Control of water weeds by grass carp in a drainage ditch in New Zealand

Transcription

1 New Zealand Journal of Marine and Freshwater Research ISSN: (Print) (Online) Journal homepage: Control of water weeds by grass carp in a drainage ditch in New Zealand D. J. Edwards & E. Moore To cite this article: D. J. Edwards & E. Moore (1975) Control of water weeds by grass carp in a drainage ditch in New Zealand, New Zealand Journal of Marine and Freshwater Research, 9:3, , DOI: / To link to this article: Published online: 30 Mar Submit your article to this journal Article views: 76 View related articles Citing articles: 6 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 22 January 2017, At: 16:00

2 .1975] 283 CONTROL OF WATER WEEDS BY GRASS CARP IN A DRAINAGE DITCH IN NEW ZEALAND D. J. EDWARDS and E. MOORE Fisheries Research Division, Ministry of Agriculture and Fisheries, P.O. Ngapuna, Rotorua, New Zealand (Received 19 September 1974; revision received 28 February 1975) ABSTRACT Two-year-old grass carp Ctenopharyngodon idella Val. were stocked at a rate of kg.ha- 1 in a farm drainage ditch in the Bay of Plenty, New Zealand. During the months December to April the fish greatly reduced the standing crop and percentage cover of the weeds Callitriche stagnalis Scop, and Nasturtium officinale R.Br., but had no effect on Polygonum decipiens R.Br. INTRODUCTION Pond studies have shown that many weed species which cause problems in New Zealand waterways are eaten by grass carp (Chapman & Coffey 1971, Edwards 1974). Successful weed control in a natural water body is, however, also dependent on factors other than weed palatability, notably rates of weed growth and fish feeding activity, and fish stocking density. Edwards (1973) reported that, even when abundant palatable weed is present, young grass carp kept in aquaria will eat invertebrates and fish fry. Studies in Poland (Fischer 1970, 1972, 1973) showed that grass carp weighing up to 400 g eat a mixed diet of animal and plant food, and that growth is retarded when animal food is not available. Preference for animal food in a natural environment could reduce the potential for weed control. It was therefore important to test the potential of grass carp for weed control in a New Zealand waterway where weeds are a problem, and where aquatic animals are also present. An experiment was designed to establish the degree to which weed control might be achieved in a farm drainage ditch. Considerable expense is incurred on mechanical and chemical methods of weed control in drainage systems, and it is likely that a successful biological control would be widely used in these waterways. This paper describes the effects of grass carp on the weed infestation in a drainage ditch. A study was also made of the effects on bottom fauna in the ditch, the results of which will be published later. N.Z. Journal of Marine and Freshwater Research 9 (3) :

3 284 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT. METHODS A drainage ditch flowing into the Awakaponga Canal on the Rangitaiki Plain in the Bay of Plenty (grid ref. NZMS 1 Sheet N68 & Pt N59, ) was selected because it did not dry up in summer and was shallow enough to allow wading and sampling by hand. The mean width of the drain was 3 m and the normal water depth fluctuated between 0.3 m and 1.0 m. The ditch was divided into three 230-m-long sections; upstream and downstream controls separated by an experimental section. Steel barriers were erected at each end of the experimental section to confine the grass carp, and a third barrier at the end of the downstream control section was a security measure to prevent escape of grass carp into natural waterways if other screens were damaged. There was no access to other waterways via the upstream end of the drain. The barriers were constructed of 5 m X 2 m rectangular welded frames of angle-iron through which 19-mm holes were drilled at 51-mm intervals along the top and bottom members. This allowed 19-mm-diameter steel reinforcing rods to be passed through the holes, producing vertical bars with 32-mm gaps between them. An additional flat-iron bar was also drilled and positioned across the centre of the frame to add rigidity to the structure. The angle-iron frames were fixed at each side into the banks of the drain, but the vertical bars were free to move up and down in their "sockets" so that they could sink into the mud of the drain bottom until they found a hard substrate. The spacing of the bars restricted movement of the grass carp to the experimental area, while allowing free movement through the drain of smaller native fishes. Weed cover and standing crop were estimated monthly in the three drain sections for the period September 1973 to April 1974 inclusive using three methods: a) Standing Crop of Weed was estimated by sampling with a 0.5-m 2 - quadrat frame. The banks of the drain were marked out at 1-m intervals, and each month 20 sampling stations were chosen for each drain section, using a random-number table; the same 20 numbers were used for each drain section in a particular month. At each station the quadrat frame was thrown into the water, and all weed growing within that 0.5 m 2 was cut with garden shears at the mud/water interface and removed. The frame was thrown in turn close to the far bank, the centre, and the near bank of the drain. Each sample was returned to the laboratory in a polythene bag and washed in a plastic basket before being spun in a domestic spin drier for 4 min to remove surface water. The sample was then sorted into component weed species which were weighed (± 2 g). b) Species Cover was estimated along standard transects across the drain at 10 m intervals along it. A beam of 100 mm X 50 mm timber was placed across the drain at each station, its ends fitting into prepared sockets in the banks. From the beam, plumblines were suspended into the water at 20-cm intervals across the drain, and the cover of weed was determined from the number of plumblines in contact with each weed species.

