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Science behind size limits?

Old 06-24-2019, 05:38 PM
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Default Science behind size limits?

I assume that size limits are set to ensure that every fish reaches the age to spawn? To me...that would make sense.
Can someone offer any insight into this?
Thanks
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Old 06-24-2019, 05:45 PM
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Originally Posted by homeby51 View Post
I assume that size limits are set to ensure that every fish reaches the age to spawn? To me...that would make sense.
Can someone offer any insight into this?
Thanks
in most cases that is correct, in other cases slot limits can be used to remove an over population of smaller fish that compete for food from larger breeder fish. Many limits are based on several factors from age to spawn, growth time frames, fishing pressure, environment, etc... not one answer fits all as it will depend on many factors.
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Old 06-24-2019, 06:11 PM
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Originally Posted by homeby51 View Post
I assume that size limits are set to ensure that every fish reaches the age to spawn? To me...that would make sense.
Can someone offer any insight into this?
Thanks
Your gonna be up all night.

It is very complicated for what they know to set limits. Specie, growth rates, harvest rates all play a roll as well as many other factors they have to guess at as managers.

Plenty of info out there but is very specie dependent and confusing to understand.

I have participated in many programs over the years "Snook, Tarpon" and read countless data and for the most part am more confused than I was many years ago.

I could tell you about what is being seen in Gag Grouper in the GOM right now and you would scratch your head and change the way you fish. But, That ain't my job and just going on info from people I trust.

From what I'm hearing the average fisherman has never caught a male gag inside of 240 feet of water. Male gags are for the most part over 20 lbs. "true rusty bellies". The fish we harvest at 24 to 32 inches are all females. Think about that.

Lots of stuff yet to be discovered even with some of the junk science floating around that refuses to use common sense.
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Old 06-25-2019, 05:23 AM
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What got me thinking was the South Atlantic Yellowtail. They allow tiny YT to be caught (12 inches) which seems too small to me. The Charter Boats have taken it upon themselves to not keep any under 14".
I generally am OK with raising the size limits because I figure then the result would be an increase in size of the average fish caught...but I know I am probably not right as there is much more in play.
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Old 06-25-2019, 06:34 AM
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Science doesn't always play a role in setting fish size limits. Historical size limits (throw the little ones back so they can grow) and politics (we don't want to piss off the fisherman too much or wipe out commercial interests) often play a large role. But science says the following:

1. Allowing the take of smaller fish has less of an impact on the population than taking larger fish. That's because the natural mortality rate of the smaller ones is higher anyway. So a larger portion of that size class can be removed before the overall population is severely affected.

2. Allowing large fish to be taken has more of a negative impact on the population because these are the most effective spawners in most cases. Their natural mortality is lower and they usually produce more and healthier eggs.

3. Setting size limits that are intended to allow fish to spawn once before they are taken reduces the average size of the fish in the population. This has been shown many times in both laboratory and field situations. Protecting smaller fish while allowing the take of large ones selects for the ones that sexually mature early. Once fish start to reproduce they put more energy into gamete production rather than growth. Early maturation is controlled in part by genetics. So over time, you end up with a population of smaller fish that spawn before they are under fishing pressure.

4. Shutting down a fishery during spawning season has less of an effect on the population than you might think. That's because fish typically produce far more eggs and fry that can be supported by the environment. So in a statistical sense, it makes little difference when fish are removed from a population. Exceptions to this are species that are density dependent aggregation spawners like sheepshead and gags. If aggregations are fished too heavily, the numbers are reduced to where spawning either does not occur or it is ineffective.

5. Slot size limits work in many situations where C&R mortality is low. Slots get around the problem of removing the largest fish from the population so the genetics for later maturation are protected. So you end up with more big fish. Larger spawners are also better at sustaining the population size than smaller ones. Slots don't work for all species, however. Mortality is high for deep water species. Don't be too encouraged by good survival rates for tagged fish that were caught deep and released by professional fisheries people. These guys know how to release fish correctly. The average angler does not in most cases. So a slot size limit can result in unintended high mortality as fishermen cull through protected size fish in order to box the larger or smaller ones.

