Rehabilitation trials involving riparian fencing and limited pool excavation were conducted on the River Piddle and DevilÕs Brook, Dorset, England, which had been degraded by intensive riparian grazing. In one trial, based on two short (94 and 99 m) treated sections and two control sections, brown trout, Salmo trutta L., numbers were monitored from 1994 (pre-treatment) to 2000. In a second trial from 1996 (pre-treatment) until 2000, trout numbers were monitored in 900 m and 1400 m treated sections. After rehabilitation, juvenile trout numbers increased in the two short sections (Trial 1) but fell in one of the long sections. Adult numbers also increased markedly in the two short-treated sections relative to the controls and they increased markedly in one of the long sections despite a reduction in juveniles. Marking of trout in the short sections showed that they selected the rehabilitated habitat in preference to the control habitat and that immigration was the main source of adult trout, as it must also have been in the 1400 m section. While the results indicate that improvements can be made to adult trout habitat, more research is required on the impact on juvenile production before the impact of such work on the true population can be established. K E Y W O R D S : brown trout,

Retention of both rigid and new soft standard size visible implant (VI) tags in brown troutSalmo trutta after 6 months varied between 42 and 97% for different batches, with no evidence of increased retention of the new type of tag. The 6 month retention of visible implant elastomer tags (VIE) also varied but with a mean of 96%. The VIE retention gradually declined with time up to 42 months.A recent development in fish marking has been the use of tags which are embedded in transparent tissue and obviate many problems of traditional external tags (Farooqi et al., 1995). The usefulness of such tags, however, depends on their retention, but for some of these tags this has not been widely tested, especially in field conditions as opposed to captive fishes. The present study, carried out over several years, investigated the retention of three types of tag in wild brown trout Salmo trutta L. in the River Piddle, a chalkstream in Dorset, England, and assessed their suitability for survival and movement experiments. The tags were rigid and soft visible implant (VI) and visible implant elastomer (VIE) tags (North-west Marine Technology Inc., Shaw Island, WA, U.S.A.).The VI tags are coloured slivers of plastic printed with unique alphanumeric codes which are supplied in two sizes, standard (2Á5 Â 1Á0 mm) and large (3Á5 Â 1Á5 mm). There are two types, a rigid plastic type and a newer soft plastic type. The tag is injected with a supplied injector into the transparent eyelid tissue, immediately behind the eye. The VIE is a fluorescent coloured liquid polymer which is mixed with a catalyst and injected into transparent tissue (e.g. eyelids and webbing between fin rays) with a syringe and it cures to a rubbery consistency after some hours. While the VI tag is intended for identification of individual fish, the VIE is generally used for batch marking.

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