Length weight relationships

Started by Goby, August 14, 2017, 06:16:08 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Goby

Hi all,
Attached is a photo showing the length weight relationship for Samson fish. These are close relatives of YTK and amberjack. They tend. To be a bit deeper than amberjack and deeper again than YTKs, but will give you a reasonable indication of those species weights if you are catch and releasing. The fish used were part of a study on Samson fish by one of my Ph.D students that turned up SE really neat stuff that I will post about tonight.

Cheers,

Howaard
Fishing, motorbikes, family, friends, beer and bourbon, but not necessarily in that order!

Goby

Hi again,
As stated in previous email a little bit about our findings on Samson fish (credit to Drew my Ph.D student) of which apoes or probably applies to YTGs and AJs.

I had started a long version of this earlier, but the dog needed a walk and I hit the wrong button and delete yes it all, dooh! So a quick rim down on our findings and history of this world class fishery, if anyone's interested will post later.

What we found, a lot through the tagging of over 12000 fish.

Off the Perth metro area there are about 20 sites that have adobe spawning aggregations between late September (just building up) and March.
Individual fish are on the aggregations for up to a month.
Fish move between aggregations.
Individuals arrive at the same time (within a matter of days) to the same aggregation every year.
Aggregations can cover the size of a football field and can go from the bottom (usually around 100 metres) to around 60 to 40 metres with fish about a metre apart. Big numbers.
Females tend to be at the bottom of the aggregation and do upward rushes followed by several males that head butt her to help egg release and they then release their milt.
After spawning fish move back to the area they came from. This may be a few thousand kilometres away and may only take a month, a couple of fish released of Perth were recaptured off Kangaroo Island in South Australia, so equivalent of one side of the States to the other.
Main food items were squid and cuttlefish, scad, mackerel and pilchards.
Survival experiments showed that stress hormones rose after capture but dropped back to normal fairly rapidly (except when a very big mako was circling their enclosure) and that the few mortalities were caught from 200 metres and spent a long time before being placed in the sock (enclosure).
Now the real biggy and, as one of Drews examiners commented on this chapter, his only comment, cool!
Sambos, YTKs and AJs and surprisingly another, but distantly related carangid (sver trevally) have a unique swim/air bladder. Herring and many other "lower" fishes have a swim adder that is attached to the oesophagus and burn air out as they go up and gulp air at the surface to go down, all taking energy and tending to limit them to the top 10 or so metres. Other "higher" fishes like groupers, snappers etc have a swim bladder that isn't connected to the oesophagus and rely on the blood system to put gases into the bladder when they want to go down or remove gases when ascending, more energy efficient and more fine control of buoyancy. However, it does have its drawbacks, fish can't ascend too quickly as the blood can't get rid of the gases quickly enough and the swim bladder will over inflate. For example, in a fish raised from 10 metres to the surface quickly the swim bladder will double in volume, result barotrauma - ruptured bladder, gut poking out its mouth, intestine out its vent, major organ damage and likely death.
Sambos, YTKs, AJs and silver trevally (this last as an evolutionary, as well as a fish biologist, still gives me sleepless nights and was found by some colleagues in NSW after hearing about our work on the sambos) have a unique system. They have a swim bladder that is disconnected from the oesophagus and the associated blood system to add and take gases. But, they have a small hole in the chamber that gases are released from that leads into a tube that runs just under the kidneys and backbone before splitting to exit just above the gills. This tube is usually flattened against the kidneys/backbone and little or no gas leaks out and the fish presumably relies on blood exchange for buoyancy regulation. However, on rapid ascent the swim bladder increases in size causing expansion of the body cavity, this in turn causes the ribs to bulge out, which in turn opens the tube and gas is quickly released. Best of both worlds, fine control and rapid ascent for spawning rushes where your eggs are in the most favourable currents for dispersal, you can chase squid, cuttlefish and pilchards which can also go up without barotrauma limitations and likewise it will aid in help in escaping your main predators, sharks.

As the examiner (Steven Cooke, who's also done some great stuff on recreational fishing) said cool!

Cheers,

Howard

PS I must give a plug to the charter skipper who kicked off the Samson fishery here and through his love of these great sport fish the project I had the great pleasure of working on. His names Al Bevan, he runs Shikari Charters. If any of you get to Western Australia give him a go. His boat is incensed for 12 but he only takes 6-8 depending on targets etc. You can go all day jigging for sambos, the record used to be 145 between 4 nutters from Adelaide, fly fish for them or target big snapper on plastics or mackerel depending on the season. He has quality gear and more importantly he is fun.

Fishing, motorbikes, family, friends, beer and bourbon, but not necessarily in that order!

sdlehr

Must've been horrible to have to go fishing all those days to collect this data!
Sid Lehr
Veterinarian, fishing enthusiast, custom rod builder, reel collector

Goby

Hi Sid,

Absolutely terrible! Though up at 3.30 to 4.00 am and not getting to bed till 12 for 4 or 5 days a week and juggling that with teaching during semester made me a bit dopey at times. But yes one of the most fun projects I've been involved in. I used to tag one day record the other and Drew would do the reverse. Once the punters were dead on their feet we'ed then have a fish. Got to play with all the "best" gear and see quite a bit die, either through angler error or being constantly ashes by big? Angry fish hitting high speed jigs at high speeds 20-40 times on a day. That sort of fishing really tests gear.

You say your into rod building, so am I, any advice on spiral wrap guide placement? And a vet, I used to teach them at Murdoch.

Cheers,
Howard
Fishing, motorbikes, family, friends, beer and bourbon, but not necessarily in that order!

CapeFish

Quote from: Goby on August 14, 2017, 06:16:08 AM
Hi all,
Attached is a photo showing the length weight relationship for Samson fish. These are close relatives of YTK and amberjack. They tend. To be a bit deeper than amberjack and deeper again than YTKs, but will give you a reasonable indication of those species weights if you are catch and releasing. The fish used were part of a study on Samson fish by one of my Ph.D students that turned up SE really neat stuff that I will post about tonight.

Cheers,

Howaard


That's a very nice fit! what were the statistics?

Dominick

Interesting stuff.  I hope to fish Australia and New Zealand some day.  Dominick
Leave the gun.  Take the cannolis.

There are two things I don't like about fishing.  Getting up early in the morning and boats.  The rest of it is fun.

Tightlines667

#6
Looks to me like that could be boiled down to a simple equation.  I believe there are similar published figures for Seriola species here in HI, or CA.  I am used to looking at larger data sets for Tuna species.  Interesting how fish from different distinct population segments show markedly different relationships.  I have been involved a number of different tagging projects here in HI over the past 2 decades.  I tagged over 3000 Uku..Green Jobfish w/darts, and 180 w/R-10codes for instance.

Good stuff!

John
Hope springs eternal
for the consumate fishermen.

sdlehr

Quote from: Goby on August 14, 2017, 03:45:32 PM

You say your into rod building, so am I, any advice on spiral wrap guide placement?

Hi Howard. No great words of wisdom, I don't think it that crucial; they say you can transition the guides around the blank so the 3rd guide is on the bottom; I usually make it the 4th. Only other thing is to go around the blank on the same side as the reel handle, so you can lay the rod flat on the deck on it's other side. Jon and Dwight are our rod builders extraordinaire. Maybe they have something to say.

Sid
Sid Lehr
Veterinarian, fishing enthusiast, custom rod builder, reel collector