Tackle and Tactics
Keep it quiet!
We have all heard, at some time, recordings of the soulful wailing songs of whales. These strange sounds are used by the great mammals to call to each other over enormous distances. In addition to the communicating sounds many whales and dolphins use sonar (a sort of underwater echo-location) to avoid obstacles, to find their way about and to detect the shoals of fish or squid that they eat. Some species have even modified their calls to act as a sort of weapon: by emitting bursts of high energy waves they are able to confuse or even stun potential prey.
Whales are far from being the only residents of the sea which make noises. There are lots of shrimps that make crackling sounds by snapping their pincers, one type that is common in the English Channel, lives inside the bodies of sponges. The loud snapping noises produced by a colony of shrimps have been measured at 40 decibels over half a mile away. In addition there are quite a few species of fish, which are capable of “talking”. Several members of the cod family are particularly vocal and it is well known that some bullheads croak loudly to attract mates, gurnards may be known as “crooners”, conger eels will often give out loud belching noises and off the coasts of North America are several species known as “grunts”.
Pulses of sound carry farther than simple continuous moans and groans, so the sounds made by most fish are intermittent.If we add to all these animal noises the facts that breaking waves crash and splash loudly, pebbles disturbed by the swell rattle and rumble on the sea bed, six-ounce grip leads thwack into the water and the swimming movements of fish and other creatures give rise to low frequency pulses which may attract predators such as sharks, the ocean must be quite a noisy place. We should also bear in mind that sounds travel through water much better than they do in air - five times as fast in fact. In view of this, living and communicating underwater must often be rather like trying to have a conversation in a disco. It is known that the low frequency propeller sounds of big ships could carry as far as a thousand miles, in all directions, under water.
Despite all this sound flying about through the oceans of the world, fish do not have external ears to help them hear. Flaps sticking out of the head, like those of dogs, cats or humans, would get in the way of easy swimming. Even with their simple internal ears, however, many fish are able to locate both the direction and distance of sounds pretty well but just how they do it is still something of a mystery. The point is that to filter out the background racket certain species may use a specialized ‘pressure detection system’ and it has already been shown that the sounds which some coral reef fish make for communication have a high pressure component.
Let’s look at one or two examples. Members of the cod family such as the pollack, the haddock and the cod itself are incredibly sensitive to low frequency sounds and are only able to hear each other properly where there is little background noise. Fish like salmon or sea trout, on the other hand have rather poor hearing. Many sea fish “sing” in chorus at spawning time and others produce loud aggressive sounds to warn off intruders who may enter their territories. The low-pitched underwater barks of sea lions are probably audible to fish but the whistles and clicks of whales and dolphins are usually above their hearing range. Wrasse often produce loud clacking noises when they are feeding.
The question is: how do fish respond to sounds? Following on from this we need to know what it means to us in terms of catching fish. Not surprisingly spawning shoals of fish often ignore the sight and sound of even large fishing vessels and, provided they will still feed, this can make them much easier to catch. Most anglers will also have come across fish in a feeding frenzy at some time (not often enough) and will have noticed that the fish seem oblivious of disturbance or movement when they are in this state. Bass which are ‘mad on’ sandeels will sometimes bump into your legs as you wade into the surf. Even thicklip grey mullet, which are among the wariest of fish, will ignore waving rods and moving anglers when they are preoccupied with maggots or offal.
A small boat approaching quietly is much less likely to scare shoals of fish than a big, noisy one, so switch off the engine and row or drift up to your mark if you can. Grey mullets and tunas have been observed to ignore constant sounds, such as steady engine noises, but to be scared by sudden changes. Irregular pulses of sound, like those of struggling or wounded fish, attract cod, pollack, sharks and some other predators, so it may pay to jig your pirk or retrieve your plug in a jerky, erratic fashion. If you do this you will also scare away some other species so it may be a matter of swings and roundabouts. Some fish can locate the source of a sound quite precisely. For example, pollack are attracted to the low frequency gurgling from the demand valves of SCUBA divers. It may be that these fish have learned that divers often disturb potential prey (just like starlings following cows around in a field). Cod are even attracted to quite distant sounds. One additional fact which is worth knowing is that fish will usually become accustomed to sounds which they hear every day and will then come to ignore them.
To sum it all up, there is no doubt that fish hear lots of sounds. Even when there is plenty of natural or everyday noise in the sea, it will pay you to minimise your banging about, stamping along the beach, changing the gear of your inboard engine or dropping anchor from the boat. Some species, particularly predators, are likely to be drawn to erratic pulsed vibrations but others will be scared away. In general, until someone produces an anglers’ ‘Walkman’ programmed with particular sounds to attract each preferred species, it is wisest to adopt the good old fashioned quiet approach.
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Keep it quiet!