Conserving Benguela endemic seabirds
All three seabirds endemic to the Benguela upwelling ecosystem that rely on anchovies and sardines – African Penguin, Cape Gannet and Cape Cormorant – are threatened by a reduction in the availability of their preferred prey. Small pelagic fish have greatly reduced in abundance off the South African west coast, where fishing effort is concentrated and most seabird breeding islands are located. Fish stocks have increased off the south coast, where fishing pressure is low and there are very few suitable breeding locations. The main challenge is to ensure adequate spatial management of this fishery.
However, not all seabirds in the region are decreasing. Numbers of Greater Crested Terns Thalasseus bergii (known locally as Swift Terns) have increased over the last few decades, despite feeding on the same small pelagic fish prey as the African Penguin Sphensicus demersus, Cape Cormorant Phalacrocorax capensis and Cape Gannet Morus capensis. And it is not only species that depend on small pelagic fish that are in trouble. Populations of Bank Cormorants Phalacrocorax neglectus, which feed on a diverse array of demersal prey, also have decreased along the South African west coast, but increased locally along the south coast. Understanding the drivers behind these population changes is the crucial first step necessary to mitigating population declines. This is a large, multi-faceted programme, with key participants including Lorien Pichegru and Pierre Pistorius (NMMU), David Grémillet (CNRS Montpellier), former post-docs Tim Cook (Paris) and Richard Sherley (Bristol), and collaborators at BLSA (Ross Wanless, Christina Hagen, Taryn Morris) and DEA (Azwianewi Makhado and Rob Crawford).
Activities in 2016
- Alistair McInnes completed his PhD on the fine-scale drivers of African Penguin prey dynamics and their impacts on penguin foraging ecology. His paper in Marine Ecology Progress Series identified the oceanographic processes affect prey availability in Algoa Bay, which now supports about half the world population of African Penguins. Lorien Pichegru is extending Alistair’s findings with the help of NMMU post-doc Dr Giannina Passuni, to investigate how climate change is likely to influence fish availability in Algoa Bay.
- Together with Pierre Pistorius (CoE team member at NMMU), Maëlle Connan investigated the diet of African Penguins using stable isotope analyses. She found that although small pelagic fish are critically important during chick rearing, squid also are important for adult self-provisioning during certain times of the year.
- The experimental closure of commercial fishing for small pelagic fish around key penguin breeding islands continued in its eighth year. The Island Closure Task Team presented its findings to the International Stock Assessment Review Panel in December 2016, which differed from those presented by the fishery consultant. The panel recommended that the experiment be continued in 2017 to strengthen the statistical power of the findings.
- Lorien Pichegru published a paper in Ibis showing that two-thirds of African Penguin chicks fledged from Bird Island were male. Male chicks grow faster and fledge heavier than females, likely enhancing their first year survival. This discrepancy in sex production and survival may eventually lead to a male-biased sex ratio, further exacerbating the species’ conservation status.
- PhD student Gwendoline Traisnel assessed how African Penguin responses to a human intruder vary among individuals. Personalities influence breeding success; shyer individuals tend to be better parents than bolder, more aggressive individuals, especially when food is scarce. Aggressive individuals may spend more energy defending their nests, limiting their investment in foraging effort.
- Lorien Pichegru and David Grémillet continued their long-term study of the foraging ecology of Cape Gannets breeding on Malgas Island. Innovative data from a range of data loggers showed that in recent years most adult gannets provisioning chicks spend more energy than they gain through foraging, with long-term fitness cost in terms of adult body condition and reproductive performance. Based on this evidence, we advocated a revision of regional fishing quotas for small pelagic fish including an experimental cessation of purse-seine fishing activities off the west coast.
- CB MSc student Tendai Chinho explored the Information Centre Hypothesis in Cape Gannets, i.e. whether individuals returning from a foraging trip communicate information about their foraging environment to their partners and neighbours during their ritual displays. Her preliminary analyses revealed that some components of the display, such as head-shakes, were correlated to indices of foraging effort.
- Pierre Pistorius also continued his studies on Cape Gannets. Jonathan Botha completed his MSc on resource partitioning (how individuals spread their foraging effort between sexes and over time). PhD student Rabi’a Rijklief showed that foraging effort, nutritional stress and hormonal stress was greater in gannets from the massive colony at Bird Island compared to birds from Malgas Island, when controlling for diet differences. She concluded that intra-specific competition forces gannets breeding on Bird Island to travel long distances to provision their chicks.
- Andrea Thiebault and Pierre Pistorius published a paper on acoustic communication in gannets. Bird-borne video cameras with built in microphones showed that gannet calls are context specific, with collision avoidance while foraging in groups being one of the key functions.
- PhD student Davide Gaglio completed a third year of diet monitoring in Greater Crested Terns breeding on Robben Island. His use of digital photography to record prey brought to the colony allows unprecedented insights into this species’ diet, and revealed some fascinating insights (e.g. although anchovy dominate their diet, the proportion of anchovy drops by 20% on foggy days, indicating the importance of social facilitation for finding anchovy schools). He will complete his PhD in early 2017.
- PhD student Ana Payo Payo from Spain visited the Fitz for two months to work with Peter Ryan and Res Altweg (SEEC). She analysed mark-recapture data for Greater Crested and Roseate Terns Sterna dougallii to estimate annual survival rates.
- Jenni Roberts completed her MSc on the non-breeding movements of adult African Penguins, and Alistair McInnes completed his PhD.
- David Grémillet’s paper on starving Cape Gannets, published in Marine Biology, resulted in a legal challenge from the fishing industry.
- Davide Gaglio published a paper in Methods in Ecology and Evolution on the use of photographs to quantify the diet of birds that carry prey to their nests, such as terns.
- Richard Sherley consolidated findings from two MSc theses on Bank Cormorants for a paper that has just been accepted in Conservation Biology.
- Several students presented papers or posters at the 9th International Penguin Congress that took place in September 2016 in Cape Town. Alistair McInnes and Noelle Tubbs received awards for the best student presentations.
BirdLife International; BirdLife South Africa; Charl van der Merwe Foundation; DST-NRF CoE grant; Raggycharters Whale Watching.
Prof. Peter Ryan (FIAO, UCT)
Prof. Res Altwegg (SEEC, UCT)
Dr Maëlle Connan (NMMU)
Dr Timotheé Cook (FIAO, UCT)
Dr Rob Crawford (Oceans & Coasts, DEA)
Dr Jon Green (U. Liverpool)
Dr David Grémillet (FIAO, UCT and CNRS)
Dr Azwianewi Makhado (Oceans & Coasts, DEA)
Dr Lorien Pichegru (NMMU)
Dr Pierre Pistorius (NMMU)
Dr Richard Sherley (U. Bristol)
Dr Ross Wanless (FIAO, UCT and BLSA)
Students: Alistair McInnes (PhD, UCT), Rabi’a Rijklief (PhD, NMMU), Davide Gaglio (PhD, UCT), Gwendoline Traisnel (PhD, NMMU), Jenni Roberts (MSc, UCT), Noelle Tubbs (MSc, UCT), Jonathan Botha (MSc NMMU)