Occurrence and distribution of Cape hakes Merluccius capensis Cast. and M. paradoxus Franca in the Cape of Good Hope area

A brief history of research into, and the fishery for, Cape hake is given. From twelve monthly surveys in 1972/73, abundance of the two species (Merluccius capensis and M. paradoxus) at depth was found to vary, larger individuals of both species being found deeper than the smaller ones. Off the Cape of Good Hope, M. capensis was never found deeper than 440 m, and there was significant species overlap between 150 and 440 m. M. paradoxus was numerically dominant except at the shallowest station sampled (150 m). Little overlap of mature specimens of each species was recorded. The research data were applied to commercial trawl statistics, revealing that M. capensis accounted for only 12,9 per cent by mass and 4,8 per cent by number of the commercially caught hake in the years 1955–1974. Such low percentages justify considering the Cape hake fishery as a single-species entity for the purposes of stock assessment and management.     

Prevalence of Kudoa thyrsites (Myxozoa) in South African sardine Sardinops sagax,kingklip Genypterus capensis,and Cape hakes Merluccius capensis and M. paradoxus

Prevalence of infection with the myxozoan parasite Kudoa thyrsites is not well documented in sardine Sardinops sagax, the Cape hakes Merluccius capensis and M. paradoxus, and kingklip Genypterus capensis. Quantitative polymerase chain reaction assays were used to determine the prevalence of K. thyrsites in wild-caught S. sagax (n?=?296), Merluccius spp. (n?=?162) and G. capensis (n?=?70), harvested in 2015. Sardinops sagax were harvested from the east, south and west coasts of South Africa, whereas M. capensis, M. paradoxus and G. capensis were taken from the west coast only. Relationships between K. thyrsites infection prevalence and fish capture locality, season, sex and size were determined with Chi-square tests. Prevalence was highest in S. sagax (91%), followed by M. capensis and M. paradoxus (87%) and G. capensis (40%). Prevalence was independent of sex of the host for all fish species. In the case of S. sagax only, the prevalence of infection was independent of locality of capture but depended on season, with prevalence lowest during spring and highest during autumn. No significant relationship (p?>?0.05) was found between infection prevalence and host size for any of the fish species.     

Diel effects on bottom-trawl survey catch rates of shallow- and deep-water Cape hakes Merluccius capensis and M. paradoxus off Namibia,using solar zenith angle

Diel patterns in survey trawl catches for the Cape hakes Merluccius capensis and M. paradoxus off Namibia were studied in order to examine the effect of diel bias on catchability, and its implication for survey abundance estimation and the consistency of the survey time-series. Catch rates (numbers per haul) by species and length from summer demersal biomass surveys conducted during the period 2002–2013 were used, together with a computation of the corresponding light-level data from which the solar zenith angles were obtained. Generalised additive models were fitted to assess the relationship between the catches and a number of explanatory variables. Significant covariates were zenith angle, depth and geographical position. The final models explained 78% and 59% of the variability in catch rates of M. capensis and M. paradoxus, respectively. For M. capensis, the response to zenith angle increased sharply for values above 100°, which represents the time between sunset and sunrise. For M. paradoxus there was a moderate increase in the response to zenith angle during the night. In cases where some fishing took place at night in shallow water, the survey results for M. capensis were more greatly affected than was the case for M. paradoxus, which is related to the different depth preference of the two species. Fishing in depths shallower than 400?m outside daylight hours should therefore be avoided in order to reduce bias and ensure consistency in abundance estimates from surveys.     

