Occurrence and Distribution of the Eggs and Larvae of Anchovy, <Emphasis Type="Italic">Engraulis japonicus</Emphasis>, in Jeju Strait,Korea, with Descriptions of Environmental Characteristics

The occurrence and distribution of eggs and larvae of anchovy, Engraulis japonicus, in Jeju Strait, Korea from May to November 2002 were investigated, and the relationships between the abundances of anchovy eggs and larvae and the oceanographic conditions, including meteorological data, were analyzed. During the sampling periods, the anchovy eggs occurred from May to October and about 95% of total egg abundance occurred in only two months from July to August, suggesting that the main spawning season of anchovies is confirmed in summer from July and August in Jeju Strait. The spawning area of anchovies gradually moved to the southern part of the survey area with time. The predominant anchovy larvae collected in this study were mostly smaller than 16.0 mm TL. Correlation analysis and multiple regression analysis showed that the anchovy egg abundance in the study area depended strongly on the wind conditions, especially less than 10 m/s, and increasing water temperature. Salinity variations also had significant effects on the abundance of anchovy larvae.     

Stock-environment recruitment analysis for Namibian Cape hake Merluccius capensis

The factors modulating recruitment success of Cape hake Merluccius capensis in Namibian waters are still unresolved. In this study, we used generalised additive models, regression tree analysis and the conventional Ricker model to examine the effect of environmental indices and spawning stock biomass (SSB) on hake recruitment success for the period 1984–2012. Results indicated that upwelling strength explained 51% of the recruitment variability, whereas SSB had no significant influence. The effect of SSB on recruitment only became significant when combined with upwelling strength, explaining 89% of the recruitment variability. SSB influenced recruitment during periods of strong upwelling. Optimal conditions for hake recruitment were associated with moderate upwelling strength. Low and high upwelling intensities reduced recruitment success. Our results are consistent with those of other studies suggesting a significant influence of environmental conditions on recruitment at a low spawning stock level. Our study highlights the importance of assessing the combined non-linear effects of both biotic and abiotic factors on hake recruitment.     

Anchovy spawning in relation to the biomass and the replenishment rate of their copepod prey on the western Agulhas Bank

Anchovy biomass and copepod standing stocks and growth rates on the Agulhas Bank were compared during the peak spawning period (November) in 1988 and 1989. In 1988, copepod biomass over the western Agulhas Bank was low (1,0 g dry mass·m^?2) relative to anchovy biomass there (14,7 g dry mass·m^?2). In November 1989 in the same area, fish biomass was much lower (5,7 g dry mass·m^?2), following a recruitment failure, and copepod biomass was higher (2,4 g dry mass·m^?2), possibly as a result of lesser predation by anchovy. By contrast, the eastern Agulhas Bank had a larger biomass of copepods (4–6 g dry mass·^?2) and a lower biomass of anchovy during both years. Knowing, from laboratory studies, that a prey biomass of 0,78 g·m^?2 is required for fish to obtain their daily maintenance ration, it is suggested that spawning on the western Agulhas Bank was food-limited in 1988. Copepods on the western Bank may be replaced by local growth or transport from the eastern Bank. Growth rates of copepods on the western Bank were 10–50 per cent of maximum in 1988, but total production (c. 100 mg dry mass·m^?2·day^?1) was low, primarily because biomass was low and less than the rate of consumption by anchovy (243 mg copepod dry mass·m^?2·day^?1). On the eastern Bank, copepod production exceeded anchovy consumption and it is concluded that the flux of copepod biomass onto the western Bank may be as important as local growth in replenishing copepod stocks there. Feeding conditions for anchovy on the western Agulhas Bank are often marginal compared to the situation on the eastern Bank, and it is suggested that the selection of the western Bank as the major spawning area is related more to the success of transport and survival of eggs and larvae on the West Coast recruiting grounds than to feeding conditions per se.     

