In this presentation I pitch the general concepts of my PhD project: 2. Fish stocks are recovering due to policy 3. Average size at age is decreasing in recovering stocks 4. Decrease in size is likely due to density dependence 5. How should we deal with these density dependent effects? 6. I will use PSPM to study this. 7. I will use DEB theory for constructing PSPM.

1. Density dependence in
recovering fish stocks
Jasper Croll
24-09-2018

2. North Sea area fish stocks are recovering
Plaice Sole
MackerelHerring
Images from ICES advises

3. Individual size is decreasing
Images from ICES expert group report
Plaice Sole

4. Density dependent growth
Low density
& large fish
Enough food
for growth
High density
& small fish
Competition
limits food for
growth
High fishing intensity Low fishing intensity

5. How should we deal with density dependent effects in recovering
fish populations?
• Which effects do fishing policies have?
• How can we optimize yield?
• Are current assessment methods still suitable?

6. Physiologically structured population models
Size-dependent processes
• Fishing mortality
• Food intake
• Growth
• Development
• Reproduction
• Mortality
• Maintenance
Individual processes Population dynamics
De Roos & Persson, 2001, Oikos.

7. Dynamic Energy Budget Models as basis
Individual processes Population dynamics
Kooijman 2010.
DEB model
Feeding Feces
Assimilation
Growth
Reserve
Somatic
maintenance
reproduction
Maturity
maintenance
reproduction
Feeding Feces
Assimilation
Growth
Reserve
Maintenance
Feeding Feces
Assimilation
Growth
Reserve
reproduction
Maintenance
Lika & Nisbet 2000. Martin et al. 2017.

8. Density dependence in
recovering fish stocks
Jasper Croll
24-09-2018