African Journal of Marine Science

Published by National Inquiry Services Centre
Online ISSN: 1814-232X
Publications
Article
The number of eastern rockhopper penguins Eudyptes chrysocome filholi breeding at subantarctic Marion Island decreased from about 173 000 pairs in 1994/95 to about 67 000 pairs in 2001/02. During 1994/95 - 2002/03 pairs fledged on average 0.40 chicks per year, an amount thought insufficient to balance mortality of breeding adults, and there was a decrease in the mass at arrival at breeding colonies of both males and females. Except in 1997/98, the mass of chicks at fledging was less than that recorded at two other localities. These factors suggest an inadequate supply of food for rockhopper penguins at Marion Island. Decreases of rockhopper penguins at several other localities also have been attributed to inadequate food. Rockhopper penguins at Marion Island continued to feed mainly on crustaceans during chick rearing. There was a marked increase in the contribution of fish to the diet in 1999/00 that coincided with an increase in mass at arrival at colonies of both males and females. Trends in numbers of pairs breeding in different sections of Marion Island were not always consistent, indicating the need for island-wide monitoring to establish the overall trend.
 
Article
The numbers of gentoo penguins Pygoscelis papua breeding at subantarctic Marion Island fell by 40% from 1994/95 to 2002/03, from 1 352 pairs to 806 pairs. Apart from a slight increase in 1998/99, there was a steady decrease in numbers breeding between 1995/96 and 2000/01, when the population stabilized. There is indication that in some years not all breeders nested and that some birds relocated to another colony after disturbance. From first clutches, pairs on average fledged between 0.01 chicks in 1997/98 and 0.58 chicks in 2002/03 (mean 0.38 ± 0.21). In 1994/95, replacement clutches increased the overall production of fledged chicks by 11%. Based on demographic parameters measured at other localities, the production of chicks at Marion Island was inadequate to maintain the population during the period 1995/96 - 2000/01. Consistency in trends in breeding success at five colonies suggests that factors operating at a mesoscale, rather than those specific to particular colonies, often influenced breeding success. Laying was later than normal in 1997/98, when there was almost total breeding failure with large losses of eggs and small chicks to returning Subantarctic skuas Catharacta antarctica. Future research on this Near Threatened species at Marion Island must take full account of its susceptibility to human disturbance.
 
Article
There is indication that numbers of macaroni penguins Eudyptes chrysolophus at subantarctic Marion Island have decreased since the early 1980s. Estimates of the population at the island fell from about 405 000 pairs in 1983/84 and 434 000 pairs in 1994/95 to about 356 000 pairs in 2002/03. Two large colonies, at Bullard Beach and Kildalkey Bay, account for about 85% of the overall population. At both these colonies, the area occupied by breeders showed no trend between 1983/84 and 2002/03, but the mean density of nests decreased. However, error on estimates of abundance at these colonies precludes demonstration of a significant decrease in the overall population. Numbers of occupied nests at other colonies decreased from 79 000 in 1994/95 to 31 000 in 2002/03. At three small colonies there was a significant decrease of 88% between 1982/83 and 2002/03. At Marion Island, macaroni penguins usually breed for the first time when aged about three years. From 1994/95 to 2002/03, pairs fledged an average of 0.46 chicks per year, a number considered insufficient to maintain the population. However, during that period there was a significant increase in reproductive success with time. In the same period, the masses of males and females on arrival at breeding colonies were significantly correlated. Both showed a marked decrease in 1998/99, after the El Niño of 1997/98. In most seasons from 1994/95 to 2001/02 crustaceans dominated the food, but the mass of chicks at fledging was significantly related to the contribution of fish to the diet.
 
Article
During the 1990s and early 2000s, populations of surface-nesting seabirds at Marion Island showed different trends, but for the majority of species numbers decreased. Reduced numbers of gentoo penguins Pygoscelis papua, eastern rockhopper penguins Eudyptes chrysocome filholi, Crozet shags Phalacrocorax [atriceps] melanogenis and probably macaroni penguins E. chrysolophus are most plausibly attributed to an altered availability of food. Decreases in numbers of dark-mantled sooty albatrosses Phoebetria fusca, light-mantled sooty albatrosses P. palpebrata, southern giant petrels Macronectes giganteus and possibly northern giant petrels M. halli may have resulted from mortality of birds in longline fisheries. However, populations of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses fluctuated around a stable level. Numbers of Subantarctic skuas Catharacta antarctica and kelp gulls Larus dominicanus breeding at Marion Island also decreased. Kerguelen Sterna virgata and Antarctic S. vittata terns remain scarce at the island. Trends for king penguins Aptenodytes patagonicus were not reliably gauged, but numbers probably remained stable or increased. There were large fluctuations in numbers of king penguin chicks surviving to the end of winter.
 
Article
The ragged-tooth shark Carcharias taurus is a large predator of inshore coastal waters in the Eastern Cape, South Africa. Born at about 1m long and attaining approximately 3m, stomach content analyses have shown that it feeds largely on teleosts and elasmobranchs, although cephalopods are taken to a lesser extent. Similar prey taxa were taken by small ≤2m) and large individuals (>2m), although the larger predators broadened their trophic niche to include a greater variety of elasmobranchs and more active prey. Maximum prey size increased with predator size. Both reefassociated and benthic fishes typical of sandy substrates were included in the diet and, in addition to inshore species, those typical of deeper shelf waters were also taken. Although C. taurus appear to prefer to swim around high relief reefs with caves and gullies by day, it is inferred that they must also hunt over soft substrates, possibly at night.
 
Article
The selection of a specific site of attachment by a copepod parasite is determined by a set of mostly unknown factors. The spatial distribution of Nemesis lamna on the gill filaments of white sharks Carcharodon carcharias was investigated. The complete set of left gills of 11 hosts was examined and the location, orientation and gender of each copepod noted. N. lamna exhibited a prevalent of 100% and a mean intensity of 74 individuals per shark. There was no relationship between the size of the host and the number of filaments per hemibranch or the number of N. lamna attached to the host. Only 13.7% of the variation in number of individuals per hemibranch was due to the variation in the number of filaments per hemibranch, and most specimens (33.6%) were collected from the fourth holobranch. Most N. lamna (86.5%) were attached to the dorsal and ventral quarters of the hemibranchs, of which 63.1% were attached to the outer hemibranchs. There was no site preference in terms of their position on the filaments, but most were attached with their cephalothoraces facing the incoming respiratory water flow, especially those attached to the proximal quarter. The N. lamna infrapopulations on white sharks are aggregated, which is probably due to the need to reproduce.
 