The red snapper recovery plan is designed to result in a population with a substantial number of 20+-year-old fish. These fish are mostly found in deep open bottom areas where there is less fishing pressure. They have been shown to produce many more and healthier eggs than smaller individuals. So they should be more effective at sustaining a population that can withstand higher fishing pressure.
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Old 06-25-2019, 08:43 AM
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Open red snapper year round but limit it to a slot size like snook and limit it to 1 per person. I believe regulations on certain fish negatively effect populations of other fish. For example, I rarely catch Mangrove snapper anymore in areas I used to catch several. The red snapper have taken over these areas.
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Old 06-26-2019, 05:49 AM
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Originally Posted by DocStressor View Post
Science doesn't always play a role in setting fish size limits. Historical size limits (throw the little ones back so they can grow) and politics (we don't want to piss off the fisherman too much or wipe out commercial interests) often play a large role. But science says the following:

1. Allowing the take of smaller fish has less of an impact on the population than taking larger fish. That's because the natural mortality rate of the smaller ones is higher anyway. So a larger portion of that size class can be removed before the overall population is severely affected.

2. Allowing large fish to be taken has more of a negative impact on the population because these are the most effective spawners in most cases. Their natural mortality is lower and they usually produce more and healthier eggs.

3. Setting size limits that are intended to allow fish to spawn once before they are taken reduces the average size of the fish in the population. This has been shown many times in both laboratory and field situations. Protecting smaller fish while allowing the take of large ones selects for the ones that sexually mature early. Once fish start to reproduce they put more energy into gamete production rather than growth. Early maturation is controlled in part by genetics. So over time, you end up with a population of smaller fish that spawn before they are under fishing pressure.

4. Shutting down a fishery during spawning season has less of an effect on the population than you might think. That's because fish typically produce far more eggs and fry that can be supported by the environment. So in a statistical sense, it makes little difference when fish are removed from a population. Exceptions to this are species that are density dependent aggregation spawners like sheepshead and gags. If aggregations are fished too heavily, the numbers are reduced to where spawning either does not occur or it is ineffective.

5. Slot size limits work in many situations where C&R mortality is low. Slots get around the problem of removing the largest fish from the population so the genetics for later maturation are protected. So you end up with more big fish. Larger spawners are also better at sustaining the population size than smaller ones. Slots don't work for all species, however. Mortality is high for deep water species. Don't be too encouraged by good survival rates for tagged fish that were caught deep and released by professional fisheries people. These guys know how to release fish correctly. The average angler does not in most cases. So a slot size limit can result in unintended high mortality as fishermen cull through protected size fish in order to box the larger or smaller ones.

The red snapper recovery plan is designed to result in a population with a substantial number of 20+-year-old fish. These fish are mostly found in deep open bottom areas where there is less fishing pressure. They have been shown to produce many more and healthier eggs than smaller individuals. So they should be more effective at sustaining a population that can withstand higher fishing pressure.
Good read. Thanks.
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Old 06-29-2019, 05:41 PM
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I read somewhere, long ago that when the females get older, they produce more eggs, but less of them hatch, due to the age of the mother. I think this was talking about striped bass. Does anyone know if this is common in other fish too? If so, would it make sense to let the prime breeders live, but allow taking fish below that age and above that age?
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Old 06-29-2019, 07:11 PM
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Originally Posted by homeby51 View Post
I assume that size limits are set to ensure that every fish reaches the age to spawn? To me...that would make sense.
Can someone offer any insight into this?
Thanks
No, only marketable size matters. They don’t care whether they spawn or not. After releasing many undersized flounder and was driving home a local restaurant had a sign that said baby flounder special.
I sh** you not.
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Old 06-30-2019, 09:44 AM
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So explain how a 47" swordfish is legal
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Old 06-30-2019, 11:34 AM
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If there was any science to it you would only be allowed to keep the little ones.
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Old 06-30-2019, 01:20 PM
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Originally Posted by BIGnUGLY View Post
If there was any science to it you would only be allowed to keep the little ones.
This is probably closer to the truth than most of us would like to admit. While not "sporting" a reasonable bag limit of fish under a certain size (with no minimum size) and perhaps one larger fish over that size as a trophy would be better for many species' health than most of our current regulations. This type of regulation already exists with some fish like Cubera Snapper where it's 10 per harvester between 12 and 30 inches and then two fish over 30 inches with the smaller fish part of your snapper aggregate and the larger two not part of it.

