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Sounder way of snapper fishing
  |  First Published: November 2016



Pink snapper are a highly prized, sought after fish. They’re distributed around the Australian coast, commonly caught from the Gascoyne region of Western Australia to South Australia, Victoria, New South Wales, and right up the southern coasts of Queensland. Here are some tips about snapper and how to use your sounder to improve your catch rate.

Fishing from the shore, from kayaks, or from deep blue water boats, anglers have the opportunity to catch pink snapper. They’re found in a wide range of water depths, from the shallow waters of estuary bays and inlets to the deep waters of the continental shelf, where fishers may see large schools finning just below the surface.

Health of snapper stocks

Snapper aggregate in large numbers, sometimes between 1000-2000 fish – the size of these fish schools can mislead people into thinking that snapper numbers are healthy. What needs to be considered is that these fish may have travelled long distances, from a wide area, and this does not necessary mean there’s a lot of them out there.

Shallow water snapper school
An observant fisher can sometimes spot dense schools of pink snapper finning around in the shallows, close to the shore in estuary bays and inlets. These fishers spot them by looking for what look like patches of black seaweed with a slight tinge of blue. This colour is created by the fishes pink body color and the sprinkling of iridescent blue spots on their backs.
Snapper hotspot

Snapper are known to form hotspots, in both shallow and deep water locations. Snapper in deep oceanic waters are commonly found in the vicinity of coral bottoms, where they gather in large schools to spawn. A single mature breeding snapper can release thousands of eggs in a season. Most of these eggs will not survive due to natural mortality. When large fish aggregations occur, the food source is quickly depleted and fish become ferociously hungry. This makes them easy to catch, but can result in pressures on the fish stocks from overfishing.

A very hungry super school of snapper can also do damage to mussel stocks. Brad Thompson, a Western Australian mussel farmer, had an encounter with a super school of hungry pink snapper a few days before Christmas last year. The super school attacked his mussel farm, crunching through thousands of dollars of mussels and ate 15t in 10 nights – wiped out his entire Christmas stock.

At times these fish can become annoying if you want to catch other types of fish. Snapper like to get to the bait first. If this happens, all you can do is move to another spot to get away from them.

snapper bait

One memorable autumn fishing trip, a group of us, including a fisher from Japan, went out fishing from Fremantle in Western Australia. On this day, we headed west 24 nautical miles from Fremantle to the 120m contour line. Fishers need the right gear and skill to catch fish at that depth.

The day didn’t look good for fishing – the swell was up to 3m and the wind was southwest between 12-16 knots. It was going to be hard work to hold the bottom, and the drift would be fast, so we decided to do some long drifts over the depth contour line, and hope for the best. The bait we normally use is octopus as it’s a good bait to use at that depth and stays on the hook.

Our Japanese friend brought his own bait. When we arrived on the grounds and were getting ready to bait up and drop our lines to the bottom, he pulled a large scaly mackerel from his esky. My first thought was “That won’t stay on the hook at 120m,” and my second thought was, “This bloke doesn’t understand deep water fishing.” It soon became apparent he did.

I watched him delicately cut two 10cm strip baits from the side of the partly defrosted 25cm mackerel. He placed each bait on the end of a single hook, leaving the barb of the hook completely exposed. We all dropped our lines to the bottom and started the first drift. Within a few minutes, our friend was hooked up on his first fish and landed a big snapper.

Our octopus bait couldn’t compete with the scaly mackerel. Mackerel bait mimics the action of a small fish when placed dangling on the end of a hook, and its strong oily odour is quickly detected by the fish’s nasal sac. Big snapper like to eat small fish, so this method of strip baits using mackerel works a treat.

sounder frequencies for snapper

Pink snapper inhabit depths from 1-250m, so different frequencies will need to be used depending on the water depth being fished. The golden rule is that high frequencies produce the best resolved images in shallower depth, and low frequencies produce the best resolved images in deeper water depth.

Snapper fishing in shallow water using 450kHz

Once a year, from April to October, snapper spawn in an area called Cockburn Sound, close to the Port of Fremantle in Western Australia. During the spawning season, the area is closed to snapper fishing. The shallow depths in this location are covered in meadows of sea grasses, which provide a nursery for the spawning snapper that have come in from the deeper oceanic waters.

During last year’s closure, in the early part of the season, I ventured out into the Sound to take a number of screen captures using a colour sounder, and to check out the fish stock numbers. This area has shallow water depth, so I was able to use two different operating high frequencies, as shown in my screen captures.

Screen capture no. 1 was taken with an operating frequency of 450kHz. This frequency can produced highly resolved screen image of bottom structures within a limited depth range. The bottom echo signal is always the most prominent signal recorded the display. Notice how the echo signals from single fish targets appear as small dots on the display ­– this is created by the frequency’s characteristics. A number of these fish targets can be seen to have gathered into a school, forming a vortex on the top of a bottom structure.

