself. (R. Min, Academic Book Center, De Lier, 1995)

This chapter discusses:

two case studies about fish, fishery and the fish regulation in an ecosystem.
Which parameters can be used for a learning and training environment?
Which variables are important for insight or training in this field of biology?
What are the most important educational aspects of the both simulation programs?

Introduction

Fish ponds are widely used by man for food production. The management of a fish pond, affects the entire ecosystem, including fish, nutrients, zooplankton, benthos, dissolved oxygen, microorganisms etc. A high efficiency of fish breeding can be achieved only with optimum values of the control parameters of the pond, like the input of fertilizers, the re-aeration of the water in case of oxygen depletion and the addition of artificial fodder. Svirezhev et al. (1984) developed optimum control strategies for a fish pond ecosystem. As part of their study they constructed a mathematical model of a fish pond. Van Schaick Zillesen designed and realised the computer simulation program FOOD CHAIN (VIJVER). Van Densen and Pet (1988) developed for fishery in Lake IJssel (IJsselmeer, The Netherlands) a simulation model for the amount of perches with certain lengths. Mous (1989) designed and realised the computer simulation program PERCH (BAARS) with that mathematical model. (Mous; 1989)

7.1. Computer simulation program FOOD CHAIN (VIJVER)

Due to the relatively simple tropic structure a fish pond can be an excellent case for the study of the characteristics of food-chains and ecosystems in general. However, fish ponds can not be studied in the biology curriculum for practical reasons (space and time). A computer simulation program, simulating a fish pond can be an excellent tool to overcome these problems.

For this reason a mathematical model of a fish pond can serve two purposes: fish pond management and education. The model constructed by Svirezhev et al (1984) simulates a fish breeding pond in which three fish species are present: carp, silver carp and bighead carp (see figure 7.1). Van Schaick Zillesen adapted the model for a pond in which only two fish species are present (carp and silver carp).

The program FOOD CHAIN is based on the adapted version of the model of Svirezhev et al. Svirezhev et al. (1984) give values the parameters used in their model. However, they do not give starting values for the variables of the model. Labordus (National Institute for Curriculum Development) gathered the data about the values of these variables from literature.

Educational value

The prototype FOOD CHAIN is designed for students in secondary education and lower vocational training. Before the start of the simulation, students should have advance knowledge of ecological processes in the fish pond. This advance knowledge is reinforced during the use of the simulation program.

Figure 7.1 The model of the computer simulation program VIJVER. (Svirezhev, et.al., 1984)

Before the start of the simulation the students should be aware of the following ecological processes:

Plants require minerals, water, carbon dioxide and oxygen.
Green plants (producers) synthesize organic material during photosynthesis. Light is required in order to do this. Oxygen is produced during photosynthesis.
For their food animals (consumers) depend on plants (directly or indirectly).
Within an ecosystem, several (long and short) food-chains and food-webs may exist.
Plants, animals and man produce organic material.
The organic material is mineralized by bacteria and fungi (reducers).

Apart from the reinforcement of this knowledge, the program is also used to teach new phenomena like:

The growth of plants is determined not only by the presence of water, carbon dioxide, light and minerals, but also by the ratio in which these prerequisites are available.
A wealthy growth of plants leads to an increase in the quantity of animals.
When two animal species use the same food an equilibrium between the two species and their food will develop.
In a complex system such as a pond an equilibrium gradually develops between all species present and the abiotic conditions. If these are changed a different equilibrium will evolve.
Computer simulation programs can be applied for prediction, research, learning, gaming and management.
The skill to work with abstract representations of systems and processes, like dynamic graphs and diagrams is trained by working with the program.
The skill to test hypotheses by means of active experimentation is trained by working with the program.

The prototype can simulate five ponds. In each pond oxygen, nitrate, phosphate and detritus (a complex of organic material and fungi and bacteria) are present. The following ponds can be simulated:

Pond 1 (Algae). In this pond phytoplankton (algae) is present.
Pond 2 (Silvercarp). In this pond phytoplantkon is present as well as silver carp.
Pond 3 (Zooplankton and Benthos). In this pond the following organisms are present: phytoplankton, zooplankton and benthos.
Pond 4 (Carp). In this pond the following organisms are present: phytoplankton, zooplankton, benthos and carp. See figure 7.2

Figure 7.2 Input window of the computer simulation program VIJVER with the conceptual model of a fishing-pound according to Svirezhev et.al.

Pond 5 (Fish Pond). In this pond the following organisms are present: phytoplanton, zooplankton, benthos, carp and silver carp. A student studying this pond is able to feed the fish with artificial fodder. Furthermore, he or she can re-aerate the water in the pond.

