Short-term seaward fish migration in the Messolonghi–Etoliko lagoons (Western Greek coast) in relation to climatic variables and the lunar cycle

In the present study we analysed the daily seaward migratory behaviour of four dominant euryhaline fish species (Mugilidae: Liza saliens, Liza aurata, Mugil cephalus and Sparidae: Sparus aurata) in the Messolonghi–Etoliko lagoon system (Western Greek coast) based on the daily landings' time series of barrier traps and assessed the relationship between their migratory behaviour and various climatic variables (air temperature and atmospheric pressure) and the lunar cycle. A 2-year time series of daily fish landings (1993 and 1994), a long time series of daily air temperature and daily temperature range (1991–1998) as well as a 4-year time series of the daily atmospheric pressure (1994–1997) and daily pressure range were used. Harmonic models (HM) consisting of annual and lunar cycle harmonic components explained most (R² > 0.80) of the mean daily species landings and temperature variations, while a rather low part of the variation (0.18 < R² < 0.27) was explained for pressure, daily pressure range and daily temperature range. In all the time series sets the amplitude of the annual component was highest. The model values of all species revealed two important migration periods (summer and winter) corresponding to the spawning and refuge migrations. The lunar cycle effect on species' daily migration rates and the short-term fluctuation of daily migration rates were rather low. However, the short-term fluctuation of some species' daily migration rates during winter was greater than during summer. In all species, the main migration was the spawning migration. The model lunar components of the species landings showed a monthly oscillation synchronous to the full moon (S. aurata and M. cephalus) or a semi-monthly oscillation synchronous to the new and full moon (L. aurata and L. saliens). Bispectral analysis of the model values and the model residuals' time series revealed that the species daily migration were correlated (coherencies > 0.6) to the daily fluctuations of the climatic variables at seasonal, mid and short-term scales.     

Impact of lunar cycle and swell on the daily catch rate of western rock lobster (Panulirus cygnus) using time series modelling

The western rock lobster fishery is one of the most valuable single‐species fisheries in Australia, valued at AU$300 million per year. The impact of environmental factors such as lunar cycle and swell on the daily catch rate of the western rock lobster (Panulirus cynus) is of particular interest in the stock assessment and management of the fishery. The variation in daily catch rates was examined for two periods (migrating period November‐January, non‐migrating period February‐June), at different depths in three management zones for three categories of lobster (undersize, legal size, and setose). Regression and transfer function models for relationships between catch rates and environmental data were considered and compared. The lunar cycle has a significant impact on the daily catch rates with c. 30% lower catch rate during the full moon and c. 20% higher catches near the new moon. This impact occurs mainly during the non‐migrating period both in deep water (40–100 m) and shallow water (<40 m). The swell on the day before fishing was also shown to be significantly related to the catch rate with an increase of c. 10–15% for an increase in swell from light to moderate or moderate to high. These environmental factors can be used to standardise catch rates to provide an improved abundance index for stock assessment. Also, management closures are being considered for 3–5 days over the low catch rate, full moon period to reduce fishing costs and lower fishing effort.     

The reproductive cycle of the humbug damselfish <Emphasis Type="Italic">Dascyllus aruanus</Emphasis> according to the changes in lunar phase in Micronesia

The moon is known to be an environmental factor that controls the reproductive cycle of fish, and fish have evolved a variety of reproduction patterns depending on the lunar phase. In this study, we examined the relationship between lunar phases and the reproductive cycle of the humbug damselfish Dascyllus aruanus inhabiting Weno Island, Chuuk Lagoon, Micronesia. We divided the one-month lunar cycle into eight phases, and measured the features of moonlight (peak wavelength and intensity) and indicators of fish maturity [gonadosomatic index (GSI) and sex hormones] in relation to the eight lunar phases. In addition, we investigated the daily rhythms of sex hormones in fish ovaries during the full moon phase. The results showed that the peak wavelength of moonlight was 430 nm (blue wavelength region) regardless of the lunar phase, and that moonlight intensity was highest during a full moon at 02:00. Furthermore, the GSI and sex hormones were both higher around the full moon phase. These findings support the hypothesis that humbug damselfish spawn once a month and that this event occurs at full moon, which is the phase of the moon with the strongest intensity. Based on these findings, we predict that blue wavelength, the dominant wavelength of moonlight, is one of the environmental factors influencing the monthly spawning of D. aruanus.     