4 1975] EDWARDS & MOORE WEED CONTROL BY GRASS CARP 285 LEGEND A Upstream control section O Experimental section v Downstream control section Sept. Fio. 1 Mean weights of Callitriche stagnalis per m 2, shown ± 1 standard error (n = 20), present at monthly intervals in the experimental drainage ditch at Rangitaiki Plain, North Island, New Zealand, September 1973-April c) Photographs (colour transparencies) were taken along the entire length of the drain (690 m) from one bank. Transparencies were viewed over squared paper under a lens, and the number of squares full and empty of weed noted. This gave an extra estimate of the total percentage weed cover in each drain section. Twenty-five 2-year-old grass carp of total weight 24.5 kg, giving a stocking density of 350 kg.ha - \ were released into the experimental section on 9 November A further 20 grass carp of total weight 21 kg introduced on 30 January 1974 increased the stocking rate to about 650 kg.ha- 1. All the grass carp were recaptured at the end of April RESULTS Figures 1-6 show the mean weight per m 2 and percentage weed cover derived from plumbline transects for each weed species each month. Figures 7 and 8 show the mean total weed weight and percentage total weed cover each month. There was a marked seasonal succession of weed species in the drainage ditch. When the experiment was started, in September 1973, only

5 286 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT. Sept. Sept Jan Flo. 2 Percentage cover of Callitriche stagnalis estimated from plumbline transects in the experimental drainage ditch at monthly intervals, September 1973 April Symbols as in Fig. 1. Callitriche stagnalis was present in significant quantity. This weed grew very rapidly before the fish were introduced, and reached a peak in cover and standing crop around the end of November (Figs 1 & 2). Callitriche subsequently died down in all three drain sections, but with the introduction of the grass carp its decline was more rapid in the experimental section than in either of the controls. By February 1974 Callitriche had almost disappeared from the experimental section, but substantial amounts of it persisted in both controls (Figs 1 & 2). The next weed to increase rapidly in density and cover was Nasturtium officinale. This weed grew rapidly in the upstream control and experimental sections, but was never very important in the downstream control section (Figs 3 & 4). There was a gradient of Nasturtium abundance decreasing from upstream to downstream in the drain. In the experimental section a peak was reached in January, but thereafter a steep decline in both cover and standing crop of Nasturtium occurred, whilst both control sections maintained their crops of this species. The third important weed in the seasonal succession was the emergent Polygonum decipiens. This species grew rapidly during the months January to March (Figs 5 & 6). It was most abundant in the downstream control section, and least important in the upstream control; there was a gradient of abundance decreasing" from downstream to upstream, the

6 1975] EDWARDS & MOORE WEED CONTROL BY GRASS CARP 287 Sept FIG. 3 Mean weights of Nasturtium officinale per m 2, shown ± 1 standard error (ra = 20), present in the experimental drainage ditch at monthly intervals, September 1973-April Symbols as in Fig A -A FIG. 4 Percentage cover of Nasturtium officinale estimated from plumbline transects in the experimental drainage ditch at monthly intervals, September 1973-April Symbols as in Fig. 1.