Screen capture no. 2 is an example of how an operating frequency of 450kHz can produce highly resolved screen images of a boat wreck. This boat wreck is sitting on a flat sandy bottom surface, and it is completely covered in fish. It is also home to a resident school of large Samson fish. Had this image been taking using a different frequency, like 200kHz, it would have looked completely different.

Snapper fishing in shallow water using 200kHz

Screen capture no. 3 was taken 100m away from No1 with an operating frequency of 200kHz. The bottom echo signal indicates a flat sandy bottom surface. The echo signals from single fish targets can be seen above the bottom echo signal. These signals are strong targets, indicating medium size fish. These fish are likely snapper, because this image was taken during the snapper spawning season. Not many fish in this location would swim well off the bottom, producing echo signals this size.

Note that echo sounder signals are not specific to any type of fish, therefore a fisher can’t identify the type of fish from the signal recorded on the display screen. A definite identification of fish can only be made by catching the fish, or by sending down a diver or camera.

Note the difference in the size between the echo signals from single fish targets in this screen capture, and then compare them to the ones in Screen capture no. 1 They are the same size fish, but the echo signals from single fish targets are bigger when using 200kHz.

Screen capture no. 4 uses an operating frequency of 200kHz. It shows three schools of fish rising up into the water column. The thickness and tails within the bottom echo signal are indicating a rough hard bottom surface. The background clutter in this image was created by switching the sensitivity gain control from auto to manual, and then tuning the sensitivity gain control up to 80% to further enhance the signal strength of fish targets recorded on the display.

Fish school no. 1 has a parabolic arch, created by the fish school being virtually stationary when the transducer’s sound beam passed through it. Echo signals from single fish targets can be see below the main school. Fish school no. 2 is the smallest in this screen capture. Echo signals from single fish targets can be seen close to the bottom to the left of the school.

Fish school no. 3 is the largest and most dense fish school. The signal strength of the fish school is similar to that of the bottom echo signal, indicating a lot of fish. When dropping a baited line on top of these types of fish schools, a fish hook-up will often occur before the lines reach the bottom. In these situations, snapper will even bite on bare hooks.

Low frequencies (83/50 kHz) are selected in deeper water-depths, and will produce reasonably good resolved screen images. The lower the frequencies, the lesser resolved the image. The depth-range at which these frequencies can be operated is not restricted due to its low acoustic absorption loss through the water during transmission. The operating range at low frequency is determined by the performance level of the transducer. Sounding in water depths of 200-600m will only be achieved with a high performance transducer.

Time Variable Gain

Fishing deeper water depths, it’s essential to use Time Variable Gain (TVG) correctly. If you’re not using it, you will be missing out on a lot of fish. The golden rule is, as you go deeper increase the TVG setting and as the depth decreases, reduce the TVG setting.

With the TVG switched off, a school of fish detected at 60m will be recorded as a strong signal. The same size school of fish detected at 160m will be recorded as a weaker signal or may not even be visible on the display screen. By switching the TVG ON, and adjusting it to the depth, a school of fish located at 160m is recorded proportionally to the same size school of fish detected at 60m. TVG works well at depths to 450m, but after that it loses effect. Some sounders allow TVG to operate on auto control, while others can only be operated on manual control.

I prefer operating TVG on manual control, where I control the amount of gain. By doing this, the image will be fully optimised to detect fish targets through the various depth ranges.

understanding echo sounders/fish finder

When I first used echo sounders, I found the information recorded on the display was a complete mystery. I discovered over time there are no mysteries or secrets attached to echo fishing, only facts. Once these basic facts and principles are understood, they can be applied to any colour echo sounders, in any water depth, anywhere in the world. If you become skillful in reading the echo sounder, you’ll be able find many new locations that produce fish. This will open up a whole new world and perspective of life under the sea.

John Adams’ book, How to use an Echo Sounder/Fish-finder is well known among anglers. John is an ex commercial fisher with a vast amount of expertise using colour echo sounders, he lives in Western Australia where he manages Fremantle Boat School and is a keen recreational fisher. To learn more about echo fishing, visit www.howtouseafishfinder.com, or contact John by email, john@ fremantle boatschool.com.au.

1

Screen capture No1 shows bottom structure and a school of fish.

2

Screen capture No2 shows a wreck clearly.

3

Screen capture No3 was taken at 200kHz ­– the same single target fish from No1 look bigger.

4

Screen capture No4 shows three schools of fish.

5

A pink snapper looks really good in the water.

6

A kayak fisher with a great catch at night.

7

The author with a cracker fish.

8

The author’s grandson, Lachlan with a nice snapper.

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