Personally I think there's a lot of room for improvement through a bottom up approach to fisheries management where we look at the carrying capacity of a given ecosystem and do our best to maximize that whether it's through habitat preservation, artificial reefs, or protection for forage fish so that more of our game fish are reaching maturity.
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Old 06-30-2019, 01:43 PM
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Originally Posted by BIGnUGLY View Post
If there was any science to it you would only be allowed to keep the little ones.
WHAT?

Some specie of little ones are not mature enough to breed. Taking them out before they ever have a chance to reproduce is not the answer.

If we ate our young before they became sexually active we wouldn't have an over fished issue anywhere.

Yep, take them out before their nuts drop or the girls can make an egg. It certainly will cut down on the fertile adults that are over harvesting the fishery on the human side.
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Old 07-01-2019, 05:10 PM
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Originally Posted by 20biminitwist View Post
WHAT?

Some specie of little ones are not mature enough to breed. Taking them out before they ever have a chance to reproduce is not the answer.

If we ate our young before they became sexually active we wouldn't have an over fished issue anywhere.

Yep, take them out before their nuts drop or the girls can make an egg. It certainly will cut down on the fertile adults that are over harvesting the fishery on the human side.
Don't get your panties in a bimini. The big ones produce 10-100 times more eggs than the little ones. And it's funny that you say killing them before their nuts drop because on grouper and sea bass they are all female until they get big enough, and then the big females turn into males. It sounds counterintuitive but if we could only keep under 15" grouper and red snapper there would be no closed season.
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Old 07-02-2019, 06:28 AM
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Originally Posted by BIGnUGLY View Post
Don't get your panties in a bimini. The big ones produce 10-100 times more eggs than the little ones. And it's funny that you say killing them before their nuts drop because on grouper and sea bass they are all female until they get big enough, and then the big females turn into males. It sounds counterintuitive but if we could only keep under 15" grouper and red snapper there would be no closed season.
That would be true because no one would want to target 2 fish under 15 inches as the limits would still be the same. Mortality rates for deep water released fish is fairly high so that will always be a factor.


I am well aware of the Grouper breeding process as it is being studied right now in the GOM. The biologist are still trying to figure out how and when male gag grouper and females interact. Most of the males they have studied have come from 240 feet of water or better as that is where the majority of the big rusty bellies live. My buddy did a research trip to the Steam boat lumps MPA with the FWC a few months back under special permit from NOAA. They caught nothing but Male rusty bellies. The thing that is puzzling them is the roe filled females they are catching are all 100 miles away from the males in 40 to 80 feet of water. The peak spawn is February and March.

Telemetry studies are showing a lot of the females travel very little through out the entire year. They obviously get together at some point. I have recovered quite a few tagged fished myself and they were all females and were caught very close to the original tag point 180 plus days later.

The concern is that there are not very many male gags out there. Technology with boats and gear are allowing the recreational harvest to increase on the male gags as compared to just 10 years ago.. I can remember when I was commercial fishing seldom seeing many rec boats out past 50 miles. There are plenty of boats today that can make the run to the 40 break in under 2 hours and many do. Sure, the commercial guys catch the big males but the quota and TAC is pretty limited on gags.

My panties are far from being tied in a Bimini. But, some of the data is getting them in a wad.
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Old 07-10-2019, 08:59 AM
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Originally Posted by 20biminitwist View Post
Your gonna be up all night.

It is very complicated for what they know to set limits. Specie, growth rates, harvest rates all play a roll as well as many other factors they have to guess at as managers.

Plenty of info out there but is very specie dependent and confusing to understand.

I have participated in many programs over the years "Snook, Tarpon" and read countless data and for the most part am more confused than I was many years ago.

I could tell you about what is being seen in Gag Grouper in the GOM right now and you would scratch your head and change the way you fish. But, That ain't my job and just going on info from people I trust.

From what I'm hearing the average fisherman has never caught a male gag inside of 240 feet of water. Male gags are for the most part over 20 lbs. "true rusty bellies". The fish we harvest at 24 to 32 inches are all females. Think about that.

Lots of stuff yet to be discovered even with some of the junk science floating around that refuses to use common sense.
Common sense isn't so common.
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Old 07-10-2019, 05:59 PM
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In some well-studied grouper populations, males and females “aggregate” into a huge spawning mass during certain tidal period. It was an absolutely astounding sight to behold, for sure. However, the sharks had also figured it out, and the carnage was impressive, but apparently the process has been successful for both groupers and sharks for a long time.
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