Forecasting in South African pelagic fisheries management: the use of expert and decision support systems

Understanding long-term variability of pelagic fish populations is important in developing forecasting strategies for fisheries management and planning. However, many current fisheries models have only short-term datasets available, whereas those of suitable duration often lack reliability. As resources are placed under increasing pressure, all available information should be used to assist management. Two simple rule-based deterministic modelling approaches are described, which use semi-quantitative and qualitative rules to relate recruitment success of South African anchovy Engraulis capensis to physical and biological indices. The first model relates recruitment success to indices of wind and sea surface temperature by way of a rule-based decision support system. In the second model, significant environmental and biological factors were identified and related to anchovy recruitment by way of an expert system approach. These two approaches are evaluated and compared. It is suggested that these types of models, when satisfactorily validated, have great potential in supporting the future management of the South African anchovy fishery in the dynamic environment of the Benguela Current.     

Impact and implications of large-scale environmental anomalies on the spatial distribution of spawning of the Namibian pilchard and anchovy populations

Trends in the spatial pattern of spawning of pilchard Sardinops ocellatus and anchovy Engraulis capensis during the period 1971–1985 were examined in relation to large-scale environmental anomalies outside the spawning area. Shifts in the locality of peak spawning of anchovy often coincided with that of pilchard, although sometimes anchovy were slower to respond to an environmental change. With negative sea surface temperature (SST) anomalies spawning shifted northwards, whereas with positive anomalies spawning took place both in the north and farther south. With a transition from negative SST anomalies early in the spawning season to zero or positive anomalies later in the spawning season, the impact on anchovy and pilchard spawning differed. Anchovy spawning was either reduced or absent during the negative phase of transitional seasons, thus avoiding unfavourable conditions. Pilchard, on the other hand, were spawning mainly in the north during the negative phase of the transitional seasons, but also in the south during the zero to positive phase. The shifts in spawning locality in response to environmental anomalies outside the spawning area imply that explanations for such shifts need not be sought in changes in biomass or age structure or in the fact that stocks may be genetically different, all theories previously advanced.     

Investigation of tropical eel spawning area in the South-Western Indian Ocean: Influence of the oceanic circulation

In the South-Western Indian Ocean (SWIO), four eel species of the genus Anguilla (i.e. Anguilla bicolor bicolor, Anguilla nebulosa labiata, Anguilla marmorata and Anguilla mossambica) were identified, while their respective oceanic spawning area remained unknown. Based on collected larvae, glass eel captures and hydrodynamical conditions, previous studies raised the hypothesis that the eel spawning area might be common to all of those freshwater eel species, and located East of Madagascar. An original modeling approach, based on backward simulations, is developed to assess how the ocean circulation in the SWIO determines the location of the spawning areas and whether a common spawning area for each recruitment site where glass eels were found is possible. We use a hydrodynamical model, which reproduces realistically the 3D open ocean circulation in the region, associated with a Lagrangian model that calculates the possible migration pathways of larvae, represented by passive particles. Some biological parameters, provided by previous otolith microstructures analysis, are taken into account to constrain our simulations. Results suggest the existence of a common spawning area located between 13°S and 19°S and westwards of 60.5°E, although these boundaries vary on the interannual timescale. Salinity fronts were reported beside the boundaries, reinforcing this assumption. We explore the impact of hydrodynamic conditions on recruitment and migration durations from three specific regions within the common spawning area. They all allow migration to each recruitment sites consistent with duration estimated from otolith microstructure analyses. Nevertheless, there is substantial variability on intra-seasonal to interannual timescale in simulated migration durations and arrival success, with specific amplitude to each recruitment site and spawning location.     

"Predation" of anchovy by an Agulhas ring: a possible contributory cause of the very poor year-class of 1989

There was a marked decrease in abundance of anchovy Engraulis capensis off South Africa between November 1988 and November 1990 caused by formation of poor year-classes in 1989 and 1990. The percentage of anchovy in the diet of Cape gannets Morus capensis indicated that the most marked decrease in anchovy biomass was between June and July 1989. A filament from the Benguela upwelling front was in the process of being entrained by a passing ring of Agulhas Current water at that time. The ring extracted a large volume of frontal water over a period of 2–3 months, prevented its return to the shelf region and possibly removed anchovy larvae and pre-recruits from the Benguela system. It may have played a role in depressing the 1989 anchovy year-class, and hence the 1989 recruit biomass.     

