We addressed the question of bottom-up versus top-down control of marine ecosystem trophic interactions by using annual fish catch data and satellite-derived (SeaWiFS) chlorophyll a measurements for the continental margin of western North America. Findings reveal a marked alongshore variation in retained primary production that is highly correlated with the alongshore variation in resident fish yield. The highest productivity occurs off the coasts of Washington and southern British Columbia. Zooplankton data for coastal British Columbia confirm strong bottom-up trophic linkages between phytoplankton, zooplankton, and resident fish, extending to regional areas as small as 10,000 square kilometers.

It is shown from hydrodynamics theory and the size composition of particles in marine food chains that there are two unique swimming speeds of importance to pelagic fish: (1) the optimal cruising speed, which maximizes the distance traveled per unit energy expenditure and (2) the optimal foraging speed, which maximizes the rate of flow of surplus energy, or production in its broadest sense. With sockeye salmon (Oncorhynchus nerka) as an example, the optimal cruising and foraging speeds were found to be proportional to the body length raised to the 0.4 power. By analogy, if pelagic fish in general tend to move at either of these speeds, their ration and growth rates relative to the body weight should be proportional to a power that varies between 0.7 and 0.8. These predictions are consistent with field growth measurements for several pelagic species. Therefore, the necessary conditions for a theory of optimal foraging exist since (1) all adaptive swimming speeds are physiologically possible and (2) there is evidence that some juvenile fish feed by moving at the appropriate speed to maximize their production rate. Key words: bioenergetics, swimming speed, optimal foraging

A set of density-dependent growth and survivorship equations is derived from evidence that the instantaneous death rate in the sea is inversely proportional to particle size. The survivorship equation reproduces several well-known phenomena observed in fish populations. It predicts: 1) that winter and spring spawning species ought to produce larger eggs than summer spawners, 2) that it is advantageous for species that spawn in batches to produce progressively smaller eggs in spring and summer, and 3) that the death rate of a cohort of fish should decrease continuously as the survivors grow and approach the critical size.The biological basis for the observed variation in the size of pelagic fish eggs and larvae is thought to be due primarily to trophic relations within the pelagic community. It is suggested from what is known of the relative abundance and foraging capabilities of different sized particles, that the survival rates of larval and juvenile fish should increase as they grow and occupy a progressively higher position in the food chain.