7 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT. Apr. FIG. 5 Mean weights of Polygonum decipiens per m 2, shown ± 1 standard error («= 20), present in the experimental drainage ditch at monthly intervals, Saptcmbcr 1973-April Symbols as in Fig FIG. 6 Percentage cover of Polygonum decipiens estimated from plumbline transects in the experimental drainage ditch at monthly intervals, September 1973-April Symbols as in Fig. 1. Apr.

8 1975] EDWARDS & MOORE WEED CONTROL BY GRASS CARP i E g g> " <= CD Sept. Nov. Dec Jan : eb. ' Mar. ' Apr. FIG. 7 Mean total weights of weed (all species combined) per m 3, shown ± 1 standard error (n = 20), in the experimental drainage ditch, Rangitaiki Plain, North Island, New Zealand, at monthly intervals, September 1973-April 1974: Symbols as in Fig. 1. opposite to that for Nasturtium. The experimental section was always intermediate between the two controls in cover and standing crop of Polygonum. There was a small standing crop of Potamogeton cheesemanii A. Bennett in all of the drain sections. By April 1974, however, none was found in the experimental section, but this species was still present in both controls. Sometimes Lemna minor L. and Azolla rubra R.Br. were present, but the crops of these weeds could not be measured because they moved freely through the drain with the water flow. Occasional blooms of Spirogyra sp. also occurred. The total weight of all weed species combined (Fig. 7) reached a peak in November. This was largely a reflection of the peak standing crop of Callitriche stagnalis, which was present in extremely large amounts (2000 g*nr 2 ) at that time. By January 1974, each control section was carrying a greater standing crop of weed than the experimental section (Fig. 7), and by the end of April 1974 the experimental section contained only about half as much weed (700g.nr 2 ) as the upstream

9 290 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT. control (1350 g.nr 2 ) and about one third as much as the downstream control (2100 g.nr 2 ). There was less seasonal variation in total percentage cover than in total weights of weed, and over 50% of each drain section was covered for most of the experiment (Fig. 8). However, by January 1974 there was considerably less weed cover in the experimental section than in either control, and this difference was maintained for the rest of the experimental period. Water temperature was measured by maximum and minimum thermometers fixed to the fish barriers. The mean temperature during the experimental period was about 16.5 c, with a range of 13 c to 20 c. All the grass carp were harvested from the experimental drain in April 1974; survival was 100%, and the fish had increased in weight to a total of 53.8 kg, or 768 kg.ha" 1. DISCUSSION The results indicate that the presence of the grass carp in the experimental section of drain caused a large reduction in the standing crop and percentage cover of Callitriche stagnalis and Nasturtium officinale, but had no significant effect on Polygonum decipiens. In the months November 1973 to January 1974, there was a large cover and standing crop of both Callitriche stagnalis and Nasturtium officinale in the experimental section (Figs 1-4). The standing crop of Nasturtium was rising during this period, whilst that of Callitriche was declining. Once the Callitriche had been eliminated from the experimental section, by February 1974, a rapid decline in Nasturtium began, whilst both control sections maintained their crops of this species. It appears that the fish did not begin to graze Nasturtium, though it was present in large amounts, until they had eliminated the Callitriche. Similarly, in the months February to April there was a large standing crop of both Nasturtium and Polygonum in the experimental section (Figs 3-6). The grass carp apparently ignored the Polygonum while there was still Nasturtium for them to eat. It therefore appears that the grass carp showed a clear order of food preference for the three most important weeds present in the drain: Callitriche > Nasturtium > Polygonum. This was the order predicted from previous pond studies on weed preference at Rotorua (Edwards 1974). Two-year-old grass carp in ponds at Rotorua will eat Polygonum decipiens during summer when no other weed is available. If the fish had been stocked heavily enough this weed might also have been grazed in the drain. Potamogeton cheesemanii, which was present in all three drain sections in small amounts, disappeared from the experimental section around the end of March In the pond studies on weed preference a related species, Potamogeton crispus L., was grazed by grass carp at about the same time as Nasturtium officinale.

