Season of moult of African penguins at Robben Island,South Africa,and its variation, 1988–1998

Counts of African penguins Spheniscus demersus in immature and adult plumage in the feather-shedding phase of moult were made at Robben Island at two-weekly intervals over a 10-year period between 1988 and 1998. For both age-classes, most birds moulted between November and January, although small numbers moulted throughout the year. In most years, the peak moult was in late November or December. Immature birds had a secondary peak in March. In 1994/95 for adults, and 1995/96 for immature birds, moult was less synchronized than in other years. This probably resulted from oiling of about 2 400 penguins in June 1994, following the sinking of the Apollo Sea. Half of those birds were cleaned and released. Their subsequent moult may have been earlier than normal.     

Factors influencing growth of the African penguin colony at Boulders,South Africa, 1985–1999

This paper reports on growth of the Boulders colony of African penguins Spheniscus demersus from inception in 1985 to the present. More than 900 pairs now breed there. Growth of the colony slowed in 1995 and 1996 and reversed in 1998, coinciding with periods of low abundance of Cape anchovy Engraulis capensis off South Africa. In December 1996, penguins were excluded from a portion of land where they had formerly bred. They responded by increasing the density of their nests in other areas and expanding their area of breeding longshore. These patterns indicate that food and not space are currently controlling colony growth rate. Much of the colony growth probably results from immigration of first-time breeders from other colonies. Of immigrants, 70–80% may be from Dyer Island to the south-east, where numbers of penguins have decreased. Boulders also is frequently visited by penguins from other colonies, and by rehabilitated birds.     

The distribution and abundance of seven commercial trawlfish from the Cape south coast of South Africa, 1986–1990

Spatial and size/age distributions of seven teleost species are described from a series of five annual trawling surveys made over the continental shelf and upper slope (20–500 m) of the South African south coast between Cape Agulhas and Port Alfred. The catch was quantified and scaled up to an estimate of an annual biomass index for each of the principal species. The fish studied were the two species of Cape hake Merluccius capensis and M. paradoxus, kingklip Genypterus capensis, Agulhas sole Austroglossus pectoralis, Cape horse mackerel Trachurus trachurus capensis, monk Lophius vomerinus and panga Pterogymnus laniarius. Each showed varying patterns of biomass fluctuation annually, although the surveys constituted too short a data series to reveal significant trends. Nevertheless, declines in abundance of panga and kingklip supported data collected from other sources over a longer period. Interpretation of the data is tempered by a realization that species which are patchily distributed or less vulnerable to the sampling gear may have been inadequately sampled. The information can be used for more-effective management of the multi-species demersal trawl fishery of the region.     

Migrations of humpback whales past Cape Vidal,South Africa,and an estimate of the population increase rate (1988–2002)

Shore-based surveys of migrating humpback whales Megaptera novaeangliae were undertaken from Cape Vidal, northern KwaZulu-Natal, South Africa, each year between 1988 and 1991, and in 2002. Daily observations of migrating whale groups were carried out from an approx. 60 m-high platform during all surveys. Whale groups were tracked by position-fixing on surfacing bouts using survey theodolites, to determine swimming speeds and headings and distance offshore, while group size estimation was carried out at each theodolite measurement. Numbers of whales observed or projected (at tracked speeds) to cross the midline of the survey area within the observation period each day were tallied in each of three distance bins. These counts were adjusted to account for daily sighting effort and for proportions that were likely to have been missed on account of their distance offshore or poor sighting conditions to produce daily sighting rates. Such daily tallies were summed over the survey period to estimate the number of whales passing Cape Vidal each year, with counts from days of <2.5 h of observation effort (due to weather or sighting condition restraints) replaced by the mean of the previous and following days. The numbers passing to the north of Cape Vidal during coincident periods of 17 days over the 1988–2002 surveys (6–22 July) and 25 days over the 1990, 1991 and 2002 surveys (6–30 July) provide statistically significant increase rates of 11.5% (SE 2.8) and 9.0% (SE 2.7) per annum respectively.     