Acoustic study on the abundance and distribution of anchovy spawners and recruits in South African waters

Direct surveys of Cape anchovy Engraulis capensis spawner and recruit biomass in South African coastal waters were made with a 38-kHz calibrated echo-sounder and custom-built digital echo-integrator. The spawning surveys were conducted each November between 1983 and 1985, predominantly on the Agulhas Bank. Recruit surveys were conducted in autumn 1985 and 1986, mainly on the West Coast. The spawning fish were widely distributed across the continental shelf, whereas recruit concentrations were highest close inshore. Employing a target strength per kilogramme expression for herring Clupea harengus, the spawning biomass in 1984 was estimated at 1,06 million tons and that in 1985 at 0,98 million tons. Similarly, recruit biomass in May/June 1985 and June 1986 was estimated at 310 and 466 thousand tons respectively. From an analysis of error in the latter two estimates, it was considered approximately 80 per cent certain that the recruitment in 1986 was greater than in 1985. The estimates of spawning biomass are 3–4 times higher than earlier estimates made by Virtual Population Analysis (VPA) of commercial catch data, and suggest that the stock is less seriously threatened by present catch levels than was indicated by VPA. It is concluded from the distribution and age structure of the spawning population that the VPA estimates are invalid because of the failure of commercial vessels to sample the major part of the adult population.     

Abundance and distribution of rhynchoteuthion larvae of Illex argentlnus (Cephalopoda: Ommastrephidae) in the south-western Atlantic

The results of ichthyoplankton surveys carried out by the Instituto Nacional de Pesca (INAPE) in the Argentine–Uruguayan Common Fishing Zone (AUCFZ) in summer 1980 and the winters of 1980–1982 are presented. In addition, the results of joint research with INIDEP, the Argentine and Japan Fisheries Agency, on larvae, juveniles and adults of the short-finned squid Illex argentinus carried out in winter 1989 are given, as are data obtained during the joint sardine and anchovy recruitment project carried out by R.V. Meteor in November/December 1989. The short-finned squid Illex argentinus is the most important cephalopod resource of the area, and an extended fishery is carried out on the Patagonian shelf and in the proximity of the Falkland Islands. The fishing season in the AUCFZ, for pre-spawning and spawning animals, extends from early autumn to winter (March–August). Abundance of rhynchoteuthion larvae (417–485 larvae·10 m^?2) was greatest in winter in surface temperatures of 12,1–16,9°C and surface salinities of 34,8 – 35,2 × 10^?3. The distribution of the larvae is related to the western boundary of the Brazil Current and the convergence front.     

Top predators in the Benguela ecosystem — implications of their trophic position

Many top predators in the Benguela ecosystem feed on prey species targeted by commercial fisheries. Their roles as indicators of the state of exploited prey resources, as competitors with commercial fisheries for resources, and as susceptible to impact from commercial fishing on those resources are briefly considered. Trends in the occurrence of anchovy Engraulis capensis and pilchard Sardinops ocellatus in the diet of Cape gannets Morus capensis off South Africa's west coast are related significantly to survey estimates of the abundance of these fish species, and they provide useful confirmation of those estimates. In the 1980s, anchovy decreased in the diet of Cape gannets, but pilchard increased. In both the northern and southern portions of the Benguela system, groundfish were thought to eat most (66–73%) of the total quantity of cephalopods and vertebrates consumed by predators and man in the 1980s. South African fur seals Arctocephalus pusillus pusillus, predatory pelagic fish and man removed roughly equal amounts, with squids, seabirds and cetaceans having a smaller impact. In the 1980s, man and seals removed about two million tons live mass more than in 1930. Indices of the rate of natural mortality of anchovy and pilchard attributable to Cape gannets are not related to biomass of the prey species. That for anchovy was high in 1989 when a poor anchovy year-class was formed. Decreased abundance of anchovy led to poor breeding by Cape cormorants Phalacrocorax capensis in 1989 and 1990. A model linking the Cape cormorant population with anchovy is used to explore the impact of possible exploitation strategies for anchovy on Cape cormorants.     