10 1975] EDWARDS & MOORE WEED CONTROL BY GRASS CARP r to Sept. I Oct. Nov. Dec. Jan Sept. Mar. ' Apr. Fio. 8 Percentage total weed cover (all species combined) in the experimental drainage ditch, Rangitaiki Plain, North Island, New Zealand, at monthly intervals, September 1973-April (Solid line and open symbol = estimated from plumblinc transects; broken line and black symbols = estimated from photographs. Symbols as in Fig. 1.) The rate of grazing of weeds in the experimental section was not as rapid as was expected from previous pond studies. This is why the fish stocking rate was increased in January The feeding rate of grass carp is closely tied to water temperature (Liepolt & Weber 1969; Edwards 1974) and the experimental drainage ditch was found to be cold in comparison with many natural waterways in New Zealand, e.g., the Rotorua lakes (Fish 1970), where summer temperatures are in the low twenties Celsius. The temperature in the drain never rose above 20 c, and was usually in the range c in the summer months. It is possible that lower fish stocking rates could be used in many warmer waters in this country. There have been many overseas studies with grass carp in aquaria and artificial ponds, but relatively few in natural conditions. Cure (1971) examined the impact of grass carp on all elements of the flora and fauna of a Roumanian lake. She found that the biomass of macrophytes was reduced from 64 t-ha- 1 to 2 t.ha^1 over a 3 y period by grass carp stocked at the rate of 75 two-year-old fish per hectare. Stott & Robson (1970) reported that a stocking density of 2-year-old grass carp giving a midseason biomass of approximately 300 kg^ha- 1 reduced weed growth to about 50% of its potential in ponds in England. Water temperatures in

11 292 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [SEPT. the English experiment were of the same order as those in the present study. A higher fish stocking rate ( kg.ha^1) was required to achieve control of weeds in New Zealand, probably because the standing crop of weed was greater. This study shows that grass carp could be used to control some species of aquatic weeds in New Zealand, but continued work on the effects on existing fauna will be undertaken before widespread use of fish for weed control is considered. ACKNOWLEDGMENTS The authors wish to thank the Rangitaiki Drainage Board for its help in initiating this experiment. Special thanks are due to Mr and Mrs P. Withy, on whose land the experimental drain is situated. LITERATURE CITED CHAPMAN, V. J. & COFFEY, B. T. 1971: Experiments with grass carp in controlling exotic macrophytes in New Zealand. Hidrobiologia 12: CURE, V. 1971: Changes in the biocoenosis resulting from the introduction of the phytophagous fish Ctenopharyngodon idella (Val.) into Lake Frasinet, Illov jjistrict. Studii si Cercetari Piscicole 4 (7) : (In Roumanian). EDWARDS, D. J. 1973: Aquarium studies on the consumption of small animals by O-group grass carp, Ctenopharyngodon idella (Val.). Journal of Fish Biology 5: : Weed preference and growth of young grass carp in New Zealand. N.Z. Journal of Marine and Freshwater Research 8 (2) : FISCHER, Z. 1970: The elements of energy balance in grass carp (Ctenopharyngodon idella Val.) Part 1. Polskie Archiwum Hydrobiologii 17 (4) : : The elements of energy balance in grass carp (Ctenopharyngodon idella Val.) Part II. Fish fed with animal food. Polskie Archiwum Hydrobiologii 19 (1) : : The elements of energy balance in grass carp (Ctenopharyngodon idella Val.) Part IV. Consumption rate of grass care fed on different types of food. Polskie 'Archiwum Hydrobiologii 20~(2) : FISH, G. R. 1970: A limnological study of four lakes near Rotorua. N.Z. Journal of Marine and Freshwater Research 4: LIEPOLT, R. & WEBER, E. 1969: Versuche mit phytophagen Fischen (Ctenopharyngodon idella). Review of Roumanian Biology (Zoology) 14 (2): (In German.) STOTT, B. & ROBSON, T. O. 1970: Efficiency of grass carp (Ctenopharyngodon idella Val.) in controlling submerged water weeds. Nature (Lond.) 5248: 870.