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Swimming activity of perch, Perca fluviatilis L
Journal of Fish Biology
Abstract
The swimming excursions of individual perch, measured automatically, within either cages in Windermere or in a trough on the shore, showed increases at dawn and dusk and in the summer. Similar measurements in troughs in the laboratory showed increased activity following a change from light to dark and vice versa, a pattern that was obliterated by either continuous light or continuous darkness. These results are discussed in relation to water temperature and catches of perch in traps.
... Perch is a common fish species in European lakes (Thorpe, 1977), occurring, for example, in >95% of all Danish lakes, where it often accounts for a substantial show a maximum in summer and a minimum in winter (Craig, 1977;Eriksson, 1978;Neuman, Thoresson & Sandströ m, 1996). Some authors have correlated activity with temperature (Eriksson, 1978;Huusko et al., 1996) or light (Craig, 1977;Alabaster & Stott, 1978). ...
... However, a sizedependent difference in activity within each sex is unlikely, as there was no grouping of the individual activity levels. The diel activity rhythm of perch generally confirms previous studies (Craig, 1977;Alabaster & Stott, 1978;Eriksson, 1978;Mackay & Craig, 1983). As found by Craig (1977), we observed that the difference in day and night activity with noticeable peaks at dusk and dawn is most pronounced in fall, winter and early spring (October-April). ...
... Differences in perch activity found in our investigations compared with previous studies could also be explained by the size of fish. The fish in our study was larger (27-37 cm) than in most other published studies where perch were £22 cm (Eriksson, 1978;Alabaster & Stott, 1978;Sandströ m, 1983;Neuman et al., 1996). It may be therefore that larger perch show more variable activity patterns independent of temperature than smaller perch, including higher activity at low temperatures. ...
1. Radio transmitters were implanted in large perch (27–37 cm) in a shallow lake in Denmark. Between 6 and 13 perch were tracked every 3 h for 24‐h periods twice (summer) or once a month (winter) from August 1997 to July 1998. Activity levels were recorded as minimum distance moved per hour.
2. No significant differences in activity levels of individual fish were observed.
3. Highest activities were observed at daytime with peaks at dawn and dusk or midday. This diel pattern was most pronounced from October to April, whereas diel variations were less in the summer months, with no peaks occurring in midsummer. The general lack of activity at night supports the idea that perch is a visually oriented forager.
4. There was no significant relationship between daytime activity during the year and temperature or day length, but nighttime activity was correlated with temperature. In contrast with previous findings, activity levels varied little seasonally, except for high activity levels that occurred concomitantly with high temperatures in August. Instead, we found a significant relationship between the total distances moved per day and temperature, indicating that perch moved at the same average speed in the wintertime, but did so for shorter periods than in summer because of shorter day lengths.
5. Diet of the tagged perch shifted from fish dominance between August and January to invertebrates from February to June. There was no correlation between the diet shift and activity levels, indicating that feeding on invertebrate requires similar activity levels as predation on fish.
6. The results of this telemetry study throughout a year suggest that perch are more active during the winter than previously inferred from gill‐net catches. This observation underscores the importance of perch as a predator of 0+ planktivorous fish in lakes and has potential implications for pelagic food web structure and lake management by biomanipulation.
... Diel activity patterns are well documented for roach and both percids (Craig, 1977; Rask, 1986; Bergman, 1988; Jamet, Gres, Lair, & Lasserre, 1990). The high numbers of perch found in the pelagic habitat during the day reflect the pronounced activity of this species under daylight conditions (Alabaster & Stott, 1978), which reflects its strong reliance upon visual orientation during foraging (Mills, Confer, & Kretchmer, 1986; Bergman, 1988; Diehl, 1988). By contrast, the night is known as a low-active period for perch, accompanied by substantial changes in the behaviour of the fish. ...
... By contrast, the night is known as a low-active period for perch, accompanied by substantial changes in the behaviour of the fish. For example, the break-up of perch shoals into individuals, settling down separately near the lake bottom (Hasler & Villemonte, 1953; Alabaster & Stott, 1978; Emery, 1973) may explain, why the numbers of caught perch in the night trawls decreased such obviously at night. In contrast, ruffe can orientate in addition by its effective lateral line sensory organs (Disler & Smirnov, 1977). ...
