NIWA BAROTRAUMA LATEST
Printed From: The Fishing Website
Category: Saltwater Fishing
Forum Name: The Briny Bar
Forum Description: The place for general chat on saltwater fishing!
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=137353
Printed Date: 01 Dec 2023 at 5:32pm
Topic: NIWA BAROTRAUMA LATEST
Posted By: Pcj
Subject: NIWA BAROTRAUMA LATEST
Date Posted: 18 Dec 2022 at 3:37pm
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Niwa doesnt say depth,appears to be under 20m. https://www.youtube.com/watch?v=eOA7GTXz5xY" rel="nofollow - https://www.youtube.com/watch?v=eOA7GTXz5xY Still think the Aussie video is more realistic https://www.fishingworld.com.au/news/video-barotrauma-in-golden-snapper" rel="nofollow - https://www.fishingworld.com.au/news/video-barotrauma-in-golden-snapper Remember both species are members of the bream family,NZ does not have true snapper ------------- Amateur's built the ark. Professional built the Titanic |
Replies:
Posted By: brmbrm
Date Posted: 19 Dec 2022 at 6:31pm
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It would be useful if they could present data about survival percentages, including related to whether the fish is obviously blown or just looks OK. Also what depth?All that affects whether to return legal fish. I normally keep anything legal that is obviously blown, but if they had an 80%, 50% 20% chance of survival I would think again maybe |
Posted By: lawabidingpoacher
Date Posted: 19 Dec 2022 at 8:01pm
| I have a simple process in my fishing , I use a larger circle hook than most and I keep every thing thats legal ! I catch very few undersize , if any , and when I have my limit I go home ! simple. |
Posted By: MB
Date Posted: 19 Dec 2022 at 9:01pm
| The study is a good start, only preliminary data released so far. Most of my time is spent lure fishing in 40 metres plus. I know survival isn't going to be high, so catch the snapper I need to eat and then either go home, or target kingfish. Catching dozens of fish and releasing them holds no appeal. |
Posted By: Fish Addict
Date Posted: 19 Dec 2022 at 10:45pm
| What I find a little surprising in the first (NZ) vid is that there is no mention of winding your fish up SLOWLY. In-fact one of the anglers seems to be going rather hard on a small fish. It's not a race to the top. Fish survival rates increase with a slow retrieve and even a short decompression stop / pause 6-10m down is recommended to further increase survival rates. |
Posted By: MB
Date Posted: 20 Dec 2022 at 12:42am
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There's a lot more that could be investigated, but it is a start. After catching hundreds (if not more) snapper from 40+ metres, it's clear to me that the bigger fish do less well and it's not just related to duration of fight. Unfortunately, the bigger fish are more likely to come up "blown".
It's a sensitive subject, everyone wants to believe they're right, so we'll see what the data shows. How many times do you read on social media that the big one was "released to fight another day"? Well intentioned, but my gut feeling is that if the fish was caught in deep water, they are just making shark food and then going on to remove a bunch of pannies from the fishery. Surely better to have just kept the big fish and stop fishing for snapper? |
Posted By: Fish Addict
Date Posted: 20 Dec 2022 at 3:50pm
Agree. The practice of venting and the use of release weights are akin the placing the ambulance at the bottom of the cliff imo. It would be more proactive to minimize the effects of barotrauma in the first place. I don't think there is any argument that barotrauma is caused by rapid changes in pressure. If you wind in slowly, you minimize those rapid pressure changes. We have found it works well with some of our local species over here, especially those that are more susceptible to effects of barotrauma than snapper.
