Productivity, diversity and exploitation

9 important questions on Productivity, diversity and exploitation

What are the steps addressing impact of fishing on ecology and stock regeneration?

1. System variability of resource system
2. Susceptibility of resource units
3. Selectivity and scale of operation of fishing patterns by resource users

What is the catch-effort curve?

- F = f*q
- At any level of fishing effort a yield can be found that is theoretically sustainable and stable with a level where the 'surplus' yield is maximized (MSY)

What are the assumptions of Schaefer model?

- Logistic growth curve with density dependence, so constant carrying capacity (K)
- Single species model with man as predator
- Equilibrium between catch and surplus -> Steady state
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In logistic growth, size N depends on

- Carrying capacity (K) = maximum size of population given environment
- Intristic grwoth rate (r0) = specific life history character of species = maximum relative growth rate a species can attain at a very low population size

Resource system variation

Large changes in productivity of fis resources is often caused by environmentally driven processes where large changes in nutrient input occur
- long term, inter-annual or seasonal fluctuations (intra-annual variability)

Framework of Regier for classifying dynamics of fish stocks:

- 2 variables: size and temporal/spatial varaibility
- 4 classes
  • Fish stocks in stable environment
  • One or few fluctuating resources
  • Relatively small but numerous resources in stable environments in lakes, reservoirs
  • System of small interacting resources that fluctuate erratically in small lakes, pond
- Easiest assessment for 1, hardest for 4
 

What is the fishing down process?

With increased fishing pressure, fisheries target smaller sizes and lower trophic levels -> length in caught, trophic level and community decreases

What are the three different classes with different vulnerability?

1. Very susceptible: Old and large sized segments and spawning concentrations
2. Intermediate susceptible: wide distribution, more resilient, intermediate size, ecologically flexible, unspecialised in food and behaviour pattern and can withstand high natural mortalities. High reproduction rate.
3. Highly resilient species: small pelagic species, high P/B ratio and high natural mortality

What are general the two types of fisheries?

- With only 1 type of gear -> More selective, large scale fisheries
- With multiple types of gears -> Less selective, small-scale fisheries

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