6. SAMPLING WITH ACTIVE GEAR

E. Dahm
Institut für Fangtechnik
Bundes forschungsanstalt für Fischerei
Talmaille 9, 2000 Hamburg

6.1 INTRODUCTION

Active fishing methods are especially suitable for sampling large proportions of the whole fish stock or large numbers of fish. The term “active” means that the fishing gear is dragged through the water by human, animal or engine power. In most cases the efficiency of active gear is considerably higher than that of “passive” gear, such as gillnets and traps, which rely for their efficiency on the movement of the fish themselves.

In this chapter the use of the following types of active gear will be discussed:

With trawls the wings are spread by otterboards, two boats towing one net or by a beam or spreader. Because beam trawls are only of local importance they are not discussed in this article.

The references cited are intended solely to provide examples and are drawn from a very extensive literature. They are not, therefore, intended as a complete review of the subject.

6.2 SEINES OR DRAGNETS

Seines (Figure 6.1) are the biggest, most expensive and labour-consuming fishing gears used in inland waters. Their use for stock assessment has been described only rarely (Table 6.1). In Eastern European countries, where well-established inland water fishery statistics apparently exist, changes in catch per unit effort over a long period can give a good method for assessing the relative changes in fish stocks (Leopold et al., 1975). In West European countries, with their use of inland waters by conflicting leisure activities, the use of seines has had to be either completely abandoned (Le Cren, Bagenal and Kipling, 1975) or protected by legislation. For example, in the lakes around West Berlin it is forbidden to use pleasure-boats or angling gear at night in order that seines can work undisturbed (Grosch, 1974).

Figure 6.1 Different kinds of seines:

1. beach seine without bag
2. normal inland water seine
3. special form of a seine with a bag asymetrically attached (from Brandt, 1972)

The main advantage of using seine nets for stock assessment experiments is the size of sample which can be caught in a relatively short time if the fishing conditions are favourable (Table 6.1, see “Efficiency”). The morphology of the bottom is one of the most important of these conditions. Leopold et al. (1975) point out that seining beaches should have hard, clear, gently sloping bottoms. Efficiency of the net is considerably reduced if it is hauled into a boat. The type of shore or bank, and various human activities may also limit the use of seines (Le Cren et al., 1975).

The disadvantages of the net are its great cost and the number of personnel needed for its use. If assessments in several different waters are intended, the transport of the gear is very difficult. Furthermore, not all areas of the water body are accessible, as with some other gears, but only certain selected sites. There snags, etc., have to be removed, and the preparation of special sampling beaches may well influence the fish behaviour. Seine nets are mesh-selective for certain sizes of fish (Backiel and Korycki, 1972) and avoidance reactions by fishes encircled by the wings of dragnets also select against larger and more active fish (Holcik and Bastl, 1975). In running waters seines can only be used in quiet bays. The maximum depth which can be fished is given by the wing height of the nets. Average values range from 6 to 15 m.

6.3 TRAWLS

6.3.1 Where trawls can be used

The following characteristics of a lake have to be considered where trawls are to be used:

(a) Area

Modern inland water trawls measure 20 to 30 m in length, to which should be added the length of legs and sweeplines (about 40 m). The length of the towing warps should be five times the depth of the water (or as much as ten times in shallow waters). Thus, an additional distance of about 150 m is necessary for the playing out of the net. After the start of towing, the trawl does not immediately reach its optimum catching performance. The time during which the net is actually catching should represent a reasonable proportion of the total time the net is in the water including that expended for paying out and hauling. Towing times of less than 10 minutes do not meet this condition. Assuming an average towing speed of two knots, i.e. circa 3.7 km/h, a minimum towing distance of 600 m must be available. In the two-boat fisheries described below (6.3.4) the two boats should be separated by 50– 100 m and a security distance of 25 m from each shore is needed. This means that waters where two-boat trawling is to be used must have a minimum area of 125 m × 600 m = 7,500 m² free towing space and must cover at least a total area of 10 ha for one haul even under the most favourable shoreline conditions. One-boat trawls seem to impose fewer conditions since the distance separating the two otterboards is less than that needed between the two towing boats. On the other hand, one-boat fisheries make it necessary to operate on almost flat grounds in order to ensure optimal spreading. Steep slopes, edges and underwater canyons hamper the efficiency of the boards and should, if possible, be avoided. This needs plenty of space, hence it is obvious that the minimum area of waters suitable for trawling by the one-boat method must be even more extensive.

