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

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—nutrient pollution 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 Lepeophtheirus salmonis

Total Phosphorus µg ● L -1 Fish community biomass kg ● ha -1 Log B = (± 0.09) Log TP (± 0.05) L/R, RMS=0.27, R 2 =0.71 Rivers Lakes Rivers support more fish biomass than lakes for the same TP Level? Why?

Zooplankton abundance in reservoirs depends on the physical regime.

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 2 o 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.

Lakes have zonation structured by physical forces such as light, wind and waves. different zones in the lake had different types of plants and animals

The River Continuum Concept Zones in a river system are less distinct But they are functionally very important Physical forces change gradually along a river Elevation ↓ Slope ↓ Temperature and nutrients ↑ Drainage area and discharge ↑ Width of channel and floodplain ↑ Mean velocity ↑ Mean depth ↑ Turbidity ↑ Sediments, erosional, alluvial, to depositional Shading ↓ Periphyton, macrophytes ↑, then ↓ Phytoplankton and zooplankton ↑ Coarse detritus input highest upstream Fine detritus accumulates downstream Benthic invertebrate community changes shredders, grazers, collectors Fish community changes Cold water to warm water species

Allochthonous input—Detritus processing Dead plant biomass breaks down slowly and their nutrients can remain tied up in as organic detritus for long periods of time Primary production in many ecosystems depends more on its recycling rate ie mainly decomposition of plant detritus, than on loading rates Aquatic plants break down more rapidly than terrestrial plants, and woody plants are very slow to decompose because they contain lignin, which most bacteria and fungi can’t digest.

Leaf processing Wetting and breadown of cuticle Leaching of soluble components (DOM) Colonization by bacteria and fungi Increase in protein content Colonization by invertebrates Enhances microbial action Breakdown into small fragments

Invertebrate detritiivores find leaves much more to their liking after they have been colonized by bacteria and fungi

Shredders enhance microbial action (bacteria & fungi) convert CPOM to FPOM Food for microdetritivores Detritus processing in a stream

Processing of FPOM by microdetritivores Shredders-macrodetritivores collectors-microdetritivores Filter-feeders, deposit-feeders

Litter bag experiments have been used to study decomposition of detritus Weight remaining % 0.5 mm mesh 100 % mm mesh Larger invertebrates get into the litter bags if the mesh is coarse Nutrient content of the detritus, especially N greatly increases decomposition rate, as does increased temperature and mesh size days

The interplay between the autochothonous and the allochtonous food chain Allochthonous input Autochthonous input

Stream Fragmentation, A wier blocking fish movement a hanging culvert can block fish movement The River Discontinuum: Dams and wiers

Dams/Reservoirs interrupt the river continuum create entirely new habitats

Fisheries Management using a population model

Time Exponential

b<m b=mb>m

B m0m0 b0b0 K Per capita birth,death b=b 0 -b 1 B m=m 0 +m 1 B Slope=b 1 Slope=m 1 Biomass K is called the carrying capacity Density dependent birth and death

Is called the logistic equation BK per capita rate of increase slows down linearly as the biomass increases and reaches 0 when the carrying capacity (K) is reached. per capita rate of increase reaches an upper limit of r 0 as B approaches 0 It becomes negative when B>K

B KK/2

B K

B K C What would happen to a population at K/2 subjected to a harvest rate of is called the Maximum Sustainable Yield (MSY)

B KK/2 C The logistic model *

CPUE Kg/hr Year A lake that hasn’t been fished for 20 yr is opened for fishing and annual creel surveys show that CPUE is declining rapidly Catch Kg/yr The estimated total catch varies from year to year but the trend rapidly becomes apparent and the lake is closed After a 9-yr moratorium the population has gradually bounced back, and the fishery is opened again with more restrictive limits After signs of tapering off limits are tightened even further. An operational example

CPUE Kg/hr Year How can such a population be managed with the logistic model? We don’t know B, K or r 0 We can assume that CPUE is a linear function of Biomass (eg B=q*CPUE Where q is called the “catchability” factor We can also assume that the population is at K to start with Catch Kg/yr

The catch (C) in the first year was 1020 kg, at the rate of 1.0 kg/fisherman hr. The following year the CPUE went down to 0.9 kg/fisherman hr. Assuming that the population was at its K, and that the CPUE reflects the biomass linearly, B=q *CPUE, then dB/dt at K will be 0, and the entire catch will be subtracted from the biomass present. That is we assume that there will be no significant recruitment or growth response to compensate for thinning within the first season The response to the first year’s thinning will be reflected in the next year’s catch data assume the change in CPUE reflects the change in B,  CPUE)/CPUE = (  B)/B, 0.1/1=1000/K. Therefore K =10,000 kg And CPUE =q B, that is 1.0 kg/hr =q * 10,000 kg, so q =1kg/hr/10000 kg = kg/hr/kg The next year the catch rises to 1050 kg, and the CPUE falls to 0.83 kg/hr. This catch appears to be unsustainable at this B level, but how much would have been sustainable?

