Calcasieu Croaker Science

[MathGeek]

LDWF has been kind enough to share all their fishery independent stock assessment data in Big Lake with us for the past five years. We're just digging into it with the intent to correlate it with our original relative condition factor data from our annual creel surveys where we have weighed and measured 1800 specks, reds, drum, and gafftops. The idea is to see which forage species in the food web are more strongly correlated with the predator species.

If a predator gets fat when there are lots of croaker, it suggests that predator species is more heavily dependent on croaker than other forage species which show little correlation with the plumpness of the predator.

Here is the CPUE for croaker from Jan-Jun for the past 5 years.

OK, experts, which bioindicator species (specks, reds, drum, or gafftops) will have its plumpness most strongly correlated with the croaker stock assessments?

[seatrout]

Ok professor,

I don't pretend to be as smart as you but, I don't think you have given enough information to draw a conclusion to your question.... Plus your second paragraph does not make sense to me. Predators get fat when croaker abundant which is there main forage but shows no correlation with plumpness of predator. Am i the only one confused here????

[DaPointIsDaBomb]

Looks like the weirs were closed til month 3 in all those graphs but 2013 where they were closed til later. That keeps all the croakers behind the weirs

Or that the guides were all soaking croakers January through March and all the bait was in the bait tanks at Spicers. Once they start soaking shrimp in April, the croaker population goes back up

[jpeff31787]

what is cpue?

[barbarian]

Originally Posted by jpeff31787

what is cpue?

I'm so glad it wasn't just me.

[Bumfisherman]

Give us a little help here. I am confused but this is very interesting.

[MathGeek]

Originally Posted by jpeff31787

what is cpue?

Catch per unit effort.

LDWF catches fish in nets. CPUE is the number of fish caught divided by the total amount of time the net was out in a month.

[jpeff31787]

Originally Posted by MathGeek

Catch per unit effort.

LDWF catches fish in nets. CPUE is the number of fish caught divided by the total amount of time the net was out in a month.

ok... was 2013 weather different from the rest? maybe the croaker were in a different area of the lake that year. Or do you already know why there weren't as many in 2013?

[MathGeek]

Originally Posted by seatrout

Ok professor,

I don't pretend to be as smart as you but, I don't think you have given enough information to draw a conclusion to your question.... Plus your second paragraph does not make sense to me. Predators get fat when croaker abundant which is there main forage but shows no correlation with plumpness of predator. Am i the only one confused here????

You're right. I was asking for a prediction regarding what the results will be after further analysis is completed.

In other words, I was challenging the experts regarding which predator species make the most use of abundant croaker. We'll be working on that part of the analysis starting today. Here's my prediction for the rank ordering of the four bioindicator predator species:

1. Gafftopsail Catfish
2. Spotted Seatrout
3. Redfish
4. Black Drum

I think reds and specks may be close. But in recent years, we've caught more gafftops than anything else when hooking up croaker for bait. Gafftops also are showing much more piscivory in the esturary over the past 5 years than they are traditionally known for.

[Duck Butter]

Originally Posted by MathGeek

LDWF has been kind enough to share all their fishery independent stock assessment data in Big Lake with us for the past five years. We're just digging into it with the intent to correlate it with our original relative condition factor data from our annual creel surveys where we have weighed and measured 1800 specks, reds, drum, and gafftops. The idea is to see which forage species in the food web are more strongly correlated with the predator species.

If a predator gets fat when there are lots of croaker, it suggests that predator species is more heavily dependent on croaker than other forage species which show little correlation with the plumpness of the predator.

Here is the CPUE for croaker from Jan-Jun for the past 5 years.

OK, experts, which bioindicator species (specks, reds, drum, or gafftops) will have its plumpness most strongly correlated with the croaker stock assessments?

Are you going to use the data from specks, reds, drums, etc that you collected during YOUR creel surveys, or data that LDWF has collected on those species?

There is a big difference

[MathGeek]

Originally Posted by Duck Butter

Are you going to use the data from specks, reds, drums, etc that you collected during YOUR creel surveys, or data that LDWF has collected on those species?

There is a big difference

Yes, our data is a lot better. We have larger sample sizes, and more accurate weight and length measurements yielding much lower uncertainties.

We've had occasion to compare our original creel survey data with state agencies on a number of occasions. The trends are always similar, but our sample sizes, measurement care, and uniform sampling window yields higher accuracy.

Only an idiot would suggest the 20 redfish LDWF measured from Jan-June 2015 would yield a condition factor estimate as accurate as the 86 redfish we weighed and measured in a 3 week window in May 2015. Similarly, their 15 gram weight measurement accuracy does not compare with our 2 gram uncertainty in weight measurements.

The other challenge with a lot of the LDWF weight measurements for the sport species (specks, reds, etc.) is that they weigh groups of fish rather than individuals. Knowing that a group of ten specks they measured on May 6, 2015 weighed 185 ounces is not near as useful or accurate for assessing fish plumpness as having all 10 weights individually with an accuracy of 2 grams. LDWF measured 50 specks in May 2015, which yields an uncertainty in plumpness of over 3%. We weighed and measured 173 specks in May 2015 yielding an uncertainty in average plumpness of about 0.5%.

[jpeff31787]

mathgeek, I guess you take some kind of ratio between length and weight to figure out "plumpness"? Just curious to how you do it. This assessment gets fairly in depth and confusing for the ones who just want to skim over the sciency part and go straight to results. lol

[mstulb]

I can tell you 2013 was a cold winter and one of the better big trout fall/winter/springs I have had, since 2007.


Lot of 7lb. fish with numerous 8lb fish and a few 9's.


Those big fish just have turned out like previous winters, last winter was the influx of fresh water and water temps not hardly getting into the 50's.