Pilchard distribution in South African waters, 1983–1985

Seasonal movements of South African pilchard Sardinops ocellatus in the relatively abundant 1982/83 year-class are inferred by means of length frequency information from predator diet analyses and from commercial and research catches in various localities. Pilchard of approximately one year of age were most abundant in the vicinity of Algoa Bay on the south-eastern Cape coast in the summer of 1983/84. The pilchard length frequency distribution in gannet diet and research midwater trawl samples in this area provided a clear linkage, through the known juvenile growth rate, with fish of an average 6 months of age, which were abundant off the West Coast during May 1983. Pilchard in this year-class were subsequently found to be widely distributed over the Agulhas Bank, with a tendency for them to inhabit deeper water towards the shelf edge as they reached the age of first spawning (about 18 months). During 1985, a noticeable increase in the abundance of large, two-year-old and older pilchard in the diet of West Coast gannets and in West Coast commercial catches indicated a movement of 1982/83 year-class fish into that area. The changes in distribution of pilchard in this year-class are discussed in relation to seasonal differences in the marine environment off South Africa.     

Diet of the South African fur seal (1974–1985) and an assessment of competition with fisheries in southern Africa

Almost 1 000 South African fur seals Arctocephalus pusillus pusillus were collected at sea (inshore and offshore) for examination of stomach contents and other biological parameters. The main prey of seals above the age of one year was teleost fish, of which at least 28 species were identified. Overall, 74,6 per cent of the diet was teleost fish, 16,7 per cent cephalopods, 4,8 per cent crustaceans such as shrimps, prawns, amphipods and isopods and 3,2 percent rock lobster. Within this overall dietary pattern there were marked regional differences. The importance of individual fish species in the diet was investigated from the numbers and the sizes of otoliths occurring in the stomachs, from which the identity and size classes of the prey species could be calculated. Again there were regional differences in the importance of different prey species. On the west coast of South Africa the most important species were anchovy and Cape hakes (each 23% of total diet), whereas on the south coast the important species were anchovy (17%), horse mackerel (14%), pilchard (12%) and Cape hake (14%). Off South West Africa the two dominant species were pelagic goby (52%) and horse mackerel (23%), anchovy and Cape hake constituting only 4 and 5 per cent respectively of total diet. The total annual consumption of anchovy and Cape hake by seals in South African waters was calculated at 125 000 and 120 000 tons respectively.     

Distribution and seasonal abundance of large cetaceans in the Durban whaling grounds off KwaZulu-Natal,South Africa, 1972–1975

Daily charts of the aerial search effort (432 206 nautical miles) of the Union Whaling Company and 1 099 sightings of 10 497 whales were available from 628 flights off Durban between 1972 and 1975. Densities of whales were analysed by month and water depth distribution over the four-year period. Low observed densities of blue Balaenoptera musculus, right Eubalaena australis, sei B. borealis and humpback Megaptera novaeangliae whales most likely resulted from earlier whaling pressure. Seasonality of blue, sei and humpback whales was bimodal, indicative of winter migrations to the north of the Durban whaling grounds, whereas the unimodal seasonality of fin whales B. physalus and minke whales B. bonaerensis or B. acutorostrata suggest the offshore region as the northern terminus of their migrations. Sperm whales Physeter macrocephalus migrate northwards offshore of the KwaZulu-Natal coast in autumn/early winter and southwards in late winter/spring, with larger males migrating later than the smaller males and females. Killer whale Orcinus orca presence was coincident with that of offshore minke whales and the southward migrations of other baleen whales, whereas densities of animals deemed as bottlenose whale Hyperoodon planifrons suggest strong early and late summer seasonal abundance in the offshore region. Such extensive surveys offshore of the KwaZulu-Natal coast are unlikely to be repeated; hence, data-extraction of whaling records provides a valuable source of seasonal and distributional information for marine management.     