... Since roach density in the pelagic area of Mu¨ggelseeMu¨ggelsee did not decline during the night, and ruffe density even increased, there is little evidence to assume that the predation risk by pikeperch was high enough to induce diel horizontal migrations of juvenile fish. Instead, the drastic decline in juvenile fish density towards the night was overwhelmingly attributed to a decline in perch density, and it can be assumed that perch rested close to the bottom thus reducing the catching efficiency of the demersal trawl for this species in darkness (Alabaster & Stott, 1978). ...
Diel cycles of changing ambient illumination have been shown to have strong influence on fish community composition in freshwater systems, mainly due to diel habitat shifts of fish between sheltered and more exposed, but profitable sites. Low information is available, however, from diel patterns of fish community composition and feeding in the central areas of large shallow lakes where lake depth and diameter may hamper diel migrations. We studied whether there are diel differences in species abundance and shifts in feeding modes of the juvenile pelagic fish species over an 8 months sampling period in a shallow lake. The strong decline of perch numbers towards the night suggests low nocturnal activity for this species. In contrast, the nearly constant numbers of roach over the full diel cycle points to pronounced activity under changing light intensities. Increased ruffe numbers at night reflect the good adaptation of this species to feed efficiently at low light intensities. Niche segregation of fish species along the diet axis was low. There was low evidence that diel shifts in the fish community composition were attributed to diel horizontal migrations of species into or out of the pelagic zone. Because availability of preferred zooplanktonic prey was high, differential diel activity patterns of species reflect their genetically fixed, albeit varying adaptations to feed under low-light conditions, instead of being an active avoidance to reduce competition.
... Hence, their response to elevated illuminations at night may produce large effects on aquatic food webs. Perch are mobile, visual predators active during daytime (Craig, 1977;Thorpe, 1977;Diehl, 1988;Okun et al., 2005), with activity peaks at dusk (Alabaster and Stott, 1978;Jacobsen et al., 2002Jacobsen et al., , 2015 and resting periods at night (Helfman, 1981;Schleuter and Eckmann, 2008). Their last foraging is often performed during dusk and then restored at dawn (Helfman, 1981;Schleuter and Eckmann, 2008;Schleuter et al., 2007). ...
Due to the widespread use of artificial light, freshwater ecosystems in urban areas at night are often subjected to light of intensities exceeding that of the moonlight. Nocturnal dim light could modify fish behaviour and benefit visual predators because of enhanced foraging success compared to dark nights. However, effects of nocturnal light could be mitigated by the presence of structured habitats providing refuges for prey. We tested in laboratory experiments whether nocturnal light of low intensity (2 lx) increases foraging efficiency of the Eurasian perch (Perca fluviatilis) on invertebrate prey (Gammarus fossarum). The tests were conducted at dusk and night under two light regimes: natural cycle with dark nights and disturbed cycle with artificially illuminated nights, in habitats differing in structural complexity: sand and woody debris. We found that nocturnal illumination significantly enhanced the consumption of gammarids by fish compared to dark nights. In addition, the perch was as effective predator in illuminated nights (2 lx) as at dusk (10 lx). Woody debris provided an effective refuge only in combination with undisturbed darkness, but not in illuminated nights. Our results suggest that nocturnal illumination in aquatic ecosystems may contribute to significant reductions in invertebrate population sizes through fish predation. The loss of darkness reduces the possibility of using shelters by invertebrates and hence the effects of elevated light levels at night could not be mitigated by an increased habitat complexity.
... Specifically, we found that perch increased their swimming activity at higher temperature and under brighter conditions, the latter in a nonlinear way. Through altering physiological processes and prey distributions (Brown et al., 2004;Hinch & Rand, 1998;Magnuson et al., 1979), temperature influences various behaviours, such as swimming intensity (Alabaster & Stott, 1978;Neuman et al., 1996), foraging rates (Kitchell, Stewart, & Weininger, 1977;Neuman et al., 1996), escape ability of prey (Wilson, Lefrancois, Domenici, & Johnston, 2010) and timing of migration and spawning (McKinzie, Jarvis, & Lowe, 2014). It is likely that perch increased the swimming activity at higher temperature to meet the elevated demand for food, considering that higher swimming activity increases prey encounter rates (Turesson & Brönmark, 2004. ...