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MB wrote:Posted By: Pcj
Date Posted: 20 Dec 2022 at 4:21pm
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Fish Addict
Date Posted: 20 Dec 2022 at 4:43pm
Yes venting with a hollow instrument is what I was referring to. Like this: http://www.ultimatefishing.tv/home/video/217/how-to-vent-a-fish" rel="nofollow - https://www.ultimatefishing.tv/home/video/217/how-to-vent-a-fish If this is now illegal in NZ then I stand corrected. |
Posted By: Pcj
Date Posted: 20 Dec 2022 at 5:29pm
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From Tindale Marine research Note: under the Animal Welfare Act that venting is illegal in New Zealand unless carried out by a vet. And thats where Watson come unstuck. 2.20 shows venting https://www.youtube.com/watch?v=912lMwDQOjI" rel="nofollow - https://www.youtube.com/watch?v=912lMwDQOjI ------------- Amateur's built the ark. Professional built the Titanic |
Posted By: MB
Date Posted: 20 Dec 2022 at 5:36pm
| My opinion on venting. It may allow a fish to swim back down, but it won't reverse tissue/organ damage. |
Posted By: Pcj
Date Posted: 20 Dec 2022 at 6:19pm
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: smudge
Date Posted: 20 Dec 2022 at 8:50pm
Fair point MB (RIP Catchelot) but in my opinion fish are hardy creatures. I've caught fish with all manner of injuries but to be fair barotrauma is harder to identify. ------------- Best gurnard fisherman in my street |
Posted By: MB
Date Posted: 20 Dec 2022 at 10:10pm
It's pretty odd that you can bridle rig a livebait through the eye sockets, but you can't vent a fish that you're intent on releasing!
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Posted By: Pcj
Date Posted: 22 Dec 2022 at 1:01am
https://www.facebook.com/paul.carnahan.58?__cft__%5b0%5d=AZWohJNx0v9x_YCxJnRqjXCKFIWrWhtKud4vb9tHJk2eM8FUcw8HypiJCSEPVS6oIibAY7Wt6I7rdmfwpXLqKh-OcpVKV9QEcjku4PZMj8o63ajKSmduRk9s_VWW_DeZHV4&__tn__=R%5d-R" rel="nofollow -
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Posted By: Fish Addict
Date Posted: 22 Dec 2022 at 1:17pm
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For interest's sake I sent an email to MPI asking them whether the practice of venting was in breach of the NZ Animal Welfare Act. The following was their response: "Kia Ora Alan, Thank you for your email regarding venting of fish with barotrauma. Our response is based on the assumption that your query is in the context of fishing for recreational purposes. Under https://www.legislation.govt.nz/act/public/1999/0142/latest/DLM6475334.html" rel="nofollow - it is an offence to wilfully or recklessly ill-treat an animal in a wild state. However, if a prosecution for wilful or reckless ill-treatment is brought, the conduct in question is defensible if the court can be satisfied that it is part of a generally accepted practice in New Zealand for the hunting or killing of an animal in a wild state. Our understanding is that venting is an accepted practice used to treat barotrauma, in order to mitigate pain and distress and increase survivability of the fish. Therefore, our assessment is that correctly venting fish that are suffering from barotrauma is unlikely to be in breach of the Act. Some further resources and options for your consideration: We recommend every fisher uses the best tools and practices at their disposal to help ensure fish survival rates and protect animal welfare."
