Phylogeographic reconstruction of the marbled crayfish origin

The marbled crayfish (Procambarus virginalis) is a triploid and parthenogenetic freshwater crayfish species that has colonized diverse habitats around the world. Previous studies suggested that the clonal marbled crayfish population descended as recently as 25 years ago from a single specimen of P. fallax, the sexually reproducing parent species. However, the genetic, phylogeographic, and mechanistic origins of the species have remained enigmatic. We have now constructed a new genome assembly for P. virginalis to support a detailed phylogeographic analysis of the diploid parent species, Procambarus fallax. Our results strongly suggest that both parental haplotypes of P. virginalis were inherited from the Everglades subpopulation of P. fallax. Comprehensive whole-genome sequencing also detected triploid specimens in the same subpopulation, which either represent evolutionarily important intermediate genotypes or independent parthenogenetic lineages arising among the sexual parent population. Our findings thus clarify the geographic origin of the marbled crayfish and identify potential mechanisms of parthenogenetic speciation.

Standardisation of alien invasive Australian redclaw crayfish Cherax quadricarinatus sampling gear in Africa

Freshwater crayfish are damaging invaders across southern Africa; however, monitoring techniques and efforts are disparate across the region as different sampling methods have been used. To develop a standard method for assessing redclaw crayfish Cherax quadricarinatus abundance, a survey was conducted to assess for differences in detection and catch per unit effort (CPUE) in Lake Kariba. Two sampling approaches were compared: opera traps baited with cooked maize meal historically used in crayfish surveys in Zimbabwe, and Promar collapsible traps baited with dry dog food, which have been used for assessments in South Africa and Swaziland. Baits were compared in the Barotse Floodplain in Zambia using the Promar trap. Detection probability (Pcapture) and CPUE were significantly lower for opera traps baited with cooked maize meal (Pcapture = 0.41; CPUE = 1.19 ± 0.24 ind.·trap-1·night-1) compared to the Promar traps baited with dry dog food (Pcapture = 0.67; CPUE = 4.53 ± 0.82 ind·trap-1·night-1). The Pcapture and CPUE for Promar traps baited with dog food (Pcapture = 0.89; CPUE = 4.29 ± 0.83 ind·trap-1·night-1) was significantly higher than for maize meal baited traps (Pcapture = 0.29; CPUE = 0.25 ± 0.17 ind·trap-1·night-1). Sex ratio and carapace length of crayfish sampled did not differ between sampling methods. Due to higher CPUE, the authors consider the Promar collapsible trap baited with dog food approach as the better method for determining crayfish population abundance and suggest that comparisons of abundance take this into consideration by applying conversion factors if different methods are applied.

Ecological and biological features of river crayfish in the modern conditions of the Kuibyshev reservoir

Crayfish are considered as objects of consumption in the modern world. An increase in their share in the production of aquaculture objects is shown. The data on the state of the crayfish population on the territory of the Middle Volga before regulation, after the formation of the Kuibyshev reservoir and at the present time are presented. It was shown that the size-weight and ecological-biological characteristics of long-toed crayfish before regulation and after the formation of the reservoir are similar. The data on the modern size-age characteristics of populations of narrow-clawed crayfish in the Volga-Kama reach of the Kuibyshev reservoir are presented. It is shown that in the catches the basis is made up of three-year-olds 13–15 cm long and weighing about 80–100 g. The equation for the dependence of body weight on the zoological length of river narrow-clawed crayfish in the Volga-Kama reach of the Kuibyshev reservoir: y = 35,588x0,3073. The equation for the dependence of body weight on the commercial length of narrow-clawed crayfish in the Volga-Kama Reach of the Kuibyshev Reservoir: y = 29,409x0,3275. Chemical analysis of narrow-clawed crayfish revealed 12 elements. The following sequences of the content of elements in narrow-clawed crayfish from the Volga-Kama reach of the Kuibyshev reservoir were noted: in the muscle tissue of edible parts — Ca ˃K ˃S ˃P ˃Cu ˃Fe ˃Zn ˃Mn ˃ Br ˃Sr; in shell — Ca ˃Si ˃P ˃S ˃K ˃Sr ˃Ti ˃Fe ˃Mn ˃Cu ˃Br ˃Zn; in entire crayfish — Ca ˃K ˃P ˃Si ˃S ˃Sr ˃Fe ˃Mn ˃Cu ˃Ti ˃Br ˃Zn. In the edible parts of the narrow-clawed crayfish of the Volga-Kama reach of the Kuibyshev reservoir, there are no such hazardous elements as lead, arsenic, cadmium and mercury. Crayfish can be used as a feed additive in feed for aquaculture objects. Crayfish breeding in the structure of aquaculture in the Middle Volga region can become an important component. The development of aquabiotechnology makes it possible to use natural crayfish populations for the tasks of creating industrial crayfish farms.

The amount of environmental DNA increases with freshwater crayfish density and over time

eDNA analysis is ideally suited to monitor the occurrence of endangered or invasive species because of its non-invasive nature and high sensitivity. European freshwater crayfish are threatened across the whole continent. Classical crayfish monitoring is challenging and time consuming due to their nocturnal activity and hidden lifestyle. Therefore, eDNA-based monitoring of native as well as invasive species seems to be of great benefit for the conservation of the native species and it has indeed been increasingly applied in recent years. Nevertheless, comparably little is known on the relationship between eDNA concentration and crayfish population densities, a prerequisite for estimating population size based on eDNA measurements. Here, we performed laboratory experiments to investigate the relationship between the concentration of crayfish eDNA and population densities - measured as crayfish size and biomass. There was a strong correlation between the two measurements. Moreover, the amount of eDNA increased at least during the first three days after crayfish stocking in the aquarium. The experiments also indicate, that crayfish activity might have a strong influence on the eDNA signal strength. Our findings will significantly contribute to an optimization of the monitoring of freshwater crayfish via the analysis of eDNA and therefore be important for the conservation of these threatened species.