Fine-scale underwater telemetry affords an unprecedented opportunity to understand how aquatic animals respond to environmental changes. We investigated the movement patterns of an aquatic top predator, Eurasian perch (Perca fluviatilis), using a three-dimensional acoustic telemetry system installed in Kleiner Döllnsee (25 ha), a small, shallow, mesotrophic natural lake. Adult piscivorous perch (N = 16) were tagged and tracked in the whole lake at a minimum of 9-s intervals over the course of one year. Perch increased swimming activity with higher water temperature and light intensity. Air pressure, wind speed and lunar phase also explained perch movements, but the effects were substantially smaller compared to temperature and light. Perch showed a strong diel pattern in activity, with farther swimming distances and larger activity spaces during the daytime, compared to the night-time. To investigate the influence of prey distribution, we sampled the prey fish in both littoral and pelagic zones in both day and night monthly using gill nets. We found that the prey fish underwent diel horizontal migration, using the littoral zone during the day and the pelagic zone during the night. However, perch showed the opposite patterns, suggesting either that the prey fish avoided predation risk or that the horizontal diel migration of perch was driven by other mechanisms. Our results collectively suggest that the movement ecology of piscivorous perch is mainly governed by a foraging motivation as a function of abiotic variables, especially temperature and light.
... At a first glance, the higher prey density in the hypereutrophic lake does not explain the difference in P. fluviatilis activity pattern in the two lakes, but interlake behavioural differences of both prey and large P. fluviatilis may explain the difference. Crepuscular feeding in the mesotrophic lake in this study, as observed in previous studies of P. fluviatilis behaviour in clear-water habitats (Craig, 1977;Alabaster & Stott, 1978;Jacobsen et al., 2002), could be explained by P. fluviatilis feeding during a short effective period being sufficient to get enough food. Crepuscular activity, however, could also indicate temporary access to the preferred prey. ...
Behaviour of large perch Perca fluviatilis was studied in two lakes differing in environmental state i.e. mesotrophic v. hypereutrophic. A total of 20 adult perch P. fluviatilis (29-42 cm total length) in each lake were tagged with radio-transmitters, tracked and located eight times a day during six 24 h tracking periods over a year, enabling detection of differences in diel activity patterns and habitat use during summer and winter under two different environmental regimes. During summer, P. fluviatilis in the mesotrophic lake showed a distinct crepuscular activity pattern and a change from pelagic residency during daytime towards the littoral zone at night. In contrast, P. fluviatilis in the hypereutrophic lake were active during the entire diel cycle and were spread throughout the lake also during dark. During winter, crepuscular patterns of activity were seen in both lakes. Condition factor of large P. fluviatilis did not differ between the two lakes. Thus, it is suggested that P. fluviatilis in the hypereutrophic turbid lake adopted an alternative behaviour for successful foraging, being uniformly active throughout the diel cycle.
© 2015 The Fisheries Society of the British Isles.
... The experimental results suggest that Perca fluviatilis individuals changed their feeding activities from diurnal to nocturnal when exposed to stress. This result is not in line with several earlier observations on the Eurasian perch in its natural environment, in which this species was described as being diurnal with peaks at dusk, dawn, and midday (Alabaster and Stott 1978, Rask 1986, Huusko et al. 1996. Moreover, laboratory observations of the self-feeding activity on demand under non-stress conditions, showed a clear and distinct diurnal feeding activity in this species (Anthouard and Fontaine 1998), but feeding patterns can change when additional predatory species are present (see below: Schleuter and Eckmann 2006). ...
Effects of stress on the feeding behaviour of the Eurasian perch Perca fluviatilis were investigated. Over a period of 32 d, the selffeeding patterns of a group of 4 fish were monitored with a light-dark cycle of 12:12 h. As the perch could obtain food by triggering a feeding apparatus at any time, food availability likely did not govern the feeding activity pattern. During the light phase, when the perch were exposed to an illumination of 2.4 W/m2, they were repeatedly (but at irregular times) disturbed through surface-transmitted vibrations and shadows. Monitoring of the self-feeding pattern over a 24 h period showed that the fish changed their feeding activity from diurnal to nocturnal when exposed to this type of stress in combination with the relatively bright illumination during daytime hours. In order to show that the perch associated the trigger with food and pulled it intentionally rather than randomly, the feeding apparatus was emptied while trigger activation was monitored for a further 6 d. As soon as food was no longer available from the feeding apparatus the perch decreased their pulling activity until they had completely lost interest 6 d later.