Biology of three Malacostraca (Decapoda) in a Mediterranean lagoon with particular emphasis on the effect of rapid environmental changes on the activity (catchability) of the species

The activity of three Malacostraca (Decapoda), Crangon crangon, Carcinus aestuarii and Paleamon squilla, was studied following rapid environmental changes in a Mediterranean lagoon linked temporarily with the sea. Nekton was sampled every 2–3 days using fixed fyke nets. A canonical analysis and a stepwise multiple regression were computed to determine which factor(s) can predict or account for the catch of these three decapods. In spite of rapid environmental changes no exceptional mortality was observed in each of the three species. Temperature is the environmental factor with major impact on the activity of C. crangon. Activity of P. squilla is controlled by water depth. At a depth of less than 20 cm two factors, salinity and phase of the moon, have a significant influence on the activity of this species. At depths deeper than 20 cm the activity is inhibited. There is only a weak relationship between the catch of C. aestuarii and salinity. Additional data on the life cycle of these species are given. The limitations of a monthly sampling period are discussed and the need for more short-term, consecutive sampling periods is stressed in order to understand the dynamics of systems with rapid environmental fluctuations.     

Micronekton abundance and biomass in Hawaiian waters as influenced by seamounts, eddies, and the moon

Micronekton abundance, biomass, and community composition was determined from 58 Cobb trawl samples taken from 2005 to 2008 at several locations in the lee of the Hawaiian Islands. The results indicated a strong influence of the lunar illumination on micronekton abundance and biomass. This effect was evident in shallow night tows and probably was the result of lunar light affecting the nighttime depths of migrating species. The abundance and biomass of micronekton is remarkably consistent between years and areas in Hawaiian waters after the affects of moon phase are accounted for. Micronekton, principally migratory myctophids, were reduced over the summit of Cross Seamount but not Finch Seamount that has a summit below the daytime depth of most migrators. However, during a new moon, micronekton abundance over Cross seamount was similar to surrounding areas either because of altered migration patterns or because predators such as tunas cannot forage as effectively at night without lunar illumination. Species belonging to the Hawaiian mesopelagic boundary layer community were found to vary in presence and abundance between years at Cross Seamount suggesting that a consistent seamount associated fauna does not exist. Sparse sampling of a cyclonic mid-ocean eddy suggested very high micronekton abundance and biomass both in shallow waters at night but also at depth during the day. Although preliminary, these results suggest that eddies may aggregate the micronekton which probably feed on the enhanced secondary productivity.     

Invasion of a New Zealand freshwater stream by glass‐eels of two Anguilla spp.

Recruitment of glass‐eels into freshwater is in two distinct phases characterised by behavioural differences: an initial invasion from the sea, and an upstream migration. Catches made at night in the Makara Stream, Wellington (41° 13'S, 174° 43’ E) indicate that the invasion by both New Zealand species commences in July, with that of the long‐finned eel Anguilla dieffenbachii Gray finishing by November, and that of the short‐finned eel A. ausiralis schmidlii Phillipps by December.

The length of post‐metamorphic sea‐life influences both morphology and behaviour of the glass‐eels. Differences in this period of sea‐life between early and late season glass‐eels explain the initial avoidance but later attraction of fresh water to the glass‐eels. Responses to fresh water also explain the preference for early season glass‐eels to invade on the flood tide and late season glass‐eels on the ebb tide. Neither the lunar cycle nor rainfall appear to be significant influences on invasion periodicity.     

