Author Topic: The Science of Catch and Release by Dr Warren Potts  (Read 2914 times)

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Offline REEFMAN

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The Science of Catch and Release by Dr Warren Potts
« on: September 09, 2016, 12:42:25 PM »
Brilliant article!
by Dr Warren Potts
Department if Icthyology and Fisheries
Rhodes University

The Science of Catch and Release

Now is not a good time to go fishing... said nobody... EVER!!

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Offline FishStyx

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #1 on: September 09, 2016, 12:55:50 PM »
Thanks Reefs. Fantastic info there. Should be required reading for all.


One little anomaly... Circle vs J... I have no idea how they managed to get a higher incidence of foul hooked on a circle than a J. I don't even know how you could foul with a circle.  :dunno:
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Offline REEFMAN

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #2 on: September 09, 2016, 02:07:53 PM »
The foul hooking with a circle happens when the knot is tied to the circle without using the snell. Not using a Snell knot on a circle defeats the whole purpose of a Circle.

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #3 on: September 09, 2016, 03:24:55 PM »
Its some interesting stuff...

Offline travelmember

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #4 on: September 09, 2016, 05:44:24 PM »
I presume this was part of a presentation to a group of SA shore anglers rather than an informed scientific paper for discussion and as such it is admirable - both in content and in the desire to educate.


However I see zero new evidence in this paper - it seems to be a collection of other studies and much of what is presented is old.
With the advent of PSAT we have a much better idea of post survival rates on a range of species. Also there have been (as one example) more recent scientific studies done on how long certain species can survive out of water and of the corresponding mortality rates. (Schlenker, 2015).
I also question some conclusions, ie slide 6, Commercial fisheries do not target or catch similar species....and then the author uses hake as an example. What about inshore yellowtail by commercial lineboats and by the treks. One trek last year took 12 tons (according to the buyer who paid for it) of spawning stock in an afternoon. What about the atlantic bluefin that used to be caught in False Bay. Their decline was not due to recreationals.
Further on the same slide it is stated that the recreational catch is 47.1 billion fish....is this globally? The quantity of global commercial landings is 86 million tonnes. So the numbers don't make sense somewhere.


The study also taints recreationals by stating that we don't stop killing when a species is under threat. So who mandated the compulsory use of circle hooks by Atlantic longliners and by tournament fisherman to stop the killing of billfish. Likewise the closed seasons in use worldwide for various species that have been angler driven. If you are exclusively talking SA, then 100% agreed and it is shameful how poor our national bodies are at lobbying effectively.


Another bone of contention is the actual handling of fish out of water and the supporting of their organs - this is a key player in post release mortality and one that could be covered in more depth.


Some really interesting studies have also been done in the last 2 years of fight times and post release mortality. To date there has been no correlation that a longer fight time (within reason by using the correct tackle, generally accepted to be less than a 3:1 ratio) = higher mortality. In fact in 4 studies, the converse has been shown by landing green fish (as the author points out) that damage themselves. Likewise that heat contributes to mortality. It was however proven that the longer the fight in warmer water the longer the released fish spent in cooler water to recover (at depth)


Also recent studies have added substance to the J vs circle debate. Figures vary between (low study and high study) 14 and 38% mortality on J's, versus 2-14% on circles.


In all honesty, whilst this is a great presentation, I think the time for anglers in SA to police themselves is long past. DAFF needs a complete overhaul, our resource management needs to be re-evaluated and we need a new, comprehensive management and policing platform to ensure sustainability in most of our sectors - especially R&S and inshore boating.


We need blanket bans on some species, slot limits and seasons on others and effective policing - and we need them quickly.


Sjoe, and I need a wine now I've had a whine.


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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #5 on: September 09, 2016, 06:32:22 PM »
I presume this was part of a presentation to a group of SA shore anglers rather than an informed scientific paper for discussion and as such it is admirable - both in content and in the desire to educate.


However I see zero new evidence in this paper - it seems to be a collection of other studies and much of what is presented is old.
With the advent of PSAT we have a much better idea of post survival rates on a range of species. Also there have been (as one example) more recent scientific studies done on how long certain species can survive out of water and of the corresponding mortality rates. (Schlenker, 2015).
I also question some conclusions, ie slide 6, Commercial fisheries do not target or catch similar species....and then the author uses hake as an example. What about inshore yellowtail by commercial lineboats and by the treks. One trek last year took 12 tons (according to the buyer who paid for it) of spawning stock in an afternoon. What about the atlantic bluefin that used to be caught in False Bay. Their decline was not due to recreationals.
Further on the same slide it is stated that the recreational catch is 47.1 billion fish....is this globally? The quantity of global commercial landings is 86 million tonnes. So the numbers don't make sense somewhere.


The study also taints recreationals by stating that we don't stop killing when a species is under threat. So who mandated the compulsory use of circle hooks by Atlantic longliners and by tournament fisherman to stop the killing of billfish. Likewise the closed seasons in use worldwide for various species that have been angler driven. If you are exclusively talking SA, then 100% agreed and it is shameful how poor our national bodies are at lobbying effectively.


Another bone of contention is the actual handling of fish out of water and the supporting of their organs - this is a key player in post release mortality and one that could be covered in more depth.


Some really interesting studies have also been done in the last 2 years of fight times and post release mortality. To date there has been no correlation that a longer fight time (within reason by using the correct tackle, generally accepted to be less than a 3:1 ratio) = higher mortality. In fact in 4 studies, the converse has been shown by landing green fish (as the author points out) that damage themselves. Likewise that heat contributes to mortality. It was however proven that the longer the fight in warmer water the longer the released fish spent in cooler water to recover (at depth)


Also recent studies have added substance to the J vs circle debate. Figures vary between (low study and high study) 14 and 38% mortality on J's, versus 2-14% on circles.


In all honesty, whilst this is a great presentation, I think the time for anglers in SA to police themselves is long past. DAFF needs a complete overhaul, our resource management needs to be re-evaluated and we need a new, comprehensive management and policing platform to ensure sustainability in most of our sectors - especially R&S and inshore boating.


We need blanket bans on some species, slot limits and seasons on others and effective policing - and we need them quickly.


Sjoe, and I need a wine now I've had a whine.



Some very valid points (clap)    :+ cred:

Looks like this is an "old" presentation to the RASSPL community... it's very good but as you pointed out, it needs to be updated. I applaud the author for the effort. Scientists tend to stick to their scientific world and forget that there must be a higher purpose of doing science apart from simply publishing papers. Communicating the results of scientific research  to the general public should be mandatory to every scientist!!!
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Offline Trevour

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #6 on: September 09, 2016, 07:54:16 PM »
Our world needs more of you travelmember.

Offline Visenvryheid

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Re: The Science of Catch and Release by Dr Warren Potts
« Reply #7 on: September 20, 2016, 05:51:40 PM »

""We need blanket bans on some species, slot limits and seasons on others and effective policing - and we need them quickly.""

Hear hear..as well as that trekking of spawning fish, disgraceful as far as I'm concerned. I'm sure the fish buyer is no fool and sees the implications for future stocks. Trekking in general gets me riled but I'll let that dog lie for now..Ja hear hear mate..