... At a first glance, the higher prey density in the hypereutrophic lake does not explain the difference in P. fluviatilis activity pattern in the two lakes, but interlake behavioural differences of both prey and large P. fluviatilis may explain the difference. Crepuscular feeding in the mesotrophic lake in this study, as observed in previous studies of P. fluviatilis behaviour in clear-water habitats (Craig, 1977;Alabaster & Stott, 1978;Jacobsen et al., 2002), could be explained by P. fluviatilis feeding during a short effective period being sufficient to get enough food. Crepuscular activity, however, could also indicate temporary access to the preferred prey. ...
Human disturbances such as angling and manual handling may have long-term effects on the behaviour of pike, Esox lucius L., an ecologically important species. Using continuous high-resolution positional telemetry, this study compared the swimming activity of handled and unhandled pike in a small lake. Pike pre-equipped with acoustic transmitters were angled and exposed to a handling protocol including measurements of length and mass. Pike not recaptured constituted an unhandled control group. Results demonstrated that the handling protocol caused temperature-dependent changes in pike activity, with higher temperatures leading to lower activity of the recaptured pike. The effects, however, were transitory and not detectable after 48-h post-release. These findings indicate that pike are relatively resilient to handling and quickly resume pre-handling activity.
... The classification of fish as nocturnal, diurnal, or crepuscular is based mainly on their swimming activity peak throughout the day (Begout Anras et al., 1997), which has a strong relation to foraging (Helfman, 1978;1981;1986). Swimming activity in Perch (Perca fluviatilis) increased following a change from light to dark, and decreased following a change from dark to light (Alabaster and Scott, 1978). American Shad (Alosa sapidissima), which under normal light conditions were capable of swimming up to 45 cm/s, swam as slow as 8 cm/s under dark conditions (Katz, 1978). ...
Photophase and illumination affect many fish activities. In this study, we examined their effects on the critical swimming velocities (Ucrit), swimming gait patterns, and oral grasping behavior of five California estuarine fishes. All species (4–5 cm SL) swam similarly (mean Ucrit range: 30–36 cm/sec) under day/light conditions. However, both nighttime photophase and darkness decreased Delta Smelt (Hypomesus transpacificus) swimming velocities. Congeneric Wakasagi (Hypomesus nipponensis) swimming performance also decreased at night/dark conditions. Regardless of photophase and illumination, Delta Smelt, Wakasagi, and Splittail (Pogonichthys macrolepidotus) exhibited three swimming gaits: intermittent stroke-and-glide at low velocities, continuous stroking at moderate velocities, and intermittent burst-and-glide at high velocities near Ucrit. In contrast, Chinook Salmon (Onchorhynchus tshawytscha) used only two swimming gaits: continuous stroking and burst-and-glide under all conditions. Inland Silversides (Menidia beryllina) used these two gaits under light conditions and all three gaits under dark conditions. Some Wakasagi, Splittail, and Chinook Salmon orally grasped the upstream screen in the flume at moderate to high water velocities. Oral grasping does not require jaw teeth and may represent adaptive behavior in natural habitats. Regarding vulnerability to water diversions that operate in the dark at night, the threatened Delta Smelt and introduced Wakasagi, comparatively, may be more at risk than the other species.
... The photoperiod in the aquarium followed the natural day length. Both predators are known to be most active at dawn and dusk (Alabaster & Stott, 1978) so these daily periods were included in the experimental periods. A shorter duration was chosen for ruffc because it was known fi'om earlier experiments to be a more effective predator than perch (Mattila & Bonsdorff, 1989). ...
Aquarium experiments were conducted to test the hypothesis that a slight increase in habitat complexity significantly increases the survival of the amphipods Corophium volutator Pallas and the isopod Asellus aquaticus (L.) when preyed upon by perch Perca fluviatilis L. and ruffe Gymnocephalus cernuus (L.), respectively. Artificial reed, stones, and natural plants were tested in different combinations. A slight increase in habitat complexity (e.g., small amount of stones) did not increase Corophium survival. However, artificial reeds in different forms, and natural plants, did increase the survival of both Asellus and Corophium. Survival increased with increasing habitat complexity. At low complexity levels the survival of the prey seemed to be higher when the elements used to provide complexity were in bigger integrated patches. Tall, shading elements like reeds or aquatic plants gave the best shelter against fish that feed visually.
