I'm trying to figure out if the Colorado Koolaid can is 16 oz or 12 oz. Not for sure if my memory is correct but didn't Coors once sell a 14 oz can?
Anyways, the crayfish are large. It will interest you to know that the dry matter of all living things LESS the mineral content has a very close relationship to energy content ... at least for those organisms that have be tested thus far
. Most of the minerals are calcium and phosphorus with other minerals in smaller quantity. The correlation to this relationship is so tight it has an R-squared >=0.97 (where perfect correlation is 1.0). This is suggests that energy content of wet weight samples can appropriately be determined by finding the ash free dry weight of a sample. A surrogate method that is much easier to do than determining its caloric content. Essentially the dry organic compound percent of the wet weight determines this value. This makes sense when you think about it. The sun powers the formation of organic molecules ... it is in these molecules that all of the energy is stored.
So the dry matter of BG less its ash is very closely as energy dense as the crayfish's. However, I think crayfish are superior prey than BG for a number of reasons (provided a predator is eating them). First they can achieve higher wet weight standing weight. In an unfed unfertilized control Paul Brown et al grew 800 lbs/acre of Northern crayfish in 5 months. BG under the same circumstances would have been limited to around 500 lbs/acre but only if the water was so fertile it would have been as productive as one that is actively fertilized to maintain bloom. So crayfish can produce
60% more wet weight forage per acre than BG. Produce is the key word here, literally the 1 season potential for gain in standing weight is at least 60% more. In a cropped system, this production could exceed the potential standing weight but that is a whole other topic
Couple higher wet weight production with 50% more energy in the wet weight and hey we are talking more than twice the energy to consume of (possibly easier to catch) prey. It would just make sense that LMB would ignore BG when crays are abundant.
So why would crayfish have higher energy content than BG? I can think of a few possible reasons.
1. They are benthic organisms that do not need buoyancy and probably benefit from having higher dry weight percentage and negative buoyancy. Nature probably selects for this greater dry weight percentage of wet weight.
2. They don't have as much investment in structures requiring minerals. So the ash content is lower.
3. The lower investment into structures requiring minerals may allow the crayfish to invest more in storing lipids which reduce wet weight are very energy dense (more so than proteins for example)