''O Sole mio' '
SOLE AND OTHER FLAT FISH Part 1
As a group, the flat fishes show a variety of feeding habits almost as great as that of all other species put together. They range from the burrowing bottom-grubbing soles to full-blown, fish-eating predators like the halibut and the turbot. They have in common a very compressed body and a coloured eyed-side that, together, provide them with a camouflage superior even to that of the renowned chameleon.
From the angler's point of view, the flat fishes alone could provide more than a lifetime of interest. Certainly in the Poole area, flounder, plaice, dab and common sole are all much sought after both for sport and for eating.
With regard to angling for that popular species, the flounder, it would be difficult to better the book Sea Angling with the Baited Spoon, written by John Garrad. Any angler, whatever his quarry and whether he fishes in the sea or fresh waters, could do worse than follow Garrad's example of how to evaluate and develop a single method of fishing. As far as we are aware, no one has continued John Garrad's experiments with the baited spoon, despite the fact that his reported catches of flounders were probably better, and certainly more consistent than any reported before or since. This apathy is all the more surprising in view of the fact that Garrad was at pains to suggest how other species might respond to the enormous variety of lures that he tested.
In no way could we claim to be as knowledgeable about flat fish as Garrad, nor indeed as many other anglers. Nonetheless some of our experiences may be of interest to others. At one time or another we have fished for and caught most of the common species. Before giving any information it is probably worthwhile to provide a fairly detailed account of scientific studies on the feeding of flat fish in the light of which some of our observations, and those of others, may be seen in perspective. The sea angler may find interesting some experiments carried out on the feeding behaviour of several common species. The idea of this work was to see which factors were responsible for stimulating feeding. In these experiments the `prey' presented to the fish was in the form of models and scents and/or tastes (hereafter referred to as taste) .
The models used were spheres of 1, 2, 4 and 8 centimetres diameter, a small model fish and a plastic shrimp. The spheres were simply meant to represent `food' items of different sizes and from our point of view they could scarcely be better because lead weights of equivalent volume would weigh about .25 oz. 1.5 oz, 12oz and 6.5 lb. The largest would perhaps be a little on the large side even for a fast tide on the Skerries Banks, but even so the sizes are of the right order. The scents used were the juices of mussel or shrimp and (for experiments with turbot and brill} the juices of sole or cucumber smelt.
The first tests were made with the sole - a highly specialised nocturnal-feeding, flat fish with a very well developed sense of touch on the underside of the head. The sole was attracted to the three smaller spheres and to the plastic shrimp but it panicked at the sight of the largest sphere. In all cases the attractiveness of the models was increased by the presence of mussel or shrimp juice in the water. Significantly the sole also showed a strong panic reaction to the presence of a small codling in its tank.
The sole, although it is almost exclusively a night feeder, uses its powers of both vision and taste to locate its prey. As in the case of the fifteen-spined stickleback mentioned earlier, the effects of each stimulus were increased by the presence of another. It is perhaps surprising that the plaice, the flounder and the dab (unlike the sole) showed no interest in any of the spheres, expressing neither feeding nor flight reactions. Occasionally all three species would approach and snap at the plastic shrimp but only when it was moving. In fact, the dab even swallowed the shrimp in one instance. In contrast, when the juices of mussel or shrimp were in the water all three swam up to, and even bit at the spheres.
A second set of tests also with plaice flounder and dab were designed to see how good these fish were at locating their food. To do this a fine jet of seawater was squirted from a tiny glass tube, the tip of which projected just above the surface of the sand on the bottom of the tank. The plaice was the only one of the three to react to a plain jet of water. Plaice, it should be noted, often feed on the siphon tubes of burrowing clams, tubes from which little jets of water are constantly being pumped by the molluscs. Where very dilute shrimp juice was added to the water jet, both the plaice and the flounder located and bit at the end of the glass tube. The dab was unable to locate the tube and just swam about aimlessly snapping its jaws. It clearly sensed the shrimp juice and when the 2-cm sphere was presented it promptly attacked it. The dab is by nature a more active hunter than either flounder or plaice, eating shrimps and similar fast-swimming creatures. All three fish are essentially daytime hunters in which both sight and taste are important.