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Posted By: Pcj
Date Posted: 22 Dec 2022 at 1:39pm
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Fish Addict
Date Posted: 22 Dec 2022 at 2:31pm
I would like to think so. It came from: "Animal Welfare Team Ministry for Primary Industries - Manatū Ahu Matua | Charles Fergusson Building, 34-38 Bowen Street | PO Box 2526 | Wellington 6140 | New Zealand Web: http://www.mpi.govt.nz/" rel="nofollow - Dare I use the words 'common sense', but it is the sensible approach. |
Posted By: waynorth
Date Posted: 22 Dec 2022 at 2:43pm
Science can be frustrating. If you don't like what one expert says, go find another expert. Or in this case bypass the issue by changing the rules perhaps - keep the first 7 snapper you catch regardless of size. Does Venting Promote Survival of Released Fish? Feature: Fisheries Management Abstract: Fishes captured and brought to the surface by commercial and recreational fishers may suffer a variety of injuries that collectively are referred to as barotrauma. To relieve barotrauma symptoms, particularly those associated with an expanded swim bladder, some anglers deflate, or vent, the swim bladder (or body cavity when the swim bladder has ruptured) of fishes before releasing them. I compiled 17 studies that assessed the potential benefits of venting in 21 fish species and 1 composite group. These studies provided 39 sample estimates that compare survival (N = 18) and recapture rates (N = 21) of vented and unvented fish. I used relative risk to summarize results of individual studies, which allowed me to combine results from experimental and capture-recapture studies. Overall, there was little evidence that venting benefited fish survival. Venting was equally ineffective for freshwater and marine fishes and its efficacy was unaffected based on whether venting was performed by fishery biologists or anglers. The effects of venting did vary with capture depth: venting was slightly beneficial to fish captured from shallow waters, but appeared to be increasingly harmful for fish captured from progressively deeper waters. The available evidence suggests that venting fish should not only be discouraged by fishery management agencies, but given the possibility that venting may adversely affect survival of fish captured from deep water, this practice should be prohibited, rather than required by regulation. Gene R. Wilde Wilde is professor of fishery ecology at the Department of Biological Sciences, Texas Tech University, Lubbock. He can be contacted at [email protected]. ------------- treat fish like fish |
Posted By: The Tamure Kid
Date Posted: 22 Dec 2022 at 4:13pm
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very interesting thread, guys. NZ Fishing News has covered this topic pretty well in the past few years, as research comes up. I know there are charter skippers who don't let their clients return fish during workup season, and other top fishos who only fish in less than 20m so they can return big snaps.
I have been watching a few Facebook vids posted by legendary Houhora charter skipper Rob Parker, and they get most of their snapper dragging softbaits in 35-40+ metres.Almost every trip they are getting 20+lb snapper which come up clearly blown. The fishos or Rob often say "that's a real fattie" or similar. Unfortunately, they appear to be full of air, not scallops... I've fished there in my own boat and out of that depth being embolised is inevitable with the big fish the area is famed for (as someone said in the thread, the smaller snapper don't seem to suffer - at least as obviously). I tried bringing fish up slowly, but that didn't seem to make a difference. I think combined with the huge effort the big fish make during a typical fight, that they just can't survive. But Rob Parker often returns them - off camera. Maybe after a quick vent or similar? Fingers crossed at least some make it. I make a conscious choice to only do that a couple of times on a Far North trip. I know that it's likely what we catch will end up in the lodge smoker. The rest of the trip we're fishing in 8-15m and release heaps of fish. Sometimes I hear an angler say, on releasing one that's a bit iffy: "they've got a better chance than if I iki them" or similar. I guess that's correct, but if it's 100% dead, versus 90% dead, that's not much difference. Hopefully research will show what the story is. Interesting what FishAddict says re drop weights. I've seen that a bit on Australian YouTube channels, and I thought it looked like a good solution... |
Posted By: Pcj
Date Posted: 22 Dec 2022 at 4:27pm
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https://www.fishing.net.nz/fishing-advice/general-articles/dealing-with-barotrauma%20" rel="nofollow - https://www.fishing.net.nz/fishing-advice/general-articles/dealing-with-barotrauma
