Egg size and growth in steelhead Oncorhynchus mykiss.

The effects of egg size on early development and growth of steelhead Oncorhynchus mykiss were recorded for more than 200 days following hatching. Fish from smaller eggs hatched sooner and at a smaller size than fish from larger eggs, but fish from smaller eggs showed consistently higher growth rates than fish from larger eggs. Since many life-history attributes appear to be determined by size or growth rate at age during the first year, egg size could be a significant predictor of important changes in the life history of individuals.

The effect of rearing structures on behaviour and movement of juvenile steelhead Oncorhynchus mykiss.

The relative movement of juvenile steelhead Oncorhynchus mykiss reared on two treatments was investigated to provide insight on the effect of structure in the rearing environment on the behaviour of the fish before potential release into a natural river system. The progeny of wild broodstock were reared either in the presence or absence of structure in the tank environment for 7 months at the Oregon Hatchery Research Center located in Oregon, U.S.A. Behavioural assessments, including movement response to a simulated predator, showed that fish reared on structure moved a similar amount (based on line crosses) as fish reared in bare hatchery tanks. No significant difference was observed in the proportion of time spent near a small structure within the behavioural test tank between the two treatments, but all fish showed decreased movement over time with each subsequent predation event. Fish from both treatments spent 30% of their time in the section of the tank containing the structure, which was one section out of a total of eight sections. In both treatments, fish foraged 20% of the time in the 2 min following the introduction of live tubifex prey (two separate events). Overall, similar movement and foraging responses occurred following mock predation events for juveniles reared either with or without structure. Developing assessment tools such as these, that measures behaviours related to survival based on rearing environment should allow managers to better predict the survival and effect of rearing conditions on the release of hatchery-origin fish into the wild.

What is a Trophic Cascade?

Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s, the term has been a central or major theme of more than 2000 scientific articles. Despite this importance and widespread usage, basic questions remain about what constitutes a trophic cascade. Inconsistent usage of language impedes scientific progress and the utility of scientific concepts in management and conservation. Herein, we offer a definition of trophic cascade that is designed to be both widely applicable yet explicit enough to exclude extraneous interactions. We discuss our proposed definition and its implications, and define important related terms, thereby providing a common language for scientists, policy makers, conservationists, and other stakeholders with an interest in trophic cascades.