Development of monitoring methods for crayfish populations

crayfish sampling;species accumulation;species richness;species distribution;sampling methods;timed search;generalized linear mixed model;burrowing crayfish;habitat preference

Engelbert, Bryan ; Taylor ; Christopher A.

关键词: crayfish sampling;    species accumulation;    species richness;    species distribution;    sampling methods;    timed search;    generalized linear mixed model;    burrowing crayfish;    habitat preference;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/46866/Bryan_Engelbert.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Standardized sampling methods for assessing the community structure and health of stream fisheries, freshwater mussels, and insects have been used for several decades. However, such methods are woefully lacking for crayfish. The research of this project involved evaluation of several methods for assessing crayfish populations.The first study (Chapter 2) aims to create standardized, robust sampling methods for assessing stream-dwelling crayfish assemblages and densities in riffle habitats at individual sites located in Missouri. Timed search sampling was used to capture all species present and assess crayfish relative abundance for each site, and quantitative kick seining was used to assess crayfish mean density (number per m2) in riffle habitats. Number of samples required for species richness estimation was analyzed by a resampling our timed search data (without replacement) to illustrate species accumulation at a site scale. Number of samples required for crayfish mean density estimation (relative to the crayfish mean population density) in riffle habitats was assessed by applying a standard deviation-based method to our sample pool from each site. By varying combinations of statistical rigor (percentage of species captured and confidence level), researchers can assess the advantages and disadvantages of alternative sampling effort scenarios. Crayfish burrow excavation was successful at capturing additional species not captured with other methods. Substrate size had a direct effect on crayfish mean density, while current velocity, water depth, and substrate size had significant effects on the mean density of one or more of the captured species. Site average current velocity had a positive effect and vegetation presence at a site had a negative effect on crayfish relative abundance.The second study (Chapter 3) focuses on defining tools for investigating crayfish population status and species distribution. Proper assessment of aquatic organisms requires standardized site selection and sampling methods over a broad geographic scale to examine communities beyond what is present at a single locality. This part of the study utilizes sampling methods for assessing crayfish species richness at the site scale, and through species accumulation analysis, determines the value of stream length (km) and area that one site adequately represents (e.g., for 100% of species richness captured, one site = 19 km of stream or 6281 ha of drainage area) in a drainage for adequate crayfish population and species distribution assessment. Our data suggest statistical balance can be made on the density of sites sampled in any given drainage to more efficiently utilize time and resources, representing a tradeoff between likelihood of capturing all species richness in a drainage and number of sites required to be sampled. Habitat variables were analyzed for potential relationships to crayfish relative abundances. Stream width and stream order were negatively correlated with crayfish relative abundance, whereas substrate size and channel unit (a single quantified description of riffle, run, and pool habitat types at a site, positively influenced by riffle habitats) were positively related with relative abundance. Habitat variables had significant, but varying effects on species-specific relative abundances at sites.We utilized and compared two different sampling methods to capture primary burrow-dwelling crayfishes in Chapter 4. Hook-and-line capture success was substantially lower than reported in another study (0.7% versus 80%); excavation of burrows was successful in capturing occupants 64% of the time, and higher than reported in a similar study (40.7%), and captured six different crayfish species in burrows. To add robustness to our study design, we introduced a broadened spatial component by sampling four randomly selected sites per county in six counties. Burrowing crayfish were caught at 13 of 24 randomly selected sites; crayfish were also collected at seven additional non-random sites, added to boost datasets so we could test the effect of temperature and Julian date on crayfish capture, and to compare capture techniques. Out of 31 total sites, three sites required effort beyond the first 15-minute search to find burrows that yielded additional species. Standing water was also sampled using lentic timed search methods at these 31 sites. Additional timed search sampling beyond the first 15-minute sample was required to collect additional species in that habitat at nine of the 31 sites. Julian date was positively correlated to number of active crayfish burrows found. Crayfish capture in standing water was positively correlated with soil temperature, but was negatively correlated with Julian date. Overall, we were able to detail sampling methods and effort amounts required to adequately assess crayfish communities across their wide ranging ecologies. This study is the first to address statistical rigor in terms of percentage of crayfish species richness captured and confidence levels, and relate these values to an amount of effort expended. Environmental variables studied can provide future insight to address crayfish habitat needs and detection possibilities, while proving that habitat variables need to be accounted for when comparing different sites or investigating reasons of temporal change of crayfish communities.