Interesting read,well covered.But Sam Mossman makes most sense. Regarding venting, Sam says he has tried it with large bore needles obtained from a veterinary supplies outlet years ago. “I found it was moderately effective against barotrauma so the fish can get down again, but not necessarily a long-term survival tool. The Americans made it compulsory in some areas for a while, then, with more research, quickly did an about face, removing the regulation.” Sam had hoped that venting might be the answer to deep water issues, but that does not seem to be the case. “I don’t use venting needles anymore.” Seems simple to me fish and keep or dont fish ------------- Amateur's built the ark. Professional built the Titanic |
Posted By: MB
Date Posted: 22 Dec 2022 at 5:03pm
| I would have though that if you're determined to release (a probably dead) fish that can't descend, it would be preferable to use a drop weight rather than stick a needle in to it's vital organs. |
Posted By: Alan L
Date Posted: 22 Dec 2022 at 6:35pm
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It has always puzzled me how the swim bladder is supposed to work again after you stick a hole in it?? How quickly is it supposed to repair itself? If at all. Alan
------------- Legasea Legend member |
Posted By: The Tamure Kid
Date Posted: 22 Dec 2022 at 6:49pm
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I agree, MB. Particularly with the fungal issue affecting Hauraki Gulf snapper at the moment, any kind of needle through the skin and internal cavities is likely to invite infection. As in my post, I thought the release weights used in Australia looked like a useful option. I presume the decompression chambers used with sick divers would act in a similar way in terms of relieving symptoms? There's a lot of pressure (no pun intended) on anglers to release big "breeders", so people are often trying to do what they're told is the 'right thing'. Every time someone posts a big snap pic on Facebook, people jump in to say "I hope you released it" or similar. There may be no point doing that - better to use the fish fully for the family - but doesn't stop the comments. What about the mortality caused by people catching under-sized fish on swallowed J hooks and releasing them (even out of shallow water); or poor handling of fish - dragged up on to sand or rocks or concrete wharf; lowered onto the floor of an ali boat that's hot enough to fry and egg; innards squeezed; gills touched; or donked on the stern on the way back into the water... I suspect some of those are bigger issues in terms of mortality than people releasing fish after venting? |
Posted By: Fish Addict
Date Posted: 22 Dec 2022 at 7:52pm
Tagging of fish suffering from the effects of barotrauma in WA have shown that fish released using either release weights or venting have survived to be recaptured. The release weight is the preferred method. For some 10-15years it has been mandatory for WA rec anglers to have a release weight onboard.
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Posted By: Kandrew
Date Posted: 22 Dec 2022 at 8:10pm
| The release weight looks like a great idea, might look into making one. |
Posted By: The Tamure Kid
Date Posted: 22 Dec 2022 at 8:36pm
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Nice one Kerry. If you type 'Release weight fishing western australia' into Google there are some good images of designs for 'pink snapper' (cousin of our snapper) and dhufish etc. Looks to be basically a tear drop sinker with a heavy wire coming out of the top which acts as the temporary hook, and the loop to attach the line to.
The two guys I've seen doing it use a heavy line on a hand spool. |
Posted By: MB
Date Posted: 22 Dec 2022 at 8:55pm
Yep, it's not a good trend in my opinion, also pushed by certain fishing TV presenters.
I would say the average standard of fish handling is appalling. Seen it first hand on mate's boats (yes, I did say something) and charters. Even some of the fish handling on mainstream TV shows is bad. I don't think they are bad people, just clueless. I'm not perfect, but do my best. If you don't have respect for the fish you catch, at least try to preserve the fishery for the next time you go out.
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Posted By: Pcj
Date Posted: 29 Dec 2022 at 11:17pm
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Maybe NIWA video was just a teaser as final results out mid 2023,meanwhile on fsheries web site. https://www.mpi.govt.nz/news/media-releases/careful-fish-handling-can-help-support-sustainable-fisheries/?fbclid=IwAR2QmiLpxnjy1vvCBQ5R_m9ZjevKU2y5XGsGsvDQEwXN5ZWHJb0CdbhPN3k%20" rel="nofollow - https://www.mpi.govt.nz/news/media-releases/careful-fish-handling-can-help-support-sustainable-fisheries/?fbclid=IwAR2QmiLpxnjy1vvCBQ5R_m9ZjevKU2y5XGsGsvDQEwXN5ZWHJb0CdbhPN3k
Final survey results are expected to be available by the middle of next year. The results will give anglers a better understanding of the consequences of throwing fish back, so there’s less unseen mortality ------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Pcj
Date Posted: 06 Sep 2023 at 12:36pm
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Still work in progress. Brief summary from email received today.