The program has been used in many levels of education varying from lower vocational training to a university course.
In lower vocational training only the most simple ponds (pond 1 and pond 2) are studied. The other ponds are too complicated to be understood by the students.
In secondary education all ponds can be studied. However, ponds 2, 3 and 4 are rather similar to each other. Because of this one or two of these ponds are usually skipped.

Hartsuijker et al. (1989) developed paper materials, which can be used in combination with the simulation program. Their publication consists of the following parts:

students' leaflets with information about the subject matter, information about the control of the program and exercises.
a teacher's guide with information about the educational goals of the program, the required advance knowledge of the students, answers to the exercises on the students' leaflets, characteristics of all ponds and an installation manual.

A complete computer simulation supported learning environment can be constructed by combining the educational computer simulation program with the paper materials.

Description

The program FOOD CHAIN, version MacTHESIS, is designed by Van Schaick Zillesen, (1988) according to the description of the students' learning environment of MacTHESIS.
In this application four windows are present:

In the first window the internal structure of the simulated pond is visualized by means of a diagram. The values of the main variables are indicated in the diagram by means of digits. Day and night conditions are indicated by means of animation techniques. Students can change the values of parameters and variables in the model by clicking in the grey rectangles in the diagram. In each pond different interventions are possible:

pond 1: quantity of algae, fertilization by means of phosphate, fertilization by means of nitrate.
pond 2: quantity of algae, fertilization by means of phosphate, fertilization by means of nitrate, quantity of silver carp.
pond 3: quantity of algae, fertilization by means of phosphate, fertilization by means of nitrate, quantity of zooplankton, quantity of benthos.
pond 4: quantity of algae, fertilization by means of phosphate, fertilization by means of nitrate, quantity of zooplankton, quantity of benthos, quantity of carp.
pond 5: quantity of algae, fertilization by means of phosphate, fertilization by means of nitrate, quantity of zooplankton, quantity of benthos, quantity of carp, quantity of silver carp, quantity of fodder, quantity of re-aeration.

The second window contains time registrations of the quantities of phytoplankton, oxygen, nitrate and phosphate in the pond.
The third window contains time registrations of the quantities of carp, silver carp, zooplankton and benthos in the pond.
The fourth window contains a time registration of the quantity of detritus in the pond.

Students may intervene with the model by means of the input-animation technique as described earlier. Furthermore, the same interventions are possible by means of the menu bar.

At the start of the program pond 1 is presented to the student. The other ponds can be selected by means of the menu bar. There is a MS.DOS version of the program FOOD CHAIN available. Since 2001 there is a internet version of the program FOOD CHAIN available. (see figure 7.3, 7.4 and the interactive applet).

Figure 7.3 The output of the computer simulation program VIJVER / FOOD CHAIN (on the internet) (during 6 x 30 days) (intervention with phosphate and nitrate that starts on june 1) (the red curve is increasing: the amount of phytoplankton, 'algen' or 'F') (the yellow curve is first increasing and than decreasing: the amount of oxigen or 'O') (Min c.s., 2004).

7.1. Computer simulation program for fishery in Lake IJssel (PERCH / BAARS)

Van Densen and Pet developed a simulation model for fishery in Lake IJssel (IJsselmeer, The Netherlands, described by Pet, 1988). This extensive model can be used for both pikeperch (Stizedion lucioperca) and perch (Perca fluviatilis). It includes the influence of two types of fishery on the stock: gill net fishery and fyke net fishery. The model is designed in order to serve two purposes: research and education.
The model differs from most other fishery models in the way that the size and age groups in the stock are treated. Whereas most other models make calculations with mean lengths per year-class, the model of Van Densen and Pet treats each size and age group separately. This is an important feature when the model is used for fishery management because more detailed predictions can be given about the influence of fishery measures on the distribution of the catch. This is also an important feature when the model is used for teaching biology students during university courses of fishery management and population dynamics. Whereas other fishery models treat concepts like catch and stock more or less as black boxes this model will provide students with a complete and dynamic view on the population structure of the stock and on the composition of the catch. It will be easier for the students to discover the relevant causal relationships between the components of this system because of this complete information.