Number of oiled African penguins admitted to SANCCOB, 1970–2005 (updated from Nel et al. 2003)  
Proportion of oiled African penguins admitted to SANCCOB that were successfully released after de-oiling, 1970–2005 (updated from Nel et al. 2003)  
Article
South Africa is a global hotspot for oil pollution. The regional oiled seabird cleaning centre, the South African Foundation for the Conservation of Coastal Birds (SANCCOB), has handled over 50 000 seabirds from its inception in 1968 until 2005. The majority of seabirds oiled in South Africa are African penguins Spheniscus demersus, followed by Cape gannets Morus capensis, both of which are classified as Vulnerable to extinction. On the basis of the proportion of the population that has been affected, the African penguin is considered to have suffered more from oiling than any other seabird species globally. The rehabilitation success (proportion of birds known to have survived for at least one month in the wild) and restoration success (proportion of rehabilitated birds attempting to breed) of de-oiling penguins and gannets are higher than has been reported for any other species. The financial costs of de-oiling African penguins are substantially lower than the costs of de-oiling seabirds in the Northern Hemisphere. De-oiling contaminated birds is thus a valuable conservation intervention for these species, both of which are relatively localised in areas within or close to major shipping routes and ports, where a single spill can threaten a large proportion of the global population. There are, however, long-term effects of oiling on penguins and gannets. De-oiled gannets survive slightly less well than un-oiled birds, but the difference is similar to inter-colony differences in survival. Approximately 27% of rehabilitated African penguins are unable to breed following their release. In addition, oiling has a long-term negative impact on the breeding productivity and cost of reproduction in de-oiled birds. The primary objective should therefore be to prevent or reduce oil spills in the first place. However, future oil spills are inevitable and the authorities need to ensure that they have plans in place and the required capacity to respond rapidly to spills when they do occur. One of the ways to reduce the number of penguins becoming oiled during a spill is to evacuate birds from the affected area. The continued capture and cleaning of penguins and gannets that do become oiled is justified on conservation grounds. Thus, de-oiling should be a twin objective to prevention in South Africa's oil spill management strategy, and every effort should be made to further improve both of these aspects.
 
Study area showing the Swakopmund Jetty and the moored oceanographic buoy 5km offshore at a water depth of 28m. Wind and current records from the buoy were adjusted by 32° (anticlockwise rotation of the coordinate system) to obtain the onshore-offshore component (positive shoreward) and the alongshore component (positive equatorward)
Time-series for the sampling period (between 28 November 1998 and 11 May 1999) for (a) the Ekman onshore transport per unit length as derived from the alongshore wind component (V) measured at the buoy, and (b) the temperature recorded at 3m and 10m deep at the buoy (B) and 8m deep at the jetty (J)
Linear regression between the daily alongshore wind (V32, positive equatorward) and the corresponding onshore (u32, positive) and offshore (u32, negative) current recorded 3m above the seabed at the buoy. Number of samples is denoted by n
Linear regression between the daily alongshore wind component (V) and the following day jetty temperature T(+1 day) (°C). The 95% confidence range follows the t-distribution 
Article
Swakopmund is a popular coastal resort in Namibia, especially during the summer holiday season when daily sea temperatures can fluctuate several degrees in a short period. Hourly measurements of the near-bottom water temperature were collected off the Swakopmund Jetty to investigate the thermal variability in relation to local winds. The thermal regime of this coastal region appears to be controlled by the locally forced Ekman offshore transport. Related changes in offshore transport led those of the surf-zone temperature by about one day. A transfer of kinetic energy from the alongshore wind into the temperature field of the nearshore zone dominated relative short time scales (hourly). The longer periods (7-9 days) are associated with the forcing of poleward-directed continental shelf waves. The origin of the 24-25 day frequencies is not clearly understood. However, it characterises the nearshore wind field as well as the water temperature of the surf zone. These relatively long quasi-cycles could originate from rhythmic changes in the regional wind field as a result of changes in the thermal contrast between sea and land areas.
 
Article
In 2002 there was a widespread epizootic involving seabirds on five of the offshore islands of the Western Cape, South Africa. Since then, avian cholera Pasteurella multocida outbreaks have been occurring annually on one of these islands, Dyer Island. This paper reports on the three subsequent summers, 2003/04, 2004/05 and 2005/06, during which further avian cholera outbreaks were recorded. It focuses on the outbreak in 2004/05, which was the largest in extent and the most closely monitored. The mortalities during 2005/06 were not as extensive as expected. The management measures used to bring these outbreaks under control are described. Removal of all the carcasses from the entire island in one day is important in reducing mortality. Management intervention is required to reduce the negative impacts of disturbance due to kelp gull Lasus dominicanus predation on other breeding seabirds, primarily the African penguin Spheniscus demersus, during the carcass collection process.
 
Article
In early September 2003, >3.0 × 105 cells l−1 of Alexandrium fundyense were detected in close proximity to salmon aquaculture sites near Grand Manan Island in the Bay of Fundy, eastern Canada. High concentrations persisted throughout the month, peaking to >8 × 105 cells l−1 on 18 September. Concurrently, some salmon farms in the area experienced elevated mortalities. Although the cause of mortality is not yet fully understood, it appears to be related to the high concentrations of A. fundyense. Paralytic shellfish poisoning toxins were not detected in the edible flesh of salmon (by mouse bioassay and high-performance liquid chromatography), but were detected at low levels in viscera and gills. Blue mussels Mytilus edulis analysed from areas affected by the bloom reached levels of 18 000μg STX equivalents 100g−1 of tissue. As a result of the salmon mortalities, a project was initiated to establish a monitoring approach for harmful algal blooms to provide an early warning of potential events and to act as a tool for mitigation actions.
 
Diel changes in the number of (a) copepods and (b) cladocerans recovered from the gut of C. hysoscella collected in Walvis Bay Lagoon during September 2003, and (c) the diversity of prey recovered. The mean (open square), standard error (box) and 95% confidence intervals (whisker) are shown. Data were pooled by hourly bins (number of samples, n, shown above); note irregular time intervals on the x-axis. Shaded portion on graph illustrates night and the clear portion day  
Article
The diet of Chrysaora hysoscella was investigated from 55 specimens caught near the surface throughout 24h in Walvis Bay Lagoon, Namibia, during September 2003. The diet was diverse, ranging from dinoflagellates to carideans, and included abundant benthic species (adults and larvae). There was no clear overall relationship between medusa size and either the number or type of prey ingested, although aspects of both measures were significantly related to size when analyses were confined to the nocturnally collected data. Whereas there was a significant difference in the diet of medusae collected by day and night, principally because of an increase in the abundance of benthic prey items, it was not possible to partition this between the vertical migration of predator (downwards) or prey (upwards) owing to a lack of information on the ambient prey environment. Regardless, the abundance of benthic prey in the diet could help explain the predominance of medusae off Namibia, where there has been an increased flow of surface production to the benthos since the collapse of the pelagic fisheries.
 
Abundance (A) and biomass (B) estimates for all euphausiids recorded with the Bongo net in the Antarctic and Subantarctic regions of the survey area Abundance (ind m -3 ) and biomass (mg dry weight m -3 )
Individual ingestion rates for the numerically dominant species of euphausiid recorded in the Antarctic (AAZ) and Subantarctic (SAZ) regions of the survey
Mean ingestion rates and daily ration estimates for the selected species of euphausiid used for the grazing experiments
Subsurface (200m) temperature (°C) contour plot of the survey region in relation to the position of Marion Island. The convergence of the Subantarctic Front (SAF) and Antarctic Polar Front (APF), and the positions of the biological stations occupied, are indicated  
Article
The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region (<25mg Chl a m−2), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 m−3 to 3.1 m−3 and from 0.1mg dry weight m−3 to 8.1mg dry weight m−3 respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). A multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, and (2) restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. Euphausia triacantha had the highest daily ingestion rate, ranging from 1 226.1ng pigment (pigm) ind−1 day−1 to 6 029.1ng pigm ind−1 day−1, whereas the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4-943.0ng pigm ind−1 day−1). The total grazing impact of selected euphausiids ranged from <0.1μg pigm m−2 day−1 to 20.1μg pigm m−2 day−1, corresponding to <0.15% of the areal Chl a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggest that phytoplankton represent a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements.
 
