W. R. C. Beaumont

Techniques for evaluating the spatial behaviour of river fish

Radio-tagging is widely used for studies of movements, resource use and demography of land vertebrates, with potential to combine such data for predictive modelling of populations from individuals. Such modelling requires standard measures of individual space use, for combination with data on resources, survival, dispersal and breeding. This paper describes how protocols for efficient collection of space-use data can be developed during a pilot study, and reviews the ways in which such data can be used for space-use indices that help answer biological questions, with examples from a study of riverine pike (Esox lucius). Analyses of diurnal activity and spatio-temporal correlation were used to assess when to record locations, and analyses of home range increments were used to define the number of location records necessary to assess seasonal ranges. We stress the importance of developing protocols that use minimal numbers of locations from each individual, so that analyses can be based on samples of many individuals. The efficacy of link-distance (e.g. cluster analysis) and location density (e.g. contouring) techniques for spatial analysis for river fish were compared, and the utility of clipping off areas to river banks was assessed. In addition, a new automated analysis was used to estimate distances along river mid-lines. These techniques made it possible to quantify interactions between individuals and their habitat: including a significant increase in core range size during floods, significant preference for deep pools, and a lack of exclusive territories.

Use of miniature radio-transmitters to track the movements of dace, Leuciscus leuciscus (L.) in the River Frome, Dorset

Advances in radio-tag design have resulted in the production of tags suitable for use with relatively small fish. A method of release intended to minimise stress and increase validity of early tracks was designed. A technique of accurately locating radio-tags was developed and tested. Preliminary tracking results show that dace are highly mobile, and are capable of extensive, and often rapid migrations, both up and downstream. Most of the dace studied exhibited similar behaviour patterns, remaining at selected sites for extended periods of time, before rapidly relocating within the river.

Habitat utilisation by pike Esox lucius L. during winter floods in a southern English chalk river

Seven pike Esox lucius L., implanted with radio-transmitters, were tracked throughout autumn and winter in the River Frome, a southern English chalk river. During the first flood events of the year, pike remained within the main river channel but during subsequent flood events, pike could also be found in flooded fields, in drainage ditches or in a millstream. Eighty percent of the fixes over flooded land occurred within 10 m of the riverbank, although distances of up to 89 m from the bank were recorded. In ditches, pike could be found over 250 m from the main river. For pike in ditches and flooded fields, distance from the main river channel was positively correlated with discharge. There was individual variation amongst pike for the habitat types selected, with some pike utilising flooded field or ditch habitat more often than others. The proportion of time spent out of the main river channel does not appear to be related to the size of the pike. It is hypothesised that pike are leaving the main river channel to exploit feeding opportunities in the flooded fields and drainage ditches, rather than using these areas as refugia from high flow conditions.

A simple activity monitoring radio tag for fish

A radio tag is described which facilitates the long-term monitoring of activity events in fish. The tag is a simple peritoneal implant and thus requires no complicated surgery to deploy. A motion-sensing mercury switch interfaced to a microcontroller is used to modulate pulse rate and thus indicate periods of activity. The tag is being used to study the feeding and activity patterns of pike (Esox lucius L.) where laboratory and field trials have shown the system to be robust, long lasting and reliable.

Movement and activity patterns of the black piranha

Adult black piranhas, Serrasalmus rhombeus, were radio-tracked using purpose built equipment in the 2.6 km long oxbow lake Coco Cocha, south east Peru during a five month period in the dry season of 1995. Fish were tagged externally in front of the dorsal fin. S. rhombeus showed generally localised movements in different sections of the lake with only one making use of its whole length during the tracking period. S. rhombeus in the shallower extreme sections of the lake were seen to make frequent trips into flooded forest. Speed plots and perceived activity plots revealed cyclic patterns of movement and activity synchronised with dawn. Those fish tracked at night were active until after dark and sometimes throughout the night into the early hours of the morning.