Description: C. acuminatus and C. superciliosus (L.) are the dominant resident fish of high shore pools in the rocky intertidal of the western Cape Peninsula, South Africa. The factors influencing pool choice were experimentally assessed to elucidate the mechanisms by which the two species partition the resources of the intertidal environment. A total of 215 5 fish were tested in extensive laboratory studies, running from 02. J une 1997 to 19. December 1997. An artificial tidepool system was erected to examine preferences of fish for tidepools equipped with different microhabitats and to examine effects of intra- and interspecific interactions on pool choice. C. acuminatus displayed a strong preference for artificial pool equipped with rock cover, and in particular, crevices with an interstitial space of 1 cm, a space which matches the body size. C. superciliosus, however, was less restricted to a specific cover type. Both species made the selection of a particular substratum almost entirely visually, rather than through the use of chemical or tactile cues. Furthermore, the position of shelter in respect to the pool bottom was found to be important, with shelter resting on the bottom being preferred to shelter raised off the pool bottom. lntraspecific territoriality by C. acuminatus was absent, whereas in C. superci/iosus agonistic behaviour appeared to result in juveniles being forced to occupy less favoured areas within the pool. Interspecific agonistic behaviour in terms of occupation of specific pools by certain individuals was found to be unimportant in regulating fish densities, since both species can be found together when shelter is limited. Recapture of tagged fish released in the pool of capture confirmed Iaboratory observations and indicated that C. acuminatus and C. superciliosus do occupy discrete low tide habitats when immersed. Those experiments were conducted from 02. October 1997 to 16. December 1997 at the natural intertidal zone of the western Cape Peninsula. The length of time individual fish stayed in pools varied considerably within species. C. superciliosus had a short average duration of stay (four days). In contrast, C. acuminatus showed a high fidelity to the pool where it was first marked (14 days). The comparison between pools which were sampled at the same time intervals indicated that site fidelity and the expansion of the pool population depend upon local topographic characteristics and morphological stability of pools. The general pattern of recaptures observed suggested that both species move over a home range, with the number of suitable pools within this range being less for C. acuminatus than for C. superciliosus. The observed differences in the pattern of pool selection of the two species may be explained in terms of their swimming ability and feeding behaviour. The ecological differences between the two species indicate that C. superciliosus is the most generalised of the South African clinids, while the specialisations exhibited by its congener, C. acuminatus, allow the two species to coexist with limited competition.The observed differences in the pattern of pool selection of the two species may be explained in terms of their swimming ability and feeding behaviour. The ecological differences between the two species indicate that C. superciliosus is the most generalised of the South African clinids, while the specialisations exhibited by its congener, C. acuminatus, allow the two species to coexist with limited competition.

Description: The widespread decline of anadromous Atlantic salmon (Salmo salar L.) populations makes it imperative to research the underlying cause and to develop mitigation measures. One of the most vulnerable phases in the life-cycle of salmon is the fry stage in early spring. Survival rates of juveniles emerging from the gravel of riverbeds are related to the three-dimensional complexity of bottom morphology and hence the variety of microhabitats within the nursery area. However, anthropogenically increased sediment supply due to changes in agricultural land-use reduces complexity, especially the roughness of the streambed. This study used a series of controlled manipulative field experiments conducted in a purpose built raceway system, to provide quantitative data on the impact of sediment pollution on salmon production in freshwaters. The comparison of in-stream habitat with an increased sediment load and control (i.e. simulated natural) situations revealed that increased sedimentation drastically reduced the salmon fry carrying capacity of a stream. A modest increase in sand bed load (15%) in semi-natural streams reduced the fry density by 50% ten days after stocking with unfed fry. Emigration patterns of fry from sedimented habitat and control habitat were significantly different. Fry from both habitat types showed unusual active upstream migration which compensated for densities exceeding the carrying capacity. Riverine habitat was optimised on a reach scale to complement the raceway results and to provide a temporary mitigation measure. The in-stream habitat of a mill leat was manipulated to build the first Eco-Hatchery for salmon in the UK based, on results from the raceway and on an extensive literature review. The hatchery achieved high survival rates of salmon juveniles throughout their freshwater life stages. Furthermore, in-stream sediment traps were developed to offer effective protection for key fry nursery habitat from excess sand bed load. The data provided by the raceway system and the Eco-Hatchery inform riparian management plans. However, addressing sedimentation related issues in salmon rivers is a politically sensitive issue and will take time. Stocking with unfed fry is being used in the interim to temporarily enhance or restore populations. But stocking programmes based on conventional hatchery methodology as a response to declining stocks have frequently failed in both respects. A semi-natural incubator for salmon eggs, the Bamberger-box, was developed to address extremely low survival of newly stocked fry from conventional hatcheries. The new incubator mimics a natural salmon redd and aims in essence to produce wild fish in a hatchery environment. The results of five years field experiments using genetically different broodstock were encouraging. There was a significant increase in the average length and body mass of fry emerging from Bamberger-boxes and the mean eyed-egg-to-fry survival was 93% - greatly exceeding published data for egg-to-fry survival in the wild. Fry from Bamberger-boxes showed a significantly different and more natural rheotactic behaviour, and fewer fry had deformities when compared with fry incubated in conventional hatchery troughs. Seasonal and diurnal emergence patterns from Bamberger-boxes correlated with natural emergence patterns. A potentially crucial advantage of this new semi-natural incubation system was to ensure larvae survival during environmental extremes when all juveniles incubated in conventional hatchery troughs did not survive. Large-scale commercial incubators based on the same principles as the Bamberger-Box were developed and proved equally effective in producing ecologically viable fry. Low costs of production and operation render the new incubators an economically viable alternative to traditional incubation systems. Exploratory research on the influence of hyporheic invertebrates abundance on fry size at emergence was carried out as a next step in continuously improving semi-natural incubation technology.