Carl D. van der Lingen

Accommodating dynamic oceanographic processes and pelagic biodiversity in marine conservation planning

Pelagic ecosystems support a significant and vital component of the oceans productivity and biodiversity. They are also heavily exploited and, as a result, are the focus of numerous spatial planning initiatives. Over the past decade, there has been increasing enthusiasm for protected areas as a tool for pelagic conservation, however, few have been implemented. Here we demonstrate an approach to plan protected areas that address the physical and biological dynamics typical of the pelagic realm. Specifically, we provide an example of an approach to planning protected areas that integrates pelagic and benthic conservation in the southern Benguela and Agulhas Bank ecosystems off South Africa. Our aim was to represent species of importance to fisheries and species of conservation concern within protected areas. In addition to representation, we ensured that protected areas were designed to consider pelagic dynamics, characterized from time-series data on key oceanographic processes, together with data on the abundance of small pelagic fishes. We found that, to have the highest likelihood of reaching conservation targets, protected area selection should be based on time-specific data rather than data averaged across time. More generally, we argue that innovative methods are needed to conserve ephemeral and dynamic pelagic biodiversity.

Are Cape gannets dependent upon fishery waste? A multi‐scale analysis using seabird GPS‐tracking, hydro‐acoustic surveys of pelagic fish and vessel monitoring systems

Summary 1. Climate change and fishing impact marine ecosystems, potentially modifying the availability of small pelagic fish to marine top predators. Some seabirds that primarily rely upon these resources have switched to feeding on fishery waste. It has therefore been argued that seabirds might become dependent upon this artificial resource. 2. To test this hypothesis, we studied the foraging behaviour of Cape gannets Morus capensis breeding off the coast of South Africa using high-resolution Global Positioning Systemtracking in relation to the availability of pelagic fish assessed by acoustic at-sea surveys, and fishing effort by the two main south African fisheries (purse seiners that compete with seabirds for pelagic fish, and demersal trawlers that process fish at sea and discharge fish waste) tracked with vessel monitoring systems. Conjoint seabird, fish and fisheries information were analysed at mesoscale (c. 100 km) and sub-mesoscale (c. 10 km) in years of high (2002), medium (2009) and low (2005) pelagic fish biomass within gannets’ foraging range. 3. We found substantial inter-annual variability in spatial use by breeding gannets, which was driven primarily by pelagic fish availability. At the mesoscale, birds and purse seiners exploited similar marine areas, but no fine-scale dependence of birds on purse seiners was detected. Crucially, fine-scale dependence of gannets upon trawlers producing fishery waste was only detected in 2005, when pelagic fish biomass was lowest, indicating a direct effect of trawlers on gannet foraging behaviour in the absence of natural prey. 4. Further overlap analyses of gannet and trawler foraging areas during 2002–2010 confirmed that breeding birds only seek trawlers when pelagic fish availability is low, strongly suggesting reversible seabird dependency upon fishery waste. 5. Synthesis and applications. Our study demonstrates that seabirds such as Cape gannets depend on fishery waste when their natural prey is scarce, but revert to feeding on natural resources whenever available, showing highly flexible foraging behaviour. These results have important implications in the context of the anticipated legislation banning at-sea disposal of fishery waste in different regions, including European seas, highlighting the necessity to concomitantly promote sustainable fishing allowing the restoration of pelagic fish stocks.

Bottom-up effects of a no-take zone on endangered penguin demographics

Marine no-take zones can have positive impacts for target species and are increasingly important management tools. However, whether they indirectly benefit higher order predators remains unclear. The endangered African penguin (Spheniscus demersus) depends on commercially exploited forage fish. We examined how chick survival responded to an experimental 3-year fishery closure around Robben Island, South Africa, controlling for variation in prey biomass and fishery catches. Chick survival increased by 18% when the closure was initiated, which alone led to a predicted 27% higher population compared with continued fishing. However, the modelled population continued to decline, probably because of high adult mortality linked to poor prey availability over larger spatial scales. Our results illustrate that small no-take zones can have bottom-up benefits for highly mobile marine predators, but are only one component of holistic, ecosystem-based management regimes.

Mitochondrial DNA is unsuitable to test for isolation by distance

Tests for isolation by distance (IBD) are the most commonly used method of assessing spatial genetic structure. Many studies have exclusively used mitochondrial DNA (mtDNA) sequences to test for IBD, but this marker is often in conflict with multilocus markers. Here, we report a review of the literature on IBD, with the aims of determining (a) whether significant IBD is primarily a result of lumping spatially discrete populations, and (b) whether microsatellite datasets are more likely to detect IBD when mtDNA does not. We also provide empirical data from four species in which mtDNA failed to detect IBD by comparing these with microsatellite and SNP data. Our results confirm that IBD is mostly found when distinct regional populations are pooled, and this trend disappears when each is analysed separately. Discrepancies between markers were found in almost half of the studies reviewed, and microsatellites were more likely to detect IBD when mtDNA did not. Our empirical data rejected the lack of IBD in the four species studied, and support for IBD was particularly strong for the SNP data. We conclude that mtDNA sequence data are often not suitable to test for IBD, and can be misleading about species’ true dispersal potential. The observed failure of mtDNA to reliably detect IBD, in addition to being a single-locus marker, is likely a result of a selection-driven reduction in genetic diversity obscuring spatial genetic differentiation.

First Account of the Metazoan Parasite Fauna of Oilfish Ruvettus pretiosus Cocco, 1829 (Perciformes: Gempylidae) in South African Waters

Parasites are an important but neglected component of ecosystems that can be used as indicators of host biology and ecology. In the present study, the metazoan parasite assemblage of Ruvettus pretiosus, an understudied but widely distributed predatory gempylid, caught off South Africa was surveyed. A total of seven parasite taxa, including four new infection records (Bolbosoma capitatum, Rhadinorhynchus sp., Hepatoxylon trichiuri and Anisakis sp.), two new locality records (B. capitatum and Rhipidocotyle sp.) as well as the ectoparasitic copepod Sagum foliaceus and the cestode Tentacularia coryphaenae were recovered from the eight specimens examined.