•Intensive aquaculture can
produce yields that are
orders of magnitude
beyond natural
ecosystems
How to maximize energy flow to fish
Increased nutrient loading—fertilization + ammonia and anoxia tolerant species
Shortening the food chain—primary consumers (eg carps, tilapia or mullets)
Don’t rely on natural recruitment and managing the life cycle—stocking/hatcheries
Increasing consumption efficiency—small pens intensive feeding
Increased assimilation efficiency—feeding with easy to digest food pellets
Increased production efficiency—low activity species that don’t mind crowding,
, highly turbid water
Lepeophtheirus salmonis
Many aquaculture proponents
argue that aquaculture reduces
harvesting pressure on wild
fisheries.
Salmonid aquaculture not very trophically efficient,
food pellets made from by-catch of wild species
Major water quality issues—nutrientpollution from
cages, anti-fouling paint, antibiotics, habitat
destruction
Transmit diseases to wild salmonids—bacteria,
viruses, protozoans, fungi, “fish lice” –parasitic
copepods and other Crustacea
Genetic problems when domestic escapees
compete with or interbreed with wild fish
Argulus
Pn
n 
Pn  1
In
An
Pn
Pn
EEn 
, AEn 
, PEn 
, GPEn 
Pn  1
In
An
In
Show
n  EEn  AEn  PEn
n  EEn  GPEn
If the productivity of a phytoplankton population is 4000 k J (kilo Joules) /yr /
m2, If sedimentation rate of dead cells to the substrate constitutes 1600
kJ/m2yr, and the phytoplankton population is dB/dt=0. If the rain of
zooplankton fecal pellets to the bottom is 1400 kJ/m2/yr. What is the
assimilation efficiency of the zooplankton trophic level (assume that they are
all feeding on phytoplankton).
1.
2.
3.
4.
5.
0.42 or 42%
0.60 or 60%
0.35 or 35%
0.25 or 25%
None of these
What is the exploitation efficiency EE (or Consumption efficiency CE) of the
zooplankton trophic level
1.
2.
3.
4.
5.
0.42 or 42%
0.60 or 60%
0.35 or 35%
0.25 or 25%
None of these
If the net production efficiency of the zooplankton trophic level is
0.40 (40%) what is the ecological efficiency () of the trophic level
1. 0.15 or 15%
2. 0.05 or 5%
3. 0.10 or 10%
4. 0.25 or 25%
5. None of these
If the zooplanktivorous fish are consuming zooplankton at the rate
of 400 kJ/yr/m2, their EE (CE) is
1. 0.40 or 40%
2. 0.60 or 60%
3. 1.00 or 100%
4. 0.25 or 25%
5. None of these
If the zooplanktivorous fish have an assimilation efficiency of 0.70
(70%) and Net production efficiency (NPE) of 0.20 (20%), the
productivity at this trophic level is
1. 40 kJ/yr/m2
2. 56 kJ/yr/m2
3. 100 kJ/yr/m2
4. 280 kJ/yr/m2
5. None of these
If in another lake with similar zooplankton productivity the
planktivore fish productivity was 2 X higher, a possible explanation
for this would be
1. the AE of the fish in that lake was 2X as high
2. the NPE of the fish in that lake was 2X as high
3. the EE (CE) in that lake was 2X as high
4. the AE*NPE in that lake was 2X as high
5. both b and d are true
6. both b and c are true
Residence time and turnover of energy by trophic levels
The standing stock of energy in the
plankton is low but it is turned over
rapidly, because the organisms are
small, grow rapidly and don’t live
long
Planktonic
Herbivore
(50mg) life span
1 month
A
H1
P
Phytoplankton (0.01mg,
life span, few days
H2
Benthic Detritivore
(0.1 g) life span 1yr
Carnivorous fish
(100g) life span
5-10 yr
Turnover is slower at higher trophic levels, since larger organisms accumulate
energy over a longer life span—longer residence time and slower turnover
Summarizing concepts on Secondary production
•The organic matter produced by primary producers (NPP) is used by
a web of consumers
•NPP is used directly by primary consumers (herbivores and detritivores), which are in
turn consumed by carnivores.
•Measurement of 2o Production is done by estimating the rate of growth of individuals
and multiplying by the number of individuals per unit area in the cohort (age or size group).
•The efficiency of secondary production ranges from 5-20% (Avg 10%)
at each trophic level.
•Efficiency depends on several factors--palatability, digestibility, energy requirements
for feeding (activity costs)(eg homeotherms vs poikilotherms , other limiting factors
eg water, and nutrient quality of food.
•Trophic efficiency can be represented as the product of CE*AE*PE, each of which
is dependent on one or more of the above factors.
•The yields of many important fisheries depends on a combination of NPP, the
length ofthe food chain leading to the fish being harvested, and the efficiency
of each step.
•Many of the species that we harvest or very high in the food chain, so a great deal
of NPP is required to support them.