The influence of long tides on ecosystem dynamics in the Barents Sea

The Barents Sea ecosystem has been associated with large biomass fluctuations. If there is a hidden deterministic process behind the Barents Sea ecosystem, we may forecast the biomass in order to control it. This presentation concludes, for the first time, investigations of a long data series from North Atlantic water and the Barents Sea ecosystem. The analysis is based on a wavelet spectrum analysis from the data series of annual mean Atlantic sea level, North Atlantic water temperature, the Kola section water temperature, and species from the Barents Sea ecosystem.The investigation has identified dominant fluctuations correlated with the 9.3-yr phase tide, the 18.6-yr amplitude tide, and a 74-yr superharmonic cycle in the North Atlantic water, Barents Sea water, and Arctic data series. The correlation between the tidal cycles and dominant Barents Sea ecosystem cycles is estimated to be R=0.6 or better. The long-term mean fluctuations correlate with the 74-yr superharmonic cycle. The wavelets analysis shows that the long-term 74-yr cycle may introduce a phase reversal in the identified 18-yr periods of temperature and salinity. The present analysis suggests that forced vertical and horizontal nodal tides influence the ocean's thermohaline circulation, and that they behave as a coupled non-linear oscillation system.The Barents Sea ecosystem analysis shows that the biomass life cycle and the long-term fluctuations correlate better than R=0.5 to the lunar nodal tide spectrum. Barents Sea capelin has a life cycle related to a third harmonic of the 9.3-yr tide. The life cycles of shrimp, cod, herring, and haddock are related to a third harmonic of the 18.6-yr tide. Biomass growth was synchronized to the lunar nodal tide. The biomass growth of zooplankton and shrimp correlates with the current aspect of lunar nodal tidal inflow to the Barents Sea. The long-term biomass fluctuation of cod and herring is correlated with a cycle period of about 3×18.6=55.8 yr. This analysis suggests that we may understand the Barents Sea ecosystem dynamic as a free-coupled oscillating system to the forced lunar nodal tides. This free-coupled oscillating system has a resonance related to the oscillating long tides and the third harmonic and superharmonic cycles.     

Demersal fish assemblages off southern New Zealand in relation to depth and temperature

We examined the relationship between demersal fish assemblage and depth, temperature, latitude and longitude off southern New Zealand (46–54°S and 165–180°E) in water depths of 80–787 m. Catch weight data were analysed by two-way indicator analysis (TWIA), groupaverage agglomerative clustering (UPGMA) and Detrended Correspondence Analysis (DCA). The spatial pattern of demersal fish off southern New Zealand conforms to the concept of species groups or fish assemblages related to environmental gradients. Shallow-water assemblages were dominated by species from the families Gempylidae, Squalidae, Triakidae and Moridae, mainly represented by Thyrsites atun, Squalus acanthias, Galeorhinus australis, and Pseudophycis bachus. Deep water assemblages were dominated by Chimaeridae, Argentinidae, Merlucciidae and Macrouridae, mainly represented by Hydrolagus novaezelandiae, Argentina elongata, Macruronus novaezelandiae, and Lepidorhynchus denticulatus. Total catch weight was often dominated by Merlucciidae, Macrouridae and Gempylidae. Fish assemblages were related to discrete ranges of depth (< and >300 m) and temperature (< and >9.5°C), but the range of sediment types was too narrow to show any correlation.     

Migrating eels in a Canterbury river,New Zealand

A fish trap in the upper reaches of the South Branch stream, Canterbury, New Zealand, caught eels from December 1957 to October 1964. The downstream migrations of immature and adult eels of both New Zealand freshwater species (short‐finned Anguilla australis and long‐finned A. dieffenbachii) were recorded. These migrations showed a seasonal and a lunar periodicity, and the larger runs were also influenced by rainfall, water volume, or the passage of a depression. Seasonal peaks were marked for mature eels of both species, and for immature A. australis, but not for immature A. dieffenbachii.     

Movement patterns of individual migrating western rock lobster,Panulirus cygnus,in Western Australia

Abstract

Migrating and pre‐migrating western rock lobster Panulirus cygnus were tagged with datastorage tags that recorded temperature and pressure, which was converted to depth (Pressure (kPa) — surface pressure (kPa)/10)) at Dongara and Jurien Bay in Western Australia between December 2005 and December 2007. All lobsters were fitted with tag flotation devices, and returns were made by either commercial fishers or beachcombers who located detached tags. A total of 135 lobsters were released with “backpack” flotation tags, but only 84 (62.2%) of the backpacks carried data‐storage tags. Depths of release ranged from 5 to 113 m. Of the tagged lobsters released, commercial fishers recaptured 52 (38.5%), whereas 11 tags (8.1%) were found by beachcombers. At least 33%, and possibly up to 63%, of animals identified by their pale coloration as pre‐migrating individuals, failed to migrate. Those that did migrate (n = 11) were at liberty from 1 to 94 days and showed generally similar movement patterns in that they migrated only at night from darkness (after 2000 h) until after moonrise. However, their movement patterns were less constrained by the rising of the moon in deep water. Only 27% migrated nightly, compared with 73% that skipped migrating on one or more nights, to restart some days later. This latter proportion would likely have been considerably greater, but some migrating animals were only at large for short periods before recapture, and therefore had little time to show any variation to the nocturnal migration pattern. Individual speeds of migration during periods of activity were estimated for nine lobsters as 0.20 to 0.68 km h^?1, with a mean speed of 0.44 km h^?1, or 7.4 m min^?1. Improved knowledge of daily movement patterns resulting from this study provides a potentially important input into technological improvements in bait and pot design.     

