I came across an interesting read regarding the NP. So I have been interested in understanding the Standing Weights that can be supported of various Esox species. Generally these species co-occur with other predators some of which are also prey. So naturally, standing weights are split among various species and in fact there isn't a lot a data on Esox standing weights. But what picqued my interest was just how little food was needed for maintenance and growth of NP. This is an excerpt from the web based article:


I am still searching for the paper which wasn't referenced in the article. So I wonder, is this true? Can a pike grow and maintain RW on as little as 3 times its weight in forage? So if so, what would give it this attribute? Cooler water, more efficient prey capture, better utilization of nutrients, lower metabolic requirements, or some other combination including things not listed? Another thing of interest to me is just how important Cooler water may be in keeping maintenance requirements low. So would other Esox, like chain pickerel, be able to attain greater standing weights than LMB could in the same waters (in the absence of other predators)?

Check your email. Not so sure of cited article "Little 1995".

That is pretty incredible. 2020 was only the second time in the last 21 years I didn't go fishing for pike in Canada. The last time I was down for medical reasons. I love pike fishing and the whole outpost experience in NW Ontario. C'mon 2021 - Open the Border.

I doubt that the carrying capacity or standing stock of NP as the only predator is much different than that of LMB. I base this mainly on they are both predators and the amount of food to sustain each of them and get good or acceptable growth from them is similar for each of them. Maintenance diet as stunted fish for each of these species may also be similar. There is probably no studies of NP in a pond or lake by themselves such as the study by Buck and Thoits where they studied one species populations in Illinois. Standing crops of LMB in the Buck study ranged from 21 to 164 lbs/ac with the mean of 124lbs/ac from 8 ponds. Other studies noted LMB as single species reported maximum pounds as 94 to 200 lbs per acre. Thus total pounds per acre of LMB as single species can vary widely. Trying to compare standing weights for LMB and NP might not be too realistic or provide informative comparisons based on the variability among ponds. Scott & Crossman(S&C) reported that NP that estimated of 5 to 6 pounds of food is needed by NP to gain one pound of weight. Compare this to the widely accepted 10 pounds of food needed for LMB to gain one pound. These authors (S&C) noted that NP is a more successful competitor for space, food, and spawning sites compared to muskellunge.

Bill Cody: "These authors (S&C) noted that NP is a more successful competitor for space, food, and spawning sites compared to muskellunge."

Bill, I wonder if this is a climate adaptation, as the NP lives in colder regions than muskellunge. NP must eat more aggressively because it has less time to do so, perhaps. Note that something similar occurs comparing northern LMB feeding habits with Florida LMB.

Eric, Thank you for sending that article. I am going to read today.

Frank, In the case of LMB which strain has the advantage? Is it the Florida or Northern?.

Bill, Thanks. Esox are species I have little knowledge of other than fishing for them on a vacation in Minnesota. They grow so large that they remind me more of a FHC than an LMB. Much of the FCR work I have seen has been done with small fish. Prather was able to select more efficient individuals to achieve 3-4 to 1 in LMB but he was working with less than 2 oz LMB and in aquaria to boot. Prey doesn't stand a chance in aquariums because the walls limit escape space and make the encounters an perpetual experience until capture. So the energy expended would seem minimal under these conditions.

More research using large fish definitely needs more work. I am always suspect of fish research especially when it is behavior related when done in tanks or aquaria and results applied to wild conditions. Any research although is a good start.

I agree completely Bill. Observation proof is abundant in the many lakes where NP stunt and a few get very big , just like LMB when the food is limited. Can you say "hammer handles". I will check some studies for more.

jpsdad, the northern LMB is, by all accounts, far more aggressive than the Florida. I was thinking this could be an adaptation to compensate for relatively shorter seasons, and wondered if perhaps this might also be the reason why NP are more aggressive than muskie.

Would love to have tiger muskie at my place if ever nanobubble tech allows them to survive below the summer thermocline.

I'm not so sure that stunting is related to FCR or even standing weights for that matter. I think it more plausible it is related to the number of mouths and the quantity of food. We can always imagine, given sufficient water, few enough mouths to sustain fish and grow them. But to your point that better FCR cannot prevent an overpopulation, yes I think this is the case also.

Eric, I appreciate the article you sent. I've been diving into it and it is just full of information that I would like know and like to know more about. Thank you. I'm not sure to what extent you have contemplated its contents, but I can tell you I will be spending some time with it. One pleasant surprise was the table of energy content of various prey. Interesting stuff man, very interesting. To the point of FCR, I am not at all sure their data can be fully relied on to predict prey consumption. I say this because, my general sense is that it takes more forage than that to grow NP at the rates that the subject lakes were reported to.

Just glancing at the charts on specific consumption rates it is clear to me that the annual consumption from the evidence they gathered is going to support the minimum 2.5 to 3 times body weight to sustain growth that was referenced in my original post. These fish are gaining 2 lbs a year and are growing near maximum rates of growth and so I think by the time I actually do tabulate the results ... the reported consumption is probably too low. What this means, if so, is that the NP were supported by consumption that they could not find evidence for. In some scientific circles, even the thought of a non-observable is not allowed. But perhaps this is a case where it should be and it might be justified by things like the rate of digestion or the loss of the weight of prey due to dissolution in the stomachs of NP.