The habitat quality of the littoral zone is of key importance for almost all lentic fish species. In anthropogenically created gravel pit lakes, the littoral zone is often structurally homogenized with limited fish habitats. We supplemented deadwood brush piles in the littoral zone of eight gravel pit lakes and investigated the diurnal and seasonal use of this and other typical microhabitats by six dominant fish species. Shoreline habitats were sampled using point abundance electrofishing during day and night in all four seasons, and patterns of fish abundance were compared amongst unstructured littoral habitats, emerged macrophytes and brush piles. We caught a total of 14,458 specimens from 15 species in the gravel pit lakes. Complex shoreline structures were used by all fish species that we examined, especially during daytime, whilst the use of unstructured habitats was highest during night. The newly added brush piles constituted suitable microhabitats for selected fish species, perch (Perca fluviatilis), roach (Rutilus rutilus) and pike (Esox lucius), particularly during winter. Supplemented deadwood provides suitable fish habitat in gravel pit lakes and may to some degree compensate for the loss of submerged macrophytes in winter by offering refuge and foraging habitat for selected fish species.
IntroductionMaterials and methodsResultsDiscussion
A stomach sampler for live fish is described and its construction outlined; 50 adult perch were sampled, subsequently killed and dissected to assess the efficiency of the device. Survival of previously sampled fish was followed using individually recognisable dorsal fin tags.
Routine oxygen consumption of turbot, Scophthalmus maximus, was determined in relation to temperature, salinity, body wet weight, and time of day. The highest routine oxygen consumption rates measured roughly followed a arabolic curve over the temperature range tested (8 to 24°C). The lowest rates showed a more linear refationship over the same temperature range. It is argued that lowest rates correspond to the standard oxygen consumption. Between 16 and 19°C, routine oxygen consumption reached a maximum. It is suggested that these temperatures correspond to the preferred ternerature of the species and are within the range of optimum temperature for growth of specimens weigkng about 100 g. Salinity effect on oxygen consumption rates was studied in five groups acclimated over 4 weeks to 8, 15, 22, 29, and 35%. salinity. Routine oxygen consumption rates were lowest at 8% salinity with no significant differences in higher acclimation salinities. Routine respiration of turbots showed conspicuous daily fluctuations. During spring, summer, and autumn, oxygen Consumption was higher during morning hours and at night. In winter, higher rates were measured only once (during morning and early afternoon). The relationship between routine oxygen consumption and body weight of turbots followed an exponential function with a slope of 0.7, which was lower compared to the slope of 0.8 usually given for roundfish-species.
The impact of predation by an avian predator (great crested grebe Podiceps cristatus) and a predatory fish (perch Perca fluviatilis) on a common resource, the small planktivorous fish smelt (Osmerus eperlanus) was studied in Lake IJsselmeer, The Netherlands, in July–October 1985–1988. At this time of the year the grebes are in simultaneous wing-moult and therefore temporarily flightless. Four factors limit the predation pressure by grebes: (1) an underwater visibility threshold of c. 40 cm Secchi depth is the lower limit at which large numbers attend the moulting site, (2) a lower density threshold of exploitable smelt biomass of c. 30 kg/ha determines the actual fishing areas, (3) a fish size threshold of 6.5 cm total length further limits prey availability, and (4) the vertical movements of the prey impose a strong (diel) time constraint on the birds, allowing only crepuscular foraging. Perch, the other main predator in this system, is less restricted in its foraging. Perch were found to be in direct competition with the grebes, preying heavily on the juvenile smelt. Over the 4 years of study 90% of all predation from 15 July to 15 October (72–233 kg/ha) was due to perch. The high level of predation by birds and fish was only possible due to a continuous immigration of smelt into the area (1.45 kg/ha per day). In three of the four years, however, the combined predation by fish and birds surpassed the immigration rate of the prey, which led to a strong reduction in smelt stocks in the study area. A conceptual model is developed to describe the different sets of constraints on the grebes' foraging. First, the state of eutrophication in relation to the weather condition determines the degree of algal blooms, and thus underwater visibility, in late summer. This is the major factor governing the numbers of grebes on the moulting area. Second, the size of the population of predatory fish determines the overall food availability (biomass and size distribution of smelt). These factors are partly interconnected and related to human action (pollution, fisheries). It is suggested that, despite deteriorating visibility conditions, the largest moulting site for grebes in Europe at Lake IJsselmeer exists because the stocks of predatory fish are kept low by overfishing.
