Redfish and Specks Benefit from Limited Weir Closings

[Duck Butter]

Originally Posted by MathGeek

I don't think I'd say there is no way to develop the hypothesis, just that we have not yet thought of a simple way.

A lot of feed efficiency issues have been worked out in great detail in freshwater trout, and a lot of ways of untangling food webs have been used in large freshwater lakes and the open oceans.

And even if the available data never becomes available to describe all the biological and life history causes behind the observations, the observations themselves (condition of the fish) and the resulting correlations are pretty solid.

no such thing as bad data. Not all studies show correlations. I looked at nesting birds for 2 years and the first year all my data lined up great and the nesting was predictable and i thought I had it all figured out. Second year, they didn't act the same and completely through me for a loop, but that data is still there for someone else to sift through


Back on original topic, I think there are a couple things that may be influencing the results of your data

1. the timing of the study is also correlating with spawning time and weirs also are open during that time (full moons in late spring/summer). Likely the fish have just spawned.

2. rod and reel catches don't show the true population, only fish susceptible to being caught, which are likely fish that are hungry and thin anyways

3. The egg-laden females may be there but are not being caught. They are only interested in one thing - spawning. They have already fed for long periods of time to be ready for the most important event in their lives.

[MathGeek]

Originally Posted by Duck Butter

1. the timing of the study is also correlating with spawning time and weirs also are open during that time (full moons in late spring/summer). Likely the fish have just spawned.

One can always take wild guesses about potential confounding factors. Redfish and black drum are not spawning during the sampling window, but specks and gafftops are. Looking at the subsample of our data taken within 48 hours of a full moon shows no significant difference in mean relative condition factors for a given year.

Originally Posted by Duck Butter

2. rod and reel catches don't show the true population, only fish susceptible to being caught, which are likely fish that are hungry and thin anyways

We've compared a lot of our data from hook and line catches to net catches in cases where data from net catches are available for comparison. The hypothesis that hook and line catches are thinner, hungrier fish (lower condition factor) has never been supported. Hook and line catches are not generally accepted as being a good representation of the length structure of a population, as all methods other than electrofishing have a lot of sampling bias with respect to lengths. However, relative condition factors in a given length class are widely accepted as not depending on the sampling method. (Others have looked at this also.)

We've got tons of data showing mean relative condition factors at or above 100% for certain species, locations, and years. If hook and line were biased toward selecting thin, hungry fish, the mean relative condition factors would almost always be under 100%, regardless of where and when they were sampled. It is also common for hook and line studies by others to find mean condition at or over 100%.

The mean condition factor of all the specks measured from Calcasieu over the four years of our study is 101%. Someone forgot to tell the fat ones not to bite.

Further, even if there was a difference between condition of hook and line catches and net sampled catches, since our methodology is the SAME every year (hook and line), the variations we see from year to year (and comparisons with other hook and line data) would still be valid.

Originally Posted by Duck Butter

3. The egg-laden females may be there but are not being caught. They are only interested in one thing - spawning. They have already fed for long periods of time to be ready for the most important event in their lives.

We do not check every fish for eggs. However, because we work at fish cleaning stations, we see many of the fish we've just sampled get filleted, and we often cut into many of of the sampled fish ourselves. There is ample evidence that there are a lot of egg-laden females in our data. You should send them a note telling them they should stop biting angler hooks to better be ready for the most important event in their lives.

The bottom line is that hook and line sampling methods are valid and widely accepted for determining relative condition factors in fish.

[Duck Butter]

Originally Posted by MathGeek

One can always take wild guesses about potential confounding factors.

I know, here is one study in which that is happening:

Inshore Saltwater Fishing Discussion: Redfish and Specks Benefit from Limited Weir Closings - SaltyCajun.com

Inshore Saltwater Fishing Discussion: Redfish and Specks Benefit from Limited Weir Closings - SaltyCajun.com

it is going to be very difficult to make any type of correlation between weirs being open and fish being less fit when they are open. Sometimes scientists overthink things and forget about common sense. On what planet does it make sense that if more food is available (weirs open) would fish be less fit? None. It doesn't, unless you subscribe to the regurgitation theory i.e. bulimic trout, which is nevermind i digress

[MathGeek]

Originally Posted by Duck Butter

On what planet does it make sense that if more food is available (weirs open) would fish be less fit? None.

Plumpness in animals depends not only on food intake, but on the balance sheet between food intake and energy expenditures.

It is very common for freshwater trout in mountain reservoirs to lose body condition over the spring and summer months (when most food is available) because their energy requirements are also a lot higher in the summer months. Conversely, it is common for freshwater trout in mountain reservoirs to gain body condition over the winter (when food is scarce), because their energy requirements are much lower.

Similarly, stream trout can lose body condition under high current conditions because the additional energy expenditures exceed the additional caloric intake.

With brackish species, osmoregulatory costs also factor in: salinity much higher or lower than the preferred range of a species significantly drives up metabolic costs.

A human counterexample would be an athlete losing BMI with the same caloric intake on which most office types would quickly gain BMI.

Originally Posted by Duck Butter

On what planet does it make sense that if more food is available (weirs open) would fish be less fit? None.

In the case of the weirs, the planet is planet earth. For additional weir openings to increase fish condition, the additional food needs to exceed the additional energy requirements of the change.

