Dag Dolmen

Habitat use during the aquatic phase of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in central Norway: proposition for a conservation and monitoring area

Amphibian populations are declining at an alarming pace in many parts of the world. Consequently, as part of the strategy for establishing a 360 km 2 conservation and reference area for amphibians in central Norway, 341 lentic water bodies were surveyed to investigate and briefly describe their hydrography and the occurrence of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in the area. In particular we investigated the factors that could explain the presence of the respective newt species, including biotic and abiotic factors. The multiple logistic regression analyses suggested that the presence of T. cristatus was best explained by altitude and ion concentration, both in a nonlinear fashion, whereas fish had a negative effect on T. cristatus , which was never found coexisting with fish. The presence of T. vulgaris was best explained by altitude (linear relationship) and ion concentration (convex relationship), besides the occurrence of T. cristatus . Triturus vulgaris was occasionally found to occur at low densities in ponds having fish. For both species the probability of presence was higher when the opposite newt species was present. pH influenced both species in a convex nonlinear fashion with highest probability of presence around pH 6.5. This area is valuable for conservation, monitoring and reference for marginal amphibian populations. Any decline in their abundance would be discovered relatively quickly, and likely causes could be inferred. It can also serve as a reference area for future comparative studies of amphibians elsewhere.

Food and feeding habits of Triturus vulgaris (L.) and T. cristatus (LAURENTI) (Amphibia) in two bog tarns in central Norway

The diets oftwo sympatric species of newts, Triturus vulgaris(L.) and T. cristatus(LAURENTI), from two localities in central Norway, have been compared. Adult T. vulgaris ate mainly those Cladocera which can be classified as planktonic, and to a lesser degree those which are predominantly benthic. The food of T. cristatus was predominantly benthic invertebrates and Cladocera associated with the bottom. T. vulgaris larvae ate planktonic - and predominantly benthic Cladocera, and to a certain degree also larger benthic invertebrates, while T. cristatus larvae (July-August) had taken almost exclusively Cladocera, 75% of which can be classified as planktonic. Large T. cristatus larvae (in September) had eaten relatively more benthic prey. These data would fit the hypothesis that the modes of feeding of the species are different: Adult T. vulgaris swim about in the water much of the time, while T. cristatus stay on the bottom. Among the young, T. vulgaris larvae are mainly associated with the bottom, while T. cristatus larvae are definitely more nektonic during most of the summer; large T. cristatus larvae, however, when nearing the time for metamorphosis, become benthic.

Distribution of Palaemonetes varians (Leach) (Crustacea, Decapoda) in relation to biotope and other caridean shrimps in brackish waters of southern Norway and southwestern Sweden

Palaemonetes varians has been recorded at 11 localities in southern Norway and one locality in Bohuslän, Sweden. Its habitat is brackish water lakes and shallow, coastal lagoons of variable salinity (0.9–25.3). In Oslofjord, lagoons are rare, and P. varians was only found at one locality, Stokke in the county of Vestfold, on the western side of the fjord. No specimens were recorded along the coast north of Strömstad, Bohuslän, which is far north of previous records in Sweden. The occurrence of P. varians in southern Norway seems to be quite isolated from its main distribution in Europe. In high and medium saline (salinity > 5) biotopes, P. varians often occurred with Palaemon elegans and/or P. adspersus, which are common in more open and turbulent biotopes along the coast. In shared localities, P. varians seemed to be competitively displaced by the larger Palaemon species into large stands of telmatophytic vegetation, and few were found in open water. At low salinities (< 5), as the only caridean present, P. varians occurred in great numbers everywhere in large, brackish water lakes and lagoons. Crangon crangon was found at similarly low salinities, but not in lagoons.

A comparison of external and internal attachments of radio transmitters on adult crested newts Triturus cristatus

Telemetry studies of newt species demand small transmitters. Two types of external attachments (sutured to epidermis and backpack) and traditional implanting in the peritoneal cavity were tested between groups of 5 adult individuals of the crested newt Triturus cristatus (mass 6-15 g) held in terrariums under controlled environmental conditions. The newts were anaesthetized with 1.5 g l −1 MS222, delivered in water and buffered to pH 6.9 by Na2CO2. Surgical plane of anaesthesia was achieved after 5-12 minutes and lasted for 30-60 minutes. External tagging proved unsuitable because transmitters became entangled in vegetation, and all animals shed their transmitters shortly after tagging, except for one that died. Transmitters that were surgically implanted in the peritoneal cavity were more successful. By the fourth day following surgery, the animals that had undergone surgery behaved similarly to control animals with respect to the use of cover. Two of the newts died, however, without showing any signs of illness in advance, and the cause of death could not be established. Based on the present experiments and published studies, implantable transmitters appear to be the best method for radiotagging small and medium sized urodele species such as T. cristatus, to gain crucial information on spatio-temporal terrestrial activity patterns, habitat utilization and hibernation sites. Additional research is needed to evaluate both short and long term effects on activity, behaviour and survival.

Palaemonetes varians (Leach) (Crustacea, Decapoda, Natantia) in Norway

Abstract The first record for many decades of the brackish-water prawn Palaemonetes varians is reported from Norway. The species was observed in June and July 1992 in great numbers in three permanent brackishwater lakes at Grimstad, Aust-Agder in southern Norway. Since the brackish nature of these lakes is only about 120 years old, the local prawn population must be relatively young, and the species is therefore probably also present in neighbouring estuaries.