Personality, density and habitat drive the dispersal of invasive crayfish.

There is increasing evidence that personality traits may drive dispersal patterns of animals, including invasive species. We investigated, using the widespread signal crayfish Pacifastacus leniusculus as a model invasive species, whether effects of personality traits on dispersal were independent of, or affected by, other factors including population density, habitat, crayfish size, sex and limb loss, along an invasion gradient. Behavioural traits (boldness, activity, exploration, willingness to climb) of 310 individually marked signal crayfish were measured at fully-established, newly-established and invasion front sites of two upland streams. After a period at liberty, recaptured crayfish were reassessed for behavioural traits (newly-established, invasion front). Dispersal distance and direction of crayfish movement, local population density, fine-scale habitat characteristics and crayfish size, sex and limb loss were also measured. Individual crayfish exhibited consistency in behavioural traits over time which formed a behavioural syndrome. Dispersal was both positively and negatively affected by personality traits, positively by local population density and negatively by refuge availability. No effect of size, sex and limb loss was recorded. Personality played a role in promoting dispersal but population density and local habitat complexity were also important determinants. Predicting biological invasion in animals is likely to require better integration of these processes.

Fish community and abundance response to improved connectivity and more natural hydromorphology in a post-industrial subcatchment.

Barrier removal and fish pass construction are increasingly used as tools to restore river connectivity and improve habitat quality, but the effectiveness of subcatchment-scale connectivity restoration on recovery of fish communities is poorly understood. We used a before-after-downstream-upstream methodology to determine the effects of subcatchment-scale connectivity restoration on fishes in a fragmented tributary of the River Wear, Northeast England, between 2013 and 2019. Following restoration (three barriers removed, five barriers fitted with fish passes, two barriers unaltered), riffle habitat increased, fine sediment decreased, and most fish species benefitted. Total fish abundance, comprising seven native species, increased 3 years after the restoration and remained elevated to the end of the study. Mean brown trout (Salmo trutta) density increased from 20.9 ±â€¯6.3 to 33.8 ±â€¯16.8 per 100m2 from 2013 to 2019, with Young-of-Year trout increasing from 10.6 ±â€¯4.6 to 19.8 ±â€¯11.8 per 100m2. Connectivity restoration reduced the mean age of trout, suggesting a change to an increased migratory component of the population. Density of bullhead (Cottus perifretum), a species with poor dispersal ability, increased from 4.6 ±â€¯2.7 to 32.6 ±â€¯17.9 per 100m2 over 2013 to 2019. Stone loach (Barbatula barbatula), also a less mobile species but tolerant to fine sediment, decreased in abundance where barriers were removed. Atlantic salmon (Salmo salar) were absent over the study timescale, despite being common in the Wear, and despite suitable habitat and water quality in the restored subcatchment, suggesting a hysteresis effect. Our findings indicate that, where good water quality exists, restoring river connectivity and hydromorphology at a subcatchment scale is beneficial for most native resident and migratory fishes. However, the ecological benefits of connectivity restoration, especially in rivers with many barriers, may take several years to develop. We encourage well-controlled long-term studies reporting the outcomes of large-scale connectivity restoration.