How to

All Is Revealed

New technology is revealing interesting info about fish behaviour and how we can use it to understand more about our underwater friends. JOHN SZYMANSKI reports.

Every angler has a theory about how and when fish bite. the more bites we get, the happier we are, so naturally we develop theories to help us get more. Formulating useful theories depends on having accurate information; however, because of water depth or low visibility, we see very little actual fish behaviour. Even with traditional 2D fishfinders, we only see poor representations of what is directly under the boat.

If other anglers share their secrets, we learn from their experience but even their theories are based on the same limited information. Despite the limitations, we actually do a reasonable job of understanding our quarry; an understanding patched together from hundreds of years of fishing experience and collective wisdom of millions of fishermen spread by word of mouth and quality magazines like this one.

Normally the only direct information we have about fish behaviour is the bites we feel and the fish we bring on board. If only we could observe fish in their natural environment we would develop better understandings of fish and target them more effectively. With the availability of imaging sonar, we now can.

My wife, Michelle, and I fish for barra in the freshwater sections of the Fitzroy River in the Kimberley region of Western Australia. Fishing with the Humminbird Imaging Sonar and actually “seeing” real-time fish behaviour has led us to new and very different understandings of fish. Up to a few years ago, I saw fish as portrayed by Dory in the kids’ film Finding Nemo, having three-second memories and little or no learning ability. Fish are viewed as only capable of responding to immediate stimuli and fixed instinctive patterns. I, too, thought this until I was able to “see” their behaviour in the wild.

As detailed in the first instalment in this two-part series last issue, Humminbird Imaging Sonar has already revealed the phenomenon of post release predation of barramundi by bull sharks. This discovery resulted in the development of “the shift”, a new release practice to protect barramundi from the sharks. With imaging sonar we regularly see bull sharks zeroing in on large barramundi we land. We soon realized if we are going to protect barramundi from bull sharks we need to shift and release them a safe distance from the point of landing.

The ability to actually “see” fish underwater added a deeper dimension to our fishing and started for us an exciting journey of learning and discovery. We started seeing barramundi responding in very “intelligent” ways to critical aspects of their environment. When we start seeing underwater, we start learning about fish at a very fast rate.

Snags are extremely important habitat to many fish species and imaging sonar has revealed how barramundi utilize them. We always trolled as close as possible to snags and made sure every pass was right on the money. Right? Wrong! Imaging sonar showed barra moving around a home snag quite considerably from one trolling pass to the next. On one pass they are inside the snag, on the next pass 30 seconds later they are 15 feet to the right, the next, 20 feet to the middle of the river. Imaging sonar gives us the ability to adjust our troll to place our lures right over fish. If you don’t have side sonar, rather than keep to the closest trolling line it may be better to mix it up a bit.

We always see schools of barra in residence, in and around snags, during the day, but come night they disappear. Around sundown, barra move from their daytime snags and come morning they fill up the snags again. Although barramundi are classified as nocturnal feeders, probably 99 per cent of barra are caught in the day because that is when fishos mostly target them. What we observed each nightfall is the temporary migration of barra to locations where food is more abundant, then a return to the safety of snags in the day.

Like other anglers we often get hits from barra before dusk. Our theory explaining this productive bite-time is barramundi are changing from opportunistic daytime feeding to “on the nocturnal chew”. As barra leave the snags they switch into nocturnal feeding mode and so more readily hit a lure. The bites continue throughout the last hour or so before dark and are likely coming from different fish as each switches into nocturnal mode at different times. Our imaging sonar shows barramundi leaving snags in dribs and drabs. Changing from floating minnow lures to fizzers usually results in the strikes continuing at a similar rate, not because there are similar numbers of fish present, but because the fewer, more spread out fish are more inclined to bite.

Most discussion of why barramundi are in snags revolves around them being ambush predators and using snags as comfortable staging posts out of the current and from which to launch attacks on unsuspecting prey. On many occasions we have dropped a video camera into snags to see large schools of barra milling around with tons of baitfish, happy as Larry, and no sign of any feeding or attack behaviour. In tides or during run-off, barra may well utilize structure to ambush prey, but our observations in still freshwater conditions suggest snags are primarily shelter from predators rather than just ambush points.

Barramundi are a major predator in our northern waters and are, in turn, an important prey item for apex predators such as sharks and crocs. A major area of marine biology research is the effect of predators on the feeding behaviour of fish. Evading predators is a critical goal of all prey species. Typical evasion behaviour includes schooling and sheltering in snags and our imaging sonar shows barra doing both. What imaging sonar never shows are bull sharks in the snags where barra are very much at home. Of the thousand hours of imaging sonar viewing, we have never seen a bull shark in a snag. Sharks probably have difficulty manoeuvring through snags and any bull shark attempting a “snag attack” is going to get pretty scarred up. It is likely sharks have few successful captures in snags and learn there is little return from hunting there.

When discussing my observation of sharks not attacking barra in snags, Ian Keay, a technical officer with WA’s Department of Fisheries, pointed out sharks are not able to swim backwards. I have since learnt some cannot stop suddenly either. If bull sharks are not very manoeuvrable in snags it makes sense they don’t hunt there. Barra probably “know” this as well and use snags as safe havens and avoid leaving them while bull sharks are present.