Hi Paul, Many thanks for your query about the snapper release
mortality experiments conducted in April and October/November 2022. The work has
been completed, and was presented to a Fisheries New Zealand Science Working
Group in June, where it was accepted, but unfortunately the final report is not
yet available for release. However, I am happy to provide you with a summary of
the findings below. Hope this is helpful. Experiments were conducted in April and October/November
2022. In April control fish were caught from a commercial longline
set in shallow (6-12m) water depth (specifically chartered for the study).
Treatment fish were caught by recreational fishers, marked (fin clip) to
identify hook site (lip, foul, gut) and put in holding nets, a different net
used depending on the day and depth of capture (<15m, 15-25m, 26-40m). The
holding nets were monitored regularly during the experiment to check for
mortalities. The same process was repeated in October/November, but as no
control fish died in April, no control was used to allow for more treatment
fish. A total of 960 treatment fish were included in the
experiment. The data were used to examine the probability of a released
fish dying, and the survival time (how quickly they die). For the probability of dying, there was no detectable effect
of season (April v October/November) or fish size, but hook site and capture
depth were important. The probability of death was lowest for lip-hooked fish in
shallow water. This probability increased when fish were foul-hooked. For
gut-hooked fish, the probability of death was higher than that for lip-hooked or
foul-hooked fish. This was most pronounced in 5 –35 m depth. However, by 40 m
depth the probability of death in foul-hooked fish was very similar to that of
gut-hooked fish.
Predicted probability of death in treatment snapper
associated with the capture depth (m) for various lip-, foul- and gut-hooked
fish. Error bands indicate the 95% confidence intervals. Survival time was also affected by hook site and capture
depth, but the analysis did not suggest the experiment missed mortality by not
monitoring long enough. 81% of mortalities took place within the first three hours
after capture and 95% of the mortality took place within the first 24 hours. All
fish were observed for at least 3 days, and some for six days. This study has provided some very useful information on the
probability of released snapper surviving, depending on hook site and capture
depth. Our next step is to survey recreational fishing activity to understand
the number of fish being released, and the nature of their
capture. Cheers Ian Dr
Ian Tuck Principal
Science Advisor, Aquatic Environment Fisheries
Science and Information | Fisheries New Zealand – Tini a Tangaroa Ministry
for Primary Industries | MPI Centre, 17 Maurice Wilson Avenue, Mangere
2022 PO
Box 53030 | Auckland | New Zealand Tel:
+64 9 909 8624 | Mobile: +64 (0)21 0227 0176 | Web: http://www.mpi.govt.nz/" rel="nofollow -
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Fish Addict
Date Posted: 06 Sep 2023 at 5:49pm
| Forgive me for being a bit dim but I am not understanding the MPI Predicted Probability of Death graphs that Pcj has posted above. The scale of the Probability of death axis has me puzzled (0 - 1.0). If you look at the hook site = Lip graph, is it suggesting that around 30% of the snapper caught from a capture depth of 25m will die, and yet a lesser number, around 20% caught from a capture depth of 40m will die? |
Posted By: murrayt
Date Posted: 06 Sep 2023 at 8:16pm
| Yes that’s how I interpret the graph. |
Posted By: krow
Date Posted: 06 Sep 2023 at 8:19pm
THANK YOU MUCH Pcj |
Posted By: MB
Date Posted: 06 Sep 2023 at 9:37pm
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Thanks Pcj for posting. I assume the Y-axis on the graph is probability where 1.0 means all the fish would be expected to die? Bell shaped curve for depth of capture vs probability of dying for lip-hooked fish is odd. Definition of foul hooked must have been broad, i.e. fish hooked anywhere outside the lip. Data is all over the place, but I think we can broadly agree that gut hooking and deep water result in reduced survival?