Transport and distribution of nutrients in anchovy spawning ground to the southern waters of Shandong Peninsula

INTRODUCTIONNutrients (N ,PandSi)areessentialforphytoplanktongrowthinmarineecosystem .Thetransportandcycling ,distributionandvariationofnutrientsaffectnotonlyonthestructureandfunctionofecosystem ,butalsoonthevariationofthebiologicalresourcesinthesea .ThesouthofShondongPeninsulaisoneofthecentralzonesofurbanandagriculturalactivities.Al thoughthereisnodirectlargeriverinput,seasonalvariationofchemicalenvironmentisobviousintheHaizhouBay .Inspringandsummer,thedistributionsofnutrientsareinflu…     

Abrupt environmental shift associated with changes in the distribution of Cape anchovy Engraulis encrasicolus spawners in the southern Benguela

Cape anchovy Engraulis encrasicolus spawners in the southern Benguela showed an eastward shift in their distribution on the Agulhas Bank that occurred abruptly in 1996 and has since persisted. We assessed whether this shift was environmentally mediated by examining sea surface temperature data from different regions of the Agulhas Bank, which showed that in 1996 the inner shelf of the Agulhas Bank to the east of Cape Agulhas abruptly became 0.5°C colder than in previous years and has since remained that way. In addition, signals, coherent with the 1996 shift recorded in sea surface temperatures, were also found in atmospheric surface pressure and zonal wind data for that region; interannual coastal SST variability is also shown to be correlated with zonal wind-stress forcing. As a result, increased wind-induced coastal upwelling east of Cape Agulhas is proposed as the main driver of the observed cooling in the coastal region. The synchrony between the environmental and biological signals suggests that the eastward shift in anchovy spawner distribution was environmentally mediated and arose from a change in environmental forcing that altered the relative favourability for spawning between regions to the west and east of Cape Agulhas. The results highlight how a relatively minor change in environmental conditions can lead to a drastic spatial reorganisation of the life history of one species in an ecosystem.     

海洋环境因子对澳洲鲐亲体补充量关系的影响——基于贝叶斯模型平均法的研究

澳洲鲐（Scomber australasicus）是西北太平洋重要的中上层经济鱼类,生命周期相对较短,资源量受补充量影响明显,了解澳洲鲐太平洋群系补充量状况对掌握其资源量及确保其可持续利用具有重要的意义。本文利用产卵场1（30°~32°N,130°~132°E）海表面温度（sea surface temperature,SST1）、产卵场2（34°~35°N,138°~141°E）海表面温度（SST2）、索饵场（35°~45°N,140°~160°E）海表面温度（SST3）、潮位差（tidal range,TR）、太平洋年代际涛动（Pacific decadal oscillation,PDO）和亲体量（spawning stock biomass,SSB）6个影响因子任意组合与补充量构建多个模型,运用贝叶斯模型平均法（Bayesian model averaging,BMA）分析各个环境因子对资源补充量的解释能力,并预测其补充量的变化。结果表明,SSB对补充量具有最长期且稳定的解释能力,其次是SST3,PDO、TR、SST2、SST1也对补充量模型具有一定的解释能力。SST3是环境因子中影响最大的因子,可能是由于补充群体在索饵场内生活时间较长,索饵场温度对仔鱼或鱼卵的生长存活有较大的影响。研究认为,基于BMA的组合预报综合考虑了各个模型的优势,优于单一模型,可用于澳洲鲐资源补充量的预测。     