Historically when the water temp holds consistently in the 50's for days or weeks is when those bid sows push up to eat. This is just strictly on the data I keep on the trips we make.


This fall was a little irregular because the 5-6lb. fish were spread out and thin in areas they are holding in. There were a lot of 3-4lb. fish in these same areas we have fished since the late 90's

[MathGeek]

Originally Posted by jpeff31787

mathgeek, I guess you take some kind of ratio between length and weight to figure out "plumpness"? Just curious to how you do it. This assessment gets fairly in depth and confusing for the ones who just want to skim over the sciency part and go straight to results. lol

The simplest way to understand "relative condition factor" is to liken it to BMI (body mass index) in humans. There is a formula that accounts for "normal" increases in weight with increases in length.

Actually relative condition factor in fish is a bit simpler. For fish of a certain species caught at a certain time of year, there is a formula derived from measuring and weighing thousands of LA fish (same species and time of year) for what the fish of that length is expected to weigh. This is called the "standard weight".

The relative condition factor is the actual weight divided by the standard weight for the length. A fish that should weigh 2.00 lbs (from the length) but actually weighs 2.10 lbs (measured) has a relative condition factor of 1.05 (5% over the expected weight). Another fish of the same species and length would also be expected to weigh 2.00 lbs, but if it only weighs 1.80 lbs, the relative condition factor is 0.90 (10% under the expected weight).

If the fish of a given species are fat on average, they are eating well and not having high stress levels. If the fish are skinny, they are not eating so well (or may be stressed).

In past publications, we've shown that this measure of plumpness can be used to study competition between species with the same forage base as well as to quantify forage overlap between different species.

[Duck Butter]

Originally Posted by MathGeek

Yes, our data is a lot better.

Originally Posted by MathGeek

We have larger sample sizes, and more accurate weight and length measurements yielding much lower uncertainties.

We've had occasion to compare our original creel survey data with state agencies on a number of occasions. The trends are always similar, but our sample sizes, measurement care, and uniform sampling window yields higher accuracy.

Only an idiot would suggest the 20 redfish LDWF measured from Jan-June 2015 would yield a condition factor estimate as accurate as the 86 redfish we weighed and measured in a 3 week window in May 2015. Similarly, their 15 gram weight measurement accuracy does not compare with our 2 gram uncertainty in weight measurements.

The other challenge with a lot of the LDWF weight measurements for the sport species (specks, reds, etc.) is that they weigh groups of fish rather than individuals. Knowing that a group of ten specks they measured on May 6, 2015 weighed 185 ounces is not near as useful or accurate for assessing fish plumpness as having all 10 weights individually with an accuracy of 2 grams. LDWF measured 50 specks in May 2015, which yields an uncertainty in plumpness of over 3%. We weighed and measured 173 specks in May 2015 yielding an uncertainty in average plumpness of about 0.5%.

A creel survey is NOT in any way shape or form an accurate way to draw conclusions for the overall health of a fisheries or any species. It only shows what is being caught and does not show what is actually in the lake itself.

Only an idiot would suggest otherwise

[MathGeek]

Originally Posted by Duck Butter

A creel survey is NOT in any way shape or form an accurate way to draw conclusions for the overall health of a fisheries or any species. It only shows what is being caught and does not show what is actually in the lake itself.

Only an idiot would suggest otherwise

We've compared our creel survey data with fishery independent data many times, and there is never a significant difference between condition factors determined from angler catches and that from net sampling.

The peer-reviewers on our published papers also had no trouble accepting our results from several hook-and-line studies.

Also, the USGS conducted a study in Big Lake using hook and line to catch fish to assess condition in the same way we are. Are they idiots too?

Assessments of fish condition based on hook and line sampling are widely accepted in the fisheries science community.

There is just no evidence to support your biased claim that fish caught by hook and line are not a representative sample, and there is a lot of evidence refuting it.

[Duck Butter]

Originally Posted by MathGeek

We've compared our creel survey data with fishery independent data many times, and there is never a significant difference between condition factors determined from angler catches and that from net sampling.

The peer-reviewers on our published papers also had no trouble accepting our results from several hook-and-line studies.

Also, the USGS conducted a study in Big Lake using hook and line to catch fish to assess condition in the same way we are. Are they idiots too?

Assessments of fish condition based on hook and line sampling are widely accepted in the fisheries science community.

There is just no evidence to support your biased claim that fish caught by hook and line are not a representative sample, and there is a lot of evidence refuting it.

Please link the usgs study. I have asked for that at least ten times and you won't link If you are looking into fitness of an ecosystem you can't make accurate assumptions by simply looking at weight and length. You need to look at the age and sex I would be willing to bet the usgs study looked at sex s d age.

Also, where have you published the other studies
?

And did you figure in weir openings? Because you told us when weirs are open fish are skinnier

[MathGeek]

Originally Posted by mstulb

I can tell you 2013 was a cold winter and one of the better big trout fall/winter/springs I have had, since 2007.


Lot of 7lb. fish with numerous 8lb fish and a few 9's.


Those big fish just have turned out like previous winters, last winter was the influx of fresh water and water temps not hardly getting into the 50's.


Historically when the water temp holds consistently in the 50's for days or weeks is when those bid sows push up to eat. This is just strictly on the data I keep on the trips we make.


This fall was a little irregular because the 5-6lb. fish were spread out and thin in areas they are holding in. There were a lot of 3-4lb. fish in these same areas we have fished since the late 90's

Great observations. Thanks for sharing. Movement of the big trout is an area of study we haven't given much consideration to.

There was a telemetry study out of LSU a few years back which studied movement.

We also see loooong, older females caught every month of the year, but in the warmer months they are not usually as heavy, because fish have much higher energy requirements when the water is warm.