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Posted By: Fish Addict
Date Posted: 07 Sep 2023 at 3:22pm
I agree, the data is all over the place. It will be interesting to see the final report. Any modeling is only as good as the accuracy of the raw data. If that's flawed it becomes a sh@t in, sh@t out exercise. There were clearly three scenarios; lip hooked, foul hooked and gut hooked. I wouldn't have thought sufficient numbers of foul hooked and gut hooked fish would have been captured for them to be categorized separately if circle hooks were used.
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Posted By: MB
Date Posted: 07 Sep 2023 at 9:21pm
You're correct, but an alternative explanation is that they haven't collected enough data. Scientists love that line because it keeps them employed!
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Posted By: kitno
Date Posted: 07 Sep 2023 at 9:47pm
It's as annoying as when someone claims to have a theory, but all they really have is a hypothesis. The difference is huge. ------------- Top 10 finish 2024 Grunter Hunter. |
Posted By: murrayt
Date Posted: 07 Sep 2023 at 10:21pm
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Confidence intervals for lip hooked fish look ok so should be reliable. Foul and gut hooked looks less robust.
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Posted By: Fish Addict
Date Posted: 07 Sep 2023 at 10:26pm
If the data and model are suggesting (as it would seem) that a gut hooked snapper captured from a depth of 40m has a 40% better chance of survival than a gut hooked snapper captured from a depth of 5m then either the data is lacking, or the model is flawed. Don't get me started on scientists, especially those of the climate variety. One of the biggest cons the world has ever seen, all thanks to the UN.
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Posted By: brmbrm
Date Posted: 08 Sep 2023 at 10:30am
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Thanks Pcj, that's very interesting. Yes, probability of 1 means death, 0 means zero mortality. I don't agree that the date is "all over the place". This is a statistical study, only 960 fish, no indication in the letter of how many in each group. The "confidence intervals" are sometimes wide, but they can be calculated using well-established statistical methods: a wide confidence interval normally means "not much data". (I also thought it interesting that "81% of mortalities took place within the first three hours....".) There seems to be some clear indications here. Gut hooked fish will almost certainly die, probably irrespective of barotrauma considerations: if you catch a legal one you should keep it. Lip hooked fish in shallow water likely live - successful return is possible, but in deeper water it looks like between a quarter and a third will die, presumably due to barotrauma effects. Don't forget they are just presenting what they measured: yes, the "bell-shape" for the lip-hooked in deeper water is odd, but is it a true reflection of what happens or just what happened in the sample they caught?
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Posted By: brmbrm
Date Posted: 08 Sep 2023 at 10:33am
Says someone typing on a computer, using the internet, mobile phone etc when they don't know how any of them work. Hilarious. (By the way, I am a now-retired scientist, still waiting for my first payment from the UN...) |
Posted By: Pcj
Date Posted: 08 Sep 2023 at 11:37am
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On the first page it does mention we maybe surprised.yep releasing is a feel good only legal keep it.