The influence of environmental cues on the activity of silver eels (Anguilla dieffenbachii) in Lake Manapouri,New Zealand

Lake Manapouri in the South Island of New Zealand has a significant hydroelectric generation facility, which potentially has a negative impact on the successful emigration of longfin eels (Anguilla dieffenbachii) from the upper Waiau catchment. Consequently, a trap-and-transfer programme has been implemented to allow silver (migratory) eels access to the sea. The present study analysed data on the timing of captures and numbers of silver eels over four seasons, including the influence of possible migration cues. Silver eels were captured over an extended season of seven months (November–May), with peak numbers during December and January. Flow at the lake outflow was found to have a weak relationship with the number of eels caught, as did lake level, but moon phase and rainfall had no significant effect. These results highlight the variability in silver longfin eel behaviour both in terms of timing and response to potential environmental cues.     

Bathyal polychaete assemblages in the region of the Subtropical Front,Chatham Rise,New Zealand

Abstract

Polychaetes were collected from eight sites across the Chatham Rise (New Zealand) in the region of the Subtropical Front from water depths of c. 2300 m to 350 m. A total of 169 putative species representing 36 families was identified. Spionidae, Paraonidae, Cirratulidae, Syllidae, and Orbiniidae accounted for 50% of all polychaete individuals. Multivariate analysis revealed that three sites at c. 350–453 m water depth on muddy sand (6–7% clay) shared similar faunal and environmental characteristics. Numerical dominants included Lumbrineris sp., P seudeurythoe minuta, Dipolydora cf. socialis, Aglaophamus verrilli, Prionospio lehlersi, Syllinae sp., Monticellina sp., and Cossura sp. Replicates from a single site at c. 750 m depth on the southern flank of the Rise produced a distinct assemblage dominated by Paradoneis, Naineris, Notomastus, Harmothoinae, Prionospio lehlersi, Levinsenia, Aricidea, Kebuita, Paraonella, and ?Leiochrus species. Replicates from greater depths north and south of the Rise presented a greater range of assemblage characteristics and environmental parameters including temperature, dissolved oxygen, median grain size, calcium carbonate (CaCO₃), and total organic matter content. Twenty‐eight taxa were found exclusively below 750 m depths including species of Ampharetinae, Chloeia, Pseudeurythoe, Capitellidae, and Cirratulidae. There was a significant difference in faunal composition between northern and southern flanks of the Rise within depth classes and also between sites at the same depth classes. Faunal density and species diversity appeared highest from the crest to 750 m depth on the southern side. Low species diversity at the deepest sites may be confounded by reduced density.     

Evidence of marine mammal predation of the European eel (Anguilla anguilla L.) on its marine migration

Temperature and depth logging tags were implanted into adult eels released on Atlantic west coasts of France and Ireland to study their oceanic migration behavior. For three of the tags, 25 to 256 days after release there was a dramatic rise in temperature from 10 °C to 36 °C and the dive profile changed from depths of 300–1000 m to repeated ascents to the surface. This indicated that the eels carrying the tags had been eaten by a mammalian predator. Two of the tags had sufficient sampling rate to resolve the dives in detail. They recorded a total of 91 dives to maximum depths of 250–860 m lasting 11–12 min and with surface intervals of 5–7 min. More than two thirds of the dives included a rapid descent from approximately 500 m to 600–700 m. From this we infer that the predator was most likely a deep-diving toothed whale. The dives logged while the tags were inside the predator revealed that the temperature usually decreased during dives, and increased again during surface periods. The temperature drops during dives were probably caused by the ingestion of prey or water. These observations provide insights into the behavior of toothed whales foraging in the mesopelagic zone.     

