Lahontan cutthroat trout, Oncorhynchus clarki henshawi, are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation in landscape and in-stream conditions. The objectives of this study were to determine if landscape topography influences trout distribution, and if water temperatures control this response. The work was carried out in a sub-basin of the Quinn River system, McDermitt Creek, which drains the sagebrush desert of southeastern Oregon and northern Nevada. Headwater tributaries of this creek consist of alternating canyon-confined and valley bounded reaches. Trout within these systems are challenged by low discharge and high temperatures during the summer, and anchor ice during the winter. Contiguous whole stream surveys were used to look at trout distribution during the summer of 2003 and spring and fall of 2004. Our results suggested that topography can affect trout distribution. Trout numbers were highest in areas with greater numbers of nick-points (the transition zones between less confined and more confined valley segments) and greater valley confinement. Additionally, in the downstream portion of our headwater reaches, more trout were found in nickpoints than expected based on the availability of this habitat type. Our data suggest that hyporheic inputs may be high in such areas, thus providing trout with shelter from warm water in the summer, anchor ice in the winter, and shallow stream depths during all seasons. Spatial occurrence of these areas of refugia can be taken into consideration when planning land use activities and restoration efforts. Further research is required to confirm that topography can affect the distribution of Lahontan cutthroat trout in other systems, and to better understand the mechanisms behind these patterns.
We examined the movement patterns and habitat preferences of Mogurnda adspersa in Pattersons Creek, a small, low-order, rainforest creek in Gillies Range State Forest, Far North Queensland, Australia. First, we conducted a capture and recapture study to document population structure and individual movements. Our results show that movement is a prominent feature of population behaviour of M. adspersa, with male gudgeons moving significantly more between pools than females, irrespective of gudgeon size. Second, we quantitatively described habitat characteristics of rainforest pools using point sampling. This data was then combined with capture data to describe the habitat preference of M. adspersa. Our results show that the number of gudgeons was positively related to pool size and decreased with increasing pool velocity. We discuss the results in light of effective management options for the species habitat in general, and Far North Queensland in particular.
Alluvial forests are under high pressure from human activities because of their value as agricultural, wildlife, timber and recreational land. Despite this, spatial patterns of alluvial forest deforestation are not well known. We studied forest alterations in a 2800 ha alluvial ecosystem using aerial photographs. During the study period , forests with canopy heights greater than 15 m (high canopy mature forest; HCM forest) decreased by 70Á4 per cent while forests with canopy heights less than 15 m (low canopy mature forest; LCM forest) forests decreased by 51 per cent, producing a highly fragmented landscape. Factors responsible for forest change included human activities and river dynamics. Although most of the deforestation was related to human disturbance, almost 27 per cent of forest losses were due to channel migration of the Meta River. HCM forests were the most affected land cover since they are easily accessed, viable for logging and occurred on fertile soils, which are valuable for agriculture. LCM forests were less affected since their soil fertilities and inundation regimes were unfavourable to human uses, and thus, less prone to anthropogenic disturbances.
Because of mineral mining threats in the headwaters that drain into Lake Clark National Park, we implemented a baseline ecological survey of the Chulitna River basin through the use of a probability study design. A total of 49 wadeable stream and raftable river sites were sampled for fish assemblages, multiple physical habitat structure variables, and multimeter chemistry (dissolved oxygen, conductivity, pH, and water temperature) by the using standard methods that are employed in the United States Environmental Protection Agency's (USEPA) National Rivers and Streams Assessment. We recorded moderate levels of canopy density, low levels of riparian woody vegetation cover, and the absence of large wood in the Chulitna River basin streams. The extremely low levels of channel incision, the absence of riparian anthropogenic disturbance, and high levels of water quality indicate insignificant anthropogenic landscape alteration in these streams and rivers. Fish were not observed at seven sites, representing 27% of the calculated 2,220 km of the target stream length in the study population. Arctic Grayling Thymallus arcticus, Dolly Varden Salvelinus malma, and Northern Pike Esox lucius were present in 10% (227 km), 38% (847 km), and 8% (181 km) of the calculated target stream/river length, respectively. The most commonly occurring and abundant species, Slimy Sculpin Cottus cognatus (now Uranidea cognata), was present in 56% (1,244 km) of the calculated stream/river length. The lack of anadromous salmon detections was associated with salmonid life histories, naturally high levels of substrate fines and embeddedness, and the presence of Northern Pike. The quality of physical habitat and water quality, as well as the occurrences of Arctic Grayling and Dolly Varden, are representative of the unimpaired waters in Alaska, compared with those in the conterminous USA. We concluded that statistically and ecologically rigorous stream and river sampling can be implemented across a roadless region at reasonable cost and with sufficient planning.
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