Factors affecting the dispersal of coarse fish

Bolland, Jonathan D.

Biological Science
March 2008

Thesis or dissertation

© 2008 Jonathan David Bolland. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Globally, freshwater fisheries are faced with numerous impacts that compromise fish populations. A knowledge and understanding of riverine fish movements are crucial for effective management and conservation of populations. However, there is a paucity of information about the spatial behaviour and ecology of wild and stocked cyprinids in floodplain rivers, especially under the influence of elevated flows. This study examined the factors affecting the lateral and longitudinal dispersal of juvenile and adult (wild and stocked) coarse fish in three lowland river catchments, namely the River Trent, the Yorkshire Ouse and the River Roding.A literature review was carried out to review the influence of floods on riverine ecosystem function and structure, and fish assemblage patterns. In unmodified lowland rivers, floods are characterized by lateral expansion onto floodplains resulting in high levels of habitat heterogeneity, essential for fish refuge, spawning, nursery and feeding. However, anthropogenic alterations to the flow regime and floodplain connectivity have had considerable detrimental impacts on fish populations. The main conclusion of the review was the need to restore and rehabilitate lowland rivers in an attempt to recover natural features or functionality. The effects of flood timing and magnitude were examined by sampling 0+ fish populations before, during and after floods in the Yorkshire Ouse, a constrained lowland river. Large numbers of eurytopic 0+ fishes were stranded on isolated floodplains when artificial levees ‘over-topped’ in summer (August). By contrast, backwaters provided refuge for high densities of 0+ eurytopic and rheophilic fishes. During floods, small fish were displaced or had lower survival. The results highlight the influence of flood timing on 0+ fish populations, the use of refuge areas and their importance of lowland river rehabilitation.In the River Trent, 0+ fish populations were sampled in the margins of the main river channel and in ten man-made floodplain waterbodies to evaluate the importance of variable connectivity between these habitats for rehabilitating the riverine-floodplain ecosystem. Fish assemblages compared favourably with studies on unmodified river reaches, i.e. succession of lotic-to-lentic habitat corresponded to a sequence of rheophilic-to-eurytopic-to-limnophilic fish species. Consequently it was concluded that the connection of man-made floodplain waterbodies to the river should incorporate variable, not just high, levels of hydrological connectivity into holistic riverine ecosystem management plans.Dual-Frequency Identification Sonar (DIDSON) was used to determine the influence of elevated flow on the lateral movements of adult fish between the Yorkshire Ouse and a marina (refuge habitat). Fish activity in the entrance was predominantly during daylight hours. Increased river flow resulted in significantly reduced fish movements, both towards and away from the marina, and fish presence in the entrance, except for larger fish (more than 30 cm) during the night. This study emphasised the importance of artificial floodplain waterbodies for adult cyprinid fish during winter months.The influence of environmental variation (flow and temperature) on movements of wild and stocked adult cyprinids is poorly understood, partially because of experimental difficulties. A laboratory study on PIT tagging individual juvenile cyprinids, identified that the method would be suitable for such investigations. In the River Roding, a combination of PIT and radio telemetry was used to compare habitat use, longitudinal movement (timing and direction), site fidelity and survival between wild populations and hatchery-reared fish. Wild cyprinids had high levels of ‘site fidelity’ but highly mobile individuals were present within the population, with movements positively correlated with temperature and flow. During elevated winter flows, wild fish occupied areas of reduced flow to reduce energy expenditure, but some fish performed exploratory movements. Movements of stocked fish were more frequent and longer than for wild fish, particularly just after release, possibly for exploratory purposes. Subsequently, movements of stocked fish were minimal, did not correlate with flow or temperature and the final distributions were more widely dispersed than found in wild fish. Importantly from a stocking perspective, stocked cyprinids had the behavioural and physiological ability to cope with elevated flows. However, differences in movements and habitat use between wild and stocked chub probably had consequences on survival.

Department of Biological Sciences, The University of Hull
Cowx, I. G. (Ian G.); Lucas, Martyn
Sponsor (Organisation)
Great Britain. Environment Agency
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