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Grunta
Date Posted: 08 Sep 2023 at 7:14pm
The points raised re handling are absolutely on the money as poor-handling techniques are undoubtedly a major factor in survival rates - damaged gills, etc. I'm not a fan of venting purely because the thought of some clown with a sharp needle taking a few wild stabs at the gut of a fish doesn't seem like it'll end well if you're on the receiving end. Maybe if you know what you're doing then it's an option but given the number of iki'd fish I've seen still flopping around in a chilly bin, the finesse and skill level possibly is beyond some people. Getting a snapper back to a depth where it can re-pressurise with a weight and a simple rig is easy and effective - we have one on the NZ Fishing News project boat which is essentially a 'puka weight on a handline and it works fine. The main reason I'll release a larger fish (when the depth and condition align for snapper in particular) is to look after the gene pool. Big healthy fish pass on big healthy fish genes and in my view that's a good option as we all want of more of those fish in our inshore fisheries don't we? ------------- Online... |
Posted By: krow
Date Posted: 08 Sep 2023 at 7:43pm
| I wonder with the gut hooked fish if they left the hook in there or ripped it out. I've caught a few with well rusted hooks still inside and they seamed to be doing well. Interesting for sure, tiz why I record and tag most of the ones I put back. |
Posted By: Pcj
Date Posted: 10 Sep 2023 at 1:13pm
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Grunta
Date Posted: 10 Sep 2023 at 7:07pm
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Hmm - well there certainly is such a thing a a gene pool and it applies to snapper and other fish species as well as humans strangely. It's well documented that larger snapper and older fish tend to produce more eggs than younger ones. The relationship is not necessarily linear or proportional to size, as reproductive success can vary with factors like environmental conditions and nutrition, reproductive condition, and genetics also influence fecundity. Have a read of https://www.fishing.net.nz/fishing-advice/general-articles/selective-breeding-in-fish/" rel="nofollow - this article Paul as it's quite relevant - by Anna Blair who did a Masters at Otago Uni majoring in genetics. Be interested in what other data/research you have too. ------------- Online... |
Posted By: smudge
Date Posted: 10 Sep 2023 at 7:43pm
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I agree with Grunta (you sycophant Smudge) in that most people can't iki a fish let alone puncture it's swim bladder effectively. I've seen plenty pop that bubble that sticks out its mouth - which is not its swim bladder and I admit I've done that before because I thought it was the right thing to do. I've also released plenty of snapper in deep water that have shown no signs of being 'blown' that have headed straight on down. As for the big fish genes, I'm a fence sitter there simply because if there is such a thing (I don't have to agree with everything Grunta says :) ) then clearly the big fish have it. Of course all big fish were once little fish too but we can't tell if that 27 to 70cm snapper has those genes. Here's another one, most of these debates revolve around snapper. I've never seen a 'blown' kahawai or kingfish, Jack mackerel, tuna, marlin etc. It's predominately the demersal fish that have these problems but not always. Snapper & gurnard are especially prone but other demurrals such as spiny dogfish, of which I've caught at least two billion (you're exaggerating again Smudge) don't get blown. I've also seen crayfish caught in 50m still looking healthy as Random musings but everyone seems to only think this is a snapper problem. Hapuku seem to be affected pretty badly too but then again I've yet to catch a snapper in 300m ------------- Best gurnard fisherman in my street |
Posted By: Fish Addict
Date Posted: 10 Sep 2023 at 8:21pm
| Just to add to your last comment there smudge I've caught snapper (as by-catch) over here in 220-240m. These show no signs of barotrauma and they go like scolded cats straight down when released. Fish are generally in the 3-4kg range. Do they survive? I have no idea. |
Posted By: MB
Date Posted: 10 Sep 2023 at 9:11pm
Does anyone release hapuka?  My own musing. What I've seen time and again is that bigger snapper suffer barotrauma to a much greater degree than smaller fish. Apart from being annoying, I've never heard an explanation or anyone else talk about it. You have to factor in length of fight, i.e. bigger fish will have a longer flight and may be exhausted from the fight itself and therefore more likely to die, but you would have thought a longer fight would mean a slower ascent and less barotrauma?
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Posted By: Fish Addict
Date Posted: 10 Sep 2023 at 9:42pm
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I agree MB, the larger snapper appear to be more susceptible to the effects of barotrauma for whatever reason. Other demersal species we have in the <4kg weight range are far more prone to barotrauma than snapper. |
Posted By: krow
Date Posted: 11 Sep 2023 at 7:24pm
| If I'm in 35+m and expect to release the snapper I am winding in I try to pause at 5-10 or so meters from the surface. Easy enough with multi coloured braid or as soon as I see colour. I wait till I see bubbles and this indicates the fish has degassed and if released has no trouble descending. |
Posted By: Pcj
Date Posted: 12 Sep 2023 at 4:43am
------------- Amateur's built the ark. Professional built the Titanic |
Posted By: Phantom Menace
Date Posted: 12 Sep 2023 at 9:29am
That is sensible Krow. The killer here is volume change. Those of you who dive will know that every 10m of water puts another atmospheres pressure on the body and any gas spaces. Net result is that the largest volume change is close to the surface. Going from 10m to the surface the volume of any gas spaces will double (Going from 20m to 10m depth the volume increases by two thirds).
