Recreational fishing is a growing component of the total fishery harvest in many countries, but the impacts of this sector on aquatic resources are often ignored in the management of aquatic systems. Recreational fishing is open-access, and in many inshore regions, the recreational harvest exceeds the commercial harvest. The environmental impacts from recreational angling can be both ecologically significant and broad in scope and include: the removal of a considerable biomass of a wide variety of species; discarded by-catch; possible trophic cascades through the removal of higher order carnivores; impacts on habitat through bait harvesting; impacts of introduced and translocated species to support angling fisheries; direct impacts on sea-birds, marine mammals and reptiles; and angler generated pollution. Management, for several reasons, has largely ignored these environmental impacts from recreational fishing. Recreational fishing impacts are cumulative, whereas there is a tendency for consideration of impacts in isolation. Recreational fishing lobbyists have generally been successful in focusing public and political attention on other impacts such as commercial fishing, and recreational fishing has tended not to come under close scrutiny from conservation and environmental groups. Without changes to the monitoring and management of recreational fisheries that incorporate the broad ecological impacts from the activity, it may not be ecologically sustainable in the long term and Australia will not meet its international obligations of protecting aquatic biodiversity. The definition of property rights and appropriate measures to prevent or manage large scale marine restocking are two emerging issues that also need to be addressed.
An understanding of how habitat structure influences physical environmental processes that are important to organisms utilizing the habitat is a necessary basis for predicting biological responses to habitat variation. Seagrass meadows represent an important coastal nursery habitat that modifies the local flow environment. We used basic fluid-dynamic balances to construct a simple model of the effects of seagrass habitat structure on mean flow within and above the canopy, and tested quantitative predictions of the model against published flume observations and our own field measurements. In the field, flow reduction was detected in 10 of 13 cases inside the canopies of 5 seagrass beds varying in vegetation density (11 to 52 m 2 m-3) and upstream flow (5 to 14 cm s-1). The field data demonstrated greater flow reductions inside the canopy with increasing vegetation density. Flume data further confirmed a quantitative prediction of our model that the vertically integrated flow velocity inside the canopy would vary inversely with the square root of vegetation density. The model also predicted that the width of the 'seagrass-edge zone', in which flow decelerates, is a declining function of vegetation density, indicating that 'edge effects' (and by inference variation among patches of differing sizes) change predictably with seagrass bed structure. Empirical observations and simplified theory relating mean flow reduction to seagrass vegetation density can now be used to generate predictions of dependent biological responses such as variation in gamete fertilization, larval and spore settlement, and growth rates of organisms responsive to fluxes.
Shorebird population decreases are increasingly evident worldwide, especially in the East Asian-Australasian Flyway (EAAF). To arrest these declines, it is important to understand the scale of both the problem and the solution. We analysed an expansive Australian citizen science data set spanning the years from 1973 to 2014 to explore factors related to differences in trends among shorebird populations in wetlands throughout Australia. Of seven resident Australian shorebird species, the four inland species exhibited continental decreases, while the three coastal species did not. Decreases in inland resident shorebirds were related to changes in water availability at nontidal wetlands, suggesting that degradation of wetlands in Australia's interior is playing a role in these declines. The analyses also revealed continental decreases in abundance in 12 of 19 migratory shorebird species, and decreases in 17 of 19 migratory species in the southern half of Australia over the past 15 years. Many trends were most strongly associated with continental gradients in latitude 2 or longitude, suggesting some large-scale patterns in the decreases with steeper declines often evident in the south of Australia. After accounting for this effect, local variables did not explain variation in migratory shorebird trends between sites. Our results are consistent with other studies indicating that migratory shorebird population decreases in the EAAF are most likely being driven primarily by factors outside Australia. This reinforces the need for urgent overseas conservation actions. However, substantially heterogeneous trends within Australia, combined with inland resident shorebird declines indicate effective management of Australian shorebird habitat remains important.
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