Redfish and Specks Benefit from Limited Weir Closings

[dmtfish]

Originally Posted by Duck Butter

many things to point out, but a couple are:

1. angler creel surveys (fish caught by rod and reel) do not always show the true picture of what is happening as a whole in the population. These are only fish that are susceptible to being caught (it can be argued that these fish were hungry, therefore that is why they are 'thin'). To get a true picture of the ENTIRE population, seines, nets, and electrocshocking are used. They are all equally susceptible of being captured. Angler creel surveys are good for a general picture of what is going on such as success rates, but for actual population data you need to sample all the fish not just fish that were caught by rod and reel

2. the assumption is being made that the weirs have something to do with all the fish in the lake. These fish may not have even been within a mile of a weir ever in their lives, for all we know they came straight in from the gulf and went to Prien Lake. Possibly if the fish that were measured were all caught in front of the weirs, maybe, but these fish were caught all over the lake and possibly in Prien or Lake Charles

3. no distinction between males and females, it does matter

Point #2 was why I originally responded to MGs thread. Also, forgive me for not going back and reading your points MG, but did you say that the 90 days prior to sampling are key to body mass??? If such is the case, you mentioned lower body mass in May and June, which would correspond to Feb-Apr feeding. Are not the wiers typically closed during these months??

[Duck Butter]

Originally Posted by dmtfish

Point #2 was why I originally responded to MGs thread. Also, forgive me for not going back and reading your points MG, but did you say that the 90 days prior to sampling are key to body mass??? If such is the case, you mentioned lower body mass in May and June, which would correspond to Feb-Apr feeding. Are not the wiers typically closed during these months??

also if the weirs are not really' closed' and bait can get through per MGs post#18 also kinda makes me take the study with a bigger grain of salt:

You need to realize that the weirs are never completely closed. Even when all of the mechanical gates and flaps are closed, over 10% of the total area coupling the marsh and lake remain open. And the operating procedures for opening the mechanical gates are such that, over most 90 day operating periods, the average coupling between the marsh and lake is at least 40% of the possible total.

So, you may be right that extended closures (90+ days) of all the gates so that only 10% remained open might negatively impact the fish. However, the historical operating data shows that the gates are never all closed for more than a couple weeks at a stretch, and that this only occurs during high salinity periods.

You cannot judge the openings from the boat bay or from the surface gates. There are numerous gates and flaps and slats below water level that allow bait to move back and forth even when the boat bay and surface gates are closed.

[dmtfish]

Originally Posted by Duck Butter

also if the weirs are not really' closed' and bait can get through per MGs post#18 also kinda makes me take the study with a bigger grain of salt:

You need to realize that the weirs are never completely closed. Even when all of the mechanical gates and flaps are closed, over 10% of the total area coupling the marsh and lake remain open. And the operating procedures for opening the mechanical gates are such that, over most 90 day operating periods, the average coupling between the marsh and lake is at least 40% of the possible total.

So, you may be right that extended closures (90+ days) of all the gates so that only 10% remained open might negatively impact the fish. However, the historical operating data shows that the gates are never all closed for more than a couple weeks at a stretch, and that this only occurs during high salinity periods.

You cannot judge the openings from the boat bay or from the surface gates. There are numerous gates and flaps and slats below water level that allow bait to move back and forth even when the boat bay and surface gates are closed.

Bingo... Really appreciate your efforts MG, and keep it up. Just no way to develop your hypothesis

[MathGeek]

Originally Posted by dmtfish

Bingo... Really appreciate your efforts MG, and keep it up. Just no way to develop your hypothesis

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.

[dmtfish]

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.

"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."

AMEN!!

[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'