G.A. Steven, in his interesting account of the feeding of the `lemon sole', which is scarcely an angler's fish, describes how this fish is a specialist worm-feeder- and pounces from a 'head in air' position vertically down on the worms as they emerge cautiously from their sea-bed burrows. In this account he mentions that the plaice is not nearly so good at catching worms because it attacks by swimming with its body horizontal and its head close to the seabed. The dab, which is much more active than either, takes up an intermediate posture with its head slightly raised in an alert fashion. It feeds on a much wider range of food items.
Returning to the feeding experiments, the turbot and the brill are closely related and very similar. They are active daytime feeders, mainly eating fish. Both species ignored the three smaller spheres even when mussel, shrimp or fish juice were in the water, nor did they show any reaction to the juices alone. As in the case of the sole, the largest sphere caused a very strong flight (panic) reaction. Fish that were previously buried in the sand came out and swam quickly away. The conclusion would seem to be: when fishing for turbot or brill, beware the use of short traces, which place the bait too close to large leads.
If they were moving, models of fish were approached and snapped at by turbot and brill. Moving plastic shrimps were also attacked, but neither mussel, shrimp or fish juice enhanced the feeding behaviour.
Generally, sight feeders such as turbot, bass, pollack or mackerel, react only to something that looks and moves right (i.e. like the normal prey) and not to mere lumps of material such as rough old chunks of bait. They may even be terrified of large non-food objects such as lead weights.
The structures of the brains and in particular of the guts of the flat fishes considered above bear out the observations described. The fish feeders have larger mouths and stomachs and shorter intestines than the other species. The gill rakers (comb-like teeth on the inner edges of the gills) of the turbot and the brill are few and large and serve to prevent the escape of large prey through the gill openings. In contrast, fish such as the sole, which feed on bottom-living animals containing a large proportion of indigestible material, have small mouths and stomachs, very long intestines and small fine gill rakers. Dab, plaice and flounder fall into an intermediate group.
To put into perspective some of the behaviour described, it is worthwhile having a look at the food of the species considered. When possible the results are separated into small and large fish as was done for rays.
The common sole is unquestionably a nocturnal feeder which, during the daylight hours, remains buried in the sand, moving little. Observations made by W. Bateson in 1890 are also of great interest to the angler in search of these strange little fish. He describes how the sole creeps about the seabed using its fringe of fin rays almost like the legs of a millipede. As it moves slowly along it gently pats the sand with its head, with the sense organs on its blind side feeling for objects lying on the surface. The sole only succeeds in finding food that lies on the seabed and will not notice material suspended above it. Even the mouth of the sole is positioned so as to facilitate picking up objects from the bed of the sea.
Associated with its cryptic behaviour and specialised way of feeding, quite a lot of work has been done on the chemical senses of the sole. Young soles weaned from live brine shrimps would only eat an artificial diet when it was flavoured with the juice of the mussel or with the substance Glycine-betaine, a component of mussel juice. Both detection and selection of food items depend on this chemical. Various amino acids are also involved in recognition of food, both in small sole and in other fish. Glycine-betaine is a true feeding stimulant for sole, because its presence increases food consumption over a long period of time. The worms, small molluscs and crustaceans on which the sole feeds are known to contain large amounts of this feeding stimulant and the fish has a special sense for detecting it. The Glycine-betaine is absent from the flesh of fish (other than dogfish and rays) so attractants such as pilchard oil are, presumably, useless for sole. The sole is quite a slow-growing fish and takes ten to fifteen years to reach about 15-inches in length. The fish are in poor condition in June and July but reach a peak in the autumn and winter.