Opening the weirs in addition to the baseline opening may not provide a net gain in additional food at all if the net change in forage flow is negative.

Opening the weirs in addition to the baseline opening may provide additional food, but it may increase the metabolic costs by a larger amount. This seems more likely.

It's like giving away Big Macs on the top of a mountain with the parking lot at the bottom. The people eating the extra burgers would probably lose BMI.

[Duck Butter]

Originally Posted by MathGeek

Plumpness in animals depends not only on food intake, but on the balance sheet between food intake and energy expenditures.

It is very common for freshwater trout in mountain reservoirs to lose body condition over the spring and summer months (when most food is available) because their energy requirements are also a lot higher in the summer months. Conversely, it is common for freshwater trout in mountain reservoirs to gain body condition over the winter (when food is scarce), because their energy requirements are much lower.

Similarly, stream trout can lose body condition under high current conditions because the additional energy expenditures exceed the additional caloric intake.

With brackish species, osmoregulatory costs also factor in: salinity much higher or lower than the preferred range of a species significantly drives up metabolic costs.

A human counterexample would be an athlete losing BMI with the same caloric intake on which most office types would quickly gain BMI.



In the case of the weirs, the planet is planet earth. For additional weir openings to increase fish condition, the additional food needs to exceed the additional energy requirements of the change.

Opening the weirs in addition to the baseline opening may not provide a net gain in additional food at all if the net change in forage flow is negative.

Opening the weirs in addition to the baseline opening may provide additional food, but it may increase the metabolic costs by a larger amount. This seems more likely.

It's like giving away Big Macs on the top of a mountain with the parking lot at the bottom. The people eating the extra burgers would probably lose BMI.

seatrout (drum/apples) freshwater trout (salmonids/oranges) but anyhoo

[MathGeek]

Originally Posted by Duck Butter

seatrout (drum/apples) freshwater trout (salmonids/oranges) but anyhoo

Your statement about more food always leading to plumper fish seemed quite global:

Originally Posted by Duck Butter

On what planet does it make sense that if more food is available (weirs open) would fish be less fit? None.

Since there are well-known counter examples on planet earth, it seemed worthy to point them out. Why would spotted seatrout not be subject to the same balance sheet considerations of every other fish species? To gain weight, the caloric intake must exceed the calorie requirements. More food is not enough if the energy requirements increase by more than the energy intake. This would be true on every planet, and for every fish species on planet earth.

We've been looking through the data and analyzing in more detail. One notable fact is that there are almost always high flow conditions (full moon, new moon, high water behind weirs) when more than 40% of the gate area is opened. It would be useful to know what current speeds are present at the weirs under these conditions, and how these current speeds compare with the naturally occurring current speeds in the estuaries over the past few thousand years.

If the freshwater trout energy expenditures can be strongly impacted by the same current speeds they have seen continuously for thousands of years, it would stand to reason that current speeds much higher than Gulf inshore species have seen for thousands of years could also have a big impact on energy expenditures. Natural selection has done its job preparing freshwater trout for stream current conditions, but natural selection may not have made inshore species well adapted to the current conditions present at the weirs.

[Duck Butter]

Originally Posted by MathGeek

Your statement about more food always leading to plumper fish seemed quite global:



Since there are well-known counter examples on planet earth, it seemed worthy to point them out. Why would spotted seatrout not be subject to the same balance sheet considerations of every other fish species? To gain weight, the caloric intake must exceed the calorie requirements. More food is not enough if the energy requirements increase by more than the energy intake. This would be true on every planet, and for every fish species on planet earth.

We've been looking through the data and analyzing in more detail. One notable fact is that there are almost always high flow conditions (full moon, new moon, high water behind weirs) when more than 40% of the gate area is opened. It would be useful to know what current speeds are present at the weirs under these conditions, and how these current speeds compare with the naturally occurring current speeds in the estuaries over the past few thousand years.

If the freshwater trout energy expenditures can be strongly impacted by the same current speeds they have seen continuously for thousands of years, it would stand to reason that current speeds much higher than Gulf inshore species have seen for thousands of years could also have a big impact on energy expenditures. Natural selection has done its job preparing freshwater trout for stream current conditions, but natural selection may not have made inshore species well adapted to the current conditions present at the weirs.

i hear you and my original comments were just in response to you asking for some hypotheses to why which I think are very plausible. I think the weir openings correlating to thinner fish in a system that is almost 80 square miles is pretty unplausible especially when the weirs are not stopping all bait from getting through.

There are likely several factors if not 10 or 20 that are contributing to thinner fish. A correlation does not = causation.

[Duck Butter]

Originally Posted by MathGeek

We do not check every fish for eggs. However, because we work at fish cleaning stations, we see many of the fish we've just sampled get filleted, and we often cut into many of of the sampled fish ourselves. There is ample evidence that there are a lot of egg-laden females in our data. You should send them a note telling them they should stop biting angler hooks to better be ready for the most important event in their lives.

Fish having eggs doesn't mean they are about to spawn. Egg production can take months. They feed extensively during these periods (pre-spawn). Seeing eggs does not mean they are spawning. Most female trout caught in April and May will have eggs

All animals are here to do 3 things: survive, grow, and reproduce. Reproduction (getting their genes into the next generation) is the most important thing to them and what defines being successful. Makes you wonder about those people with 10 kids from 10 baby mamas. From one standpoint, they are 'successful'