Article
Algicidal bacteria offer a promising tool for the prevention of red tides, because they are able to play a key role in terminating blooms in coastal areas. This study details the detection of vast numbers of algicidal bacteria attached to the surface of seaweeds such as Ulv a sp. and Gelidium sp. (of the order of 106 cells g−1 wet weight in some cases). Algicidal bacteria were isolated from Ulva sp. and Gelidium sp. from the coast of Osaka Bay from April to September 1999, and their algicidal properties were assessed using the prey microalgae Karenia mikimotoi, Heterosigma akashiwo, Fibrocapsa japonica and Chattonella antiqua. K. mikimotoi was the red tide species most susceptible to the algicidal bacteria isolated from seaweeds. Sequence analyses of the 16S rDNA gene revealed that these algicidal bacteria belonged to the genera Alteromonas, Pseudo-alteromonas, Vibrio, Cytophaga, Cellulophaga and Octadecabacter, and the family Rhodobacteraceae. Algicidal properties of five of 10 strains of bacteria isolated from seaweeds, belonging to the genera Alteromonas, Pseudoalteromonas and Cytophaga, have been previously reported in coastal red tide areas. It is therefore possible that seaweed beds play a significant role as providers of algicidal bacteria in preventing red tides to coastal waters.
 
Map of South Africa showing the Breede Estuary and other localities mentioned in the text  
The Zambezi shark that was caught, tagged and released with acoustic tags in the Breede Estuary on 24 January 2009 (photo: Alison Towner)  
Google Earth image of the Breede River showing the track of the tagged Zambezi shark over a 43 h period during 24–26 January 2009. The positions shown (white dots) are those logged at 15 min intervals. Date, time and direction of major movements are indicated by grey arrows. The hooked and landed positions are shown  
Article
The Zambezi or bull shark Carcharhinus leucas is a large, predatory shark that occurs in warm-temperate, tropical and subtropical coastal and estuarine systems worldwide. To confirm reports of Zambezi sharks in the Breede Estuary on the south-west coast of South Africa, a survey was undertaken during 20-26 January 2009. On 24 January, a large female Zambezi shark was caught on rod and reel. Measuring 400 cm total length and 320 cm precaudal length, it is the largest recorded Zambezi shark. Furthermore, its occurrence in the Breede Estuary is the southernmost record of the species, extending its previously documented range by 366 km. The shark was tagged with a continuous acoustic tag and tracked for 43 consecutive hours. During that period, it swam as far as 20 km upstream, but it also briefly exited the estuary and travelled 2 km out to sea. Most of the time (24%) was spent 11-13 km upstream, where it actively inspected boats and shore-anglers, a behaviour considered to be an opportunistic foraging strategy. Estuaries appear to represent critical habitats in the life history of Zambezi sharks.
 
Increase in body weight (mean + se) of post-weaning juvenile H. midae grown on five formulated feeds which were then supplemented with fresh kelp and Ulva lactuca. 
Growth parameters of post-weaning abalone grown on the 10 diet treatments. Diets are ranked by their SGR. Means with
Article
The effect of five formulated feeds supplemented with fresh wild seaweed on the growth of post-weaning juvenile abalone Haliotis midae (6-20 mm shell length) was investigated by means of a growth trial at a commercial abalone farm over a period of 11 months. The experiment included 10 diet treatments with two replicates each (n = 50 individuals per replicate). The first five diet treatments comprised four fishmeal-based formulated feeds: Abfeed®, Adam & Amos® 'a', Adam & Amos® 'b' and Adam & Amos® 'c'; and an all-seaweed-based formulated pellet, FeedX. The additional five diet treatments comprised the formulated feeds above, supplemented with fresh wild seaweeds: the kelp Ecklonia maxima (5-15% protein) and Ulva lactuca (3.7-19.9% protein). The fishmeal-based protein feeds produced significantly better growth than the all-seaweed-based protein feed (FeedX: 0.49 ± 0.03 specific growth rate [SGR]; 27.15 ± 0.02 daily increment increase in shell length [DISL]; 0.864 final condition factor [CF]). Abfeed® (1.00 ± 0.02 SGR; 60.79 ± 0.04 DISL; 1.312 final CF) performed best of all the formulated feeds. Supplementation with fresh, wild seaweed, however, significantly improved growth of all abalone with supplemented Abfeed® (1.05 ± 0.02 SGR; 63.61 ± 0.05 DISL; 1.447 final CF), outperforming all supplemented feeds. A noteworthy observation was that the condition factor of abalone fed the feed that performed particularly poorly in the growth trials (FeedX) was dramatically improved by supplementation. It was shown that supplementation with fresh wild seaweed enhances the growth of abalone reared on formulated feeds.
 
Article
This study was undertaken to investigate whether the accumulation of end products of anaerobic metabolism can be used as an early indicator of deteriorating conditions during transport of live abalone Haliotis midae. A first series of experiments revealed that the enzyme tauropine dehydrogenase, responsible for the production of tauropine, is present in high activities (54 U g wet weight−1) in the shell adductor muscle, but D-lactate dehydrogenase, responsible for the production of D-lactate, is the predominantly active enzyme (10 U g wet weight−1) in foot muscle. The next series of experiments investigated the potential of anaerobic metabolism in the abalone by subjecting the gastropod to either functional anoxia (exercise metabolism) or 6 h of environmental anoxia (seawater gassed with nitrogen). Exercise, primarily powered by the shell adductor muscle, was mainly fueled by glycolysis resulting in the production of tauropine, whereas during 6 h of experimental anoxia, fermentation of glycogen led to the formation of mainly tauropine in the shell adductor muscle and mainly D-lactate in the foot muscle. The last experiment, investigating changes in these metabolites during simulated (abalone packed in oxygen-filled plastic bags resting on foam sponges soaked in seawater) transportation stress of up to 36 h at 7 and 10°C, clearly showed that tauropine accumulation in the shell adductor muscle and D-lactate accumulation in the foot muscle is time-dependent. Both metabolites are already produced during the first 6 h of simulated transportation (especially at 10°C), indicating that aerobic metabolism is impaired at an early stage of transportation. Hence, these metabolites can serve as indicators of the conditions abalone were subjected to during transport. Furthermore, abalone use the strategy of metabolic depression in this simulation experiment, as indicated by the decreased glycolytic flux in various tissues.
 
Article
A study was conducted to identify and quantify the spionid polychaetes that infest cultured abalone Haliotis midae at aquaculture facilities on the west (Farm A), south (Farms B and C) and east (Farm D) coasts of South Africa. The relationship between total intensity of infestation by the polydorids and the condition of their hosts at Farms A, B and D were also measured. The abalone were infested by Dipolydora capensis, Polydora hoplura and a Boccardia sp. However, the intensity of infestation differed among sites, suggesting that both geographical and farm-specific conditions may influence species composition. Total intensity of infestation has a negative impact on the condition of abalone at the three farms tested, but at Farms A and B, this effect was reduced in larger abalone.
 
