Page 1

17 Summer survey technique for great crested newt Triturus cristatus T. LANGTON Background Planning applications for small-scale development now require determination of the presence or likely absence of a wide variety of wildlife species (Langton T.E.S. p. 11). Many applications with a pond within 100 metres or so require the evaluation of potential impacts of the development work and recommendations on the need for follow-up surveys. Work to check for aquatic species tends to be done during the seven-month March to September ‘window’, when most species that hibernate over winter are active. The work often requires the cooperation of one or more adjoining landowner. Most of the emphasis on surveying for GCN and other amphibians have concentrated on the spring breeding season, when adult numbers in ponds are highest. Afterwards, from the post-breeding dispersal of many individuals, GCN adults can still be found in ponds, but become progressively easier to overlook in day time netting. From May onwards, aquatic submerged, floating and marginal plants begin to fill open water areas around the pond edge. The presence of many other breeding species, such as birds and invertebrates makes heavy disturbance of ponds from netting less desirable and in some cases even unlawful. GCN tend to be less active at pond margins in daytime than at night and are generally more frequently surveyed by torch light counting or bottle trapping. They are larger and generally seem to be less easy to catch than the commoner newt species with daytime netting using standard sized dipping nets. Search for GCN eggs on preferred vegetation from mid-March to the end of May is often the quickest and easiest way to check for presence, but the season is relatively short and varies between ponds. However, looking at ponds from July to September using night torching or bottle trapping can also be risky in terms of overlooking adult GCN. From numerous inspections carried out in Suffolk over three years 2007–2010, new netting techniques have been developed to supplement the existing methods. The first concentrates on locating the tadpoles/larvae of GCN which if present are always in the water from July until August/September and at a time of year, particularly in August and September when they are large and can be readily distinguished from the commoner species. GCN larvae, like adult and occasionally juvenile GCN, seem to change their location in ponds during foraging and in response to disturbance and predation. They are generally more open water swimmers than the dense water-plant skulking smaller species and at night can usually, though not always be seen by torch-light, spaced out quite evenly in the water column, feeding on zooplankton and larger species such as phantom midge larvae (Chaoborus). Amphibians can be netted in pond shallows in aquatic and overhanging grass and terrestrial vegetation with leaves just under the surface. Pond edge is the traditional place to search. Less well known, however, is that like smaller newts, frog tadpoles and GCN larvae can be detected further out from the

Trans. Suffolk Nat. Soc. 46 (2010)


18

Suffolk Natural History, Vol. 46

pond edge, and during sunny days, directly under and sometimes touching the underside of floating leaved aquatic plants. This has been observed most frequently from June to August in Suffolk. A rapid ‘blip’, a little like small fish surfacing, can be observed around floating water plant leaves, particularly the native yellow water lily Nupha lutea, hybrid lilies Nymphaea or floatingleaved Potomogeton species. The amphibians responsible for the small splashes are not always obvious, but they dive to the pond bottom using a tail flick for propulsion. The splash may also give a distraction to predators. The reason for this near-surface ‘hiding’ behaviour, beyond safety from predators, may be the increased warmth and possibly increased oxygen levels released by plant leaves during photosynthesis. They may be using the dark green leaves like radiators gaining ‘safe’ warmth that aids growth. I have also seen adult newts do this but it is most spectacular when dozens of individual tadpoles/ larvae do it in synchrony. Hiding under leaves may also prevent over exposure to sunlight. Equipment and methods Following trial and error using a wide range of nets bought from fishing tackle shops and biological supply companies over many years, I have found that an ultra lightweight dipping net is best for summer surveys for amphibian larvae from bank or boat and for general use too. The net specifications are outlined below. The net pole is 2·0 metres in length and made of 25 mm hollow alloy. The net head is light alloy with a plastic joint/fixing with the pole and is 700 mm long and 58 mm wide at the widest part, more-or-less a rounded square, slightly wider at the front. The net is called a ‘pan’ net, used for Koi inspection (gently lifting fairly placid fish out of ornamental pools) and is different from the more commonly available koi inspection net type that is almost flat across the head, like a sport racquet. The net is black, with a 2·5 mm mesh bag that is 120 mm deep and flat at the base, resembling the shape of a deep frying pan. As a result, the net is readily moved through the water and folds only a little over netted animals. It provides a broad catching basket that can be easily slid at distance under or into vegetation before animals get a chance to move away. As plants are reached and knocked into, the animals tend to move down into it. The net is very different to traditional types such as the robust FBA (Freshwater Biological Association) and Duncan Associates 250 mm squareheaded nets with 1 or 2 mm white mesh bags. These have wood and brass or aluminium poles of 1·6–1·8 metres total length only – and around half of the reach of the lightweight net. These smaller dip nets weigh around 1·3 to 1·4 kg – about twice the 700 gram alloy net described here. The weight difference means that the net can be easily held and manipulated in difficult terrain. Although not always necessary, it can even be used with one hand, and this can be very helpful while in a small dingy or while balancing. The net bag does not hang down far and snag so easily in bramble or branches or debris on the bottom of ponds. Being light and quick to manoeuvre and having four times the head surface area, it is extremely effective at catching at distance. Its