(b) Depth

There are less severe requirements for the minimum depth of a water to be trawled. In Lake Chilwa, Malawi, Ratcliffe (1974) proved that a trawl fishery can be successfully established even in very shallow waters which dry up completely at times. However, the water depth should not be much less than the theoretical opening height of the nets in use. The correct shape of the trawl, hence maximum catching efficiency, is no longer guaranteed if the water is too shallow, especially with four-panel nets (see Figure 6.2).

Any attempt to get samples from the bottom of relatively deep waters (more than 30 m) may only succeed where the gear has been especially adapted. It was shown during investigations by the Institute for Gear Research, Hamburg, in Finnish lakes and in Lake Constance that a two-boat trawl could not be manoeuvred deeper than 25–30 m at an average speed of 2 knots (3.7 km/h) with towing warps of 200 m long, even when front weights were used which were almost too heavy to be handled by manpower. Maximum depths of 80 m have been reached only when ships have been especially equipped for fishing at greater depths. Modifications include winches of appropriate strength, heavy weights and towing warps of strong wire, such as described by Bergstrand and Cordone (1971) or Roberts (1975) (see Table 6.2).

Figure 6.2 Different views of two-panel and four-panel nets

6.3.2 Main difference between bottom and midwater trawls

Bottom trawls and midwater trawls for inland water fisheries differ in construction. Bottom trawls are mostly two-panel nets, and midwater trawls are usually four-panel nets (Figure 6.2). In the pelagic fisheries in inland waters with slow towing boats the latter construction results in a bigger opening area than in two-panel nets for an equal length of the headline. Two-panel nets are preferred for bottom fisheries because the spreading forces of otterboards or towing boats are transferred to the complete net. In four-panel nets the spreading force acts only on the upper panel, and the vertical opening is obtained by attaching weights. This lets the netting go slack when the net touches the bottom, resulting in decreased catching efficiency and increased susceptibility to damage. The four-panel nets as used by Ratcliffe (1974) for a bottom trawl survey were so adapted to the special conditions that they strongly resembled two-panel nets (the removal of the lower wings, the combination of legs as a spreader, the ground rope attached to the upper part of the side panel).

6.3.3 One-boat method

(a) One-boat bottom trawls

Gear of this kind has been used for fish sampling and stock assessment on several occasions (see Table 6.2). The use of otterboards, which is necessary for the one-boat method, cannot be recommended in all cases because the towing resistance of such a net is then increased up to 40 percent and additional towing force is needed. Otterboards may run into the often soft bottoms of inland waters and have then to be lifted with great labour. The repeated “ploughing” of the bottom by the otterboards can result in undesirable ecological changes of the bottom fauna. Although used in several water bodies (Table 6.2), the one-boat method of bottom-trawling in inland waters is only to be recommended when two boats are not available for towing.

Notes on the size of the otterboards used are relatively scarce. Bergstrand & Cordone (1971) employed flat otterboards of 1.2 m², Lange (1975) used 0.5 m² boards of a round cambered type for nets of similar dimensions.

(b) One-boat midwater trawls

One-boat midwater trawls with their otterboards, hydrofoils and depressors suffer from the same disadvantage of high towing resistance met in the one-boat bottom trawls. But this may be overcome by appropriate towing power. Two examples are given in Table 6.3.

The net of Houser and Dunn (1967) is of special interest, since it demonstrates that a midwater trawl may also be towed with a single towing warp. The technique is known from the lsaac-Kidd trawl used in deep sea research, but has, until now, seldom been applied to normal trawling where, as a rule, two towing warps drag the net. It may be of interest that in the early days of midwater trawl development, trials with as many as four towing warps have been conducted. On account of its complications this technique has been abandoned.

(c) Advantages and disadvantages of the one-boat method

The main advantage is that only one vessel is needed for the fishing operation. One man is therefore responsible for the steering of the vessel. The fishing gear and measuring instruments are close at hand during operations.

The disadvantages of the one-boat method are the increased requirement for towing power, the ecological effects on the bottom, the spreading performance of the net which is not always optimal, and the danger of running the otterboards into the soft bottom (which may also be important for midwater trawls during the paying out and hauling in of the net). To overcome these disadvantages, adequate towing power-driven winches are necessary for a one-boat trawl fishery.