Article
Polydorid polychaetes can infest cultured abalone thereby reducing productivity. In order to effectively control these pests, their reproductive biology must be understood. The population dynamics and reproduction of polydorids infesting abalone Haliotis midae from two farms in South Africa is described using a length-based, age-structured model. Shells were infested mainly by introduced Boccardia proboscidea. Polydora hoplura and Dipolydora capensis were also present but in numbers too few to identify factors influencing infestation. At both farms, B. proboscidea lived for a minimum of 12 months. Growth rate, size at maturity, maximum size, infestation intensity, recruitment, percentage of the population brooding and mortality appear to be affected by abalone feeding regime and water temperature, and these factors need to be considered in controlling infestation. Brooders and recruits were present throughout the year, but increased significantly during mid- to late winter/early spring when water temperature and day length increased. Treatment measures should therefore be implemented throughout the year but with increased effort when water temperature increases.
 
Article
Despite the widespread distribution of the genus Haliotis, chromosome numbers are only known for a small subset of species. In South Africa, no chromosome studies have been conducted on any of the five species occurring in the region. This study is the first report for Haliotis midae, the largest and only economically important species in South Africa, with a somatic chromosome number of 2n = 36. The study also provides the first count for a species in the southernmost radiation of abalone comprising South African, Australian and New Zealand species, and corroborates the hypothesis of the radiation of the genus into the Southern and Northern hemispheres from the Indo-Pacific area.
 
Article
Good-quality biological material is needed to obtain intact deoxyribonucleic acid (DNA) for use in molecular techniques such as the polymerase chain reaction (PCR). Non-destructive sampling protocols of juvenile abalone Haliotis midae (7-15 months old) were tested in order to collect material for DNA extraction. DNA was successfully extracted from epipodial tentacles and mucus samples. PCR results confirmed the good quality of the DNA and the reliability of the method.
 
Article
Hydro-acoustic surveys have been used to provide annual estimates of May recruitment and November spawner biomass of the South African sardine Sardinops sagax and anchovy Engraulis encrasicolus resources since 1984. These time-series of abundance estimates form the backbone of the assessment of these resources, and consequently the management of the South African sardine and anchovy is critically dependent on them. Upgrades to survey equipment over time have resulted in recent surveys providing more accurate estimates of abundance, yet in order to maintain comparability across the full time-series, estimates of biomass mimicking the old equipment were used for a number of years. In this paper we develop a method to revise the earlier part of the time-series to correct for receiver saturation in the older generation SIMRAD EK400 and EKS-38 echo sounders and to account for attenuation in dense sardine schools. This is applied to provide a revised time-series of biomass estimates for the South African sardine and anchovy resources with associated variance-covariance matrices. Furthermore, the time-series presented here are based on updated acoustic target strength estimates, making this the most reliable time-series currently available for both resources.
 
Trends in (a) numbers of African penguins breeding in the Western Cape Province, (b) at Robben Island numbers of penguins breeding, penguins in adult plumage moulting and an index of the proportion of penguins breeding, (c) in South Africa the spawner biomass of anchovy, sardine and these two species combined, (d) in South Africa the recruit biomass of anchovy, sardine and these two species combined and (e) the biomass of spawning (mature) sardine available to penguins in the Western Cape  
Results of cross-correlation between pairs of residuals from prewhitened time-series
Article
Off South Africa, anchovy Engraulis encrasicolus and sardine Sardinops sagax are the main prey of African penguins Spheniscus demersus. The combined spawner biomass of these fish increased from less than one million t in 1996 to more than nine million t in 2001 and then decreased to four million t in 2005. The combined biomass of young-of-the-year of these species increased from 0.2 million t in 1996 to 3.2 million t in 2001 before falling to 0.4 million t in 2005. There was a large eastward shift in the distribution of sardine between 1999 and 2005. The number of African penguins breeding in the Western Cape Province increased from 18 000 pairs in 1996 to more than 30 000 pairs from 2001 to 2005 before falling to 21 000 pairs in 2006, as the availability of fish decreased near breeding localities. Numbers of penguins breeding and numbers of birds in adult plumage moulting were significantly correlated with the young-of-the-year biomass of anchovy and sardine and with the available biomass of spawning sardine. The increase in the number of penguins breeding was mainly attributable to a greater proportion of birds breeding and improved breeding success. The decrease probably resulted from high mortality. Delayed first breeding and abstinence from breeding during periods of food shortage may both increase survivorship when food is scarce and enable seabirds rapidly to take advantage of improved feeding conditions. Although long-lived seabirds are buffered against short-term variability in food supplies, environmental change that influences the abundance and availability of prey can have severe consequences for central-place foragers, such as penguins, if there is long-term displacement of prey to regions where no suitable breeding localities occur.
 
Article
The recruitment of distinct year-class cohorts in two sparid species, Rhabdosargus holubi and Lithognathus lithognathus, were linked to records of daily mouth state in the intermittently open East Kleinemonde Estuary, South Africa, between 1995 and 2006. L. lithognathus only recruited into the estuary in years when the mouth opened between late August and January. This was attributed to a limited spawning season and inability to recruit during wave overwash events. In contrast, R. holubi recruitment was uninterrupted and not influenced by seasonality of estuary access opportunities (mouthopening and overwash events). Estuarine-dependent residency periods ranged from 27 months to 48 months for L. lithognathus and 12 months to 23 months for R. holubi. The interannual abundances of these estuarydependent sparids were determined by reproductive seasonality, recruitment strategy and seasonal timing of estuarine access opportunities.
 
Article
The date of first introduction of the North-East Pacific acorn barnacle Balanus glandula to South Africa is unknown, but it is depicted in photographic records dating back to at least 1992. Its present range and population density were determined by surveying 24 sites on the west and south coasts of South Africa. B. glandula occurred over approximately 400 km of coastline, from Elands Bay in the north-west to Misty Cliffs on the west coast of the Cape Peninsula. The abundance of B. glandula was affected by site, zone, prevalence of upwelling, and orientation of the shore. Its distribution was very patchy, both on macro- and microscales, with Bloubergstrand and Moullie Point having the highest abundances of 28 445 and 24 500 individuals m−2 respectively. B. glandula was the dominant barnacle at all West Coast sites where it was recorded, comprising 78.5% of all barnacles found. The successful invasions of B. glandula in South Africa, Argentina and Japan suggest that this species poses a potential threat to intertidal communities in cool, temperate waters.
 