Impact of protective shark nets on sea turtles in KwaZulu-Natal,South Africa, 1981–2008

Shark nets were established along the KwaZulu-Natal coast in 1952 to protect bathers against shark encounters. Sea turtle bycatch data for the period 1981–2008 in these shark nets indicated that loggerheads Caretta caretta were caught most frequently at 40.9 y^–1 or 1.11 km-net^–1 y^–1, followed by green turtles Chelonia mydas at 0.32 km-net^–1 y^–1 and leatherbacks Dermochelys coriacea at 0.14 km-net^–1 y^–1. Catch rate of loggerheads increased throughout the study period, and was positively correlated with the increase in the number of nesting females from the recovering population in Maputaland, South Africa (r = 0.52, p < 0.05, n = 28). This increase is ascribed to successful nest conservation. Leatherback bycatch remained stable, following their nesting trends, although they receive similar conservation efforts on nesting beaches as loggerheads. Bycatch of green turtles, although not a nesting species in South Africa, was stable over time. Mortality varied between species (from 53.2% to 70.6%) with loggerheads being the most hardy, followed by leatherbacks and green turtles. Few hawksbills Eretmochelys imbricata and olive ridleys Lepidochelys olivacea were caught in the shark nets. Fewer sea turtles are caught by shark nets than by longlines and because the nesting populations of loggerheads, green turtles and leatherbacks are either stable or increasing in the South-West Indian Ocean, shark net bycatch was considered negligible and sustainable.     

Declined trends of chlorophyll a in the South China Sea over 2005-2019 from remote sensing reconstruction

Chlorophyll a concentration(CHL) is an important proxy of the marine ecological environment and phytoplankton production.Long-term trends in CHL of the South China Sea(SCS) reflect the changes in the ecosystem’s productivity and functionality in the regional carbon cycle.In this study,we applied a previously reconstructed15-a(2005-2019) CHL product,which has a complete coverage at 4 km and daily resolutions,to analyze the longterm trends of CHL in the SCS.Quantile regression was used to elaborat...     

δC and δN biogeographic trends in rocky intertidal communities along the coast of South Africa: Evidence of strong environmental signatures

Ecosystem dynamics driven by top-down controls have been well documented in rocky intertidal communities, while the effects of bottom-up influences are comparatively poorly understood. We hypothesized that large-scale signatures of the physical environment may be identifiable along the South African coastline as it is subject to two very different current systems (Benguela and Agulhas Currents) that profoundly influence primary production and thus both food type and availability. Through stable isotope analysis, we examined biogeographic patterns in multiple trophic levels at four sites along a 1400-km stretch of South African coastline and investigated the dietary role of macroalgal-derived organic carbon in rocky intertidal communities. The general positioning of trophic groups was comparable across all sites, with animals from the same trophic levels grouping together and with a δ¹⁵N fractionation of 1–2‰ between levels. The species found at all sites demonstrated east–west δ¹⁵N enrichment, presumably reflecting a biogeographic shift in nitrogen sources linked to upwelling on the west coast. Filter-feeders gave particularly clear results. Using discriminant analysis, mussels could be categorized into four geographic groups based on carbon and nitrogen signatures: east coast, southeast coast, south-west coast and west coast. Barnacles and polychaetes showed similar geographic groupings to mussels, but with shifts in actual values (1‰ depletion in δ¹³C and 3‰ enrichment in δ¹⁵N relative to mussels). This suggests that fractionation varies between species within a trophic level.     

Nutrient variability in the mixed layer of the subarctic Pacific Ocean, 1987–2010

