No abstract

Since the collapse of the pelagic fisheries off southwest Africa in the late 1960s, jellyfish biomass has increased and the structure of the Benguelan fish community has shifted, making the bearded goby (Sufflogobius bibarbatus) the new predominant prey species. Despite increased predation pressure and a harsh environment, the gobies are thriving. Here we show that physiological adaptations and antipredator and foraging behaviors underpin the success of these fish. In particular, body-tissue isotope signatures reveal that gobies consume jellyfish and sulphidic diatomaceous mud, transferring "dead-end" resources back into the food chain.

Utne-Palm, A. C. and Hart, P. J. B. 2000. The effects of familiarity on competitive interactions between threespined sticklebacks. -Oikos 91: 225 -232.In this study, pairs of juvenile sticklebacks either familiar with each other or pairs unfamiliar with each other met to share a food source. The study showed that sticklebacks were less aggressive towards a partner when sharing a common food source with a familiar conspecific, compared to when sharing a food source with an unfamiliar conspecific. The results showed that the aggressive behaviour was built up and broken down gradually depending on how long the two competitors had been together or apart. A decrease in aggressiveness was found after the sticklebacks had been together two weeks, with a further decrease after four weeks together. Conversely there was an increase in aggressiveness after the sticklebacks had been parted for two weeks or four weeks. The chance of food being equally distributed between the competing pairs increased with time spent together and decreased with time parted. The observed decrease or increase in the amount of aggression is discussed as a build-up or a breakdown of rank knowledge or of a co-operative partnership.A. C. Utne-Palm,

The reaction distance of Gobiusculus flavescens to mobile and immobile copepod prey of different transparency was studied in water conditions with different turbidity levels or spectral composition. Both prey contrast (red or transparent Calanus spp.) and prey mobility caused reaction distance of G. flavescens to increase. The effect of prey mobility or prey transparency on reaction distance was independent of turbidity level. Longest reaction distances were measured for mobile and red prey at intermediate turbidity levels (10-20 JTU). Contrast threshold decreased with increasing turbidity. Although contrast of red and transparent copepod prey increased with increasing wavelength, longest reaction distances were observed at shorter wavelengths (blue-green). Lowest contrast threshold was found at shorter wavelengths. Visual pigments of G. flavescens are adapted to its natural environment. Both turbidity and spectral composition influenced G. flavescens contrast threshold. 1999 The Fisheries Society of the British Isles

SUMMARY We examined the effect of turbidity (0.5–14 beam attenuation m–1) and predator attack speed (150 and 296 cm s–1) on escape responses of juvenile cod Gadus morhua in the laboratory. We triggered escape responses using a predator model and measured escape timing, direction and locomotor performance. We also measured responsiveness and estimated the likelihood of fish escaping the`predator attack' (putative escape success, PES). Turbidity affected both PES and the type of escape response used by the fish, but these effects depended on predator speed. PES for the fast predator attack declined from 73% in clear water to 21% in highly turbid water, due to decreased responsiveness and poorly timed escapes. Intermediate turbidity enhanced PES and responsiveness to the slow predator attack. Locomotor performance was reduced by turbidity, whereas predator speed had the opposite effect. Our results suggest that both predator attack speed and turbidity have important roles in determining the vulnerability of fish attacked by piscivorous predators.