Yield-per-recruit for A. berda in Kosi Bay  
Biological reference points for the A. berda population in Kosi Bay, calculated using the age-dependent selectivities of the gear currently used within the different fi shing sectors 
Spawner biomass-per-recruit for A. berda in Kosi Bay  
The effects of altering natural mortality (M) and age-at-first capture (t c ) on the spawner biomass-per-recruit (SB/R) and yield-perrecruit curves for Kosi Bay  
Article
A stock assessment was undertaken for the tropical sparid Acanthopagrus berda harvested in the Kosi Bay estuarine system, northern KwaZulu-Natal, South Africa, by a multi-sectoral fishery using traditional traps and gillnets, and recreational angling using rod-and-line. Input parameters used in a catch curve analysis included age and growth parameters, and an estimate of natural mortality derived from life-history parameters. The values of spawner biomass-per-recruit estimated from this model, using different selectivity curves for the gear types used in the different fishing sectors, indicate that A. berda is likely to be reduced to around 24% of its unfished level of spawner biomass-per-recruit by current levels of fishing mortality. These results indicate that A. berda in Kosi Bay is heavily overexploited. The longevity of the species, coupled with its late maturation, sex change and estuarine dependency, and the increasing catches of A. berda give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal.
 
Article
Field observations in Thau Lagoon, southern France, indicate that the growth of natural populations of Alexandrium catenella during blooms is limited by nitrogen and exhibits a storage rather than a growth response to an ammonium pulse. Therefore, ammonium uptake and accumulation under transient conditions were investigated in detail in laboratory cultures. Following nitrogen exhaustion from the medium, ammonium pulses of varying magnitudes were induced, and measurements of extra- and intra-cellular ammonium were carried out for 24-72h along with measurements of ammonium incorporation (15N tracer) and inorganic carbon fixation (13C tracer). During vegetative growth, values of intra-cellular ammonium reached 30% (Strain TL01) and 2% (Strain ACT03) of cell nitrogen. When ammonium was available in the culture medium, ammonium uptake estimated by the 15N tracer technique accounted for only 65% of the decrease in external ammonium. This discrepancy is probably due to organic nitrogen excretion. Once external ammonium was exhausted, the observed isotopic dilution of both 13C and 15N cell content indicated uptake of a compound containing both unlabelled carbon and nitrogen atoms.
 
Article
To detect behavioural patterns of individually tagged squid Loligo vulgaris reynaudii in a Radio-Acoustic Positioning Telemetry (RAPT) buoy array, trajectories reflecting the four dimensions of latitude, longitude, depth and time were plotted from data collected during field experiments in South Africa. Finding a continuous curve to represent the sampled trajectories required dealing with anisotropic precision and accuracy, non-uniform sampling rates and improbable outliers. A combination of an operator-controlled smoothing option of an approximating cubic spline and a weight factor assignment based on distance from the mass curve gave the most expedient results when compared with video recordings.
 
Article
The acoustic target strength (TS) of Cape horse mackerel Trachurus trachurus capensis was measured in situ at 38 kHz during two surveys over the Namibian continental shelf in 1998 and 1999 using a SIMRAD EK500 echosounder/ES38D submersible split-beam transducer. Scattered aggregations of horse mackerel 100-200 m deep were ensonified. The transducer was lowered to a depth of 85-140 m in order to resolve single targets at short ranges (5-50 m). Individual fish were tracked using specially developed software. Samples of ensonified fish were obtained using pelagic and demersal trawls; the former was fitted with a codend Multisampler for depth-specific sampling. Recorded TS estimates were low, producing b20-values ranging from −77.5 to −74.9 dB (−76.0 dB ± 1.3), considerably lower than published estimates for horse mackerel (−73.4 dB < b20 < −65.2 dB). An explanation for the weak acoustic backscattering may be swimbladder compression. Surface-projected b20 values, which were computed using the depth of each target and the scattering area reduction rate previously found for herring (γ=−0.29), corresponded to −72.6 dB. This value is close to the TS constant of −72 dB currently applied for horse mackerel in Namibian and Angolan waters.
 
Station data for the respiration measurements of C. carinatus during the BENEFIT 2002 cruise
Article
Stage C5 copepodids and adult females of the herbivorous copepod Calanoides carinatus were sampled in the Angola-Benguela frontal region and northern Benguela upwelling area off Namibia in February-March 2002, using a multiple opening/closing net system. Respiration rates of C5s collected between 400m and 700m were measured onboard at the simulated in situ temperature of 8°C and at sea surface temperature (SST ≥20°C). These data were compared to the oxygen demand of epipelagic individuals of C. carinatus caught in the upper 30m and incubated at ambient SST. Deep-living C5s consumed 0.21 ± 0.08ml O2 h−1 (g dry mass)−1 at 8°C and 0.96ml O2 h−1 (g dry mass)−1 (range 0.84-1.09) at 25.9°C. These results were substantially lower than respiration rates of 5.23 ± 0.55ml O2 h−1 (g dry mass)−1 in epipelagic individuals incubated at SST. The results reveal a reduction by 96% of metabolic rate in deep-living, diapausing C5s relative to surface-dwelling, active individuals. Only 14.4% of this metabolic reduction is explained by the lower ambient temperature at depth and a Q10 value of 2.34. Therefore, the major fraction (81.6%) of the metabolic reduction is attributable to active physiological changes or processes during diapause at depth. The study emphasises the importance for herbivorous copepods, in areas with a highly variable food supply, to adopt a dormant phase in their life cycle in order to survive long periods of starvation.
 
Article
This work investigates simple methods for simultaneous extraction of astaxanthin and chitin from industrial waste of the South African West Coast rock lobster Jasus lalandii. Removal of proteins from waste is the critical step to yield intact chitin and astaxanthin. Because common chemical methods destroy astaxanthin and damage chitin, we investigated partial proteolysis by papain followed by removal of adhering tissue/protein by centrifugation. Incubation time of waste with papain, papain concentration, waste:medium ratio, duration of centrifugation and the size of holes in the centrifuge rotor were altered to achieve a complete removal of protein/tissue and at minimum cost. From lobster waste that was deproteinised this way, chitin and astaxanthin could be extracted using existing methods. The most suitable extraction conditions (0.5% papain, 1:10 waste:medium ratio, 24 h incubation, centrifugation for 5 min with 5 mm holes) yielded 2.4 ± 0.6 g chitin (4.2%) and 3.1 ± 0.7 mg astaxanthin from 56.8 ± 5.8 g crushed lobster waste. From deproteinised exoskeleton, astaxanthin was extracted in methanol, transferred into various vegetable oils, and its concentration measured using spectrophotometry. Maximum stable concentration of astaxanthin in oil was approximately 80 mg ml−1, above which astaxanthin precipitated. Astaxanthin oil prepared from J. lalandii material included in feeds for shrimps Palaemon pacificus and tilapia Oreochromis mossambicus caused deposition in whole shrimps but not in tilapia tissues.
 
Article
Large-scale longshore movements (>10 km) of adult male Jasus lalandii (>70 mm carapace length) were examined on the west coast of South Africa using tag-recapture information from the period 1968 to 2000. The average rate of recovery of tagged rock lobsters was 15.7% per fishing season. Only 0.48% of 43 885 recaptured rock lobsters moved >10 km, 0.31% southwards and 0.17% northwards. The mean distance moved by those lobsters was 28.6 km and the mean time at liberty was 241.8 days. In recent years, densities of J. lalandii have increased substantially at the south-eastern end of their geographic range. The data indicate that this could not be attributable to a population migration of adult male rock lobsters from the west coast of South Africa.
 