In our limited experience of fishing for sole, an interesting series of observations led us to an approach subtly different to the one that we used at first. It was clear that sole were to be caught in the autumn and at night from the sandy, rather featureless beaches off Bournemouth and Swanage. Harry and I, keen to catch one of these gourmet's delights, fished with long traces, small hooks and worm baits, much as we had been accustomed to do for flounder and plaice. The results were, to say the least pathetic. We caught a few flounders, some small plaice, tiny school bass, poor cod and more poor cod. We would cast out and retrieve slowly across the sand as was our custom and, every minute or two we would catch a poor cod, or sometimes, a pouting.
The answer was revealed to us by Fred Philpott who, during a stay at the Lowestoft marine labs, had specialised in catching plaice and sole. Fred was full of confidence when we told him of our desire to catch a sole. `No problem,' he said. Disbelieving, we said we would wait until the fish was under the grill before we were convinced. On the following Monday as we arrived at work, there was Fred with a fine 2-pound plaice and (wonder of wonders) a 0.75-pound sole. We were incredulous. `Where did you get them?' The reply was even more surprising: Fred had spent the Sunday afternoon and evening fishing from the same stretch of beach on which Harry and I had waged our campaign on the uncatchable sole. We were astounded but, the following Wednesday, our astonishment grew to the proportions of hero worship when the indomitable Fred produced two more sole of 1 -pound and 2.5-pounds. How do you do it? we asked. Legered lugworm, came the reply. `What do you mean, 1egered lugworm?' we said. We have fished lug and rag for hours and all we catch are pouting and poor cod!'
The next time Fred went fishing for flatfish, Harry and I were with him. We inspected Fred's tackle minutely as he set it up. It was virtually identical to our own. A simple paternoster with a flowing trace and a long-shanked No.1 hook baited with a plump lugworm. The hook was a fraction larger than ours but this seemed unlikely to make any difference. We arranged our-selves along the beach and cast out our respective tackles. Harry and I stood holding the rods, retrieving slowly and feeling carefully for the slightest hint of interest from a sole. Fred cast out, propped the rod on its rest and lay down on the beach.
Every couple of minutes Harry or I would, as normal, get a rattling bite, strike, and reel in a poor cod, a small bass, even an 8-ounce flounder. For over an hour Fred lay, practically immobile the back of his head cradled in his interlocked fingers. Occasionally he would whistle a tune or crack a joke but, in the main, he was motionless. As Harry was reeling in his twentieth or so, 2-ounce poor cod, Fred stood up. `There's a knock,' he said and a little later he picked up his beach caster. A minute or more after this he struck hard and reeled in a 1-pound common sole, the only one caught that night. The answer to the conundrum was staring us in the face - presentation! Harry and I, constantly alert and searching the sea bed with fingers on the trigger, were really geared up to attracting the actively-hunting school bass and pouting. Fred's inert lugworm on the other hand was tailor-made to avoid these nuisance fish and tempt the sniffing, pitpatting soles.
On later trips we adapted our methods and even managed to catch some sole from the beaches we had fished unsuccessfully for years. By leaving the worms to fish quietly for themselves, the number of pout bites was reduced enormously and our intended quarry had time to find and take the baits. Even the movement of a lively ragworm seemed sufficient to attract pouting and, perhaps for this reason, lug was a better bait for sole. We will, I fear, never be good sole fishermen, the essential enthusiasm is lacking but these fascinating fish gave us an object lesson in the importance of bait presentation.
To those who wish to try `lazing' for sole, there is a technique devised by the natives of the South Pacific for fish called escolar that might be of interest. The fish are caught on set ground lines that lie loosely on the seabed. The key to success is a specially fashioned wood hook with an inturned point. Scientific tests involving modern long lines for deep-sea fish compared the value of metal hooks of normal design and others based on the design of the escolar hook. The latter were much more successful and it would seem that a similar pattern could be worth a try for the sedentary sole (Circle hooks are now all the rage in some branches of angling).