6.3.4 Two-boat method

(a) Two-boat bottom trawls

This kind of net is illustrated in Figure 6.3 and its use is exemplified in Table 6.4. Further examples can be found in Steinberg (1964, 1967, 1968, 1971, 1973) and in Steinberg and Dahm (1974). The headline in the nets, and thus the size of the gear described by the above-mentioned authors, is more or less the same. However, the towing vessels ranged from 5.2 m boats with 4.5 hp outboard motors to 9 m cutter-like boats with 36 hp inboard engines and the towing speed differed. The mesh size of the codend from 12 to 64 mm stretched measure were used; the smallest boats used the smallest mesh.

Figure 6.3 Schematic presentation of the rigging for freshwater two-boat bottom trawls

Two-boat trawling achieves the lateral spreading of the net by maintaining a prescribed distance between the towing boats; this distance being controlled by means of a marked connection line between the two boats. Ratcliffe (cited by Nédélec, 1975) used a connection line between the two wing tips of his net, the length of which was 11 m with a 21 m headline length but the efficiency of such a line seems doubtful.

As a rule of thumb to estimate the distance between towing boats Steinberg (1967) used half the length of the towing warps of at least 50 m. A more appropriate formula is:

Taking into account that the length of the towing warp should be ten times the depth of trawling, the distance between boats for a trawl with 23 m headline and 26 m of legs and sweeplines working at 10 m depth, would be 68.3 m. At greater depths (25–30 m) the towing warp can be five times the depth and the distance accordingly proportional (i.e., 79.4– 90.7 m). In general, in inland fisheries shorter sweeplines are used and the weighting of the forenet and the weights in front of the net are limited to only a few kilogrammes (Nédélec, 1975). The reason is that the bottom of inland waters is often soft and nets tend to run into mud. Steinberg (in Nédélec, 1975) showed that attaching a weighted additional rope as a garland to the actual ground rope prevents the trawl from running into mud.

The two-boat bottom trawls used in inland waters can be paid out and hauled by hand but at least hand-operated winches are necessary for heavier kinds of nets.

(b) Two-boat midwater trawls

Nets of this type are relatively unknown in inland fisheries. Details of the construction, rigging, and mode of operation during shooting and hauling can be found in the publications of Steinberg (1967, 1971), and Steinberg et al. (1975) (see Table 6.5). The depth at which this kind of trawl is to be towed is regulated by lines connecting the front weights attached at the ends of sweeplines with surface floats (Figure 6.4). This method of depth control may also be used in one-boat trawling when the otterboards are hung up by means of floats at the surface instead of the weights. Any further regulation of the depth of the net by changing the speed of the boat or the length of the warps is only possible to a very limited extent. With adequate engine and which power (see Table 6.5) midwater trawling can be carried out in lakes as well as in inshore areas.

The use of a netsonde is essential throughout this type of operation. The depth at which the net operates for any given length of towing warp and number of engine revolutions is more precisely determined by this equipment than by the towing speed, which is more difficult to determine (Steinberg and Dahm, 1975).

(c) Advantages and disadvantages of the two-boat method

The advantages both for bottom and for pelagic trawling lie mainly in the fact that boats with only limited engine power can be used. By keeping a fixed distance between boats the net is always towed at its optimum spread. A spare net can be kept ready for shooting in the second boat should a net be damaged, so that there is no interruption in the fishery. Lack of the heavy otterboards permits the handling of the lighter types of the gear by manpower alone.

Figure 6.4 Schematic presentation of the rigging for a freshwater two-boat midwater trawl

Figure 6.5 Fishing operations in setting and hauling a simple purse seine

The disadvantages are in the sometimes restricted manoeuvrability of the towing boats (changes of course require a lot of space) and in the difficulty of communication between the boats, which is especially severe at night. Both handicaps can be overcome in a trained team.

6.4 PURSE SEINES

Purse seines (Figure 6.5) seem to be the most effective fishing gear for catching fishes living near the surface. Examples of sampling fish with small and large nets of this kind are given in Table 6.6.