Estimation of the annual consumption of food by Cape hake Merluccius capensis and M. paradoxus off the South African west coast

Information on hake stomach contents collected during research cruises off the west coast of South Africa between 1988 and 1990 is analysed. Estimates of the annual consumption and daily ration of the Cape hakes Merluccius capensis and M. paradoxus are obtained. Coefficients of variation (CVs) for these estimates are estimated by a bootstrap variance-estimation procedure. Cape hakes are opportunistic feeders. Juveniles feed mainly on crustaceans and the diet becomes increasingly piscivorous with age. Anchovy were the dominant dietary item of juvenile M. capensis, although this may be a reflection of the fact that anchovy were readily available at the time of the surveys. The large number of anchovy found in the diet during this study highlights the dangers of extrapolating consumption estimates for opportunistic feeders to other time periods. Pooling of data across geographic and seasonal strata introduces substantial bias in estimates of consumption and daily ration for only the pelagic prey species. Estimates of annual consumption are highly sensitive to the cruise selected to provide the estimates of numbers-at-length, because these latter estimates vary substantially between cruises. Furthermore, estimates of annual consumption and daily ration by prey species are very imprecise due to the effects of small sample sizes, the opportunistic nature of and natural variability associated with feeding. This implies that it is unlikely that model-estimation procedures which utilize these data will be able to provide particularly precise predictions. Therefore, before any larger-scale stomach collection exercise is undertaken, it is advisable to perform simulation studies to assess the sampling intensity required to achieve the desired levels of accuracy and precision for predictions from multispecies model-estimation procedures which make use of such data.     

Spawning strategies and transport of early stages of the two Cape hake species,Merluccius paradoxus and M. capensis,in the southern Benguela upwelling system

Seasonal and short-term variability of environmental parameters influence the spawning strategies of fish species. In this study, the spawning strategies and the transport of early stages of the two Cape hake species off South Africa were investigated. Distribution of eggs and larvae of Merluccius paradoxus and M. capensis was analysed in order to derive more detailed and species-specific information on spawning season, spawning location, and transport of early stages. Samples were collected during three pilot surveys between January and October 2007 and during an extensive survey in September/October 2008 in the southern Benguela upwelling system off South Africa. Eggs and larvae of M. paradoxus were found in greater numbers than those of M. capensis during all surveys. Highest abundances were found from September to October, indicating one spawning peak for M. paradoxus during late austral winter to spring. The western Agulhas Bank was identified as the primary spawning ground, and smaller spawning events occurred on the West Coast. Larvae of both species were mainly distributed in subsurface waters between 25 and 100 m. More than 50% of all larvae caught had a total length between 3 and 4 mm and size increased significantly with decreasing latitude. Merluccius capensis were found closer inshore than M. paradoxus, indicating that early stages of the two species followed separate drift routes. We assume that this distribution pattern most likely evolved from differences in spawning location and phenology. The spawning strategies of M. paradoxus and M. capensis are well adapted to a time-frame of optimal transport conditions favourable for larval survival in the highly variable environment of the southern Benguela upwelling system, but the peak spawning of the two species is separated in time and space.     

Population abundance and seasonal migration patterns indicated by commercial catch-per-unit-effort of hakes (Merluccius capensis and M. paradoxus) in the northern Benguela Current Large Marine Ecosystem

We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance indices for assessment purposes and to infer ecological and behavioural information on northern Benguela hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration patterns were described for the first time and were found to correspond to the known spawning areas and seasons for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons.     

Characterisation of the dietary relationships of two sympatric hake species,Merluccius capensis and M. paradoxus,in the northern Benguela region using fatty acid profiles

The two sympatric species of Cape hake, Merluccius capensis and M. paradoxus, have been the main targets of bottom-trawl fisheries off Namibia for several decades. The feeding ecology of these hakes has been studied mainly using stomach content analyses and thus there remain some gaps in our knowledge about food assimilated over the longer term. In this study, we used fatty acid (FA) profiles to characterise the dietary relationships of M. capensis and M. paradoxus. Muscle samples from hake (n=110) and their known prey (n=68) were collected during trawl surveys off Namibia during 2011. Significant differences between the neutral FA profiles of the hake populations were detected in December 2011 but not in January 2011, an indication of temporal variations in diet and resource partitioning. Comparisons of the neutral FAs in hake and the total FAs of potential prey showed no clear trophic connections, with the exception of flying squid Todarodes sagittatus, which had FA profiles very similar to those of M. paradoxus in December 2011. Our results highlight the complex and temporally shifting relationships that exist between hake and the large pool of prey available to them, and between the two hake species that overlap in their feeding habits and distribution within the highly productive Benguela Current region.     

