Natural fishing experiments in marine reserves 1983–1993: community and trophic responses

 This study examined the effect of fishing on the density, biomass, species richness and overall structure of the reef fish community at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. A series of natural fishing experiments over this period involving marine reserves were monitored at each island, where estimates of fishing intensity and selectivity were available. Fishing intensity (15% and 25% of biomass removed per year at Sumilon and Apo, respectively) was high enough to affect total community biomass, but not density, significantly. Species richness was not affected significantly by fishing, except at Sumilon reserve. The fishery was relatively non-selective with most families/trophic groups caught roughly in proportion to their contribution to community biomass. Thus fishing did not alter the relative abundance of the major families/trophic groups significantly, except during a period of use of explosives and drive nets in the Sumilon reserve. At the level of family/trophic group the community displayed strong resilience of structure. There was little evidence of secondary effects e.g. declines in abundance of large predators resulting in measurable increases in abundance of their prey. This resilience of the community to the effects of fishing most likely results from three important community attributes (open nature of the component populations, likely maintenance of upstream recruitment supply and apparent lack of any obvious “keystone” species or families) and one important characteristic of the fishery (relatively non-selective with respect to the components of the community). Accepted: 30 June 1998     

An experimental study of the habitat preferences and movement patterns of copper,quillback, and brown rockfishes (Sebastes spp.)

Synopsis A study was designed to test whether habitat association affects the movement patterns and habitat preferences of copper, quillback, and brown rockfishes. Resighting of tagged rockfishes (512 tagged rockfishes and 726 resightings) from July 1986 through June 1988 indicated that home ranges, movements from reefs, and tendency to return from experimental displacement (up to 8.0 km) were significantly different on the three habitat types compared. On high relief rocky reefs, rockfishes maintained small home ranges (most within 30 m²) and displayed strong reef fidelity that was not affected by season; no off-reef movement was detected and rockfishes generally returned from displacements. On artificial reefs, rockfishes also maintained small home ranges (most within 30 m²), however, there were pronounced seasonal habitat preferences. In the summer, artificial reefs become less suitable; considerable off-reef movement occurred and rockfish did not return from displacements. In contrast, during fall and winter, rockfishes remained on artificial reefs and returned from displacements. On low relief rocky reefs, rockfishes maintained considerably larger home ranges (most within 400 m² and some up to 1500 m²) and habitat use was strongly affected by season; rockfishes only inhabited low relief reefs in the summer and only returned from displacements in the summer coincident when peak algal cover. In addition, there was substantial movement between artificial reefs and adjacent low relief reefs; many rockfishes leave artificial reefs in the summer, move to low relief reefs, and return to artificial reefs in the fall when kelp disappears on low relief reefs. Through habitat assessment, movement in response to habitat quality, and ability to home, these rockfish maintain a flexible behavior for optimal habitat use.     

Carnivorous and detritivorous feeding of Mesocyclops leuckarti Claus (Cyclopoida Copepoda)

Food preference of M. leuckarti was experimentally analysed in relation to different species of live and dead crustaceans. Also their possibility of using detritus from bottom sediments as a source of food was tested.It has been found that M. leuckarti readily feed on dead organisms, and detritus from bottom sediments is sufficient for their survival.On the basis of experimental results the feeding strategy of M. leuckarti in lakes is discussed. It seems that the availability of different species of live prey depends on the mode of their swimming and on their body cover, while the availability of dead prey depends only on the body cover. Detritus may be an important source of food, particularly when the live prey are scarce in the pelagic zone, or not easily available.     

Cycling of amino-nitrogen between shoots and roots in wheat seedlings

Summary One part of a split root system of wheat seedlings received full nutrient solution with¹⁵N-nitrate, the other received an identical solution with unlabelled nitrate. Appearance of labelled amino compounds was measured in the xylem sap exuding from roots not supplied directly with¹⁵N-nitrate after removal of the¹⁵N-nitrate-fed roots. This material indicates cycling of nitrogen from the shoots and through the roots. About 60 per cent of the nitrogen in the xylem appears to be cycling in this way.     

Mice and the Reactor: The “Genetics Experiment” in 1950s Britain

The postwar investments by several governments into the development of atomic energy for military and peaceful uses fuelled the fears not only of the exposure to acute doses of radiation as could be expected from nuclear accidents or atomic warfare but also of the long-term effects of low-dose exposure to radiation. Following similar studies pursued under the aegis of the Manhattan Project in the United States, the “genetics experiment” discussed by scientists and government officials in Britain soon after the war, consisted in large-scale low-dose irradiation experiments of laboratory animals to assess the effects of such exposures on humans. The essay deals with the history of that project and its impact on postwar genetics. It argues that radiobiological concerns driven by atomic politics lay at the heart of much genetics research after the war and that the atomic links are crucial to understand how genetics became an overriding concern in the late 20th century.     

Natural fishing experiments in marine reserves 1983 – 1993: roles of life history and fishing intensity in family responses

 This study examined the effect of fishing on the abundance and species richness of families of coral reef fish at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. Natural fishing experiments occurred in marine reserves at each island, where long term estimates of fishing intensity were available. Responses to fishing were interpreted in terms of life histories of fish. The intensity of fishing and fish life histories were generally good predictors of the differential rates of decline and recovery of abundance in response to fishing. Large predators had vulnerable life histories (low rates of natural mortality, growth and recruitment) and were subjected to high intensity fishing. They declined significantly in density when fished and increased significantly but slowly when protected from fishing. Caesionidae, a family with a life history resilient to fishing (high rates of natural mortality, growth and recruitment) but fished intensively also declined rapidly in abundance when fished. Thus, knowledge of life history alone was insufficient to predict response to fishing. Acanthuridae were fished relatively hard and had a life history of intermediate vulnerability but displayed weak responses to fishing. Thus level of fishing intensity alone was also not sufficient to predict response to fishing. For Chaetodontidae, effects of fishing conformed to expectations based on life history and fishing intensity at one island but not the other. Three families with intermediate vulnerability and subjected to intermediate to light fishing (F. Scaridae, Labridae and Mullidae) displayed predictably weak responses to fishing, or counter-intuitive responses (e.g., increasing in abundance following fishing). These counter-intuitive responses were unlikely to be secondary effects of increase in prey in response to declines of predators. Two lightly-fished families with resilient life histories (F. Pomacentridae, Sub F. Anthiinae) predictably displayed weak numerical responses to fishing except during a period of use of explosives and drive nets. Accepted: 30 June 1998