Data collected primarily from commercial ships between 1987 and 2010 are used to provide details of seasonal, interannual and bidecadal variability in nutrient supply and removal in the surface ocean mixed layer across the subarctic Pacific. Linear trend analyses are used to look for impacts of climate change in oceanic domains (geographic regions) representing the entire subarctic ocean. Trends are mixed and weak (generally not significant) in both winter and summer despite evidence that the upper ocean is becoming more stratified. Overall, these data suggest little change in the winter resupply of the mixed layer with nutrients over the past 23 years. The few significant trends indicate a winter increase in nitrate (~0.16 μM year⁻¹) in the Bering Sea and in waters off the British Columbia coast, and a decline in summer phosphate (0.018 μM year⁻¹) in the Bering. An oscillation in Bering winter nutrient maxima matches the lunar nodal cycle (18.6 years) suggesting variability in tidal mixing intensity in the Aleutian Islands affects nutrient transport. Nitrate removal from the seasonal mixed layer varies between 6 μM along the subarctic–subtropical boundary and 18 μM off the north coast of Japan, with April to September new production rates in the subarctic Pacific being estimated at 2 and 6 moles C m⁻². Changes in nutrient removal in the Bering and western subarctic Pacific (WSP) suggest either the summer mixed layer is thinning with little change in new production or new production is increasing which would require an increase in iron transport to these high-nutrient low-chlorophyll (HNLC) waters. Si/N and N/P removal ratios of 2.1 and 19.7 are sufficient to push waters into Si then N limitation with sufficient iron supply. Because ~3 μM winter nitrate is transferred to reduced N pools in summer, new production calculated from seasonal nutrient drawdown should not be directly equated to export production.     

Spatial and temporal seasonal trends in coastal upwelling off Northwest Africa, 1981–2012

Seasonal coastal upwelling was analyzed along the NW African coastline (11–35°N) from 1981 to 2012. Upwelling magnitudes are calculated by wind speed indices, sea-surface temperature indices and inferred from meteorological station, sea-surface height and vertical water column transport data. A permanent annual upwelling regime is documented across 21–35°N and a seasonal regime across 12–19°N, in accordance with the climatology of previous studies. Upwelling regions were split into three zones: (1) the Mauritania–Senegalese upwelling zone (12–19°N), (2) the strong permanent annual upwelling zone (21–26°N) and (3) the weak permanent upwelling zone (26–35°N). We find compelling evidence in our various indices for the Bakun upwelling intensification hypothesis due to a significant coastal summer wind speed increase, resulting in an increase in upwelling-favorable wind speeds north of 20°N and an increase in downwelling-favorable winds south of 20°N. The North Atlantic Oscillation plays a leading role in modifying interannual variability during the other seasons (autumn–spring), with its influence dominating in winter. The East Atlantic pattern shows a strong correlation with upwelling during spring, while El Niño Southern Oscillation and Atlantic Multi-decadal Oscillation teleconnections were not found. A disagreement between observationally-based wind speed products and reanalysis-derived data is explored. A modification to the Bakun upwelling intensification hypothesis for NW Africa is presented, which accounts for the latitudinal divide in summer wind regimes.     

Peculiarities of the Rock–Fluid System of the Subduction Zone in the South Caspian Basin

Izvestiya, Atmospheric and Oceanic Physics - The goal of this study is to identify the properties of the rock–fluid system in the subduction zone of lithospheric plates using the example of...     

The features and generation of CWB near the South Shetland Islands in austral summer of 1987

-STD Data obtained from the Third Chinese National Antarctic Research Expedition from January to February 1987 in the region near the South Shetland Islands are used to investigate an oceanic front, continental water boundary (CWB), north of the South Shetland Islands. The characteristics of the CWB in surface and subsurface layers as well as deep layer are discussed respectively. The estimations of the geostrophic currents and the baroclinic deformed radius Rbc in this area show that the flow along the front is in the geostrophic equilibrium approximately, and the formation of the front is mainly due to the strong boundary current north of the South Shetland Islands. Its length along the front is estimated to be about 360 km and its width across the front is about 30 km.     

Changes in recreational shore anglers’ attitudes towards,and awareness of,linefish management along the KwaZulu-Natal coast,South Africa

Management of recreational fisheries cannot be based on biological and stock assessment data alone but needs to include appropriate social aspects (including knowledge, attitudes and behaviour) of anglers within the fishery. The primary purpose of this study was to evaluate and complement existing recreational fisheries research, through the analysis of demographic and psychographic angler attributes collected from two independent, shore-based snapshot monitoring surveys conducted on the KwaZulu-Natal (KZN) coastline of South Africa, in 1994–1996 and 2009–2010. Results show significant changes between the two survey events in the demographics of anglers (including ethnic composition, age distribution, years of fishing experience and employment status) participating in the KZN shore-based linefishery. Traditional management regulations (minimum size limits, daily bag limits and closed seasons), though appearing to have support, have had limited effectiveness, based on the increased levels of admitted non-compliance and poor knowledge of regulations for target species. Anglers in both surveys believed that catches had declined over the years, with overfishing being the most common reason given. The results are discussed in the context of changing management practices in the KZN recreational shore-based linefishery. The implications of changes in fisheries management policies and responsibilities along the KZN coast are highlighted.     