南麂列岛海域蟹类群落结构及其与环境因子的关系

根据2013年11月、2014年2月、5月、9月在南麂列岛国家海洋自然保护区海域进行生物资源调查所获得的资料,分析了南麂列岛海域蟹类种类组成、优势种、生物多样性等群落结构特征,并定量分析了群落结构与水文环境因子之间的关系。结果表明,周年4个季度月调查共鉴定出蟹类21种,隶属7科、12属,其中优势种为三疣梭子蟹（Portunus trituberculatus）、日本蟳（Charybdis bimaculata）和双斑蟳（Charybdis bimaculata）3种。不同季节的蟹类种类组成差异较大,而优势种类组成变化较少,其中,以秋季的蟹类种类数最多,冬季最少。从不同水深区域的渔获种类分布趋势来看,蟹类种类以20~30 m水深带较多,30~40 m水深带较少。夏季多样性指数低于其他季节,以水深来看,多样性指数在10~20 m水深带较高,30~40 m水深带较低,蟹类多样性指数与水深呈反比。根据冗余分析认为,水深、水温和盐度是影响调查海域蟹类种类组成和群落结构特征的主要环境因子。     

Prediction of local scour around circular piles under waves using a novel artificial intelligence approach

Abstract

The scour phenomena around vertical piles in oceans and under waves may influence the structure stability. Therefore, accurately predicting the scour depth is an important task in the design of piles. Empirical approaches often do not provide the required accuracy compared with data mining methods for modeling such complex processes. The main objective of this study is to develop three data-driven methods, locally weighted linear regression (LWLR), support vector machine (SVR), and multivariate linear regression (MLR) to predict the scour depth around vertical piles due to waves in a sand bed. It is the first effort to develop the LWLR to predict scour depth around vertical piles. The models simulate the scour depth mainly based on Shields parameter, pile Reynolds number, grain Reynolds number, Keulegan–Carpenter number, and sediment number. 111 laboratory datasets, derived from several experimental studies, were used for the modeling. The results indicated that the LWLR provided highly accurate predictions of the scour depths around piles (R?=?0.939 and RMSE = 0.075). Overall, this study demonstrated that the LWLR can be used as a valuable tool to predict the wave-induced scour around piles.     

长江口环境条件对日本鳗鲡(Anguilla japonica)鳗苗溯河洄游的影响

长江口是日本鳗鲡鳗苗的手要产区,利用2007年1-5月在长江口的长兴岛、横沙和杭州湾小洋山4个取样点得到的日本鳗鲡鳗苗渔获量数据,初步研究了鳗苗的补充时间分布以及补充量与潮汐、月相等环境因素之间的关系.发现鳗苗在长江口的补.充时间从1月下旬开始到5月中旬结束,鳗苗日产量峰值出现日期从长江口外向内逐渐推迟,与其洄游路线致.长江口附近潮汐为半月潮,每月有两次涨落潮,鳗苗溯河量与潮汐周期呈现一定的节律性,每月有两次鳗苗峰值.河口区鳗苗溯河具有潮流选择性,长江口内鳗苗溯河量起汛潮多于落汛潮:长江口外鳗苗溯河量和潮汐振幅呈现正相关趋势.日本鳗鲡鳗苗的溯河量与月相变化也有一定的关系;朔月望月的平均单网捕捞量之和占总平均单网捕捞量的93.13%,而上下弦只占6.87%.经过方差检验,朔月鳗苗溯河量多于望月,且二者之间存在极显著差异(P<0.01).     

Diffusive and total oxygen uptake of deep-sea sediments in the eastern South Atlantic Ocean:in situ and laboratory measurements

Total O₂ uptake rates were measured by the benthic flux chamber lander ELINOR, and O₂ microprofiles were measured by the profiling lander PROFILUR in the eastern South Atlantic. Diffusive O₂ fluxes through the diffusive boundary layer and the depth distribution of O₂ consumption rates within the sediment were calculated from the obtained microprofiles. The depth integrated O₂ consumption rate agreed closely with the diffusive O₂ uptake at all stations. Total O₂ uptake was 1.2–4.2 times the diffusive O₂ uptake, and the difference correlated with the abundance of macrofauna in the sediment. Diffusive O₂ uptake and O₂-penetration depths correlated with the organic content of the sediments and exhibited an inverse correlation with water depth. Total and diffusive rates of in situ O₂ uptake were higher than previously published data for shelf and abyssal sediments in the Atlantic, but were comparable to rates from upwelling areas in the eastern Pacific. Laboratory measurements on recovered sediment cores showed lower O₂ penetration depths and higher diffusive uptake rates than in situ measurements. The differences increased with increasing water depth. We primarily ascribe this compression of O₂ profiles to a transiently increased temperature during recovery and enhanced microbial activity in decompressed sediment cores. Total O₂ uptake rates measured in the laboratory on macrofauna-rich stations were, in contrast, lower than those measured in situ because of underrepresentation and disturbance of the macrofauna.     