Modelling the influences of atmospheric forcing conditions on Baltic cod early life stages: distribution and drift

Retention or dispersion of larvae from the spawning ground has been identified as one of the key processes influencing recruitment success in fish stocks. An exercise combining 3-D hydrodynamic model simulations and field data on spatial distributions of juvenile Baltic cod was utilised to investigate the potential drift of larvae from the centre of main spawning effort in the Bornholm Basin, Baltic Sea. In the simulations cod larvae were represented as Lagrangian drifters. Habitats in which larvae and juvenile cod potentially dwell and where juveniles settle were identified to ascertain the importance of predicting transport. The transport of Baltic cod larvae was investigated by detailed drift model simulations for the years 1986 to 1999. The results yielded a clear dependency on wind-induced drift of larval cod, which is mainly controlled by the local atmospheric conditions over the Baltic Sea. Seasonally averaged distributions of drifters were compared with actual distributions of 0-group cod, as determined from bottom and pelagic trawl surveys conducted in autumn of the years 1993 to 2000 in and around the Bornholm Basin. The results suggest that juveniles caught in different areas can be assigned to different times of the spawning season. Because of seasonal differences in the circulation patterns, the southern coastal environment is on average most important for early and late spawners, whereas larvae hatching in mid-summer were on average transported towards the north or to a higher degree remained in the spawning ground.     

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.     

东海鲐鱼(Scomber japonicus)仔幼鱼游泳行为对输运和补充量的影响

采用物理环境因子,确定鲐鱼仔幼鱼运动和物理环境之间的响应关系,建立起了基于个体具有游泳行为的鲐鱼早期生长史模型。结果表明,具有游泳行为仔幼鱼前期对输运分布的影响不大,后期随着游泳能力的增强,逐渐在温盐梯度较大锋面,靠近暖水的一侧进行集群和滞留,并使向东北输运速度降低,输运到太平洋和日本海的幼鱼数量下降,所处水深降低,适应生长发育,死亡率降低。产卵场位置的变动使偏西产卵的集群受台湾暖流影响较大,导致集群偏西,主要聚集在偏北的台湾暖流水和长江冲淡水交汇区高温、高盐一侧。偏东产卵受黑潮影响较大,集群偏东,不形成大量聚集和滞留;在生存率方面正常产卵位置是最佳产卵位置。研究认为,物理环境和生物因素同样会对具有游泳行为仔幼鱼的输运和补充产生影响。     

Towards rational harvesting of the South African anchovy considering survey imprecision and recruitment variability

Alternative harvesting schemes for the South African anchovy resource are considered. For this preliminary study, strategies in which quotas are simply related to the pre-catch survey estimates of spawning biomass and recruitment are investigated, using a Monte Carlo simulation approach. The schemes evaluated are the strategies of a constant catch, a constant proportion of the recruitment estimate, and a variant on constant escapement. The relationship between modal recruitment and spawning biomass is assumed known, and the values of parameters such as natural mortality and mass-at-age are initially taken to be exact. True recruitment is assumed log-normally distributed about its modal value. The annual survey estimates of recruitment and spawning biomass are generated with typical measurement errors included. The results show the cost (expressed as a loss of potential annual yield) of imperfect survey information, natural recruitment variability, and constraints on year-to-year catch variability. The analysis is extended to integrate the outcome of specific harvesting strategies over the current estimates of the probability distributions for the model parameters, assuming that these are not updated as harvesting is continued. The final results suggest that the mean annual yield of the South African anchovy resource could be increased by about 40 per cent through use of a more flexible harvesting strategy than is the current practice, without at the same time increasing the risk of collapse.     