Van Densen and Pet included some phenomena in their model in order to accommodate it to the specific conditions of Lake IJssel. Beside gill net fishery another, usually less important, type of fishery was simultaneously described by the model: fyke net fishery. Furthermore, the model provided for inter-year temperature fluctuations and for fluctuations in the characteristics of fishery.
However, these specific and to some extent obsolete characteristics might confuse the students and distract them from the more general educational objectives of the simulation program (like the effect of the prototype FOOD CHAIN on university students). For this reason a more generalized model might be more useful for educational purposes. The original model of Van Densen and Pet was generalized for this purpose by Mous (1989). PERCH is based on this generalized model. PERCH simulates gill net fishery on perch only. Fyke net fishery and fishery on pikeperch are not included. Inter-year fluctuations in fishing efficiency, temperature and recruitment are not included in PERCH. Furthermore natural mortality has been made length-independent and intra-year fluctuations in fishing effort before and after the close season have been omitted.

Educational value

With the simulation program PERCH students can study the effects of several management measures (increasing or decreasing the fishing effort, changing efficiency and mesh size of the nets, adjusting the close season) on the distribution of the catch and on the structure of the population of a single fish species under conditions of gill net fishery. It is hard to understand the mutual dependency on the effects of these measures when the concepts are taught in a purely theoretical way. PERCH allows the students to build a conceptual model of the relations in the Lake IJssel system and to adjust this model to concrete experience gained by active experimentation. By means of induction students will generalize from the specific case of Lake IJssel to more general concepts of fishery management. The conceptualization's of these general concepts may help students specializing in fishery management to solve other fishery problems which they may meet in their future careers. Apart from courses of fishery management PERCH can also be used in more general university biology courses like courses of population dynamics or courses of nature management. In these courses PERCH may be used as an example for the way modelling techniques are applied in fishery management and in nature management in general.

Results

During simulation time the student can study 30 screens with graphic output showing the characteristics of the Lake IJssel system. The output consists of two display forms: dynamic graphs and dynamic, model-driven histograms. In the dynamic graphs time registrations of the following variables are presented:

mean length and deviation of mean length in the standing stock
sex ratio
biomass of standing stock
biomass of spawning stock
number of fish in the standing stock
mean length and deviation of mean length in the catch
daily catch
cumulative catch

In the model-driven histograms the distributions of the following variables are presented:

length-frequency in the standing stock
length-frequency in the daily catch
length-frequency in the cumulative catch

In many cases it is relevant to the students to attain information about the development of a specific age class or about a specific sex of the fish population. Furthermore, in some cases it is relevant to compare the exploited situation with the unexploited situation. In these cases a more detailed output is provided (e.g. separate time registrations for age class or for each sex).

The results of the simulation are stored in a file. This file has a heading in which the initial values are given of the parameters used in the simulation. During simulation, tables are written to this file containing the values of the variables shown in the displays described above. Tables are generated automatically at the start of the close season, on day 273 and on day 365. Furthermore the student may order the generation of a table on-line during runtime using the option 'write' at simulation level. Beside starting initial values of parameters and tables the following information is recorded in the file in order to facilitate the reconstruction of the course of the simulation later on:

the parameters which are changed by the student during simulation
the moments at which the student restarts the model

During simulation the student can change the following parameters by means of a pull down menu:

Index effort (relative number of gill nets)
Percentage of monofilament nets
Mesh size
Start of the close season
Length of the close season

Note: This chapter is first published by P.G. van Schaick Zillesen in his Ph.D thesis at the University of Twente, Enschede. Edited by F.B.M. Min.

References

Svirezhev, Y.M., V.P. Krysanova & A.A. Voinow (1984). Mathematical modelling of a fish pond ecosystem. Ecol. Modelling, vol. 21, pp. 315-337 (Elsevier Science Publ. 0304-3800.84).

Densen, van, and Pet (1988) Fishery in Lake IJssel (IJsselmeer, The Netherlands) a simulation model for the amount of perches.

Mous, P.J. (1989). PERCH, a user-friendly length- and age-structured gillnet fisheries program ten behoeve van/voor o.a. de Nederlandse visserij. Stageverslag / interne publicatie simulatie project; University of Twente, Department of Education, Division of Instrumentation Technology, Enschede & Agricultural Univeristy of Wageningen, department of Fish Culture and Fishery, Wageningen.Stage bij het SLO-TO project vakgroep ISM, TO, (Begeleiding: Van Schaick Zillisen, supervisie: F.B.M. Min). Stageverslag.

Schaick Zillesen, P.G. van, and F.B.M. Min, (1988). Een R. & D. project in de onderwijskunde; een computersimulatiesysteem voor VWO en MBO. In: Onderwijskundige technologie: modellen & emperie (Red. P.H. Been & K.B. Koster) Swets & Zeitlinger, Lisse.