Fishery design - Fishery management is made easy when you avoid these common design mistakes.

October 13, 2023 0 Comments

I promise that simplicity is the fast lane to positive stock progression that drives your angling demand and fishery profitability.

(There's a link at the bottom of this article for the YouTube version)

If you're a diversifying farm business or you're investing in land to fulfil that dream of developing your own fishery from scratch. You have a perfect opportunity to create a progressive business, saving yourself time and money by understanding what makes a healthy, fertile and manageable environment for fish.

Ignore that creative designer inside of you that wants to over-engineer a fabulously complicated fishery. Avoid them costly mistakes and needless design features that we see restricting long term fishery success so, so often.

We’ve worked for many fishery owners, diversifying farm businesses and start-up businesses who started with a green field site. We see the same handful of fishery design mistakes made time and time again.

The mistakes stem from designing a fishery with anglers in mind, you need to distance yourself from that mind-frame. Instead picture it through the eyes of a livestock manager. Stillwaters are very fertile environments, particularly newly excavated clay ponds. The fish that you stock are going to grow fast and spawn successfully. Therefore, you NEED to be able to manage the livestock that you have if you want your fish to show positive progression year after year. You can think about the anglers when it comes to managing the fish populations, but not when designing the construction of the lake. So what should you consider?

Depths

Lake depth is the first consideration when it comes to creating a manageable environment. Chest depth makes the whole waterbody easy to manage, any problems and you can jump into a pair of chest waders, no drama. Although the shallower you go, the more challenging management can become also because things become much more fertile with reduced water volume which concentrates any water quality issues and oxygen demand.

Deep lakes are more susceptible to variable water quality, despite what you might think about more water volume meaning more dilution of pollutants and less risk of algal complications, that's true, but it doesn't always mean healthier. You’ll still get algae developing in deeper waters, but it will occur in the surface layers, reducing sunlight penetration to the deeper layers. If sustained for a long period, the depths of water can become void of life and submerged weeds can start to die back causing an oxygen depletion as the bacterial processes digest this dieing weed. The fish then naturally head to the areas of highest oxygen concentration, which is the surface (the layers of water causing the problem where micro-algae have become incredibly successful). Some single celled algae can have a hard exterior which can be abrasive on the gills. This can lead to respiratory distress and further secondary infection or external parasitic loading which thrive off the excess mucus production of stressed fish.

Shallower pools mean that the fish naturally spend much more time closer to the lake bed and closer to the surface, which creates a good amount of water mixing with every movement each fish makes. Every waft of the tail is going to mix the layers of the water so that algae thriving in the upper layers are tumbled down through into deeper layers where they will get less UV energy from the sun. This means the algae presence is more consistent through the layers and naturally controlled by the mixing of the water. This is far healthier for consistent water quality and the food chain in comparison with the earlier deep water example which allows algae to thrive off the sunlight in the upper layers, capping the waterbody with a surface algae bloom without any mixing.

An important note here is to consider your water source and how a dry summer might impact water levels. So consider chest depth during a dry summer rather than maximum winter depth!

Islands

An obvious feature that the majority of fishery designs feel the need to include. They split up areas of water to stop anglers casting into other anglers waters, they have a visual appeal and offer a refuge for birds. However… from a population management angle, they complicate things! Islands make is much more laborious when it comes to netting the fish and controlling populations, which also have a negative effect on the success of the job.

A small island in a large lake is not so much of an issue, but we often see small lakes with big islands. They’re often constructed by digging the pond deeper to obtain the soil required to build the island. We’ve already been over the benefits of shallower waters, but the key point here is that surface area of water is more important than water depth. Although deeper may mean more water volume, the surface area is fixed, therefore efficiency of surface oxygen diffusion doesn’t improve.

Surface area is not only the critical factor for oxygen diffusion, but also sunlight exposure required for algae to photosynthesise and absorb the nitrates produced from the organic digestion of waste materials from fish, feed, bait and leaf fall.

