Monday, 30 January 2017

Length-weight Relationship of rod caught Warwickshire Zander (Sander Lucioperca)

Piscatorial Quagswagging and obviously bored blogger Mick Newey presents the relationship between total length (TL) and wet weight (W) for rod caught Warwickshire Zander. The Zander a non-native species in the UK are now very much naturalised and established within Warwickshire waterways.

In 1878 20 odd Zander averaging 0.9kg in weight were netted from Bothkamper Lake in Schleswig-Holstein, Germany and transferred to the enclosed waters at Woburn Park Bedfordshire. Apparently a number of successful stockings from Woburn to enclosed waters in Southeast England took place between the end of the Second World War and 1962.

One of many from Hatton Locks that turned me in to a Zed Head

A release of 97 fingerlings in 1963 to the Great Ouse Relief Channel is where the situation changed dramatically, and the species subsequently bred very successfully in the wild and spread through the adjoining rivers of East Anglia. Currently the colonization of the extensively interconnected rivers of this region of England is still only partial but the species is steadily extending its range and has been illegally introduced to other parts of the U.K. by anglers.

Zander can now be found in most of the Midlands Canals the Warwickshire Avon, River Severn, the Nene, the Trent as well as the East Anglian fens and ditches and also various lakes in England, now even in the Thames apparently which has given rise to fears of further extensions of the species range over a considerable area in the future.

This data is generated from Zander caught from the Warwickshire Avon, the Stratford-Upon-Avon and Grand Union Canals and many a fish is featured in this blog of mine if you want to peruse the archives, there is plenty to look at.


Length-weight relationships are important because they allow the conversion of growth-in-length equations to growth-in-weight, for use in stock assessment, allow the estimation of biomass from recorded length and also allow an estimate of the condition of the fish and also the between-region comparison and life histories of this particular species.

Could I find something similar online, not a sausage, I found lots of good reading material mind you and enjoyed the research….

Zander tend to spawn in spring (March-April) when water temperatures reach 8 to 12 degrees. Eggs are generally deposited on the roots of aquatic plants, gathered together in the form of a nest by the male, in sites where the depth of water is between 40 and 50cm’s. Sexual maturity generally occurs at 2-3 years in males and 3-4 years in females when the fish have reached a length of 50cm and a weight of around 1kg.

Fecundity is very high and after hydration the eggs are 1.5mm in diameter. The male appears to guard the nest during incubation which lasts between 13 to 14 days.


A short but fat'un, a canal 8lb 10oz

Due to the excellent eyesight of the Zander which love to hunt in low-light conditions, at night, murky water and certainly in rivers and lake large depths, puts them ahead as the waters predator to be feared.

The Zander’s eyes shine with a silvery glow even by the most delicate light source. Its reflective guanine layer covering the inside of the eyeball is unbelievably sensitive and allows it to see perfectly in conditions and water clarity when other fish, let alone humans, cannot see anything at all. Having fished for them on countless occasions they are intriguing fish to catch as they are very unlike the indigenous species that share the Midland waterways.

A small River Severn Zander

They like lures too, green particularly works well....

In this study the records over many Zander captures have allowed fish to be measured for total length (TL) in the field and weighed (W ,wet weight) to the nearest oz for ease of excel chart generation. For the wooden-headed 1 lb = 16oz.

Fish may weigh less than expected for their length for many reasons. Lack of food/prey being a likely cause but maybe because of the overpopulation of the Zander as a predator and competition from other similar fish. A fish may also well weigh less than expected due to change in activity levels or metabolism due to environmental factors.

An 8lb 3oz Warwickshire Avon Zander

Over many field trips/fishing for Zander which is consequence of keeping and maintaining this fishing blog of mine I really have enjoyed catching them and I will continue to do so. I’d grown to love one particular area of habitat on the Stratford-Upon-Avon canal which not only brought me some much needed solitude but it was home to young but seemingly very well fed fish due to their characteristic larger girth compared to the neighbouring stretches I fished.

Having being given some location tips previously I happened upon some shared knowledge and these fish were more than likely down to a fruitless electro fishing exercise by the waterways authority at the time to remove Zander and by way of compensation for the fish removal, it was heavily stocked with a large number of silver fish.

Greedy they are....

Someone who witnessed the day of the electrofishing was amazed at the amateurish way the task was carried out and subsequently large areas of the canal remained untouched.

Those lucky Zander that avoided the cull thrived on these new introductions and are still there to be caught today (transient mind you), and despite the apex predator being present (I haven’t seen an Otter on the canal yet), large numbers of prey fish appear to still exist and as on most stretches I fish there has been a balance reached on the often neglected stretches of the canal.

The Roach section rig used on the canal....

Boats aplenty, anglers not so….

Anglers are a rare sight on the waters I fish you see, why? many factors I suppose, commercial fisheries have sprung up everywhere over the last number of years, Carp fishing has taken over for the tackle tarts and those with bottomless pockets and also many don’t know how to approach a canal, let alone to try and catch an ickle Roach, you can ditch that 6lb line and size 12 hook, try a 1lb bottom and a size 20 hook, you might do a little better.

The fish are there to be caught despite the often misguided notion that the Zander have eaten everything.


A long but very lean 7lb 6oz canal Zander caught from 'Mick's Bush' swim
Anyway back to the job in hand, length and weight feature in this graph. Girth is factor for sure, but I’m not Einstein so it isn’t featured but it surprised me just how accurate the chart was for predicting weight on a given length of Zander that populate and seemingly love the Warwickshire waterways.

I added some references too, one being detail from the 1979 book Zander from Rickards and Fickling and also generic Walleye data for comparison which seems to fit very well indeed. The curve,well I've used canal data and a polynomial line.

My Patch
There isn't a secret to catching these fish, certainly for the canals travel light, alternate your tactics and methods and rove around as much as you can. It also helps fishing with fellow Zed Heads as apart from the social side of it, it's far easier to cover as much water as possible and also how different approaches can single out fish from stretches that may prove difficult.

Predators thrive on neglect so one last tip is so fish waters where others don't. 

Having caught hundreds now there doesn't appear to be a feeding pattern either, certainly the larger canal fish unlike the river fish are transient and the lower the clarity the catch rate improves but one thing to mention is even the most sunny of days I've caught, even on the river, so get that bait in the water.

So the graph, here you go….



The conclusion, well, to get a life me thinks, the Wife's eyes rolling once again....

5 comments:

  1. Fascinating Mick.

    Great piece. Hatt-esque, dare I say.

    Now maybe I can estimate whether that zed I caught when my scales were at home was a p.b.

    Leave it with me...I'll be back.

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  2. It was how close it was to the Walleye I wanted to see for myself. They look very similar after all.

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  3. Very intriguing mick, I wish I had Zander close to home, I'd love to give them a much more thorough going over. Alas, I don't so I'm enjoying the Zander fishing through your blog. Keep it up mate, sure a lump will come your way.

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    Replies
    1. Cheers James, likewise I'm jealous of the game and roach fishing down your way.Then again, need to take full advantage of whats in the area, stupid if we didn't.

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    2. I completely agree, I'd like to fish the W.Avon again, maybe give it a go this summer if the time presents itself, Zander down here in the wild are very rare fish, something I'd love to catch more of!

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