Pond Boss Forums INTRO Questions & Observations Pond carrying capacity

My view is a little different than Bill's conceptually but not factually.

Standing crop is a fixed in time measurement (what is there) while carrying capacity is a theoretical limit for a given habitat (set of facts).

The facts (habitat) include all of the physical ,chemical and biological features of the environment needed to sustain life (Fisheries Techniques 2nd). There are a lot of factors all included in the energetics concept of total energy input into a habitat.

See the archive http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=92440#Post92440

I have pasted Bruce's excellent listing of some factors :

1. Water clarity/lack of suspended sediment--Lack of suspended sediment allows for better sunlight penetration into the water column, which in turn increases simple and complex plant growth, which in turn enhances micro and macro-invertebrate populations, yielding more fish.

2. Fertility--Nutrients are necessary for the above mentioned phytoplankton growth to occur. Increased fertility can occur naturally or be helped along artificially when necessary by fertilization.

3. Competition--Predator carrying capacity is directly impacted by competition from other predators, even in the form of so called "prey" species early in life, i.e. bass YOY need abundant zooplankton for several weeks before they can prey on larval fish. Carrying capacity for any one species needs to account for other species in the fish community.

4. Weather/Environment--Does warm water have a greater "carrying capacity" than cool water? I'm not so sure. Fish in a cooler pond require less oxygen, and may therefore be able to push the envelope, so to speak, as far as pounds per acre. I would guess that a warmer pond may get to carrying capacity quicker, but may not ultimately support more weight of fish. I'd be interested in comments in regards to this.

5. Feeding--This may simply be a subgroup of fertility, but experience tells me that at least for short periods of time, I can support more pounds of fish per acre in a fed pond. In the long run, however, I may be more prone to crashes. Perhaps the fed pond has a higher "carrying capacity", but implies more risk.

6. Waste removal/flow through--As nutrients build up in the form of waste products, a pond's carrying capacity decreases if it is unable to rid itself of waste. Ponds with efficient bacterial communities process waste better, thereby probably have higher "carrying capacity". Ponds with high natural flow through, such as those with a large watershed/volume ratio, have better ability to support more fish per acre.

7. Aeration--Maybe a subgroup of #6, enhance a pond's ability to rid itself of waste, thereby increasing carrying capacity. Perhaps more importantly, aeration makes "usable" water more plentiful within a pond by bringing oxygen throughout the water column. Obviously a pond that only has oxygen in the top five feet, but has seven feet of anoxic water has less net carrying capacity per acre.

8. Forage diversity--If a pond has species diversity that is appropriate to the goals of that particular ecosystem, it allows for more efficient movement of biomass up the food chain. In other words, if there is plentiful invertebrate life available that is utilizable by gizzard shad, then the presence of gizzard shad allows biomass to "flow" more efficiently up to a top end predator such as largemouth. This means a higher carrying capacity for the predator, although the carrying capacity could simultaneously decrease for species that would compete directly with the gizzard shad, such as bluegill.

9. pH--Another way that carrying capcity can be increased would be to have pH levels that minimize the presence of unionized ammonia. In water, ammonia occurs in two forms, which together are called the Total Ammonia Nitrogen, or TAN. Chemically, these two forms are represented as NH4+ and NH3. NH4+ is called Ionized Ammonia because it has a positive electrical charge, and NH3 is called Unionized Ammonia since it has no charge. This is important to know, since NH3, unionized ammonia (abbreviated as UIA), is the form which is toxic to fish. Water temperature and pH will affect which form of ammonia is predominant at any given time in an aquatic system. At high pH there is more UIA because of the OH- groups readily available in basic water. The OH- groups attract the H+ ion to form water (H2O). By stripping this ion away from NH4+ it leaves the unionized, or toxic form in the water. Toxic water means fewer fish, and less carrying capacity.

10. Social interaction--The carrying capacity is lower in a pond amongst species that spend large amounts of energy fighting over cover territory, and spawning substrate. A limited expample would be an aquarium that might be able to hold three pounds of green sunfish biomass, but ultimately never reaches that carrying capacity because the GS spend most of their time attacking and killing each other. Ponds ecosystems can behave in a similar manner if a particularly agressive species, like bluegill fight over territory during late spring and summer.


In summary, all of these factors need to be considered to evaluate "carrying capacity". It might also be more useful to think of this in terms of pounds of fish per unit of water volume instead of surface area, since one surface acre could mean anywhere from one to twenty acre feet of water.

As you can see with all these factors which are variable it is next to impossible to say X pond has Y carrying capacity. I have seen natural ponds and small lakes have CC as little as 100 lbs of fish per acre and as high as 3500 lbs (estimated based on standing crop). The problem is that for any given pond the only way to find that point is to push the limits to the crash point.

That leads us to this thread : Trophic Continuum - natural to aquaculture http://www.pondboss.com/forums/ubbthread...ite_id=1#import which has a good discussion of some factors.

A very generally used number is 400 lbs of fish per acre in a fertile pond . That is a conservative number as most people and FS writers are cautious about pushing the limit. An example is in aquaculture operations there are studies where from 13,000 lbs to 22,000 lbs per acre of tilapia were commonly grown in SE Asia.