Nüman (1972) cites the “Klusgarn”, a purse seine which has been used for centuries in Lake Constance, and which has been forbidden since 1967 on account of its excessive efficiency. Experiments in 1939 showed that the selectivity of the gear is dependent mainly on the speed of hauling. The fishery authorities therefore forbade the gear to protect undersized fishes. Efficiency is also confirmed by Johnsen and Sims (1973) who state that no other fishing method yields the same amount of fish for a sample as did the purse seine, and it is one of its advantages.

The operational limitations for beach seines do not affect this gear, since the purse seine fishes the surface and can be handled even under the often rough weather conditions of an estuary.

The disadvantage of the purse seine is, that to work effectively, it must have a length of about 200 m to avoid escape reactions by the target fish school. Because of its size strong winches must be available and the personnel should not only be trained to handle the gear but also should be able to spot fish aggregations by eye. Apart from the cost of such a gear (at least 20 times that of an inland water trawl), the benefit for stock assessment is not easy to determine. If a complete assessment of all stocks in an inland water body is intended, other gears have to be used since purse seines can only catch bottom-living fish near to the shore, and even then with doubtful efficiency.

6.5 GENERAL LIMITATIONS, SELECTIVITY AND EFFICIENCY OF ACTIVE GEARS

The active gears described above can be used in about any kind of standing and running waters if properly scaled and no obstacles to drag them through the water exist. Small beach seines (dragnets) can work in small areas of a few hectares, small trawls, such as that used by Dadswell (1975), can sample small fish and invertebrates, commercial summer beach seines and winter seines fish in lakes of an area about 100 ha, trawls designed to catch table size fish in freshwaters can be effectively used for sampling in rather larger water bodies.

Size of lakes (area and depth) and the structure of the bottom may impose limitations on the use of active gear.

Active gears are less sensitive to the current of water than the passive ones. Thus, for example, German fishermen have used bottom trawls for many decades at the mouths of the Elbe and Weser Rivers, where tidal currents of up to 4 knots (7.4 km/h) occur. Pelagic trawls and purse seines used in open water are independent of currents as shown by Johnsen and Sims (1973), in the Columbia River. To some extent beach seines and dragnets are hampered by currents but may be used in selected sites (Northcote, 1975). Obviously limits do arise, and where current is strong such as in the Magdalena River (Colombia) where currents of 8 knots occur, most gear which needs bottom contact to function, will fail. The other limitation is the likely interference of large size fishing gear with various commercial and recreational uses of rivers and lakes.

In common with other types of fishing methods, active gears are selective for size of fish. For instance, Backiel and Korycki (1972) compared the length distribution of roach caught by a beach seine with the mesh size in the codend of 2.5 cm with the distribution found in gillnets with the same mesh size. It appeared that the two distributions were of the same shape but that from the seine was shifted by 1 cm only toward larger roach. The beach seine was much more selective than a set of three gillnets with 2.5, 2.8 and 3.2 cm mesh sizes.

The selective action of trawls in freshwaters has been dealt with by Ferguson and Regier (1963), Cordone and Kudhongania (1972) and Turner (1977). The technique for selectivity determination applied in marine fisheries involves the use of a fine meshed cover bag drawn over the original codend to retain escaping fish. Experiments with this kind of contraption enables the proportion of fish at each length entering the trawl to be assessed as compared with those which are retained in the codend. Plotting these proportions (e.g. percent of fish retained in the codend) versus respective length of fish, one can find a length at which 50 percent of fish is retained by a particular codend. This length is termed mean selection length or 50 percent retention length 1_c and it is proportional to mesh size in the codend (m). Thus, the selection factor F is :

and usually varies between 2 and 4.

When sampling fish with trawls this factor should be estimated. Dryer (1966) gives results from synchronous catches with trawls and gillnets that show distinct differences in the average total length of three species depending on the gear used. Gillnets from 25 to 27 mm mesh size were used and compared with a trawl codend of 12.5 mm meshes and the average length of the fish caught in the gillnet was always greater.

For estimation of fish stocks by means of active gears both catch per unit of effort and catch per area or volume swept by a gear can be used. With the latter method there is always a danger of under-estimation of numbers of larger fish due to their avoidance reaction especially against slow-moving dragnets (e.g., HolĎik and Bastl, 1975). Alverson and Pereyra (1969) report that several authors assumed that catch per unit of effort is a function of stock density in any area surveyed and that the average density of fish in the path of a bottom-trawl can be calculated. They see two main objectives against the assumption: Firstly, that the net might over-roll fish such as plaice and flounder which are buried in the seabed or fail to capture fish which are farther off bottom than the headrope height of the trawl.