Feeding ecology,diet and field-based studies on feeding selectivity of the Cape anchovy Engraulis capensis Gilchrist

Samples collected during four cruises on board R.S. Africana were used to study the trophic ecology and feeding behaviour of Engraulis capensis in the southern Benguela region. Previous work had indicated that this species was a non-selective filter-feeding omnivore, diatoms comprising the bulk of the diet. The results of the present study reveal that anchovies selectively feed on mesozooplankton, especially calanoid copepods and euphausiids. Investigation of the feeding behaviour of the species indicates that raptorial feeding is dominant over filter-feeding and that prey appears to be selected primarily on the basis of size.     

Reproduction and recruitment patterns of the surf clam Donax serra (Bivalvia,Donacidae) on two Namibian sandy beaches

Reproduction and recruitment of the surf clam Donax serra on two Namibian beaches were studied over a period of two years. Histological examination of the gonads indicated a discontinous annual reproductive cycle, related to monthly mean sea surface temperature. The spawning season lasted from August/September to February, but juveniles (2 – 6 mm anterior-posterior shell length) were only present for three months in the intertidal zone. The condition index indicates that the species spawns during autumn and summer, but histological validation is needed. The period when juveniles are abundant is decoupled from the spawning period and therefore cannot be predicted clearly, even if the spawning period is known. Starvation, hydrodynamic processes, chemical parameters and different release times during the spawning period are thought to cause the differences in settlement time and recruitment strength between locations.     

Occurrence and feeding of three shark species,Carcharhinus brachyurus,C. obscurus and Sphyrna zygaena,on the Eastern Cape coast of South Africa

The shark species Carcharhinus brachyurus, C. obscurus and Sphyrna zygaena, which attain more than 2 m when adult, occur in coastal waters of the Southern Cape as juveniles. They use these coastal waters as nursery areas and their relative abundance there varies through the year, possibly because of seasonally varying oceanographic conditions. Adult C. brachyurus occur in the same geographic area but usually deeper, although there is some overlap in juvenile and adult depth ranges. Adult C. obscurus prefer the warmer subtropical and tropical waters north of the study area. Adult S. zygaena are found over deep reefs at the edge of the continental shelf. There was considerable dietary overlap between the three species, the prey of all three being dominated by small schooling fish, such as pilchard, and squid. For the three species, animals of total length >2 m took larger prey, such as elasmobranchs, with greater frequency, although they continued to prey on squid and schooling fish. It is postulated that the nursery areas are in the study area because of the abundance of food there, and that avoidance of cannibalism would be enhanced by the use of such nurseries.     

Effects of laughing gull and shorebird predation on the intertidal fauna at Cape May,New Jersey

The intertidal flats of the Cape May, New Jersey shore of Delaware Bay are populated by large numbers of laughing gulls and migrating shorebirds during the spring and early summer. Exclusion of birds from a shallow slough and a sand bar had only minor effects on the infaunal benthic invertebrate assemblage at either site. The Cape May beaches provide a rich source of food in the form of horseshoe crab (Limulus polyphemus) eggs; foraging on this item may be more profitable than probing the sediment for infauna. Gemma gemma, a small, thick-shelled bivalve, composed over 98% of the benthic infauna at both sites in 1980, and this species may be resistant to predation by certain shorebirds, as suggested by Schneider (1978).     

Diets of eight fish species from the upper slope off the Wairarapa coast,North Island,New Zealand,with notes on the diets of others