Results of a descriptive field study showed that goldeneyes preferred lakes without fish to those with fish. Field experiments were carried out in order to investigate whether or not this preference could be ascribed to a higher food supply in the lakes devoid of fish, as goldeneyes and some freshwater fish (perch and roach in the studied lakes) to some extent feed on the same kinds of prey. Changes in the abundance of prey common to fish and goldeneyes and the use by goldeneyes of lakes after experimentally changed predation pressure from fish were studied. Some aquatic insect groups, Cloeon larvae, Odonata larvae, water bugs, dytiscids, and Chaoborus larvae, proved sensitive to predation from fish. Goldeneyes increased their use of an experimental lake after fish were removed, and they used this lake more than an adjacent control lake. It is suggested that fish are able to reduce the availability of foods common to the goldeneyes to such an extent that the selection by the ducks of feeding localities is affected, and that exploitation competition between freshwater fish and goldeneyes may occur.
Activity patterns of some common Baltic fish species and macrocrustaceans have been investigated in natural light/dark conditions — in most cases for periods of at least one full year. The fauna of the northern Baltic proper consists of species of both marine and freshwater origin, with both types represented in the study. The different patterns found are discussed in relation to light period, light intensity and to the structure and function of the eyes. The following species were considered nocturnal: Idothea baltica, Mesidothea entomon, Gammarus oceanicus, Palaemon adspersus, Anguilla anguilla, Spinachia spinachia, Pholis gunnellus, Zoarces viviparus, Scopthalmus maximus, and Platichtys flesus. These species were considered diurnal: Clupea harengus, Scardinius erythrophthalmus, Gasterosteus aculeatus, Perca fluviatilis, Gobius niger, Taurulus bubalis, and Cyclopterus lumpus. The next three species showed a crepuscular pattern of activity: Praunus flexuosus, Esox lucius and Gymnocephalus cernus. Four species were considered to show inversions of the activity patterns: Pungitius pungitius, Pomatoschistus minutus, Myoxocephalus scorpius and M. quadricornis.
1.1. Increased activity at dawn and dusk has been observed in roach, bream and perch and breaking up of shoals at night has occurred in perch and bream.2.2. Roach became active at dawn even when the temperature and dissolved oxygen concentration were kept fairly constant. This suggests that another factor, probably diurnal change in light, stimulates the fish.3.3. Non-lethal changes in temperature and dissolved oxygen concentration cause fish to become more active irrespective of light. This reaction is considered to have survival value for fish in rivers polluted by heated and oxidizable effluents.
The number of perch caught weekly in traps set in Slapton Ley, Devon has been considered. Five traps were laid in each of six regions during 1970 and 1971. The numbers caught in each region were averaged for eight lifts during 8 weeks and the logarithms of these numbers calculated. The figures obtained showed marked seasonal trends in the catch of the traps and these trends were consistent when both years were compared. If single traps were considered there was marked variability at one time which was attributed to differences in habitat. However, the combined data from each region did give a good comparison of the density of perch between regions.
Perch Perca fluviatilis L. newly introduced into waters were markedly vulnerable to traps for up to four or five days. Thereafter catches tended to be positively correlated with water temperature up to about 10.5°C and negatively correlated at higher temperatures. The catching power of traps is low; at a density of one per 354 m2 water surface, traps caught from 0.9 to 6.8 % and 0.3 to 1.4% of a perch and roach Rutilus rutilus (L.) population per day. Perch did not become ‘trap-shy’ and fin clipping did not affect their vulnerability. Applications of 0.1 to 0.5 ppm copper sulphate resulted in up to an 11-fold increase in catches.
Six years' data from the River Coquet together with published information for other British rivers show that upstream migrant salmon and sea trout tend to be intercepted at counting fences and be caught on rod and line when river flows are somewhat higher than average and not when they are at their extreme values, though there is no particular river flow favoured all the year round. In years of highest river discharge the number of fish entering the River Coquet and the number of fish caught on rod and line are highest but the efficiency of angling is lowest.
An automatic electro-mechanical dawn and dusk machine An eighteen-point fish movement recorder Some factors affecting the catching power of unbaited fish traps
- R E Iszard
- L Walker
Iszard, R. E. & Walker, L. An automatic electro-mechanical dawn and dusk machine. Lab. Pract. 19, 495, 499. Moore, W. H. (1961). An eighteen-point fish movement recorder. Proc. Inst. Electronics 4, 3842. Stott, B. (1970). Some factors affecting the catching power of unbaited fish traps. J. Fish. Biol. 2, 1-13.
- Hasler A. D.
An automatic electro‐mechanical dawn and dusk machine
- Iszard R. E.
An eighteen‐point fish movement recorder
- Moore W. H.