The ecosystem approach to fisheries attempts to define objectives for the target species, the wider ecosystem and, critically, the fishery itself. Proposals for implementing this approach often include spatial restrictions on harvesting and it is therefore important to understand how these will affect fishery performance. One metric of potential performance is the probability of encountering exploitable densities of the target species at the scale of fishing operations. The probability of encountering exploitable densities of Antarctic krill, Euphausia superba, at the 1 nm scale during an acoustic survey was predicted by both bathymetry and the mean krill density at the larger scale at which the fishery is managed. This suggests that the risk to fishery performance will increase if management actions relocate the fishery into deeper water. The results also suggest that ecosystem models resolved to the spatial scale of management units could usefully predict effects at the scale of fishing operations. However, correct parameterisation of these models will require better characterisation of threshold densities for efficient exploitation. Finally, the distribution of both catch and fishing effort over an entire fishing season reflected the distribution of krill density observed during the survey.
Abstract:
Penguins are adapted to live in extreme environments, but they can be highly sensitive to climate change, which disrupts penguin life history strategies when it alters the weather, oceanography and critical habitats. For example, in the southwest Atlantic, the distributional range of the ice-obligate emperor and Ade´lie penguins has shifted poleward and contracted, while the ice-intolerant gentoo and chinstrap penguins have expanded their range southward. In the Southern Ocean, the El Niño-Southern Oscillation and the Southern Annular Mode are the main modes of climate variability that drive changes in the marine ecosystem, ultimately affecting penguins. The interaction between these modes is complex and changes over time, so that penguin responses to climate change are expected to vary accordingly, complicating our understanding of their future population processes. Penguins have long life spans, which slow microevolution, and which is unlikely to increase their tolerance to rapid warming. Therefore, in order that penguins may continue to exploit their transformed ecological niche and maintain their current distributional ranges, they must possess adequate phenotypic plasticity. However, past species-specific adaptations also constrain potential changes in phenology, and are unlikely to be adaptive for altered climatic conditions. Thus, the paleoecological record suggests that penguins are more likely to respond by dispersal rather than adaptation. Ecosystem changes are potentially most important at the borders of current geographic distributions, where penguins operate at the limits of their tolerance; species with low adaptability, particularly the ice-obligates, may therefore be more affected by their need to disperse in response to climate and may struggle to colonize new habitats. While future sea-ice contraction around Antarctica is likely to continue affecting the iceobligate penguins, understanding the responses of the ice-intolerant penguins also depends on changes in climate mode periodicities and interactions, which to date remain difficult to reproduce in general circulation models.