First record of the stone crayfish in the Romanian lowlands

The stone crayfish is a native European freshwater species with significant population declines caused by anthropogenic pressure onto its habitats, climate change and spreading of non-indigenous invasive crayfish and their pathogens (e.g., Aphanomyces astaci). We present the first record of an Austropotamobius torrentium population in a small stream from the southern lowlands of Romania, in an area without limestone or karst, known as a typical stone crayfish habitat in this country. No additional populations were found in the neighbouring streams. The mtDNA analysis based on sequencing a short fragment of the cytochrome c oxidase subunit I (COI) gene revealed that specimens from this newly discovered population belongs to the most widespread phylogroup of A. torrentium (CSE) and share the same haplotype as the specimens found in Croatia. Unfortunately, this crayfish population has disappeared most likely because of the crayfish plague since pathogen A. astaci was isolated from moribund crayfish. Our study highlights the vulnerability of isolated relic populations in the face of outside stressors.

New Findings of White Clawed Crayfi sh, Austropotamobius pallipes (Decapoda, Astacidae), and Peculiarities of its Spatial Distribution in Neretvica (Bosnia and Herzegovina)

At the territory of Bosnia and Herzegovina, Austropotamobius pallipes (Lereboullet, 1858) is present mainly in the Neretva basin, partly in the Una and Tsetina river basins (Trožić-Borovac et al., 2012). This species was registered at elevations from 180 to 1024 m a.s.l., but most habitats are located at elevations from 300 to 600 m a.s.l. Based on indirect data, one can state that more than 2/3 of the crayfish population in the Neretva basin is concentrated in the Neretvica basin. Our studies showed that the crayfish are very irregularly distributed in the Neretvica basin. The crayfish are almost absent at well-flushed habitats without CPOM (deposits of coarse particulate organic matter, e. g., fallen leaves), as well as at habitats with monotonous boulders or gravel-sand bottom. The study of the size structure of the crayfish population showed the presence of juvenile crayfish with a size of less than 5 cm in the Neretvica river course. The most balanced structure of the crayfish population represented by juvenile as well as adult species is observed in Gorovnik.

Diversity and Ecology of the Freshwater Crayfish in the Northwest of the Republic of Srpska

The existence of three autochthonous crayfish species is confirmed in the northwest of the Republic of Srpska: Astacus astacus, Pontastacus leptodactylus and Austropotamobius torrentium. There is a lack of information on the European crayfish population status in the Republic of Srpska comparing to other European countries. Our aim is to generate the latest information on crayfish distribution and population status, and make it the basis for managing and preserving natural population. The present study was implemented in the period from April 2018 until September 2019. Mostly distributed crayfish species in the Republic of Srpska is A. torrentium registered in 12 locations at altitude ranging from 201 to 846 m in the Vrbas river basin, but it is also present in the tributary streams of the Sana river, in ecologically-like habitats, in particular in relatively clear waters with low quantity of organic substances (I and II water category). A. astacus is mainly present in the Crna river basin, forming both river and lake population (a great number thereof is present in the Balkana lake) – waters with oxygen concentration over 8g O2 m-3 and with BOD5 values below 0.5g O2 m-3. P. leptodactylus was found only in two locations: The Matura river (in Srbac) and the Vrbas river (upstream from Razboj), in the I-III category waters. The identified possible threats for autochthonous crayfish in fresh water ecosystems of the Republic of Srpska require urgent water management and preservation actions.

Simulation of different fishery regulations to prevent population decline in a large freshwater invertebrate, the Murray crayfish (Euastacus armatus)

Globally, overharvest contributes to population declines of fish and invertebrates. Quantifying the effects of fishing and associated harvest is essential to preventing such declines. Murray crayfish Euastacus armatus exhibit slow growth and late age at maturity, and were historically abundant in Australia’s Murray–Darling Basin, but river regulation, pollution and overfishing have reduced their range and abundance. Diminished recreational fisheries still exist, but data to quantify catch, effort and harvest are not available to inform management decisions. We used a population model to assess the status of a harvested Murray crayfish population, informed by data collected from a fishery-dependant survey. Quantitative fisher surveys were undertaken in the Murrumbidgee River during the 2012 Murray crayfish open season (May–August inclusive). Shortly after the surveys, and in light of fishery-independent data that indicated a Murray crayfish decline, the crayfish recreational fishery was spatially reduced and shortened to a 3-month season (June–August), bag limits were reduced and size limits were changed from a minimum length limit of 90mm to a harvest-slot length limit (HSLL) of 100–120mm. Modelling of the Murray crayfish population indicated it was most likely to be relatively small with a mean population size of 2777 individuals and affected by a high rate of crayfish harvest (harvest probability 0.4), indicating vulnerability to further decline should fishing effort and harvest persist. The population model was used to assess the regulation change to a HSLL, with the results supporting the regulation change and indicating that implementation of the HSLL would stabilise the population, albeit over many years. This study demonstrates that empirical data and population modelling are crucial to inform fishery regulations for threatened species.