Kevin M. Bailey

Functional responses and scaling in predator-prey interactions of marine fishes: contemporary issues and emerging concepts

Predator-prey interactions are a primary structuring force vital to the resilience of marine communities and sustainability of the worlds oceans. Human influences on marine ecosystems mediate changes in species interactions. This generality is evinced by the cascading effects of overharvesting top predators on the structure and function of marine ecosystems. It follows that ecological forecasting, ecosystem management, and marine spatial planning require a better understanding of food web relationships. Characterising and scaling predator-prey interactions for use in tactical and strategic tools (i.e. multi-species management and ecosystem models) are paramount in this effort. Here, we explore what issues are involved and must be considered to advance the use of predator-prey theory in the context of marine fisheries science. We address pertinent contemporary ecological issues including (1) the approaches and complexities of evaluating predator responses in marine systems; (2) the scaling up of predator-prey interactions to the population, community, and ecosystem level; (3) the role of predator-prey theory in contemporary fisheries and ecosystem modelling approaches; and (4) directions for the future. Our intent is to point out needed research directions that will improve our understanding of predator-prey interactions in the context of the sustainable marine fisheries and ecosystem management.

Structural dynamics and ecology of flatfish populations

Abstract The concept of structure in populations of marine fishes is fundamental to how we manage and conduct research on these resources. The degree of population structure ranges widely among flatfishes. Although we know that large populations tend to be subdivided into local populations, based on morphological, meristic and reproductive characteristics, these data often conflict with evidence on genetic stock structure, due to the scale and organization of movement within the metapopulation. Movement of individuals between local subpopulations and colonization events on a macroecological scale are probably important to some flatfish populations. Dispersal of larvae is known to be a major factor affecting population mixing. Some flatfishes have planktonic stages of long duration and for these species there is often, but not always, little population structure; gene flow sometimes may be limited by oceanographic features, such as eddies and fronts. At the juvenile stage dispersal can result in colonization of under-utilized habitats; however, for flatfishes with strong habitat requirements, this type of event may be less likely when suitable habitats are fragmented. Complex population structure has major implications for management, e.g. lumping harvested populations with little gene flow can have detrimental local effects. Moreover, the issue of population structure and movement influences the interpretation of research data, where populations are generally treated as closed systems. There is currently a strong need for a multidisciplinary approach to study fish population dynamics and the structure of their populations. This research should involve molecular geneticists, population geneticists, animal behaviourists and ecologists. Migration mechanisms, colonization and extinction events, gene flow and density-dependent movements are subject areas of great importance to managing large harvested populations, but our understanding of them at ecological scales, at least for marine fishes, is at a rudimentary level.

The effects of feeding periodicity and ration on the rate of increment formation in otoliths of larval walleye pollock Theragra chalcogramma (Pallas)

The effect of feeding conditions (periodicity and ration level provided) on otolith increment counts of laboratory reared larval walleye pollock Theragra chalcogramma (Pallas) was tested. Increments were deposited with daily periodicity for larvae growing under optimal feeding conditions (high, continuous ration). Increment counts determined by light microscopy were less than expected, assuming a rate of formation of 1 · day−1 for larvae grown at low rations. Increment deposition and length (and therefore growth rates) were positively correlated. Daily increment resolution was disrupted after 4 days of starvation. Evidence is discussed indicating that increments continue to be deposited on otoliths of slow-growing and starved larvae, but are too narrowly spaced for resolution by light microscopy. Feeding larvae more than once daily had no effect on increment deposition rates. For up to 38 days, increment counts from the sagitta and lapillus were equivalent, but for the first 20 days increment counts were easier from the lapillus, which was larger. After 20 days, the sagitta was larger and overall easier to read.