Secondly, the net may catch more fish than are really in the water column sieved by the net opening by herding with otterboards and sweeplines. For most species the authors, therefore, assume an efficiency where these adverse effects neutralize each other. Predictions of standing stock using this assumption have given reasonable results.

Houser and Dunn (1967) seem to support their assumption in their considerations of the number of midwater trawl hauls suitable for a given water body, since they assume the fish to be uniformly dispersed over the area and to not react to the gear or to other fish. Their work is a useful attempt to determine the fishing effort necessary for the assessment of a pelagic stock.

Behaviour of fish and their reaction to the moving net also affect fishing effeciency and should be taken into account in sampling designs and interpretation of data.

In a reservoir in the Federal Republic of Germany, 30 kg/h vendace (Coregonus albula) were caught with a pelagic trawl during daytime whereas soon after dusk, when optical stimuli disappear the same ships and gear caught 200 kg in 20 minutes. Changes in the behaviour of fish with season also affect catches. Steinberg and Dahm (1975) indicated that in lakes in northern Germany some fishes are to be caught by bottom trawls during winter only. In summer, with a stable temperature stratification, they leave the near-bottom poor of oxygen layers and ascend to the metalimnion. During this season they can be caught only by pelagic trawls at night.

A comparison of different sampling methods including a mark-recapture experiment, pots, trawl and counts by divers is given by Barr (1971). Although he deals with the stock of shrimp in a confined area, his work seems a most valuable example of how to handle the data and how to plan a study on stock assessment.

6.6 REFERENCES

Nadreev, N.N., 1966 Handbook of fishing gear and its rigging. Jerusalem, Israel Program for Scientific Translations, IPST Cat. No. 1654:454 p.

Alverson, D.L. and W.T. Pereyra, 1969 Demersal fish exploration in northeastern Pacific Ocean-an evaluation of exploratory fishing methods and analytical approaches to stock size and yield forecasts. J.Fish.Res.Board Can., 26(8):1985–2001

Backiel, T, and A. Korycki, 1972 Smiertelnosc ploci i wrarg gi u jerione Klebruskien (Mortality of roach and rudd in Klebarskie Lake). Rocz.Nauk.Roln.(Ser.H), 94(1):23–39

Barr, L., 1971 Methods of estimating the abundance of juvenile spot shrimp in a shallow nursery area. Trans.Am.Fish.Soc., 100(4):781-7

Bergstrand, E. and A.J. Cordone, 1971 Exploratory bottom trawling in Lake Victoria. Afr.J.Trop. Hydrobiol.Fish., 1(1):13–23

Brandt, A. von, 1957 Fischfanggerate und Fangmethoden - ein Beitrag zu ihrer Systematik. Protok. Fischereitech., 5(22/23):27–49

Cordone, E. and A.J. Kudhongania, 1972 Observations on the influence of codend mesh size on bottom trawl catches in Lake Victoria with emphasis on the Haplochromis population. Afr.J.Trop.Hydrobiol.Fish., 2(1):1–19

Dadswell, M.J., 1975 A small boat otter trawl for limnological studies. J.Fish.Res.Board Can., 32(12):2535-8

Dryer, W.R., 1966 Bathymetric distribution of fish in the Apostle Island region, Lake Superior. Trans.Am.Fish.Soc., 95:248-59

Durkin, J.T. and D.L. Park, 1967 A purse seine for sampling juvenile salmonids. Prog.Fish-Cult., 29:56-9

Ferguson, R.G. and H. Regier, 1963 Selectivity of four trawl cod ends towards smelt. Trans. Am.Fish.Soc., 92:125-31

Freytag, G., W. Horn and R. Steinberg, 1971 Erfolgreiche Weiterentwicklung binnenfischereilicher Schleppnetze durch Elektrifizierung. Protok.Fischereitech., 12(58):417-26

Grosch, U., 1974 Uber die Fischerei auf der Berliner Havel und die Arbeiten des Fischereiamtes. Fischwirt, 24:9

Hattop, H. -W. and G. Fredel, 1969 Die Anwendung elektrischer Schleppnetze in den Binnengewässern der Deutschen Demokratischen Republik. Z.Fisch., 17:215-26