The diets of eight demersal fish species from the upper continental slope (c. 24CM‐50 m) were determined from samples taken during late January and early February 2004, off the Wairarapa coast, North Island, New Zealand. Diets were from a combination of benthopelagic and benthic sources, with most species exhibiting ontogenetic shifts in diet, in that larger‐bodied food (fish and/or natant decapod prawns) was more important in the diets of larger fish. Javelinfish (Lepidorhynchus denticulatus), silver roughy (Hoplostethus mediterraneus), and capro dory (Capromimus abbreviatus) had predominantly benthopelagic diets, whereas the diets of sea perch (Helicolenus percoides), Bollons’ rattail (Caelorinchus bollonsi), two‐banded rattail (C. biclinozonalis), and silverside (Argentina elongata) were predominantly benthic, with the crab Carcinoplax victoriensis an important food item. The diet of Oliver's rattail (C. oliverianus) was a mix of benthopelagic and benthic organisms. Generally, levels of dietary overlap between the eight species were low. Overall, the diets of these fish probably reflect regional and seasonal levels of food availability. Notes on food observed in the stomachs of a further 18 species, for which there were fewer than 10 stomach samples per species are also provided.     

Seasonal fluctuations in occurrence of inshore Bryde's whales in Plettenberg Bay,South Africa,with notes on feeding and multispecies associations

Seasonal fluctuations in the occurrence of inshore South African Bryde's whales Balaenoptera edeni were investigated between November 2005 and June 2008. Sighting data were collected in Plettenberg Bay on the south-east coast of South Africa. Bryde's whale occurrence was modelled in relation to the following environmental covariates: sea surface temperature, chlorophyll a concentrations and wind speed. Seasonal increases in encounter rates (sightings per day) were observed during summer and autumn, with a peak in April that corresponded to increased feeding activity and above average aggregation sizes. All three environmental covariates were significant factors in terms of explaining variability in the occurrence of whales. Multispecies associations with common dolphins Delphinus capensis and Cape gannets Morus capensis were most common in summer and autumn, when feeding activity was highest.     

中国南海中南部花水母亚纲一新属四新种记述

本文描述了采自中国南海中南部花水母亚纲一新属四新种：南海宽管水母,新属、新种Laticanna nanhaiensis gen.nov. et sp.nov.,芽拟原帽水母,新种Protiaropsis gemmifera sp.nov.,南海潜水母,新种Merga nanhaiensis sp.nov.和顶室无球水母,新种Rhabdoon apiciloculus sp.nov.。编制了深帽水母科已知属分属检索表和拟帽水母属、潜水母属以及无球水母属已知种分种检索表。模式标本保存于中国水产科学研究院南海水产研究所。     

Effect of salinity on the growth, biological activity and secondary metabolites of some marine fungi

The study investigated the effects of salinity on growth,antimicrobial activities and secondary metabolites of 47 marine filamentous fungi isolated from the East China Sea near the western shore of the Taiwan Straits.The results indicate that NaCl promoted the growth up to 91.5% of test strains.However,only 14.9% of them showed a significant increase of antimicrobial activity against Candida albicans.When incubated in different concentrations of NaCl,the colony growth, antimicrobial activities and composition of secondary metabolites of the strain Ty01b-8 of Penicillium sp.varied.Treatment with KCl also showed a similar effect.An alkaloid isolated from the fermentation broth of Ty01b-8 was identified as chrysogine,inhibition activity of which against Hela cells was 15.05% at 20 μ g/ml,and yield was 4.4 and 4.9 times higher in 3 percent and 6 percent NaCl treatments,respectively, compared with the non-salt culture condition. These findings prove that salinity is an important factor influencing growth and secondary metabolites of some marine fungi,which can be used to screen for new metabolites from marine fungi,and to enhance their metabolites production in industrial fermentation.     

Density distribution by depth of Geryon maritae on the northern crab grounds of South West Africa/Namibia determined by photography in 1983, with notes on the portunid crab Bathynectes piperitus

The density of red crab Geryon maritae between 18°00′ and 18°30′S and in depths of 350-1 000 m was quantitatively examined by photography. This area, estimated to be approximately 92 000 ha, is part of the commercial crab ground off South West Africa. The biomass of red crab, up to 55,5 kg·ha^?1, is one of the highest recorded off the African coast for the species. Density of red crab was highest in depths exceeding 600 m, the greatest density (350,2 crabs·ha^?1) being recorded in the 600-699 m depth zone. Another crab, Bathynectes piperitus, was also photographed in the shallower depths of the survey area (300-500 m), and some density estimates for this species at those depths are presented.