CRAYFISH OCCURRENCE IN RELATION TO LAND-USE PROPERTIES: IMPLEMENTATION OF A GEOGRAPHIC INFORMATION SYSTEM (GIS)

On the basis of inventory data collected since 1994, the recent stocking situation for freshwater crayfish in three 10 by 10 km study sites in northeastern Germany (Uckermark) and northwestern Poland (Szczecin area, Koszalin area) is described. The native crayfish Astacus astacus (L.) was found in two of the three study sites (Uckermark, Koszalin area) with 1 and 7 stocks, respectively, while the American species Orconectes limosus (Raf.) was found in all three study areas, and in two of them (Uckermark, Szczecin area) was the dominant crayfish species. By means of spatial analysis on the basis of a geographic information system (GIS), influence of land-use properties and other human impact on crayfish distribution was estimated. A. astacus was found only in lakes with a proportion of arable land below 10% within a 50 m buffer around the shoreline. Proportion of forest around these lakes was above the average for all lakes. In contrast, O. limosus appeared indifferent to all factors related to land use. Average lake size was clearly different for the two species. A. astacus was found in smaller lakes without direct contact to settled areas, whereas O. limosus preferentially inhabited larger lakes, indicating the importance of human activities in respect of extinction of native crayfish stocks and propagation of alien crayfish species. GIS proved a suitable tool for the assessment of land-use effects and overall human impact on crayfish distribution on a landscape level

Highly sensitive bend sensor with hybrid long-period and tilted fiber Bragg grating

We demonstrate a new type of fiber optic bend sensor with a hybrid structure made up of a long period grating (LPG) and a tilted fiber Bragg grating (TFBG). The sensing mechanism is based on the spectrum of power transfers between the core and cladding modes from a TFBG located downstream from a LPG. We show that the curvature of a beam can be determined by the reflected power difference between the core mode and the recoupled cladding modes. We further provide design rules for the LPG and TFBG to optimize and linearize the sensor response. In addition, the temperature cross-sensitivities of this configuration are also investigated for two different types of fiber

Interactions between non-indigenous and indigenous crayfish species.

The main object of the present essay is to summarise some aspects underlying the interactions between non-indigenous (NICS) and indigenous (ICS) crayfish species. The discussion has been also extended to the effects exercised by NICS on the natural habitats they occupy. While doing research on the dyads NICS/ICS, one starting point is to extrapolate common traits that make NICS good invaders from the analysis of their biology, ecology and ethology and the comparison with indigenous species. A subsequent step is to switch attention to the understanding of the characteristics that make ecosystems less vulnerable to invasions and then to analyse both the complex interactions of invaders and target communities and the negative and positive impacts exerted by NICS on the occupied habitats. Examples from Sweden, Britain, and Italy have shown that NICS can replace the native species by a combination of several interacting mechanisms. Besides the transmission of the crayfish plague fungus, mechanisms into action include mostly competitive interference, but also diverse life history traits, recruitment failure, differential susceptibility to predation, and reproductive interference. It has been claimed that invasion theory is full of rules of thumb that, having no precise predictive powers, are thus useless to guide reliable public policy. The solution of the prediction problem requires an in-depth study of every potential invader and target community, trespassing the boundaries among disciplines and having a look at crayfish as a whole and not a single entity. The expectation is thus the return to precise and clear empirical generalisations that can be most useful to develop management strategies

OCCURRENCE OF NATIVE AND INTRODUCED CRAYFISH IN NORTHEASTERN GERMANY AND NORTHWESTERN POLAND.

On the basis of monitoring undertaken in 300 lakes since 1994, the recent stocking situation for freshwater crayfish in northeastern Germany (Uckermark) and northwestern Poland (Szczecin area) is described. The two native species Astacus astacus (L.) and Astacus leptodactylus (Esch.) were found in five and two sites, respectively, while the introduced species Orconectes limosus (Raf.) and Pacifastacus leniusculus (Dana) were found in 214 and two sites. No crayfish were present in 77 sites. Historical stocking data from 1959 for 92 sites in the area of Szczecin and Koszalin, northwestern Poland taken from the litterature were compared with the recent stocking situation according to our own investigations. In 1959, a total of 22 sites contained A. astacus and 13 sites contained A. leptodactylus. Both species were absent after 1994. In contrast, the number of stocks for O. limosus has increased from 57 in 1959 to about 90 after 1994. Differences in juvenile growth and female fecundity studied in two lakes are suggested as a potential mechanism for extinction of native crayfish by introduced species, apart from infection by crayfish plague. Juvenile (1 year old) O. limosus showed a higher weight (8.03 ± 0.12 g) and length (64.7 ± 0.9 mm) than juvenile A. leptodactylus (2.11 ± 0.05 g and 44.8 ± 6.9 mm, respectively). The correlation between number of ovules and female total body length indicates a significantly (p = 0.004) higher number of eggs at the same length for O. limosus (regression coefficient : + 89.5) than for A. leptodactylus (regression coefficient : + 36.4)

ROUNDTABLE - SESSION 2 EXPLOITATION, CONSERVATION AND LEGISLATION

The link between socioeconomics and conservation and the role of legislation in conservation work was discussed in the group with participants from nine European countries. Interest and knowledge among the general public, stakeholders and managers is the key to successful conservation of native crayfish species. Exploitation and conservation do not necessarily exclude each other. A controlled fishery, where it can be sustained, may be an essential tool for conservation by increasing the general awareness and involving more people in the task of protecting the native crayfish species. This strategy is mainly possible for the noble crayfish in the northern part of its distribution, where strong traditions connected to crayfish also exist. A balance between utilisation and overexploitation has to be found and local guidelines for sustainable exploitation produced. Media, the Internet and educational material aimed at schools and stakeholders are excellent ways of reaching a wide audience with information. Universal objectives, rules and regulations at the European level are desirable and the noble crayfish and the stone crayfish should be included in Annex II of the Habitat Directive. Based on this framework detailed regulations are best worked out at the national level, considering the specific crayfish situation in the country. Information about the legislation, the purpose of the legislation and the consequences when not obeying it should be distributed. Stricter regulation of the trade with live alien crayfish is vital because of the associated risk of introducing new diseases and species