During our last barra trip we started putting the pieces together. We enticed plenty of boofs at night, but despite 25 years of barra fishing on this river and classifying myself as a Fitzroy River freshwater specialist, we got bugger all strikes during the day on a variety of techniques and proven Fitzroy River lures such as Classics and Koolabung Bony Breams. Our imaging sonar showed us why.

“The Den”, a collection of snags on the river, is always home to large numbers of barra. We saw schools of barra there over the entire two weeks we fished but hardly got a hit. We also saw numbers of bull sharks patrolling. We made the connection: barra were not going to bite freely while bull sharks swam nearby. While barra were focused on evading predators, they would not take the risk to swipe at our lures.

Had we fully understood this at the time, we would have ignored the fish at The Den and concentrated our efforts where we saw fewer fish but no bull sharks.

We also observed barramundi changing their predator evasion behaviour in response to different light conditions at night. During nights with a strong moon presence, we generally only observed barra hugging very close to the bank and rarely in the open; but in dark conditions, barra travelled up and down the middle of the river. Apart from one occasion, we have never seen schools of barra in the snags at night. I suspect when feeding, it is every barramundi for itself as they not only compete for food with other species but also with each other. We’ve also observed barramundi delaying their nocturnal feeding migration in response to heavy presence of bull sharks. Late one day, a school of barra were in Death Row, called so because it is almost impossible to troll past without getting snagged. What surprised us was on this particular night these barra stayed in Death Row for more than an hour after dark. Every other night we see barra leaving Death Row and other snags around sundown and we always entice numerous boofs with Koolabung and Bills Bugs fizzers just before they leave. On this occasion the barra stayed in Death Row after sundown and we could not elicit a boof. We found out why. Every time we trolled past Death Row we saw one or more patrolling sharks. Barramundi were delaying their regular nocturnal migration and were not going to leave the safety of the snag while bull sharks where outside.

Laboratory studies show fish can read other fish’s body language and can differentiate hungry predators from satiated ones. The snapshot on page 84 from the Humminbird is one of many showing a bull shark actually swimming with barra. No fish is being attacked with no frantic movement showing. It is a scene of apparent tranquillity but powerful pent up forces. Both bull shark and the barra know each other are there, but while they hold their nerve, no one gets hurt.  The barra recognize the shark was not in full-on predator mode and so don’t engage in full-on evasion mode but nevertheless maintain vigilance. However, this situation only needs a trigger, and a barra would be very unwise to take a swipe at a baitfish or lure and risk being swiped at themselves.  

When we first observed barra shut down in the presence of bull sharks, we initially thought it was an all or nothing affair. If bull sharks were around, then surely barra would not bite if their attention to a lure prevented them from maintaining vigilance on the predators. Connecting our observations with the research, we realised that far from being an all or nothing affair, barra were actually balancing the risk between the critical need to feed and the need to evade predators.

Some visual observations supported this theory. Just before nightfall I chucked a fizzer into the heart of a snag we call “End of the Line” (don’t ask) and a 90cm plus barra shot out to hit the lure. I failed to hook up, but what struck us was the speed with which the barra came out of the snag, hit, turned and headed back. Barra are well aware of the presence of bull sharks but rather than completely shutting down when sharks are present, they balance the risk of predation with the need to feed. In this instance the barra minimised the danger by a fast attack on the lure, only having one go and immediately heading back to the safety of the snag. It is considered that hooked barra head back to snags as this is their best chance of freedom. I’m more inclined to believe they head back to the safety of structure because they know that while they’re out in the open they are vulnerable to predators other than us.

How often have we experienced a great barra session and suddenly have barra go off the bite? Knowing what we know of the effect of predators, I wonder how many times bull sharks turned up?

Fresh from our last fishing trip and full of new observations and theories had me straight into the latest research. Far from having three-second memories and little learning ability, a recent review of fish research describes fish as exhibiting “a rich array of sophisticated behaviour with impressive learning capabilities entirely comparable with those of mammals

and other terrestrial vertebrates” (Fish Cognition and Behaviour, Editors, Culum Brown and others 2006). What marine biologists are discovering in the lab, we are seeing with imaging sonar in the wild. Fish have far more ability to learn and their behaviour is far more complex than we previously thought. We now know fish actively respond and adapt, moment by moment, to the opportunities and threats in their environment. This also means our theories to explain their behaviour must be more sophisticated but this also makes fishing a far greater and more interesting challenge and all the more satisfying when it comes together.

We now understand fish behaviour is directed towards feeding, evading predators and reproduction, and fish can only be fully understood if we take these factors into account. Humminbird Imaging Sonar enabled us to observe barramundi in the very act of evading predators, balancing the risks and migrating to feed. Possibly, for the first time, these behaviours have been directly observed with barramundi in the wild. Who knows what we will learn next? There’s a view that we will never fully work fish out. Now we have imaging sonar, I don’t subscribe to that.

Keen angler John Szymanski is a WA-based tackle distributor whose list of products includes Humminbird marine electronics.

What's your reaction?

Related Posts

Load More Posts Loading...No More Posts.