Bottom Type (bottom + type)

Distribution by Scientific Domains
Earth and Environmental Science80%

Selected Abstracts

Effects of bottom substrate and presence of shelter in experimental tanks on growth and survival of signal crayfish, Pacifastacus leniusculus (Dana) juveniles

AQUACULTURE RESEARCH, Issue 4 2003
R Savolainen
Abstract The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m,2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials. [source]

Trawl-induced bottom disturbances off the south coast of Portugal: direct observations by the ,Delta' manned-submersible on the Submarine Canyon of Portimão

MARINE ECOLOGY, Issue 2007
Paulo Morais
Abstract The effects of marine fishing activities on benthic habitat and communities have become an important environmental issue. In addition to the direct removal of target species, effects include by-catch, damage to benthic organisms and alteration of habitat structure. The growing number of studies on the impact of fishing on bottom habitats indicates that the effects vary with the physical nature of the seabed and with the local natural disturbance regime. Several studies have been conducted on fisheries by-catch and discards off the south coast of Portugal since 1996. The results provide an idea of the impact on biodiversity: more than 60% of the species caught by the trawl fishery are discarded. The crustacean trawl captures the greatest number of species, probably due to the greater fishing depth range. In April 2004, the manned submersible ,Delta' (from DELTA Oceanographics, USA) conducted a sea campaign integrated in the SEMAPP programme (Science, Education, and Marine Archaeology Program in Portugal) to directly observe and assess the biological, geological, and archaeological aspects. A total of 15 dives were conducted mainly near the head and in the flanks inside Portimão canyon, down to 300 m. Observations showed variations in bottom type, the sedimentary framework and biological communities. These dives (150,300 m depth) also revealed a heavily trawled canyon bottom and erosion structures leading to changes in habitat structure and biodiversity. Of special interest was the occurrence of low-relief boulder substrates with relatively high densities of demersal finfish and shellfish. These sites served as a refuge for several species, whose abundance here was greater than on the surrounding areas of fine-grained substrates. Strong marks on the bottom are apparently caused by the doors of the trawl nets. Their impact will be examined in greater detail in future studies. [source]

Effects of bottom substrate and presence of shelter in experimental tanks on growth and survival of signal crayfish, Pacifastacus leniusculus (Dana) juveniles

AQUACULTURE RESEARCH, Issue 4 2003
R Savolainen
Abstract The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m,2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials. [source]

Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes

JOURNAL OF FISH BIOLOGY, Issue 3 2007
F Juanes
The transition phase describes a distinct post-settlement stage associated with the recruitment to benthic habitats by pelagic life stages. The habitat shift is often accompanied by feeding shifts and metamorphosis from larval to juvenile phases. Density-dependent settlement, growth and mortality are often the major factors controlling recruitment success of this phase. Habitat use also becomes more pronounced after settlement. The role of habitat-mediated post-settlement mortality is elucidated by focusing on the early life history of Atlantic cod (Gadus morhua) and cunner (Tautogolabrus adspersus) in the north-west Atlantic. In these species, settlement can occur over all bottom types, but habitat-specific differences in post-settlement mortality rates combined with size and priority at settlement effects on growth and survival determine recruitment and eventual year-class strength. These results and those from other temperate marine fish species along with work on tropical reef species emphasize the generality of habitat-based density-dependent mortality during the transition phase and its potential for population regulation. These results have implications for fisheries management and can be used to outline a procedure to assist managers in identifying and managing essential transitional habitats including the potential role of marine protected areas in habitat conservation. [source]

Effects of bottom substrate and presence of shelter in experimental tanks on growth and survival of signal crayfish, Pacifastacus leniusculus (Dana) juveniles

AQUACULTURE RESEARCH, Issue 4 2003
R Savolainen
Abstract The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m,2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials. [source]