Thank you Eric, especially for the Tidwell reference. I am hoping this reference will help me to piece together the range of temperatures I don't have enough data points for.
Your post supports what I previously thought. The peak of metabolism occurs before 86 F.
The peak of consumption and growth however is not at the preferred temperature but rather very modestly above that temperature. It falls off sharply with additional increments of temperature. The most efficient use of feed is at the temperature that is preferred (something that is line with optimum foraging theory). Under a satiation diet, LMB apparently optimize the use of resources by preferring the most efficient temperature. This is apparently preferred by LMB over growing faster at modestly higher temperature.
I reviewed the Tennessee paper and there were red flags. First, they did not measure growth from the samples but rather these were calculated. To actually measure growth, you have to get two weights. They reported growth in specific units of calories gained per unit weight. Being a daily rate of gain per unit body weight (a specific rate of gain), we could presumably compound the rate over the days of the month and get the growth for a month. But if we do that, we have a two-year-olds gaining from ~ 1 lb on March 1st to 2.64 lbs on November 30th. This modestly exceeds the growth potential of NLMB in that climate and is not consistent with the reported weight of 2.5 year olds.
The measurement of consumption was inferred from stomach contents and the state of decomposition of the consumed prey. I think the consumption estimates were reasonably close to actual (judging from simulating the consumption with my model) but the results from that exercise were very much different from the study in terms of reported growth. In July and August, the model calculated that consumption was insufficient to fully meet metabolic demands and that the weight of fish declined slightly in July and August. The reported consumption (per the model) supported maximum rates of growth in October and modestly lower than maximum in September and November. This is consistent with your analysis. Slow to no growth in the heat of Summer and good growth in the Fall. Our analysis, contrasts with theirs pertaining to growth in the summer months (the red flags I was mentioning). They reported higher growth in July and August than in September, October, and November for female LMB. Given the consumption they reported, the model implies that LMB growth was forage limited. Consumption was most prevalently limited in July and August per the model. That consumption was limited in July and August is something we agree on.
But what we may not be able to agree on is why LMB were not consuming what was required to make their potential for growth. Estimating the water temperature for Watts Bar Reservoir, I am very confident that the reason was sourced to prey availability. I think they would have consumed more if prey had been more abundant. You may, however, think that the LMB were stressed by temperature in July and August leading to lower consumption. If anything, this demonstrates how what we "observe" or "experience" of any particular set of observations can vary depending on perspectives. Truth be told, LMB can have slow growth in July and August as a result of an insufficient supply of prey OR due to the stress of excessive temperatures. Both occur. What we should seek to do is to understand the reason for slow growth for each particular circumstance where slow growth occurs. There are also cases, even in the deep south (for example Lake8's pond) where LMB that are managing July and August temps while setting the standard of maximum growth. It is for these exceptions that we need to be able to discern the cause of slow growth for any arbitrary pond in the heat of summer.