Rhythmic swimming of the isopod Exosphaeroma obtusum (Dana)

The tidal swimming rhythm of the New Zealand rocky shore isopod Exosphaeroma obtusum (Dana) is described. Peak swimming was on the ebb tide about 2.5 h after high water; the peak in the dark period was 6–8 times greater in amplitude than the daytime peak. Positive thigmotaxis was shown at all other times. The rhythm period in continuous darkness (free‐running period) was greater than tidal periodicity, and there was a semi‐lunar swimming pattern with peaks at the first and third quarters of the moon. Rheotropic experiments showed that changes in water flow did not initiate the swimming rhythm. The work was compared with the infaunal species Pseudaega punctala and the northern Eurydice pulchra. It was concluded that infaunal species rely more on endogenous control of the swimming rhythm because of their isolation, when buried, from exogenous Zeitgeber.     

Residual depth and residual geoid anomalies of the South Atlantic ocean

Abstract

We have obtained the residual depth and residual geoid anomalies of the South Atlantic Ocean and interpreted them in terms of upper mantle processes. Starting from the 5’ X 5’ SYNBAPS data, we computed the 1° X 1° mean water depth. We digitized a recent sediment thickness map of the South Atlantic and corrected for the isostatic sediment loading effects. A plot of the corrected basement depth against crustal ages shows a good match to the depth‐age curve of the plate model. We then subtracted the predicted plate model depths from the corrected basement depths and obtained the 1° X 1° residual depth. The residual depth anomalies have positive values over the topographic highs and relative negative values over the ocean basins. A prominent asymmetry is observed between the residual depth over the Argentine Basin and that over the Cape Basin.

We have obtained the 1° X 1° residual geoid of the South Atlantic by subtracting both the long wavelength features and the geoid variations due to the plate cooling from the 1° X 1° Seasat altimeter derived geoid. The long wavelength features are represented by the degree and order 10 geoid of GEM1OC, and the geoid variations due to the plate cooling effects are predicted by the plate model geoid‐age relationship. The residual geoid anomalies also show an asymmetry although weaker than the case of the residual depth, between the Argentine and Cape basins.

By taking the 5° X 5° averages, we removed possible plate bending effects on the depth and geoid anomalies. We then compared those two data sets with respect to the reported hot spot tracks in the South Atlantic. The residual depth generally shows positive values over the hot spot tracks, whereas the residual geoid does not show any sign of them. A prominent asymmetric feature of depth and geoid anomalies is observed over the Argentine and Cape basins. This asymmetry is probably caused by hotter and less dense materials beneath the Cape Basin. Hot spots or other mantle upwellings may be the heat sources.     

Cyclonic eddies reveal Oegopsida squid egg balloon masses in the Agulhas Current,South Africa

In 2005, 2006, 2007 and 2011, distinct Oegopsida squid egg masses were observed by scuba divers on the narrow southern KwaZulu-Natal (KZN) shelf in depths of 35–50 m off the coastal resorts of Park Rynie, Pumula and Port Edward, South Africa. In 2006, larvae in the egg balloons were sampled. DNA barcoding (i.e. cytochrome c oxidase subunit 1 sequencing) linked the larvae to the genus Lycoteuthis, a group commonly found on the continental slope of the Agulhas Bank and the west coast of South Africa. In all cases, the sightings were concomitant with low water temperatures of 14–18 °C, indicative of shelf edge upwelling. Historical ship-collected CTD data show these cooler waters to originate from a depth of 100–180 m on the KZN continental slope. Complementary satellite imagery revealed the cooler water and discoveries of the egg balloons to be coincident with cold core cyclonic eddies embedded in the shoreward boundary of the Agulhas Current. The temperature data suggest that these egg balloons, in the absence of cyclonic eddy activity, would normally be found in the current on a density surface at a depth of ～130 m where velocities are typically around 100 cm s^–1.