Catch & Release
New sonar technology has revealed that we may be releasing our barra right into the jaws of ravenous sharks. JOHN SZYMANSKI explains what’s happening and how we can reduce the carnage.
FOR the first time recreational anglers have access to sonar technology which allows us
to actually “see” fish and the structure they live in. Even more interesting is the fact that we can also “see” what happens to fish after we release them.
Up until recently depth sounders showed depth, structure and fairly imprecise images of fish and bait.
Enter “imaging sonar”. Nothing we had previously comes anywhere near what imaging sonar shows below the surface of the water. Make no mistake, without imaging sonar on board you will be left behind when it comes to finding, and identifying, fish and structure.
Imaging sonar has been available for commercial applications for some time but at a cost of hundreds of thousands of dollars. Humminbird released the first affordable recreational Side Imaging Sonar to the recreational market in late 2004, with all units having GPS, normal 2D or downward viewing colour sonar and chartplotters. From this year, Humminbird Imaging Sonar will also feature Down Imaging in addition to Side Imaging. Although I haven’t had a chance to evaluate Down Imaging, if it’s anything like Side Imaging it’ll add a further dimension to underwater fishing surveillance. Lowrance has also recently released its StructureScan system, which is similar to the Humminbird system.
I’ve been fishing with Humminbird Imaging Sonar for the past two years and have more than 1000 hours of viewing side imaging. One look at the snapshots featured in this article will immediately indicate we are on to something special.
To understand Side Sonar technology, think of the sound pulse from the transducer as a light beam from a torch. The beam hits an object, fish or snag, which is then reflected or echoed back to the transducer and shown as white on the screen. However, it’s not a light beam but a narrow sound pulse, which is also reflected off the bottom of the water body, creating an image of its contours. As with a torch, an object in the path of the sound pulse also casts a shadow on the bottom of the river, lake or ocean. The shadow of an object is in fact a sound shadow or an absence of sound. The object blocks the sound pulse and so the sound pulse does not reach the bottom to be reflected back to the transducer and thus a sound shadow is formed. This sound shadow is shown as black on the screen and gives the best image of what the object may be. Take a look at the image on page 48; there is no mistaking what this is (a snag with a school of barra in it). The shadows also give us the best indication of how far objects are off the bottom. The closer the white mark or primary return of a fish is to its shadow, then the closer the fish is to the bottom. The further they are apart, the higher the fish is from the bottom. Generally, fish or other targets may not have a very distinct primary return but their shadows are usually discrete and clear, and will even look exactly like the fish shape itself.
Side imaging screens are typically displayed with the boat shown at the top of the screen and the water to the left and right of the boat shown on the left and right on the screen. Normal 2D Sonar has the screen or history scrolling to the left but side sonar scrolls from top to bottom, with the more recent images at the top.
As you’ll see in the screen snap shots above and on page 48, side imaging shows structure extremely well – rock bars, snags or bottom contours – but when we can place fish into the scene we have an extremely powerful fish and structure finding tool.
My wife, Michelle, and I lure fish for barra in the freshwater sections of the Fitzroy River in the Kimberley region of the far North West of Western Australia. We are absolutely amazed by what we can actually “see” under the surface with our Humminbird side imaging unit. Because of this new information we are learning much more about the behaviour of barra and other species, resulting in more theories about fish and fishing. What we did not anticipate discovering was the extent of the lethal danger barra face when released … not from deeply embedded hooks or poor fish handling but something far more sinister and immediate: predatory bull sharks!
Bull sharks (Carcharhinus leucas), the most prevalent of all the elasmobranchs (sharks and rays), are present in all our rivers across the northern part of Australia and are considered a highly dangerous shark. They spend the early part of their lifecycle in the freshwater reaches of these rivers and generally grow to 1.4 to 1.5m and 40 kilos before they migrate downstream to the salt to complete their adult life. Bull sharks are an apex predator and barramundi feature in their diet.
Michelle and I fish barbless and Boga grip everything. We don’t have saltwater crocodiles in plague proportions in the Fitzroy so mostly we remove lures without bringing barra onboard and thus are able to release barra very quickly after capture. We thought our release practice was doing the best by the fish we love to stalk, capture and theorise about, but what Side Imaging revealed below the surface resulted in a dramatic change to how we release barra.
At the end of many barra captures, Side Imaging shows bull sharks zeroing in around the boat. Side Imaging also showed feeding frenzies of bull sharks, crocodiles, sawfish and catfish all in the melee when a barra has been hit after release or where live baiting has occurred and fish have been busted off.
It was obvious that bull sharks are attracted to fighting barra and yet there’s absolutely no evidence of this at the surface. After more than a thousand barra we have lost only a handful to sharks during the fight and rarely see other sign. Occasionally we see a barra tailed by a shark on the surface or in the shallows. Sometimes we would smell an aroma, which Michelle originally thought was salty, and attributed it to the presence of estuarine crocodiles. During times of greater fishing pressure, particularly live baiting, we encountered this smell more frequently. We finally realised the fatty, fishy smell emanated from the decimation of barra by predators and scavengers, which we saw on the side sonar. Only rarely would we see fats and oils on the surface and catfish feeding on small fragments of fish, but it was Side Imaging which revealed the whole picture under the water. Bull sharks were decimating released or injured barra in far greater numbers and frequency than any surface evidence suggested. Post release predation of barra by bull sharks is a far greater problem than previously considered.
During the early part of a fight the screen is clear of sharks, but towards the latter part, sharks suddenly appear. After seeing what was happening below the surface we changed our release practice to increase the survival rate of the released barra. Even if the side sonar does not show sharks after a capture we boat barra on a wet Truth Mat and speed away, 50m or more, and release the fish into a bull shark free shoreline snag.
Interestingly, Side Imaging reveals few if any bull sharks turning up after landing small barra but the bull sharks invariably turn up with larger barra. Most likely, the modest acoustic signature of smaller barra and the relatively short landing times provide less opportunity for sharks to successfully home in. Very likely, bull sharks have learnt small barra are not an easy mark, as small barra are much stronger and more active when released. The longer landing times with larger barra give bull sharks a larger and longer duration acoustic signal to home in, and the longer recovery times and higher stress levels make larger barra more susceptible to post release predation. This is particularly true during periods of higher water temperatures, which adds further stress to barra. It’s not a great leap to conclude that barra are more susceptible to predation immediately after post release. We need to change our release practice to protect them.
Humminbird Side Imaging discovered and showed the importance of releasing barramundi some distance away from the point of landing. We call this practice “the shift” and it should be employed in all waterways bull sharks are present. It is particularly important in the Northern Territory where a very high percentage of barra are released and where bull sharks appear to be in the highest abundance than anywhere in northern Australia. In the NT, more than 70 per cent of all barra caught by recreational anglers, equating to around 300,000 barra, are released into heavy bull shark country. The evidence of post release barra predation obtained with the Humminbird Imaging Sonar was sufficient to convince Dr Thor Saunders, senior scientist on barra with NT Fisheries, to actively promote “the shift”. If this practice is widely adopted in all barra states, it has the potential to significantly increase barra stocks right across northern Australia for the benefit of all anglers.
WA-based John Szymanski is a tackle and marine electronics distributor. This is his first article for Fishing World. Check out the April issue for the latest that side sonar is revealing on barra behaviour.