Trans. Suffolk Nat. Soc. 46 (2010)


19

The author with ultra lightweight dipping net. size means that you do not need to change position so frequently, saving time and reducing disturbance. There is probably less ‘wave’ disturbance from moving a less bulky net and less capture of debris and mud too. To clean the net, it can be reversed in seconds by turning over while extended, rather than being brought in for cleaning out and rinsing. With the surveyors arms included, a total netting ‘reach’ of around 3000 mm is achieved from the pond or boat edge. In shallower ponds with little silt, using chest waders with such a net, much of a pond can be easily inspected. The 2000 mm one-piece detachable pole just fits inside a car. Surveying Sampling for amphibians using a sideways and then upwards sweep of a net under floating vegetation has produced positive results in mid to late summer. At one location, four ponds were surveyed and showed GCN present under lily leaves in a little under 15 minutes in total. Bank netting surveys with standard small nets over a period of two hours on other days had only demonstrated GCN presence in one of the ponds. In deeper ponds, the net can be used to catch invertebrates, amphibian larvae and adults at depth in ways not previously achievable from the bank. In one large, gravelly, clear water, 40 metre-wide, spring-fed pond in July 2008, I caught hundreds of nearly metamorphosed toadlets in each net sweep at a depth of up to 2 metres. They were sitting in high density in carpets of

Trans. Suffolk Nat. Soc. 46 (2010)


20

Suffolk Natural History, Vol. 46

Stonewort (Charophyte) under a large open stand of floating Pondweed, 20 metres or more from the edge of the pond. In many individuals, the tails were all but absorbed and they were apparently waiting for the right weather conditions to emerge. I have always wondered why the relatively easily observed mass exodus of toadlets is not preceded by the observation of large numbers of late metamorphic toadlets at the pond edge. ‘Waiting’ in the middle of the pond at depth in water plants is likely to be a strategy aimed at increasing survival. The toadlets leave the water over a period of a few days when land conditions become favourable, often after rain. Boat surveys For larger pond surveys, an inexpensive fibreglass boat is used. It is 2·5 metre long and 1·2 metre wide with wood trim and a base flat enough to stand up in. It can be transported on a car roof rack or in a small trailer. It is light enough for a reasonably fit and strong person to carry upside down on their back for short distances. Since 1990, I have had two such small boats made up in boat workshops in Essex and even with heavy use, they last for over ten years with maintenance and a few repairs. A survey technique has also been developed for use in ponds outside the breeding season that are ‘ringed’ with dense stands of Common reed Phragmites communis, Reedmace Typha latifolia or Bur-reed Sparganium spp. and other aquatic plants. This is often where fish species (particularly goldfish) that are known to co-exist with GCN are found, but where it is not known if GCN or other species of fish are present. Bottle trapping can be used but can be inconclusive in choked margins in late summer. Where this is the case, or where a day inspection initiates site inspections, a small dingy is pushed through the bankside rooting zone of emergent vegetation, often less than 3·0 metres in width. A second person (at night with a powerful hand lamp) stands on the bank at the end of a long mooring line. The person in the boat sits or stands up and operates a single oar or pole to steer, and uses a hand lamp with battery on shoulder strap (for work after dark) to scan the pond to locate animals and plants. They can also use the lightweight net to sample the inner edge of the emergent plant stand and vegetation in the middle of the pond. In clearer ponds, this is also a great way to observe fish and nocturnal invertebrates. Obviously, care is needed working at night and a self-inflating lifejacket recommended. Care must be taken not to disrupt nesting birds. Reference Langton, T., Beckett, C. & Foster, J. (2001). Great Crested Newt Conservation Handbook. Froglife, Halesworth. Tom Langton Dews Farm Bramfield Suffolk IP19 9AE E-mail: t.langt@virgin.net

Trans. Suffolk Nat. Soc. 46 (2010)

Summer survey technique for great crested newt Triturus cristatus  

Tom Langton

Read more
Read more
Similar to
Popular now
Just for you