A general swimming response in exhausted obligate swimming fish.

Marine organisms normally swim at elevated speeds relative to cruising speeds only during strenuous activity, such as predation or escape. We measured swimming speeds of 29 ram ventilating sharks from 10 species and of three Atlantic bluefin tunas immediately after exhaustive exercise (fighting a capture by hook-and-line) and unexpectedly found all individuals exhibited a uniform mechanical response, with swimming speed initially two times higher than the cruising speeds reached approximately 6 h later. We hypothesized that elevated swimming behaviour is a means to increase energetic demand and drive the removal of lactate accumulated during capture via oxidation. To explore this hypothesis, we estimated the mechanical work that must have been spent by an animal to elevate its swim speed and then showed that the amount of lactate that could have been oxidized to fuel it comprises a significant portion of the amount of lactate normally observed in fishes after exhaustive exercise. An estimate for the full energetic cost of the catch-and-release event ensued.

An analytical and hypothesis-driven approach to elasmobranch movement studies.

The study of elasmobranch movements has increased steadily since the early 1970s. A great deal is now known about the horizontal and vertical movements of many elasmobranch species over multiple spatial and temporal scales. These studies illustrate that many species share certain behaviours such as diel shifts in habitat (both horizontal and vertical), continuous yo-yo bounce diving and in many cases, seasonal migrations. Hypothesis-driven studies explaining these behaviours or utilizing an eco-physiological predictive framework are, however, relatively rare. In this review, the descriptive and hypothesis-driven studies of elasmobranch movements are discussed, in addition to some of the analytical tools that can be used to generate or test predictions. There are many tools and analytical techniques available which are not currently being utilized for most studies of elasmobranch movements. With the constant improvement in technology and statistical techniques, the development of hypothesis-driven studies of elasmobranch movements should continue to increase.

Distribution, size frequency, and sex ratios of blacktip reef sharks Carcharhinus melanopterus at Palmyra Atoll: a predator-dominated ecosystem.

Blacktip reef sharks Carcharhinus melanopterus were the most abundant predator in the lagoons at Palmyra Atoll. They were evenly distributed throughout the lagoons, although there was some evidence of sexual segregation. Males reach sexual maturity between 940-1,020 mm L(T). Bird remains were found in some C. melanopterus stomachs. C. melanopterus at Palmyra appear to be smaller than those at other locations.