Holcik, J. and I. Bastl, 1975 Sampling and population estimation with small mesh size as used during icthyological research on Da bian backwaters. EIFAC Tech.Pap., (23) Suppl. 1, vol. 2:627-40

Houser, A. and J.E. Dunn, 1967 Estimating the size of the threadfin shad population in Bull Shoal Reservoir from midwater trawl catches. Trans.Am.Fish.Soc., 96(2):76–84

Hunter, J.R., D.C. Aasted and C.T. Mitchell, 1966 Design and use of a miniature purse seine. Prog.Fish-Cult., 28:175-9

Johnsen, R.C. and C.W. Sims, 1973 Purse seining for juvenile salmon and trout in the Columbia River Estuary. Trans.Am.Fish.Soc., 102:341-5

Lange, K., 1975 Einsatz eines Eiboot-Grundschleppnetzes (Schernetz) bei der Regulierung von WeiBfischbeständen. Fischwirtsch.Hamb., 22(6):181-2

Le Cren, E., T.B. Bagenal and C. Kipling, 1975 Experiences with fish sampling methods in Windermere. EIFAC Tech.Pap., (23)Suppl.1, vol. 1:58–65

Leopold, M. et al., 1975 Effectiveness of seine catches for the estimation of fish populations in Polish lakes. EIFAC Tech.Pap., (23)Suppl.1, vol. 1:49–57

Nedelec, C. (ed.), 1975 FAO catalogue of small-scale fishing gear. West Byfleet Survey, Fishing News (Books) Ltd., for FAO, 191 p.

Nelson, W.R. and M.F. Boussu, 1974 Evaluation of trawls for monitoring and harvesting fish populations in Lake Oahe, South Dakota. Tech.Pap.U.S.Fish Wildl.Ser., (76):15 p.

Northcote, T.G., 1975 Sampling of fish populations for evaluation of water quality conditions in large British Columbia lakes and rivers. EIFAC Tech.Pap., (23) Suppl.1, vol. 2:704-21

Numann, W., 1972 The Bodensee: effects of exploitation and eutrophication on the salmonid community. J.Fish.Res.Board Can., 29(6):833-47

Ratcliffe, C., 1974 Commercial small craft pair trawling trials. Lake Chilwa, Malawi, 1971. Afr.J.Trop.Hydrobiol.Fish., 3(1):61–78

Roberts, P.A., 1975 Developing a lake fishery in Northern Kenya. Fish.News Int., 14(2):21-5

Rupp, R.S. and S.E. De Roche, 1960 Use of small otter trawl to sample deep water fishes in Maine lakes. Prog.Fish-Cult., 22:134-7

Steinberg, R., 1964 Versuchsfischerei mit Tuckzeesen in norddeutschen Binnenseen. Fischwirt, 14:305-11

Steinberg, 1967 Zur Frage der Schleppnetzfischerei in Binnenewassern. Fischwirt, 17:306-16

Steinberg, 1968 Zur Frage der Schleppnetzfischerei in FlieBgewassern. Fischwirt, 19:130-3

Steinberg, 1971 Two-boat bottom and midwater trawling. In Modern fishing gear of the world, edited by H. Kristjonsson. London, Fishing News (Books) Ltd., for FAO, vol. 3: 423-30

Steinberg, 1973 Schleppnetzfischerei zur Bestabdsregulierung in Binnengewassern. Fischwirt, 23:119

Steinberg R. and E. Dahm, 1974 Moglichkeiten zur Regulierung von WeiBfischbestaden mit dem Zwei-Schiff-Schleppnetz. Fischwirt, 24:4

Steinberg R., 1975 The use of two-boat bottom and midwater trawls in inland waters - experiences in the German fishery. EIFAC Tech.Pap., (23) Suppl.1, vol. 1:23–35

Threinen, C.W., 1956 The success of a seine in the sampling of a largemouth bass population. Prog.Fish-Cult., 18:81-7

Turner, J.L., (in press) Influence of codend meshsize on demersal trawl catches in Lake Malawi. Afr.J.Trop.Hydrobiol.Fish., 6(1)

von Geldern, C.E., 1972 A midwater trawl for threadfin shad, Dorosoma petenense. Calif.Fish Game, 58(4):268-76