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Posted By: smudge
Date Posted: 12 Sep 2023 at 7:01pm
Wow, I didn't know that ------------- Best gurnard fisherman in my street |
Posted By: krow
Date Posted: 12 Sep 2023 at 8:29pm
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Yep every 10m = 1 extra atmosphere (I dive too). 10m to surface pressure change is 100% 100m to 90m is still a 10m change but the change in pressure is 10% Puka fishing I've noticed they put up the last hurrah desperate struggle at around the 100m mark and I'm guessing that's when they start to get blown.
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Posted By: smudge
Date Posted: 12 Sep 2023 at 9:26pm
Thanks Krow. I wonder if there's a relationship between that 10 metre thing and the results that PCJ posted. ------------- Best gurnard fisherman in my street |
Posted By: waynorth
Date Posted: 13 Sep 2023 at 10:16am
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Couple of technical corrections from the physics police here guys. [Phantom Menace] Going from 20m to 10m depth the volume increases by two thirds Increases by half not 2/3. [krow] 100m to 90m is still a 10m change but the change in pressure is 10% Getting picky here but it's 1/11th - about 9% [krow] I wait till I see bubbles and this indicates the fish has degassed That's the swim bladder bursting. Controlled degassing by the fish takes time, as the oxygen has to be re-absorbed into the bloodstream. Probably better to take those ones home.
------------- treat fish like fish |
Posted By: krow
Date Posted: 13 Sep 2023 at 8:22pm
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Thanks for the corrections. Maths was a long time ago for me. I might have to disagree on that one though. If you keep winding to the surface the swim bladder or stomach stays inflated and the fish cannot descend but pause and let it degas itself and it's much more alive/active and will swim off (down) strongly. If it was the bladder busting then why would it not be more likely to do so as meets the surface? Interesting I guess more research required. |
Posted By: Phantom Menace
Date Posted: 15 Sep 2023 at 8:39am
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Yeah -I got it wrong ... (which is a little embarrassing)
------------- It was the Law of the Sea, they said. Civilization ends at the waterline. Beyond that, we all enter the food chain, and not always right at the top. |
Posted By: smudge
Date Posted: 15 Sep 2023 at 5:48pm
Don't be embarrassed Phantom, we all get it a little wrong at times ------------- Best gurnard fisherman in my street |
Posted By: Phantom Menace
Date Posted: 18 Sep 2023 at 3:34pm
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Thanks Smudge. I was just a little frustrated with myself because I used to explain this stuff to beginner free divers - although that was usually explaining the volume change as you go deeper (so the reverse of this swim bladder case) as people needed to understand the core of why different equalising techniques were needed as you got in to deeper freedives.
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Posted By: smudge
Date Posted: 18 Sep 2023 at 8:28pm
My knowledge of this is zero. I understand it better now after reading this. My biggest regret fishing wise is that I never learnt how to dive. A good life should have at least a regret or two  ------------- Best gurnard fisherman in my street |
Posted By: MB
Date Posted: 18 Sep 2023 at 8:38pm
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Diving took some of the magic away from fishing for me. That said, there's no doubt that it has made me a more efficient angler. I've actually been to some of the spots where I work my softbaits
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Posted By: Phantom Menace
Date Posted: 19 Sep 2023 at 7:39pm
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That's interesting MB. On Saturday Shelly and I took her brother out for a fish (he's very keen and knows his stuff). We covered a lot of ground but it was interesting talking to him when we stopped at places I had previously spent time swimming round with a speargun. I explained the details of the underwater terrain, what it did to current in certain places and how it all impacted fish behaviour / where the fish were (e.g. there are some bricks that don't show up on charts but are enough to influence things and some other bricks that are on the charts). It was an interesting conversation and he kept quizing me.
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