The next year the catch rises to 1050 kg, and the CPUE falls to 0.83 kg/hr. This catch appears to be unsustainable at this B level, but how much would have been sustainable? Using the catchability estimate q we can translate the drop in CPUE and estimate that the biomass dropped from 9000 to 8300 kg (a drop of 700), and reason that if a catch of 1050 caused a drop of 700, then a catch of 350 would have been sustainable at that level of biomass. We can then repeat this for every year, including the years where the fishery is closed CPUE can still be estimated from catch and release fishing if the fishery is closed. In this way each year’s catch combined with the change that takes place in CPUE the following year can allow you to estimate the sustainable catch for that year

Actual catches in kg/yr Estimates of sustainable catch By comparing the catch for each year to the change in biomass (estimated from change in CPUE) we can estimate the catch that would have been sustainable each year For the first 10 yr catches were unsustainably high and the population crashed, After the new limits were put in they tended to oscillate around the estimated catch. CPUE Kg/hr Catch Kg/yr

K/2 = 5000 (r 0 K)/4=990 MSY Biomass dB/dt If (r 0 K)/4 = 990 kg/yr and K=10000 kg, then r 0 =0.39 kg*kg -1 yr -1 Fit to the logistic curve from the lake time series

Suppose we have a lake with a population of 10,000 kg of pike where fishing has not been allowed for at least 20 years. Fishing is then opened up for several years and the population is knocked back to 5,000 kg. Assume that growth follows the logistic curve. (a) What would the biomass be after 10 yr if r 0 were 0.2 kg/kg/yr (b) If after closure it recovers to 9,800 kg in 10 years. Find r 0 ?

(c) What should be the maximum sustainable yield of this fishery? (d) If the population were reduced to 2,000 kg, would a quota of 500 kg/yr be sustainable?, 1000kg?

Suppose we have a lake with a population of 10,000 kg of pike where fishing has not been allowed for at least 20 years. Fishing is then opened up for several years and the population is knocked back to 5,000 kg. Assume that growth follows the logistic curve. Over what range of biomass would a yield of 600 kg/yr be sustainable without causing a reduction in biomass?

B KK/2 Catch rate Constant Quota fishing at levels approaching the MSY shortens the biomass range the population will recover, and the likelihood of entering the danger zone increases. Once the danger zone is entered fishing must stop or be severely curtailed Maximum Sustainable Yield (MSY) Danger zone Stable biomass range

The red zone is much bigger if the curve is strongly skewed right

Solutions that are being considered by fish managers

B KK/2 C What if we consider a fishery based on constant effort rather than constant quota Catch = qB Slope=q The catch isn’t as great but the likelihood of entering the red zone is lower Stable range

Foodweb relationships between fish predators and prey Bottom up Richer systems have higher productivity at all trophic levels Enrichment usually increases the biomass of the top trophic level in the web. Top down Predators usually reduce the biomass of their prey And cause changes in the structure of prey communities Lake Michigan example

Reductions in fish biomass usually accompany reductions in nutrient loading Bottom-up Fish biomass dependent on nutrient loading

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 Increasing consumption efficiency—small pens intensive feeding Increased assimilation efficiency—feeding with easy to digest food pellets Increased production efficiency—low activity species, highly turbid water

Original Lake Michigan Food web Phtoplankton Benthic algae Aquatic macrophytes &detritus Benthos& zooplankton Lake trout Trophic position Offshore food chainInshore food chain sedimentation “Once upon a time”

Changes in the Lake Michigan Food web during the 60’s Top-down cascade Phtoplankton Benthic algae Aquatic macrophytes &detritus Benthos& zooplankton Lake trout Trophic position Offshore food chainInshore food chain sedimentation Lamprey wipes out lake trout Alewife invades and outcompetes other zooplanktivores; becomes very abundant Large zooplankton decimated Algal blooms Transparency drops Mysis very abundant Reduction of littoral zone

Test of the top-down cascade theory: introduce pacific salmon Phtoplankton Benthic algae Aquatic macrophytes &detritus Benthos& zooplankton Offshore food chainInshore food chain sedimentation Alewife declines Large zooplankton recover Algal blooms stop Transparency increases Littoral zone expands

A F1F1 H1H1 H3H3 A2A2 H2H2 F2F2 P1P1 P2P2 Zebra mussel invading a compartmentalized food web As water clears light reaches the bottom and plants & benthic algae grow Prior to the zebra mussel invasion, the rich nutrient regime allowed the phytoplankton to shade out the littoral zone vegetation

Light is a key physical factor— determines the boundaries within which photosynthesis (primary production) can take place Rooted plants cannot grow at depths beyond the light limit. In offshore regions where the bottom is below the photic zone suspended phytoplankton are the main photosynthetic organisms Phytoplankton compete for light with littoral vegetation (macrophytes, epiphytic, and benthic algae) and enrichment by nutrients usually leads to a reduction in the extent of the littoral zone community. Photic zone Light limit

Managing access to renewable resources—eg groundwater and fisheries

This analysis involves three assumptions that simplify it without sacrificing too much realism 1.)The Benefits depend on the amount of fish caught times a price assumed to be constant. 2.)The Cost of each additional unit of fishing effort is constant. 3.)The fish catch per unit of effort is directly proportional to the size of the fish population. (Thus the benefit curve looks like the reverse of the fish renewability curve, and the cost function is a straight line)

"Too many people, in too many boats, chasing too few fish". The problem of open-access fisheries in a fishery the most efficient allocation of effort (maximum net benefit) requires an effort level well below that required to obtain the MSY. This effort level would be both ecologically sustainable and economically efficient Many owner-operated fisheries, both recreational and commercial do seem to operate in this manner. Most open-access fisheries do not operate efficiently and often not sustainably either. Most suffer from over-capitalization (too much effort), leading to stock collapse, and socio-economic hardship

What can be done about the overcapitalization problem in open- access fisheries? 1.)Aquaculture or ranching of wild fish good for shellfish, salmon, catfish, trout, doesn't work for tuna, cod, percids takes up a lot of space, and causes significant environmental damage 2.)Raising the costs, use less efficient gear or methods 3.)Taxes on fishing permits 4.)Individual Transferable Quotas (ITQs) 5.)Small-scale co-operatives and sea-tenure system 6.)Eliminate government subsidies

(c) If this population at K were fished at the rate of 4000 kg/yr at what biomass level would it level off at? At K, dB/dt would be 0, but it would gradually increase as the fishing pressure reduced B