Article
Along the coast of Washington State, USA, periods of downwelling-favourable winds increase in frequency in late summer and may advect domoic acid (DA)-producing Pseudo-nitzschia to the coast where they toxify coastal razor clams Siliqua patula. During the late summer and early autumn of 2002, measurements of Pseudo-nitzschia species, particulate DA (pDA) and salinity were made in nearshore waters and at Kalaloch Beach. A shift in the relative abundance of Pseudo-nitzschia species was observed following a storm during 8-10 September. After a second storm during 16-18 September, Pseudo-nitzschia cell numbers and levels of pDA increased in nearshore waters. Salinity measured with moored sensors showed the presence of relatively fresh Columbia River plume water on the inner shelf for several weeks, beginning on 8 September and persisting for approximately eight days after the second storm. During that time, DA in intertidal razor clams accumulated to levels that exceeded the regulatory action limit. This study helps to clarify the complex role of the Columbia River plume in the advection of Pseudo-nitzschia populations to the Washington coast.
 
Stock assessment results of the Namibian horse mackerel stock using an age-structured production model with catch-at-age data derived from catch-at-length data of the midwater fleet, pelagic fleet and acoustic biomass surveys, and four different cases of age-length-keys (ALKs) generated from 
Article
We explore the influence of age-estimation errors on the results of the age-structured production model (ASPM) used for horse mackerel stock assessment in Namibia for the period 1961-2003. The analysis considered age data from eight readers collected during an otolith-reading workshop. Four scenarios of age-estimation errors were assumed: Case 1 — a reference age computed as the modal age of estimates obtained by the four most experienced readers; Case 2 — age readings from a precise and experienced (Namibian) reader of horse mackerel otoliths; Case 3 — age estimates from a reader that displayed positive bias compared with the reference ages; and Case 4 — age estimates from a reader that displayed negative bias compared with the reference ages. The age-length key of each case was applied to length distributions of survey, pelagic fleet and midwater fleet landings (1991-2003) to obtain catch-at-age data. These data were then used in the ASPM. Results obtained from Case 3 differed most significantly from the others and appeared to be unrealistic in terms of the state of the stock and negative log-likelihood estimates. The conclusion is that more resources need to be directed towards age determination, because management recommendations are highly sensitive to errors in ageing. Most effort should be placed into age estimation of age groups 3-5 (20-30 cm total length), but significant effort needs to be devoted to age estimation of midwater commercial samples. Finally, the extent of sampling and the raising strategy of length frequencies should be improved.
 
Article
From 1997 to 2005, the distribution of sardine Sardinops sagax, an important prey item for four seabirds off South Africa, shifted 400 km to the south and east, influencing its availability to breeding birds. It became progressively less available to seabirds in the Western Cape Province, where the number of African penguins Spheniscus demersus breeding decreased by 45% between 2004 and 2006, survival of adult penguins decreased and penguins established a new eastern colony in 2003. In that province, the number of Cape gannets Morus capensis breeding decreased by 38% between 2001/2002 and 2005/2006 and the contribution of sardine to the diet of gannets fell from an average of 40% during the period 1987-2003 to 5-7% in 2005 and 2006. The proportions of Cape cormorants Phalacrocorax capensis and swift terns Sterna bergii breeding in the south of the province increased as sardine moved south and east. In the Eastern Cape Province, the number of penguins breeding halved between 2001 and 2003, whereas after 2002 there was an increase in the number of Cape gannets that bred and in the contribution of sardine to their diet. It is likely that in that province sardine became increasingly available to gannets but remained beyond the shorter feeding range of penguins. Management measures that may mitigate the impacts on seabirds of an unfavourable, long-term change in the distribution of their prey include the provision of breeding habitat where prey is abundant, spatial management of fisheries competing for prey, and interventions aimed at limiting mortality.
 
Article
A review is provided of the African sea level dataset, which is limited not only in size, especially given the great length of the African coastline, but also in quality. The review is undertaken primarily from Permanent Service for Mean Sea Level (PSMSL) and Global Sea Level Observing System (GLOSS) perspectives, but the conclusions on the need for major new investments in sea level infrastructure are undoubtedly the same as would be arrived at through any other approach. Stations to be installed as part of the Ocean Data and Information Network for Africa (ODINAfrica) programme are described and a survey of currently existing and planned sea level stations in Africa is presented, together with information on where data for existing stations may be found.
 
Observer effort, 19 – 24 January 2000: number of 10-minute counts, hours of observation, positions (latitude, longitude), area surveyed and distance travelled during surveys 
Range in surface salinity and temperature in Mauritanian and West Saharan waters in deep ocean, shelf edge and shelf waters 
Article
Cold-water upwelling supports abundant and diverse faunas. Upwelling off Mauritania has been highlighted as being important for seabirds, but very few systematic offshore surveys have been conducted in that region. Mauritanian waters are increasingly targeted by commercial fisheries along the shelf break and, with the likelihood of future exploitation of mineral oils on the continental shelf, the absence of information on seabirds is worrying. This paper describes the distribution of wintering seabirds in the context of fisheries and hydrography. The avifauna was dominated by surface-feeding and shallow plunge-diving, often planktivorous, seabirds, originating from West Palaearctic breeding grounds (Arctic, subarctic and temperate zones). Many seabirds were associated with fishing trawlers around the shelf break, but the fleets were more evenly distributed than the birds, with certain hydrographical parameters influencing or overruling the attraction of trawlers by seabirds. The results support the belief that West African waters are of prime importance for seabirds.
 
Article
The feasibility of a directed trap-fishery for panga Pterogymnus laniarius was investigated with special emphasis on minimising the bycatch. A total of 1 302 fish, representing 19 species, was captured in 59 trap deployments at three locations along the Eastern Cape coast of South Africa between September 2002 and July 2004. Panga comprised over 55% of the total catch, with an average of 12 panga per trap haul. Depth and substrate type had a significant effect on the species composition of the catch. Panga comprised 77% of the catch in depths >50m, whereas other commercially important species contributed 11% to the total catch in water >50m. No kingklip Genypterus capensis were captured in the traps and shallow-water Cape hake Merluccius capensis accounted for only 0.2% of the total catch composition. The findings suggest that trap-fishing provides a new fishing opportunity in South Africa with a high catch per unit effort for the target species and a low level of bycatch.
 
Article
A group of 70 false killer whales Pseudorca crassidens and 124 bottlenose dolphins Tursiops sp., and a separate group of 13 Risso's dolphins Grampus griseus, assembled close inshore off a known mass-stranding site in St Helena Bay, South Africa, in October 2003. However, only a single Risso's dolphin attempted to strand and 13 bottlenose dolphins had to be shepherded out of the shallows the next day, the remainder leaving of their own accord. This is considered to be the first near-stranding phenomenon recorded for the region.
 
Article
In attempts to achieve sustainability, ecosystem-based approaches to fisheries management are becoming increasingly applicable. Indicators to assess the success of management measures are an important component of this approach. Data from a recreational linefishery are used to develop and propose a simple set of indicators to assess local fishery sustainability. The indicators have been organised within a framework based on the ecological, institutional and social sustainability domains and scored through a rapid assessment matrix. Results indicate that the estuarine, rock-and-surf (coastal) and skiboat-based fisheries in Plettenberg Bay on the south coast of South Africa are presently non-sustainable. The institutional domain had very low scores whereas the socio-economic domain had the highest scores. The validity and usefulness of the indicators as a tool for the development of local fishery management plans are discussed.
 
