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Bait blocks for bream.

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Dick Pitman's letter in this issue regarding the possible effects of baiting for bream with game blocks, or feeding an area to concentrate the fish, bears a little further investigation.

The niloticus fishery in Lake Kariba can be considered stable and very healthy. An introduced fish over much of southern Africa, it is renowned for its prolific reproduction, fast growth and general hardiness and is capable of attaining considerable mass quickly, making it attractive to sport anglers too. Kariba is a veritable inland sea, and as such cannot be micro-managed by us mere mortals--the tigerfish being a case in point. Harvesting 4-5 tons of tigerfish during KITFT has little to no effect on their numbers. Destroying their breeding grounds does. Nillies do not need specialized river environments to breed, and will spawn for longer periods throughout the year. The only way to dent their population really, would be to poison them ... and again, given Kariba's size, this is not likely. Damage to shallow water habitat and breeding areas (usually by illegal net poachers) can have an affect on localized fisheries. However, population crashes are often related to several other factors at play at the same time. Lack of suitable nursery structure for young fish, a change in the chemical balance of the water and food chain, and so on. Any one of these on their own is not too serious, but combine a few of them, and a problem develops.

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Neil Deacon, an ichthyologist, avers that legal subsistence fishermen, if using the right gauge nets (catching bigger fish) can only aid the fishery. Some years ago, there was much debate on the suspected damage commercial net fishermen were doing to bream populations at Kariba. Much of the argument was supposition, and a contradiction to the negative effect netting has on the nillie population in Kariba was published in an article in 2004 following a discussion with Dr. Neil Deacon relating to research being done on Lake Kariba cooperative fishermen with Professor Brian Marshall from the University of Zimbabwe.

We reported then that "Probably the most interesting point to emerge from Neil's comments, is the unexpected conservation effect niloticus coupled with commercial fisherman is having on the lake's resources. Historically, the legal minimum net size for seine nets has been a mesh size of four inches. The thinking behind this is that only bigger fish are harvested, allowing recruitment of juvenile fish (able to swim through the net) to the overall fishing resource. Traditionally, illegal nets with a smaller hole size (less than four inches) have been employed by some commercial (and some illegal) fishermen to increase their harvest illegally, admittedly with little regard for the future. By-catch of all species (aside from, say the targeted bream) was significant, and coupled with the harvest of juvenile fish from shallower waters placed unsustainable pressure on the fish resources of the lake. This was not peculiar to Kariba, and happens on many inland dams too.

"With the introduction and proliferation of nillies across the lake, their faster growth rate, considerably bigger overall size and market value, has made them a preferred target species for commercial net fishermen. In order to successfully exploit this resource though, fishermen have had to move to deeper or open water, using a bigger diameter net. A larger mesh size means there is less by-catch of other non-targeted species, mostly because they are too small to get caught, and also no harvest of juvenile fish stocks. Commercial fishermen, because they are operating in deeper more open water, generally do not come into contact with the common sport fish targeted by rod and line anglers."

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Fish poaching aside--the practice of which contradicts everything stated above--it is unlikely that commercial fishing with either rod and line, or nets will see the demise of Kariba's bream fishery. The use of feed blocks--as it is a food source--will ultimately be providing sustenance to that same fish population. While the continual use of bait blocks or massese (the by-product in the manufacture of opaque beer) in smaller bodies of water will increase bacterial action and thus de-oxygenate the water, it would be almost impossible to introduce enough bait into Kariba to cause such damage. Other fonns of ground baiting include the use of pet food and other offal popular with catfish anglers and carp fishermen--not unlike modern-day nillie fishermen--who often throw out a handful of sadza or other dough baits in the vicinity of their hook-bait. Of course, if you want to wonn fish, then pinkies and especially the Kariba bream will prefer this type of bait over any kind of dough concoction. It is all just a case of targeting the right habitat and areas and having the time and inclination to put in the work to find those fish, rather than shnply dropping a bait block.

As an interesting aside to "ground baiting", well known angler Trevor Wilton for many years utilized his vast skill and knowledge of the feeding habits of fish while captaining his angling team in the 1970s. They used the fact that rendalli, or pinkies, are partial to eating the green shoots of various reeds, grasses and other wateredge vegetation, and using a technique that later became known as the "Darters Whistle", they introduced a number of green shoots into an area to attract the bream and then fished with a similar bait. The method proved very successful as a fish attractant, but in no way harmed the enviromnent.

As to the legalities or ethics of ground baiting, let's first establish the meaning of the tenn. It is the introduction, of a FOREIGN substance, in BULK, into a body of water, which acts as an attractor and a stimulant towards fish. To give you some examples, this includes the use of cattle feed blocks, blood meal, pet food and of course 'massese'. It is often confused with the term CHUMMING, which is defined as the RE-INTRODUCTION of a NATURAL food (ie: fish) into the water. The use of kapenta in Kariba as a chum for tigerfish is not ground baiting. By I.G.F.A. (International Game Fish Association) rules, catches will be disqualified if the angler has been "Chumming with the flesh, blood, skin, or any part of mammals".

Techniques, and indeed our fisheries are evolving all the time and it is possible that in coming years we will see a shift in the way we fish for many of the Kariba species, tigerfish included. The crayfish are having more of an impact than many realize, and are turning up in most fish guts analysed. Some anglers are experimenting using the flesh as bait for nillies and tigerfish too. Crayfish have become an integral part of the food chain in Kariba and I believe will dominate in years to come.

While the use of bait blocks for catching nillies is the "flavour of the month" at the moment, it would seem unlikely that the fishery will be hanned by this in the long-tern, and even those fishermen using rod and line on a quasi-commercial basis are unlikely to dent the nillie population. Watch this space, as I believe some interesting evolutions are about to take place.
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Author:Williams, Ant
Publication:African Fisherman
Date:Aug 1, 2015
Words:1205
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