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Lüderitz, Namibia

Elwen S.H.,University of Pretoria | Gridley T.,University of Pretoria | Roux J.-P.,Luderitz Marine Research | Roux J.-P.,University of Cape Town | And 3 more authors.
Marine Biodiversity Records

Dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales occur in pelagic waters around southern Africa. Here we report the first record of K. sima from Namibia and provide information on the basic morphometrics and diet of that record and of two recent strandings of K. breviceps. All known records (N = 29) of K. breviceps from Namibia are also collated. Eight families of cephalopod were identified in the stomach contents of the K. sima but no fish remains and few crustacean parts were present. Nine and ten families of cephalopod were identified in the stomachs of the two K. breviceps specimens respectively. This report expands the known range of K. sima by more than 1000 km from previous published records in the region. The sparsely populated nature of the Namibian coast and bias of records towards centres of human habitation suggest Kogia strandings are under reported. The low number of stranded specimens of K. sima from Namibia and west South Africa, in comparison to K. breviceps suggests that K. sima occur rarely or at very low densities in the area influenced by the Benguela current ecosystem. Specimens from Namibia are valuable due to uncertainties about taxomony of kogiids in the region. © Marine Biological Association of the United Kingdom 2013. Source

Roux J.-P.,Luderitz Marine Research | Roux J.-P.,University of Cape Town | Braby R.J.,Namibian Coast Conservation and Management Project | Best P.B.,University of Pretoria
Marine Mammal Science

Right whales off Namibia were severely depleted by early 19th century whaling, and rarely featured in modern whaling catches in the 1920s. Aerial surveys of the Namibian coastline from 1978 and onwards revealed increasing numbers of right whales, but few cow-calf pairs. Aerial surveys off South Africa since 2009 showed a major decline in the availability of animals without calves. Twenty individual matches were made between 94 whales photographed off Namibia/Northern Cape in 2003-2012 and 1,677 photographed off South Africa in 1979-2012. Eight were adult females that calved in South African waters, but only one was also seen with a calf off Namibia. Twelve out of 13 individuals off Namibia with distinctive dorsal pigmentation were first seen as calves off South Africa. These results strongly indicate connectivity between the two regions, while the presence off Namibia of three adult females from the South African population in the season in which they are believed to conceive suggests that there is unlikely to be any genetic differentiation between the two areas. We conclude that the reappearance of right whales off Namibia represents range expansion from South Africa rather than the survival of a few remnants of an originally separate stock. © 2015 Society for Marine Mammalogy. Source

Wilhelm M.R.,University of Cape Town | Roux J.-P.,Luderitz Marine Research | Roux J.-P.,University of Cape Town | Moloney C.L.,University of Cape Town | Jarre A.,University of Cape Town
ICES Journal of Marine Science

Scat samples were collected regularly at several breeding colonies of Cape fur seals along the Namibian coast. Merluccius capensis otoliths were obtained from these samples, identified, and measured. Cohorts were easily distinguishable using otolith length measurements converted to fish total length. Growth rates of 2- to 21-month-old hake and hatch dates for each of 15 cohorts were estimated from September 1994 to October 2009 (1994-2008 cohorts) using a Schnute growth function and a non-linear mixed-effects model. The function describing growth of these young hake was length Lt (cm) at age t (years) Lt = 3.17 + (25.0 - 3.17) × [1 - e -0.665 × (t - 0.140)]/[1 - e -0.665 × (1.74-0.140)]. Cohort-specific random effects showed a population hatch date estimate of 31 July (austral winter), varying by 94 days among cohorts, from 31 May (1996 cohort) to 1 September (2004 cohort). The mean growth rate from ages 6 to 12 months was 1.26 cm month-1 for the population, ranging between 0.97 cm month-1 (1996 cohort) and 1.38 cm month-1 (2004 cohort). As this rate is almost double the previously estimated value, which is currently used in the stock assessment models, this result may have major implications for the current stock assessment results and the management of the stock. Re-examination of growth rates needs to be extended to older fish. © 2013 International Council for the Exploration of the Sea. Source

Cury P.M.,Institute Of Recherche Pour Le Developpement | Boyd I.L.,University of St. Andrews | Bonhommeau S.,French Research Institute for Exploitation of the Sea | Anker-Nilssen T.,Norwegian Institute for Nature Research | And 11 more authors.

Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, we quantified the effect of fluctuations in food abundance on seabird breeding success. We identified a threshold in prey (fish and krill, termed "forage fish") abundance below which seabirds experience consistently reduced and more variable productivity. This response was common to all seven ecosystems and 14 bird species examined within the Atlantic, Pacific, and Southern Oceans. The threshold approximated one-third of the maximum prey biomass observed in long-term studies. This provides an indicator of the minimal forage fish biomass needed to sustain seabird productivity over the long term. Source

Ludynia K.,University of Cape Town | Jones R.,Luderitz Marine Research | Kemper J.,Luderitz Marine Research | Garthe S.,University of Kiel | Underhill L.G.,University of Cape Town
Endangered Species Research

We studied the foraging and diving behaviour of male bank cormorants Phalacrocorax neglectus at Mercury Island, Namibia, during the 2007-2008 breeding season. The island hosts the world's largest breeding colony of this endangered species. Population numbers are currently stable at Mercury Island, whereas numbers at other colonies in Namibia are decreasing, including those at formerly important colonies. This trend is presumably due to reduced food availability. At Mercury Island, bank cormorants foraged inshore (ca. 2 km off the coast) in close vicinity to their breeding site (ca. 3 km off the colony) and dived to an average depth of 30 m. Diet at Mercury Island was dominated by demersally occurring pelagic goby Sufflogobius bibarbatus. Our findings suggest that bank cormorants are benthic feeders along their entire range and that their foraging behaviour in Namibia does not differ from that suspected in South Africa. Further studies, extending to other breeding sites, are needed to explain the different population trends and how these may be influenced by food availability. The identification of important foraging sites will play a crucial role in the management of Namibia's first Marine Protected Area and will contribute towards the protection of this species. © Inter-Research 2010. Source

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