Article
This study assesses seabird bycatch in the demersal longline hake (Merluccius capensis and M. paradoxus) fishery in the southern Benguela region. Observers collected seabird bycatch data from 2 412 sets (14 million hooks) in the South African fishery, accounting for 6.8% of total effort for the period 2000-2006. Of the 107 seabirds caught, at a rate of 0.008 per 1 000 hooks, 41 were killed (0.003 per 1 000 hooks). There was a significant decrease in catch rate, from 0.033 per 1 000 hooks in 2000 to 0.001 per 1 000 hooks in 2006. An estimated total of 225 (range 220-245) birds were killed per year by the South African fishery. Vessel, area and light conditions were all significant predictors of seabird bycatch. The white-chinned petrel Procellaria aequinoctialis was the species most commonly caught by the South African fleet, at a rate of 0.0027 per 1 000 hooks. From interviews with 13 observers and six members of the Namibian demersal longline fishery, seabird bycatch was estimated at 0.05 per 1 000 hooks and 0.13 per 1 000 hooks respectively. Observations were taken during four trips in Namibian waters in November 2006, in which 21 sets (456 000 hooks) were monitored. White-chinned petrels were killed at a rate of 0.14 per 1 000 hooks during these trips. Differences in catch rates between trips were investigated and moon phase, area and gear type were all found to be significant. All birds were caught using light gear, which sank significantly slower than heavier gear. The South African hake longline fishery has a relatively small impact on pelagic seabird populations compared with the Namibian fishery.
 
Chemical structure of gymnodimine  
Map showing the location of the mooring off Lambert's Bay and the sites of collection of shellfish in both Saldanha Bay and near Lambert's Bay on the west coast of South Africa  
LC-MS/MS chromatogram in the multiple reaction monitoring mode of the mass transition m/z 508>490 showing a gymnodimine standard and an oyster extract STO 8  
Article
Mussels Choromytilus meridionalis and oysters Crassostrea gigas were suspended from a mooring off Lambert's Bay, South Africa, to study the kinetics of lipophilic phycotoxin accumulation and detoxification. The shellfish were subsequently harvested daily over approximately three weeks and analysed for lipophilic phycotoxins by liquid chromatography coupled with tandem mass spectrometry in the multiple reaction monitoring mode. A mass transition typical for the cyclic imine toxin gymnodimine was detected in low but consistent levels in all oyster samples throughout the sampling period, whereas this peak was detected with lesser intensity in only some mussel samples and was frequently below the limit of quantitation (0.02 μg g−1 fresh weight). Comparison of retention times and collision-induced mass spectra of a certified standard of gymnodimine and an oyster extract provided unambiguous confirmation of the identity of gymnodimine in the shellfish extracts. The absence of known producers of gymnodimine in the plankton, and the non-detection of gymnodimine in filtered water samples collected during the period of study, lead to the conclusion that the shellfish were contaminated at their site of initial collection in Saldanha Bay prior to deployment off Lambert's Bay. This finding is the first confirmed evidence of gymnodimine in the southern Benguela upwelling system.
 
Average benthic cover of phyla on reefs in four sections of the Pondoland Marine Protected Area, grouped from north to south. Error bars denote ±SD
Percentage cover of benthic categories recorded on reefs in the Pondoland Marine Protected Area
Characteristics of three ecologically distinct benthic communities on the Pondoland reefs, separated by cluster analysis and multi- dimensional scaling of the Bray-Curtis similarity matrix of benthic category abundance Cover ± SD (%)
Agglomerative hierarchical cluster analysis based on the Bray-Curtis similarity matrix of benthic categories in 26 transects recorded on reefs in the Pondoland Marine Protected Area. Clusters were ecologically distinct groups at approximately 50% similarity. Transect numbers are the same as in Table 1
Location of the photographic transects recorded during the benthic survey of the reefs in the Pondoland Marine Protected Area, between May and June 2002 and 2003
Article
A subtidal marine biodiversity survey was carried out on shallow reefs (−1m to −30m) in the proclaimed Pondoland Marine Protected Area between Port Edward and Port St Johns, South Africa. A total of 26 benthic reef transects was undertaken involving the capture and processing of 1 042 photographic images of the reef benthos. Results of the benthic survey showed a shift from algal-dominated reefs in the north to suspensionfeeder-dominated reefs in the south, probably on account of turbidity (reduced sunlight penetration) and high nutrient levels from riverine input. A similar shift was found with increasing reef depth with algae dominating shallower reefs and suspension-feeding communities dominating deeper reefs. Non-exhaustive inventories were compiled of dominant organisms, including algae, sponges, other invertebrates and fish. The results of this survey confirm that the Pondoland region has a rich marine biodiversity and is situated within a unique transition zone between subtropical and warm temperate waters. It is imperative that this rich biodiversity, coupled with the aesthetic beauty of the Pondoland coastline, be adequately zoned for protection within the proclaimed marine protected area.
 
Article
Phoronis ovalis is a cosmopolitan, shell-boring phoronid worm reported from 24 locations worldwide in temperate latitudes, but not previously from Africa. We identified a shell-boring phoronid in Namibia that is morphologically similar to P. ovalis and subsequently surveyed its latitudinal and tidal elevational range, host distribution, and evidence for long-term occupation of this shoreline. Phoronis ovalis in Namibia leaves characteristic burrows in its hosts (0.2 mm diameter), primarily the native brown mussel Perna perna. In all, eight additional host species were identified, including one barnacle, four gastropods and three bivalves. The distribution of P. ovalis was strictly subtidal, where it reached 99% prevalence in P. perna at some sites. Latitudinally, it occurs at least from the northern border of Namibia (17.4° S) to Walvis Bay (22.74° S). Its long-term presence was evident in subfossil shells. We hypothesised that extensive shell-boring could be energetically costly to the host due to the need for ongoing shell repair. Perna perna with higher phoronid infestation made thicker shells, which were less dense. In addition, colonised mussels had lower body condition (dry meat weight relative to internal shell volume), which implies a significant energetic cost to the host.
 
Article
An oxytetracycline (OTC) marker was used to validate the periodicity of opaque zone deposition in the otoliths of Chrysoblephus laticeps, Cheimerius nufar, Cymatoceps nasutus (Sparidae) and Dichistius capensis (Dichistiidae) in the wild. Fish were injected with OTC and tagged with external dart tags within a research fishing area of the Tsitsikamma National Park marine reserve on the southern Cape coast of South Africa. Recaptured fish, injected with OTC, were at liberty for between 711 and 2 102 days. Examination of their otoliths revealed that all deposited one opaque zone each year. The study confirmed the age estimates from previous studies that made use of marginal zone analysis as a validation method.
 
