Tubular eyes of deep-sea fishes: A comparative study of retinal topography

The world's deep oceans are home to a number of teleosts with asymmetrical or tubular eyes. These immobile eyes possess large spherical lenses and subtend a large binocular visual field directed either dorsally or rostrally. Derived from a lateral non-tubular eye, the tubular eye is comprised of a thick main retina, subserving the rostrally or dorsally directed binocular visual field, and a thin accessory retina subserving, the lateral, monocular visual field. The main retina is thought to receive a focussed image, while the accessory retina is too close to the lens for a focussed image to be received. Several species also possess retinal diverticula, which are small evaginations of differentiated retina located in the rostrolateral wall of the eye and thought to increase the visual field. In order to investigate the spatial resolving power of these retinae (main, accessory and diverticulum), the distribution of cells within the ganglion cell layer was analysed from retinal wholemounts and sectioned material in ten species representing four genera. In all species, the main retina possesses a marked increase in cell density towards a specialised retinal region (area centralis), with a centro-peripheral gradient range between 7.1 and 60:1 and a peak density range of between 30 and 55 x 10(3) cells per mm(2). The accessory retinae and the transitional zone between the main and accessory retinae possess relatively low cell densities (between 1 and 10 x 10(3) cells per mm(2)) and lack an area centralis. Retinal diverticula examined in four species possess mean ganglion cell densities of between 7.2 and 109.4 x 10(3) cells per mm(2). Analyses of soma areas show that the ganglion cell layer of most species possesses cells with areas in a range of 8.0 to 15.4 mu m(2) in the main retina and between 15.1 and 17.4 mu m(2) in the accessory retina. The peak spatial resolving power of the main retina of the ten species varies from 4.1 to 9.1 cycles per degree. The positions of the retinal areae centrales relative to each species' binocular visual field are discussed in relation to what is known of feeding behaviour of these fishes in the deep-sea.

Conservation and economic benefits of wildlife-based marine tourism: Sea turtles and whales as case studies

Tourism development can have positive and/or negative impacts on wildlife. However, if tourism is developed in accordance with the basic tenets of wildlife tourism such an activity can be sustainable and can aid the conservation of species. Based on two case studies in Queensland, Australia, this article outlines the various economic and conservation benefits arising from wildlife-based tourism. Some of the benefits are direct, such as tangible economic benefits, others are less tangible, such as increased visitors’ willingness to pay in principle for the conservation of species. Wildlife-based tourism is shown to foster political support for the conservation of species utilized for such tourism by various mechanisms. Non-consumptive uses of wildlife are not only sustainable, but may provide a viable alternative to consumptive uses.

Does ecotourism contribute to sea turtle conservation? Is the flagship status of turtles advantageous?

There is little doubt that marine turtles are a flagship species for wildlife tourism. In some cases, this has turned out to be liability for sea turtle conservation, but in other cases, where for example turtle-based ecotourism has been developed, it has made a positive contribution to turtle conservation. Examples of both cases are given. Particular attention is given to the development of turtle-based ecotourism at Mon Repos Beach near Bundaberg, Australia. This development is set in its historical context and its contribution to conservation is discussed. Headstart projects for sea turtles in Sri Lanka are a tourist attraction. While they are promoted as having positive conservation consequences and a survey indicates that visitors are on the whole convinced of this, their effects on turtle conservation is uncertain. The farming of sea turtles provides a basis for tourism and can contribute to turtle conservation in ways outlined. It is argued that insufficient attention has been given to legends, culture and history associated with sea turtles in the promotion of turtle-based tourism. This is supported by Australian evidence. Insufficient use has been made of the connections of indigenous Australians with sea turtles in turtle-based tourism. Beneficial scope exist for developing connections between man and turtles further than at present in promoting turtle-based tourism. This could add further to the role of turtle-based tourism in promoting turtle conservation.

Molluscan stable isotope temperature estimates of the southwestern Ross Sea during the early oligocene and early miocene, CRP-2/2A and CRP-3, Victoria Land Basin, Antarctica

Stable isotope analyses of marine bivalve growth increment samples have been used to estimate early Oligocene (29.4 - 31.2) Ma and early Miocene (24.0 Ma) seafloor palaeotemperatures from the southwestern continental margin of the Ross Sea. Measured δ18O values average +2.5‰ in the early Miocene and range between +1.26 to +3.24‰ in the early Oligocene. The results show that palaeoceanographic conditions in McMurdo Sound during the mid-Cenozoic were significantly different from those of today. The minimum estimated spring through late summer seasonal temperature range was 3°C during the early Miocene and between 1 and 5°C during the early Oligocene. This compares to the equivalent modern day range of

Development of the pulmonary surfactant system in the green sea turtle, Chelonia mydas

This study describes the developmental changes in pulmonary surfactant (PS) lipids throughout incubation in the sea turtle, Chelonia mydas. Total phospholipid (PL), disaturated phospholipid (DSP) and cholesterol (Chol) harvested from lung washings increased with advancing incubation, where secretion was maximal at pipping, coincident with the onset of pulmonary ventilation. The DSP/PL ratio increased, whereas the Chol/PL and the Chol/DSP ratio declined throughout development. The phospholipids, therefore, are independently regulated from Chol and their development matches that of mammals. To explore whether hypoxia could elicit an effect on the development of the PS system, embryos were exposed to a chronic dose of 17% O-2 for the final similar to 40% of incubation. Hypoxia did not affect incubation time, absolute, nor relative abundance of the surfactant lipids, demonstrating that the development of the system is robust and that embryonic development continues unabated under mild hypoxia. Hypoxia-incubated hatchlings had lighter wet lung weights than those from normoxia, inferring that mild hypoxia facilitates lung clearance in this species. (C) 2001 Elsevier Science B.V. All rights reserved.