Conserving indigenous crayfish: stock assessment and habitat requirements in the threatened Austropotamobius italicus

Abstract

ABSTRACT1. As part of the Austropotamobius pallipes species complex, the crayfish Austropotamobius italicus is a species of community interest whose preservation requires the designation of Special Areas of Conservation (SACs) (Annex II, EU Habitats Directive). This study aimed at (1) assessing the conservation status of this threatened indigenous species by stock assessment in Central Italy and (2) identifying some aspects of its elective habitat.2. Surveys were conducted in nine streams harbouring A. italicus (streams WI) and in 10 streams where crayfish populations became extinct at least 5 years before the study (streams WO).3. The results confirmed that A. italicus is a K-selected species, with a relatively slow growth rate (males: 0.34; females: 0.37) and a long life expectancy (males: 8.2 years, females: 7.8 years). The extant populations are healthy, showing balanced sex-ratios and well structured age-class compositions. Mortality is mainly due to fishing, which is illegal in Tuscany.4. Principal Components Analyses showed that the streams WI and WO differ in the abundance of allochthonous plant detritus but not in the taxonomic composition of their macroinvertebrate communities. Age classes were found to be spatially segregated, juveniles mainly using cobbles as substrates and adults seemingly avoiding them.5. The loss of the pristine riverine landscape seems to have been responsible, together with illegal fishing, for the local extinction of the species. As a consequence, retaining, enhancing, and restoring the habitat and its complexity are required for the preservation of A. italicus.6. The designation of SACs might help in this endeavour if accompanied by programmes aimed at publicizing the need for conservation of this species. Unfortunately, crayfish-focused projects supported by LIFE in Italy since 1992 (4%) and the SACs involved (1.4%) have been relatively few, despite the poor conservation status of this species and its well recognized ecological role.

Estimating age composition in Alpine native populations of Austropotamobius pallipes complex

“…In this study we showed that modalprogression analysis is a useful approach as a source for obtaining basic information necessary to assess population structure of species of conservation interest (Bjorndal et al, 1995;Salvidio and Delaugerre, 2003;Brusconi et al, 2008). Indeed, conservation and reintroduction strategies ideally require characterization of donor populations regarding growth curves and size and age at sexual maturity (Grandjean et al, 1997a tions and estimates of growth parameters are known to be potentially affected by the selectivity of the sampling gear used to collect the animals (Montgomery et al, 2010).…”

“…In order to avoid this bias, we chose to adopt hand sampling by experienced researchers, which is one of the less-selective capture methods for large crayfish (Peay, 2004), and allowed us to obtain a large data set collected within a very short time (only few hours) at night, when crayfish activity was similar in size class, temperatures and sexes (Barbaresi and Gherardi, 2001). The YOY (0 + class) did not occur in the frequency distributions since hatching took place some weeks before sampling and the independent juveniles were still too small to be captured (Bernardo et al, 1997) or were still adopting an elusive behavior, which made them difficult to find (Brusconi et al, 2008).…”

“…Because the hatching period had just ended (only a female with larvae was collected), we did not find the young-of-the-year (YOY) during night sampling due to their low movement capability (Gherardi, 2002) and their elusive behaviour (Brusconi et al, 2008). Therefore in order to fill this gap, daily samplings were conducted by turning cobbles to find and measure the YOY.…”

“…Datasets smaller than about 100 could not discriminate even the number of age components existing in the sample (France et al, 1991), but several studies used successfully smaller datasets when dealing with threatened or endangered species (Bjorndal et al, 1995;Salvidio and Delaugerre, 2003;Brusconi et al, 2008).…”

The freshwater grass shrimpPalaemonetes antennariusin the diet of fish in Lake Bracciano (Central Italy)

“…Scientists are often expected to indicate the most important species which disturbance may originate the main detrimental effect on both occurrence and abundance of other taxa in a community (Jones et al, 1994). From this viewpoint, P. antennarius ought to receive the same attention recommended for other freshwater decapods (see Brusconi et al, 2008) as proposed for Austropotamobius pallipes species complex sensu Chiesa et al (2011) and Scalici and Bravi (2012) significant role of the freshwater grass shrimp and the dynamic consequences due to its presence need to be confirmed, since understanding the dynamic implications of a species role in the food web may provide useful information when scientists have to dialogue with institutions for deciding which taxa is of main concern in conservation and managing efforts, and to focalize on those with the strongest involvement in community persistence.…”