Article
In July 1998, a bottom-mounted Acoustic Doppler Current Profiler was deployed at 36m depth in the centre of the Tsitsikamma National Park on the eastern Agulhas Bank, South Africa. The purpose was to investigate transport of chokka squid Loligo vulgaris reynaudii paralarvae hatched on the inshore spawning grounds (<60m) and ichthyoplankton spawned within the park. Analysis of the first 12 months of data (July 1998-June 1999) shows that surface flow was mainly eastward (alongshore), with a maximum velocity (u-component) of +115cm s−1 and an average of +24cm s−1. Generally, velocity decreased with depth, with a maximum bottom velocity (u-component) of +65cm s−1 and an average of +10cm s−1. Data from a nearby thermistor array show that the water column was usually isothermal during winter (July-September), with bottom flow in the same direction as the surface layer. In summer (December-March), vertical stratification was most intense, and surface and bottom flows differed in velocity and direction. Potential net monthly displacements calculated for three depths (5m, 23m and 31m) indicate that passive, neutrally buoyant biological material (e.g. squid paralarvae, fish eggs and larvae) would likely be transported eastwards in the surface layer for eight of the 12 months, and would generally exceed distances of 220km month-1. Displacement in the bottom layer was more evenly distributed between east and west, with net monthly (potential) transport typically 70-100km, but reaching a maximum of 200km. Wind-driven coastal upwelling, prevalent during the summer, causes the surface layer of the coastal counter-current to flow offshore for several days, resulting in potential displacement distances of 40km from the coast. These results suggest that squid paralarvae hatched on the inshore spawning grounds are not generally transported towards the 'cold ridge', a prominent semi-permanent oceanographic feature of cold, nutrient-rich upwelled water, where food is abundant, and that fish larvae, whether from the surface or bottom layer, are exported beyond the boundaries of the Tsitsikamma National Park.
 
Map of study area showing position of the 13 grid squares, and major oceanographic features (modi¢ed from Gibbons et al., 1995). The 200 m isobath is illustrated. 
Dendrogram of per cent similarity amongst the siphonophores found in the 13 inshore (A) and o¡shore (B) grid squares around southern Africa. 
Article
This work represents the first systematic analysis of the common Siphonophora from the Agulhas Current (South-West Indian Ocean). A total of 56 species of siphonophores was collected from a series of three largely epipelagic cruises between Algoa Bay and the Tugela River along the east coast of South Africa. Although no readily identifiable Cystonectae were observed, four families and nine species of Physonectae were collected. Calycophorae were the most common and abundant siphonophores, and five families and 47 species were recorded. Details of locations where each species was collected are given, but descriptions and illustrations are provided only for taxa that represent new records for the region.
 
Article
Between 1980 and 2001, a total of 661 African angel sharks Squatina africana was caught in the protective nets off KwaZulu-Natal, South Africa. The mean annual catch was 30 sharks (range = 11-69, SD = 12.4), with no trend in catch rate over the study period. Individuals were caught throughout the year and through much of the netted region, with a higher catch to the south. The sex ratio of the catch was 2.9 females:1 male. Males matured between 640mm and 700mm and females at about 700mm precaudal length (PCL). Mature males had clusters of thorn-shaped denticles, each about 2mm high, near the anterio-dorsal margins of both pectoral and pelvic fins. Of the mature females, 44% were pregnant, many of which contained only ova in utero. Embryos were present from April through to January. The average litter size was six, with length at parturition at least 240mm PCL. Most early-term pregnant females and all mature males were caught in the south. The reproductive cycle showed some seasonality and appeared to be biennial, with a gestation of about one year. Teleosts were the most common prey (76% of stomachs with food), followed by cephalopods (52%).
 
Article
Public perception has been that an apparent increase in the nearshore occurrence of white sharks Carcharodon carcharias in False Bay, on the south coast of South Africa, can at least be partly attributed to beach-seine (treknet) operations attracting sharks into this coastal area. To assess the merit of these concerns, all available beach-seine catch-and-effort data from the False Bay fishery over a 32-year period were analysed. A total of 27 cartilaginous species from 15 families was recorded in around 11 400 hauls from 1974 to 2006. Most (98%) of these comprised small benthic invertebrate feeders such as smooth houndshark Mustelus mustelus and lesser guitarfish Rhinobatos annulatus. Large sharks such as C. carcharias and ragged-tooth shark Carcharias taurus were rare, occurring in <0.2% of hauls. The only medium to large sharks that occurred frequently (15% of hauls) in any appreciable numbers (0.3 per haul) were bronze whalers Carcharhinus brachyurus. The relatively high numbers of C. brachyurus compared with C. carcharias, their overlapping size distributions and the difficulty of identifying sharks from a distance, suggests that many of the sharks observed following beach-seine nets are the bronze whalers. Overall, the frequency of occurrence of C. carcharias in the nets is much lower than would be predicted from the high number of observations in the nearshore region. Furthermore, beach-seine fishing rights in False Bay have been reduced from around 170 in the 1970s to five at present. There has been no corresponding decrease in shark incidents. On the contrary, shark incidents have increased from two in the 1970s to six during the period 2000-2005. Overall, there appears to be no strong link between beach-seine activity and human incidents with white sharks in False Bay.
 
Article
Age, growth and reproduction of the pelagic goby Sufflogobius bibarbatus was investigated for males and females caught in demersal trawls between the Orange River and Port Nolloth on the west coast of southern Africa. Females had larger otoliths than males of similar body size, suggesting slower growth rates in females. S. bibarbatus is a large and long-lived gobiid, attaining 13cm at at least 6 years of age, with late maturation at 2-3 years of age. Males were larger than adult females of a similar age and matured at a larger size and greater age than females. Two batches of yolked oocytes were present in the ovaries and the maximum gonadosomatic index was 14.3%. Batch fecundity was significantly correlated with standard length (r2 = 0.88) and ovary-free body weight (r2 = 0.92), and ranged from about 2 000 eggs in females 5.0-5.5cm long to about 10 000 in a female 9.8cm long. The mean fecundity was 842 ± 189 eggs per gramme of ovary-free body weight. The extended spawning season, from July to April, and the presence of more than one batch of yolked oocytes in the ovaries, suggest that the pelagic goby may be a serial batch spawner.
 
Seasonal variation in (a) germination and (b) incubation time prior to germination of Alexandrium catenella from May 2001 to April 2002 
Effect of temperature and light on (a) germination and (b) incubation time prior to germination of Alexandrium catenella 
Article
Cysts of the toxic dinoflagellate Alexandrium catenella (Whedon and Kofoid) Balech were found in the sediments of the southern Namaqua shelf, on the west coast of South Africa, with a maximum recorded abundance of 238 cysts ml−1 wet sediment. Experimental results indicate a short dormancy period of 15-18 days, suggesting that the cyst population does not necessarily serve as an overwintering strategy, but may rather permit rapid cycling between benthic and planktonic stages. Cysts were isolated monthly from sediments and incubated in the laboratory. Cyst germination ranged between 20% and 88% and did not show a clear seasonal pattern. The rate of germination was examined as a function of temperature and light. Cysts germinated within the temperature range 4°-22°C, but germination was highest at 10°C under both light and dark conditions. Although cysts germinated in the dark, germination in the light was higher and required a shorter period of incubation.
 
Top-cited authors
Robert J. M. Crawford
  • South Africa Government
Leslie Gordon Underhill
  • University of Cape Town
Carl van der Lingen
  • Department of Environment Forestry and Fisheries South Africa
Peter G Ryan
  • Percy FitzPatrick Institute of African Ornithology
Paul D. Cowley
  • South African Institute for Aquatic Biodiversity