Variability of the fields of concentration of microelements and strontium in seawater near the South Coast of the Crimea in 2002–2007

We study the space-and-time variability of the concentrations of 27 microelements (Sc, Cr, Mn, Fe, Ni, Co, Cu, Zn, As, Mo, Ag, Cd, Sn, Se, Sb, Ba, La, Ce, Sm, Eu, Tb, Hf, Hg, Pb, Au, Th, and U) and Sr in the sea, river, and waste waters of the South Coast of Crimea in 2002–2007. Parallel with the data about elements studied earlier, we present, for the first time, the data of investigations of the contents of rareearth elements (Lu, Nd and Yb) whose concentrations in the major part of the analyzed samples of seawater were lower than the limit of their quantitative determination. We present the ranges of the concentrations of elements and perform their comparison with the data of the previous period of monitoring.     

Seasonality of interannual atmosphere–ocean interaction in the South China Sea

The present study documents the atmosphere–ocean interaction in interannual variations over the South China Sea (SCS). The atmosphere–ocean relationship displays remarkable seasonality and regionality, with an atmospheric forcing dominant in the northern and central SCS during the local warm season, and an oceanic forcing in the northern SCS during the local cold season. During April–June, the atmospheric impact on the sea surface temperature (SST) change is characterized by a prominent cloud-radiation effect in the central SCS, a wind-evaporation effect in the central and southern SCS, and a wind-driven oceanic effect along the west coast. During November–January, regional convection responds to the SST forcing in the northern SCS through modulation of the low-level convergence and atmospheric stability. Evaluation of the precipitation–SST and precipitation–SST tendency correlation in 24 selected models from CMIP5 indicates that the simulated atmosphere–ocean relationship varies widely among the models. Most models have the worst performance in spring. On average, the models simulate better the atmospheric forcing than the oceanic forcing. Improvements are needed for many models before they can be used to understand the regional atmosphere–ocean interactions in the SCS region.     

Rift–drift transition in the Dangerous Grounds,South China Sea

Marine Geophysical Research - The South China Sea (SCS) has a long record of rifting before and after subsequent seafloor spreading, affecting the wide continent of the Dangerous Grounds, and its...     

Paleosecular Variations of the Geomagnetic Field Isolated in Pliocene–Quaternary Sediments of Western Turkmenistan

Izvestiya, Atmospheric and Oceanic Physics - Akchagyl deposits of Western Turkmenistan were studied in order to identify the spectrum of paleosecular variations in the geomagnetic field in...     

Making sense of censuses and dealing with missing data: trends in pup counts of Cape fur seal Arctocephalus pusillus pusillus for the period 1972–2004

Trends in the population of Cape fur seals Arctocephalus pusillus pusillus were estimated from counts of pups on aerial photographs of colonies taken between 1972 and 2004 to determine trends in the overall population and subpopulations. Incomplete coverage resulted in missing data in some years. Various methods of determining proxy values for missing data were assessed, and it was concluded that different methods were applicable to Namibian and South African colonies. This reflected variation in trends of pup counts between the countries, which was associated with differences in productivity between the southern and northern Benguela ecosystems. In Namibia, temporal changes in pup numbers were non-linear in some years and there was correspondence in fluctuations at most colonies. This appeared to be on account of an effect of periodic, wide-scale prey shortages that reduced birth rates. There was a northward shift in the distribution of seals in the northern Benguela system. In South Africa, pup counts were much less variable between years, probably on account of a relative stability of food supply. A linear approach was therefore suitable for determining proxy values for missing data at South African colonies. Pup counts suggest that there has been little change in the overall population of the Cape fur seals since 1993, when it was estimated at about two million animals.