Abundance estimates of an isolated population of common bottlenose dolphins Tursiops truncatus in Walvis Bay,Namibia, 2008–2012

The coastal population of common bottlenose dolphins Tursiops truncatus found in Namibia is regionally isolated and unique. This population faces several potential anthropogenic threats, especially in Walvis Bay, including boat-based tourism, a commercial harbour undergoing expansion, and aquaculture for oysters and mussels. Between 2008 and 2012, 238 boat-based surveys were conducted, resulting in 170 encounters with bottlenose dolphins. Overall, group sizes varied from 1 to 45 individuals (mean 10.7). Encounter rates, group sizes and total numbers of animals identified were higher in winter than in summer field seasons. The number, and survival and immigration parameters, of bottlenose dolphins using Walvis Bay was investigated using robust design and Huggins closed-population mark-recapture models. The highest numbers estimated were in the first and last years of the study, with estimates of 74–82 in 2008 and 76–77 in 2012 (numbers identified and upper 95% confidence limits). The only previously available data, from an incomplete study in the early 1990s, suggested that the population was between 100 and 150 individuals at the time. Although no linear trend in population size was obvious during the current study, the clear evidence of isolation, small population size, low annual birth rate, and potential long-term decrease in numbers since the early 1990s is concerning. Further work to collect data on demographic parameters is urgently recommended with a view to obtaining increased protection for this species.     

Observations of individual humpback whales utilising multiple migratory destinations in the south-western Indian Ocean

Movements of humpback whales Megaptera novaeangliae among breeding regions within the southwestern Indian Ocean are poorly understood. Understanding the relationships among breeding regions is critical for effective conservation and management strategies. Through systematic comparisons of molecular genotypes and both systematic and non-systematic comparisons of individual identification photographs collected between 1996 and 2006, we have thus far identified nine whales (six males and three females) utilising two breeding areas within this region: the northern Mozambique Channel and eastern Madagascar. Four of the nine whales were recaptured using only photographic data, two whales were independently recaptured using both photographic and genetic data, and three whales were recaptured exclusively using molecular methods. The discovery of these nine individuals provides much-needed data to guide the formulation and future revision of stock boundaries.     

Population trends of New Zealand fur seals in the Rakiura region based on long-term population surveys and traditional ecological knowledge

We estimated population abundance of New Zealand fur seal (Arctocephalus forsteri) pups on Bench Island off Stewart Island, New Zealand seven times between 1996 and 2012. Overall, there was a 29% increase in pup abundance from 1996 to 2012 at the Main Beach colony, corresponding to a mean annual growth rate of 1.6% and a doubling time of approximately 40 years. At the Sprat Point colony, there was an overall increase of 29% between 2003 and 2012 corresponding to a mean annual growth rate of 2.9% and a doubling time of approximately 25 years. The area occupied by both colonies has also increased. In 2006, we surveyed East Beach and counted a total of 201 pups. We obtained traditional ecological knowledge of fur seal distribution and breeding status from local Māori for 46 locations around Stewart Island, 36 of which have not been surveyed since Wilson in 1971–1974; this supports an expansion of fur seal presence and breeding areas in the region in the last 41 years.     

Fish community responses to invasive fish removal and installation of an exclusion barrier at Lake Ohinewai,Waikato

Introduced common carp (Cyprinus carpio) are a recognised threat to New Zealand’s freshwater ecosystems. In 2011, an invasive fish removal programme was undertaken in 16.8 ha Lake Ohinewai, a Waikato riverine lake. Active fish removal using netting and boat electrofishing was supported by installation of a one-way exclusion barrier on the outflow to Lake Ohinewai. The barrier was designed to allow fish passage downstream out of the lake, while preventing adult carp from moving upstream. The estimated carp population was reduced from 8,548 fish (5,863–12,937, 95% confidence limits) in 2011–454 fish (251–889, 95% CL) in 2014. However, by 2016 the carp population had recovered to 2,063 fish (1,070–4,328, 95% CL) with increased abundance in invasive brown bullhead catfish (Ameiurus nebulosus) also observed. This research demonstrates that carp populations can be reduced to low abundances in the short to medium term, but continued removal will be required for on-going control.     

Population dynamics of southern elephant seals: a synthesis of three decades of demographic research at Marion Island

Southern elephant seal Mirounga leonina numbers declined precipitously throughout most of their circumpolar distribution since the 1950s. A long-term intensive demographic programme was initiated in 1983 on the relatively small population of southern elephant seals at sub-Antarctic Marion Island in an attempt to identify causative mechanisms associated with this decline. Weaned pups have been tagged annually since 1983, and this has produced a large number of individuals of known identity. A regular resighting programme yielded a mark-recapture dataset that has been subjected to numerous survival-based models. This ongoing programme produced a substantial body of scientific literature on population growth patterns, vital rates (survival and fecundity) and population regulation in southern elephant seals, which are reviewed in this synthesis. We briefly describe the analytical framework common to much of the demographic research, highlight important conclusions concerning population regulation of elephant seals at Marion Island, and discuss priorities for future research.