Redfish and Specks Benefit from Limited Weir Closings

[MathGeek]

I don't mind the ship channel itself. It is responsible for most of the economic productivity of the Lake Charles, etc. The response was slow and ineffective to much of the early land loss. Too few policy makers take the long view and make policy choices based on what is best for Louisiana citizens in a generation or two.

[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

[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'

[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.

[MathGeek]

I should note that the data shows that the weir operation since 2012 has been very scientific and driven by salinity data, fishery considerations, moon, tide, fronts, and water flow needs in accordance with the principles that have been propounded.

The single weir operating event that seemed more selfish or politically motivated (rather than scientific) was the closing of the boat bay coinciding with the Federal government shutdown on 1 October 2013.

Other than that, every opening and closing is well justified by salinity conditions, flood conditions, an approaching front, full moons, new moons, the need to let fish and shrimp through, etc.

On every occasion where the weirs were closed to the fullest extent possible (about 10% remaining open in the non-closeable slats), salinity data shows measurements of 19 ppt or greater both inside and outside of every weir at the time of closing.

[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

[Duck Butter]

Originally Posted by MathGeek

I should note that the data shows that the weir operation since 2012 has been very scientific and driven by salinity data, fishery considerations, moon, tide, fronts, and water flow needs in accordance with the principles that have been propounded.

The single weir operating event that seemed more selfish or politically motivated (rather than scientific) was the closing of the boat bay coinciding with the Federal government shutdown on 1 October 2013.

Other than that, every opening and closing is well justified by salinity conditions, flood conditions, an approaching front, full moons, new moons, the need to let fish and shrimp through, etc.

On every occasion where the weirs were closed to the fullest extent possible (about 10% remaining open in the non-closeable slats), salinity data shows measurements of 19 ppt or greater both inside and outside of every weir at the time of closing.

So you are saying that the weirs are being operated as per the agreement put in place? Not per Miami Corps duckhunters? .....but the wigeongrass bruh

:mindblown

[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.

[MathGeek]

Another important point in the science centers on the attraction vs. production debate in fisheries. One viewpoint stresses that conditions that attract a lot of fish (reefs usually) must provide a net benefit to the fish through increased forage production, because the fish are drawn to food sources. The counter point stresses that this may not always be true and should be empirically demonstrated in each case, because a number of negative effects are possible when fish congregate in high densities.

This debate has raged for decades with respect to red snapper and artificial reefs/oil platforms. The empirical data has just emerged in the past few years showing that artificial reefs actually increase production of red snapper, they do not simply attract red snapper that were fed by the Gulf food web that would be present without the artificial reefs/oil platforms.

We've found some surprising results when correlating oyster stocks to fish condition factors. As we had expected, the more benthic and demersal species (redfish, drum, gafftops) show significant positive correlations with oyster stocks, suggesting that healthy oyster reefs contribute significantly to the benthic food web in ways that benefit these species.

However, fish condition in spotted sea trout is negatively correlated with oyster stock assessments. This suggests the propensity for sea trout to congregate at reefs may not be benefiting them. Their design makes them less able to utilize benthic food resources compared with the other species, and there is likely strong competition for available resources near the reefs, since the fish density seems to be much higher there. When stocks are low, specks are forced to spread out over the entire estuary and may thrive better when chasing bait higher in the water column throughout the estuary than when competing with dense populations of fish near oyster reefs.

Natural selection in specks probably drives them toward oyster reefs for protection from predators rather than increased forage that they can utilize. But specks in Big Lake today probably face far fewer natural predators than Gulf inshore and near shore specks have faced over the past few thousand years.

[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.

[MathGeek]

Originally Posted by Duck Butter

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

Right. But given 10-20 factors, when a single factor has a correlation coefficient close to -0.5 and a P value less than 0.001, the possibilities of actual causality and the physical mechanisms that might relate to causality are probably due careful consideration.

Ultimately, hypothetical causal mechanisms are supported or rejected with data. Correlation never proves causation, but it can support causation. However, correlation can disprove causation.

In this case, the claim that closing the weirs is choking the lake or starving the fish is completely unsupported in the available data.

The case that fully opening the weirs would harm the fish is only mildly supported.

One feature of Louisiana law is that wildlife management may proceed with the best available science, even if that science is imperfect and hypotheses are only supported by the data and not convincingly proven.

The assertion that current weir operations according to the established plan are not harming the fish and are benefitting the ecosystem as a whole is well supported by the data.

Fish and the fishery are not being compromised by closing the weirs as necessary to protect the marsh.

[MathGeek]

Sending a recent weir discussion back to the top!

[wishin i was fishin]

Interesting topic MG, you make SC a better place. If only we could get you over to VB and get those coastal projects prioritized. We would have some kind of chance to restore this fishery back to what it was.

You definitely have your hands full with BL.