Adding a 0.5 acre island to 1 acre pond makes the pond half an acre, so don’t stock that pond at a density suitable for 1 acre, remember the waterbody is 0.5 acres. Don’t think that by doubling the depth of the pond will allow you to stock double the amount of fish either. Although the deeper you go, the more fish you’ll need to create the same amount of water turbidity to prevent weed, surface oxygen diffusion and sunlight exposure are not improved by increasing depth. Therefore, deeper water and more fish means that:

more oxygen demand from the same supply at the surface.
more ammonia production.
more oxygen required by aerobic bacteria to convert ammonia into nitrate.
no improvement in sunlight exposure for photosynthesis required to absorb those nitrates.

All of the above leads to more inconsistencies in algae blooms and crashes.

Features

I always used to think creating a complex underwater environment with holes, humps, bars and gullies would create a fantastic playground for your fish and an inviting challenge for anglers to navigate. After 10 years working with fisheries and understanding the importance of being able to manage a population of fish in a water, I promise that you do not want these features!

The lead line on the net (the bottom of a seine net which pins the bottom of the net to the lakebed as you pull it in) maintains a lot of tension from the drag and arc created when you pull it in. It doesn’t dig into holes or recesses with any aggressive inclines/declines of depth. These features create escaping opportunities for the fish. Shoal fish like Roach and Bream don’t explore these opportunities as much as carp and tench, but you can easily lose 100% of the carp haul to an annoying hump/bar/hole.

If you can’t effectively control your populations, don’t expect to be able to control the progression of your fish. A fertile environment reaches it’s holding capacity very quickly with successful fry recruitment and growth of mature fish, it’s crucial to be able to crop fish to re-balance the biomass. The easier you can make your fishery to net, the more successful netting becomes and the more control you gain over your population.

Remember that anglers generally pick a venue based on the quality of the fish and the fishing, nobody picks a venue based on the features regardless of the stock.

If you can’t control your biomass, fish progression will be heavily restricted, angling demand is reduced and managers become desperate to attract business with constant re-stocking. That’s poor management costing perscious time and money!

Make it easy for yourself, focus on developing quality stock. Do this, and every year will be your best one, your lake record will be regularly broken, the buzz creates huge angling demand which puts you, the manager, in control of your business. I promise that’s the way to optimise the profitability of your fishery.

Shape

Similar to the piece on islands, keep this simple. We see some crazy designs with the classic ‘Snake Lake’ holding the top spot for the worst design concept for an aquatic ecosystem!

Snake lakes and funky designs limit the positive influence of wind on your water. They also create bays for organic debris to collect, areas that catch the sun more than others etc. You’ll get areas with more silt than others, which creates areas fish like and dislike. These inconsistencies not only create poor angling, but poor recycling of organic materials. These designs concentrate fish into areas which encourage fish immobility, this immobility make it easy for external parasites to leave their host fish to lay eggs and find a new immobile host fish, so parasite numbers multiply faster.

I’m afraid the best shape is the most boring one, maximum sunlight and wind exposure. Sunlight is key for the photosynthesis that’s required of algae to recycle the waste materials from fish, feed and bait into the food chain.

Wind movement helps to mix the surface layers of water for more consistent water quality throughout the lake/pond.

A featureless design creates consistency, so fish mobility is encouraged which forces the fish to burn energy, therefore they need to feed to replenish that spent energy. Feeding keeps the substrate agitated and the whole ecosystem recycling efficiently. Perfect!

Water source

Finally, before you even consider getting diggers on the ground, you need a suitable water source. I'll highlight the obvious first, a consistent flow all year round from a natural spring or from land drains is most ideal, where there’s no risk of upstream organisms, fertilisers or pollutants feeding into your water.

The key point to make in this section is that a steady consistent feed is better than large volumes of water. A strong feed of water more often than not means that your water temperatures are kept slightly cooler than a gentle trickle feed. Temperature is the north star for fish growth, bacterial reproduction and digestion processes. Although a teeny weeny temperature increase might seem like a drip in the ocean, the impact over the period of 1 year is quite significant.

A strong flow of water could be an indicator of an ecosystem upstream which is supporting aquatic organisms that could have a detrimental effect on your fishery. We’ve seen it many times before where stickleback have colonised in stillwaters, these fish carry a nasty parasite and can quickly dominate a population within a fishery.

I hope this has been useful to you, I’ve recorded a video that covers all of these areas which you can view on the BP Milling YouTube channel.

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