I noticed what appears to be a paradox. Long Lake, which supported the fastest growth, has what appears to be the lowest specific consumption. Nothing extravagant, just adding the two most prevalent prey (the two others trout & pike are insignificant) ... it is clear that fish from this lake were observed to consume less weight in prey. But one thing I notice. The two types of prey (carp and crawfish) are listed as the prey with the greatest energy density. So I am very keen to understand the consumption in units of energy which may make the lowest consumption by weight less a contradiction.

I've got a little application that can digitize the graphs and so I can transform the graphs into tabular data which I think will be an interesting exercise that will allow us to examine their findings with additional context. There is even temperature data!!!! So we can see if we can spot relationships with temperature. Will be a while, but I will try to report some findings from this data on Sunday or Monday.

I will add one last thing that really spoke to me. In the study, NP did not provide much sustenance to themselves. Neither in weight nor in energy density. But it is the energy density of NP that seems to suggest that it can assimilate greater wet mass from consuming the same quantity of energy (thus greater FCR). The energy density of LMB was reported to be 4186 J/wet-weight for LMB but only 3600 J/wet-weight for NP. So if one were to assume that they assimilated the same quantity of energy from a given consumed quantity, the NP should be able to gain 16% more than the LMB on the same quantity of food. If one or the other is more efficient, then this number would of course move.

Don't forget about cover in those BOW's. NP are ambush predators, so they need places to hide. If one BOW has more MP friendly cover than another, that might also contribute to the growth in the fish - expending less calories to catch each meal.

I have only made a quick glance at the study. Location jumped out at me first.

I was able to work with the data today and might do more but think this is about as far as I can take it. To summarize, I am not convinced the daily rates of consumption are accurate because the metrics are obtained as a snap shot of the moment the NP were sampled. So a number of things could influence the daily rate of consumption when measured in this way. One could be that "fish that are full" are less frequently caught and sampled. So possibly fish that are "filling up" are moving around and being caught in fyke nets or are caught by the hook and line sampling. Also possibly there is more than one period of filling up per day and the morning grub is digested and no longer present when they are caught with the evening grub. There just doesn't seem to be enough consumption to grow these fish @ >2 pounds a year.

The annual consumption ranged from 2.5 g/g/year to 4.1 g/g/year depending on the lake. But the growth reflected maximums when referenced with respect to the ranges of growth historically reported. Long Lake had super growth which reflects the highest growth ever documented of NP that I am aware of. These fish were >6 lbs in year 3. That is remarkable. So I don't think this data gives us a lot to go on with respect to FCR, however, I do think the observed consumption is probably highly correlated to actual consumption (if one will allow me to let a falling tree to make sound when no one was there to hear it) Because I do think there is strong correlation consumption, I do think the data allows one to make comparisons between the lakes, the growth observed in each lake, and the quality and abundance of prey in each lake.

This was a great find Eric. I learned some things I didn't know. First I didn't know that Northern Crayfish were more energy dense than bluegill or even trout, for example. For me that was a real eye opener. Also I didn't know that carp were 1.79 times more energy dense than bluegill. I have known for a while that "rough fish" presence has been observed to be associated with greater standing weights of LMB .... this was as much a surprise to me as it was to the authors. I guess its possible that rough fish make up for the bad effects by reproducing more nutritious YOY.

When the consumption of prey was transformed into energy ... the consumption was very comparable between lakes. Mary had the lowest consumption and the slowest growth (albeit phenomenal growth anyway). This lake was interesting because crays were also present but were not prevalent in the way they were at Long Lake where the consumption of crays accounted for 42% of annual consumption. Mary had a crappie population and I wonder how much they may have competed for crays. Though NP in Mary grew slower than did Long Lake NP, they were observed to consume a greater weight of prey. So the quality of prey must contribute to growth in meaningful ways where Long Lake was like the perfect storm of carp and crays. I also wonder if calories tell the fish when its time to rest and digest. The NP of Long Lake consumed smallest weight of prey but they appeared to be getting their fill of them (growing at maximum rates of growth). Perhaps the greater energy density allowed them to spend more time on the couch and less time hunting another meal? Certainly other things like cover, weeds, etc probably also play a role. I've attached a spreadsheet below and so everyone is encouraged to browse its tabs and comment.

Nice work jpsdad. I will se if I can find some northern NP data.

Guys what is g/g/year? How confident are we that the aging of the 3yr NP was correct? Did they use scales, otoliths, or was the Lake renovated?

Bill the paper can be found here. The consumptions were taken by gastric lavage where it was possible to release fish. Those that were not morts were aged by scales but mortalities aged by otolith (I presume because a combination of these two aging techniques were used.

g/g/year is the specific consumption rate which in long hand is consumption mass per predator mass per year. Except for the time rate, the metric is dimensionless and so the factor doesn't change depending on the unit of mass/weight used. In other words, lbs/lbs/year is the same number. They didn't provide yearly rates but rather daily rates of specific consumption. I converted them to yearly rates by multiplying their reported mean daily rates of each season by 91 days (~ 3 months). I did this because we generally talk about yearly consumption of prey here on the forum.

The lakes were not renovated and the Long Lake carried NP for a longer span of time than any other lake having been stocked by Arizona Wildlife in the 60's.