Distribution and abundance of eggs,larvae and early juveniles of saury Scomberesox saurus scombroides (Richardson) off the south-western Cape,South Africa, 1977/78

The distribution patterns of saury eggs, larvae and early juveniles have been investigated over the continental shelf off the South-Western Cape from August 1977 to August 1978. Young saury tend to occupy water of 18°C or warmer in all seasons and are found offshore of the Benguela oceanic front when inshore upwelling is evident. Their distribution in the region appears to be linked to seasonal hydrography. Spawning in the study area occurs mainly between Cape Columbine and Cape Point, and to a lesser extent east of Cape Point. The ratio of large larvae and early juveniles to small larvae is greater off the West Coast than off the South Coast. Most spawning appears to take place in summer, with a peak abundance of larvae and early juveniles towards the end of this season. Instantaneous natural mortality was calculated: 5 – 30 mm, Z = 0,14·day^?1; 30 – 100 mm, Z = 0,02·day^?1. There is therefore a marked but unexplained decline in mortality shortly after the transition from the larval to the juvenile phase.     

Diet of the Cape fur seal Arctocephalus pusillus pusillus at the Robberg Peninsula,Plettenberg Bay,and implications for local fisheries

Cape fur seals Arctocephalus pusillus pusillus were harvested to extirpation on the Robberg Peninsula, Plettenberg Bay, on the south-east coast of South Africa, between the 17th and early 20th centuries. Seals returned to Robberg in small numbers during the early 1990s and their numbers subsequently increased. We studied the diet of this increasing population using faecal (scat) sampling to determine: the species composition and size of prey in the diet of Cape fur seals at Robberg; to explore temporal variation in the diet; and to investigate the potential for competition between seals and the fisheries around Plettenberg Bay. Of the 445 scats collected, 90% contained hard prey remains and 15 teleost prey species were represented in the 3 127 otoliths that could be identified. The seals’ most important prey species in terms of numerical abundance, frequency of occurrence and mass in the diet, were anchovy Engraulis encrasicolus, sardine Sardinops sagax, horse mackerel Trachurus capensis, sand tongue-fish Cynoglossus capensis and shallow-water hake Merluccius capensis (in decreasing order of importance for numerical abundance). The proportion of anchovy in the diet increased during the study period (2003–2008), whereas the proportion of sardine decreased. The estimated average annual consumption of sardine by seals was higher than the average annual catch made by purse-seine fisheries in this area, suggesting resource competition between seals and purse-seiners, especially in the light of continuing growth of seal numbers in the area. However, direct competition between seals and linefisheries appeared to be minimal. Scat sampling of Cape fur seals holds potential to serve a useful and cost effective indicator of temporal changes in sardine abundance.     

The influence of mesoscale physical processes on the larval fish community in the Canaries CTZ, in summer

We have studied the relation between the hydrography, the composition and horizontal structure of the larval fish community, and the horizontal distribution patterns of larval fish abundances in an area characterised by strong mesoscale oceanographic activity, located between the Canary Islands and the African coast (the Canaries Coastal Transition Zone), during August 1999. Upwelling, upwelling filaments, cyclonic and anticyclonic eddies and island wakes are typical mesoscale features of the northwest African coast in summer. A single upwelling filament off Cabo Juby was joined in mid-August by a second that originated about 100 km to the north. The two filaments flowed together and merged 100 km offshore. The merged filament was partially entrained around a cyclonic eddy, trapped between the Canary Islands and the African coast, and interacted with cyclonic and anticyclonic eddies shed from Gran Canaria. Mesoscale oceanographic features strongly influenced the horizontal distributions of fish larvae. Eddies acted as a mechanism of concentration, while upwelling filaments were dispersive, transporting larvae from the African neritic zone into oceanic areas and towards the Canary archipelago. This transport was the major cause of the predominance of neritic larvae in the composition of the larval fish community of the area. The results also suggest: (1) that anchovy larvae are good indicators of the offshore displacement of upwelled water; (2) that the alternation between anchovy and sardine as species dominant in the larval fish community of the area during summer depends upon the water temperature in the African upwelling region, anchovy dominating at higher temperature; (3) that a coupling of anchovy and sardine spawning with the mesoscale oceanographic structure formed by the upwelling filaments and trapped eddy overcomes the negative effect that Ekman transport has on their populations.