[Smalls]

Originally Posted by wishin i was fishin

Interesting topic MG, you make SC a better place. If only we could get you over to VB and get those coastal projects prioritized. We would have some kind of chance to restore this fishery back to what it was.

You definitely have your hands full with BL.

Unfortunately, beaurocracy defines which projects are important. No amount of campaigning or science will do otherwise. These "priority" areas have already been defined. Vermilion Bay was practically given up on when the Master Plan was released. You don't plan to spend millions of dollars on levee systems if you intend on working to restore a particular area. They will turn everything into a New Orleans or Houma, and condemn anything south of those areas to their inevitable fate.

[wishin i was fishin]

Originally Posted by Smalls

Unfortunately, beaurocracy defines which projects are important. No amount of campaigning or science will do otherwise. These "priority" areas have already been defined. Vermilion Bay was practically given up on when the Master Plan was released. You don't plan to spend millions of dollars on levee systems if you intend on working to restore a particular area. They will turn everything into a New Orleans or Houma, and condemn anything south of those areas to their inevitable fate.

True dat Smalls, true dat. The increase in diversion projects there is a finite amount of water and sediment to feed them. our only hope is that will reduce the water flowing through the Atchafalaya diversion. i could go on for a while but don't want to hijack the thread.

So, back to the weirs...Has anything changed from last year?

[MathGeek]

Originally Posted by wishin i was fishin

True dat Smalls, true dat. The increase in diversion projects there is a finite amount of water and sediment to feed them. our only hope is that will reduce the water flowing through the Atchafalaya diversion. i could go on for a while but don't want to hijack the thread.

So, back to the weirs...Has anything changed from last year?

Not really. The evidence is convincing that the weirs are being operated according to the management plan which incorporates some pretty good science.

The available evidence also suggests that since the gates in the weirs are at least 40% open most of the time and never less than 10% open, there is ample flow of forage between the marsh and lake that weir closures are not having any negative impact on the lake.

Seasonal variations in what anglers see is more dependent on where the fish are chasing forage than an actual dearth or abundance of fish. The weirs concentrate the fish were they are easy to catch. Last year, when there was a dry spell and the weirs were closed, the fish were eating very well, but they were eating pogies and bait fish spread throughout the lake rather than stacking up at the weirs.

The closing of the Omega protein plant lead to a very healthy age zero class of pogies last summer. This changed the speck pattern and frustrated anglers, but the specks were well fed and began to be caught with regularity again by fall. The moving of that pogie harvest has probably done more for the fishery for the next few years than leaving the weirs open 100% of the time ever could have.

As far as I can tell, oyster dredging, salinity, erosion, and loss of marsh are the biggest issues threatening the fishery.

[Smalls]

Originally Posted by wishin i was fishin

True dat Smalls, true dat. The increase in diversion projects there is a finite amount of water and sediment to feed them. our only hope is that will reduce the water flowing through the Atchafalaya diversion. i could go on for a while but don't want to hijack the thread.

So, back to the weirs...Has anything changed from last year?

Reduction of flow through the Atchafalaya is the last thing you want if your hope is to save Vermilion Bay and the surrounding area.

As MG said, nothing has changed with the weirs, but is that a bad thing? I haven't been there in a while now, but the purpose is to maintain and improve the Cameron-Creole marsh. If any marsh was gained, then I'd say the management is doing what it is supposed to do.

[MathGeek]

Originally Posted by Smalls

Reduction of flow through the Atchafalaya is the last thing you want if your hope is to save Vermilion Bay and the surrounding area.

I think everyone is working with their own understanding about what it means to "save" an area. Some mean (including Smalls, I think) of saving an area by preserving the land and marsh from becoming open water. In this sense, preserving the flow of silt through the Atchafalaya is important.

But local fishermen and oystermen often enjoy much better years when there is less flow of freshwater and silt through the river, so they come to see reduced flow as a good thing.

Another point is that the river is not just bringing the silt needed to rebuild land and marsh, it is also bringing all the other crap that is flowing down the Mississippi, including pretty heavy nutrient loads, pesticides, antibiotic residues, hormone residues, etc. Recall that 30% of the flow of the Mississippi River is diverted to the Atchafalaya.

I am of the view that the benefits of the silt outweigh the negatives of the nutrient loading, fresh water, and chemical residues. But the attached pic shows the zone of hypoxic bottom water ("dead zone") that formed in the Gulf in the summer of 2013 which is largely attributable to the nutrient loading.

Probably the most tangible step to reducing Gulf hypoxia would be to reduce nutrient loading by ending ethanol subsidies and fuel requirements, since the artificially high corn prices encourage farmers to use more fertilizer which washes down and contributes to the problem. Lower corn prices would also reduce pressure on cattle feed operations to boost feed efficiency with heavy use of antibiotics and hormones. Ending ethanol subsidies and requirements would also increase demand for domestic oil.