The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Yolk-sac pike fry were stocked at densities of 0.74 – 81.4 m⁻² in two ponds, each divided into eight sectors (mean area 155.8 m²). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size-range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density-independent but switched by late June/July to density-dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May-July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm⁻² and in Pond 2 was 3.49gm⁻².
Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m⁻².
Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m⁻² is advised if large, density-dependent mortalities are to be avoided.     

Sibling cannibalism among juvenile vundu under controlled conditions. I. Cannibalistic behaviour, prey selection and prey size selectivity

Sibling cannibalism among vundu Heterobranchus longifilis larvae started at the age of 4 days, with the prey caught tail-first then swallowed up to the head, which was eventually discarded (type I cannibalism). At 17 days old, this type of cannibalism vanished and was replaced by the ingestion of the whole prey (type II cannibalism), which could only be exerted by predators six times as heavy as their prey. Type II cannibalism consisted of a seemingly opportunistic ambush attack by a formerly passive predator towards a disorientated prey. It required no preliminary aggression or chase, or even contact with the prey, suggesting that the attack was not mediated by the tactile sense, and that cannibalism was independent of aggressive behaviour. When alternative food resources (formulated feed, live tilapia prey) were available, the intensity of cannibalism decreased but pellet-eaters or tilapia predators always achieved lower growth rates than those feeding on conspecifics, suggesting that cannibalism was the most advantageous foraging tactic. Losses to cannibalism among populations of 30-day old juvenile vundu with an initial ratio of 4% of cannibals were as high as 75·5–79·9% over 15 days. Predation peaked during the first days (up to 2·8 prey C⁻¹ day⁻¹), then vanished progressively as surviving prey grew faster than cannibals and escaped their predation. Cannibals preferred consuming the largest prey available with respect to the logistics of cannibalism (body weight ratio of 6·0). This preference for large prey was interpreted both as a foraging tactic aiming to maximize the energetic return, and as foraging strategy enabling the cannibals to exploit their prey as long as possible. Based on these data, comprehensive models of the impact of cannibalism on vundu populations were developed.     

The relationship between temperature and the size and age of larvae and peri‐metamorphic stages of Pleuronectes flesus

Habitat use of 0+ year pike Esox lucius (mean 20–31 mm L _T) was evaluated in artificial ponds (surface area = 16 m²) in relation to water transparencies (low and high), habitat complexity (low and high), food availability (zooplankton) and cannibalism (mortality in the ponds). Pike could choose freely between a structured area, an open water area and a structure and open water interface area. Habitat use shifted towards the structured habitat type in the presence of high habitat complexity and low water transparency. Both findings could be explained as a consequence of territorial behaviour. When cannibalism was intense, the proportions of pike using the structures were reduced and the largest pike, and hence the potential cannibals, were found inside the structures. Since the smallest pike were constrained to the unsheltered, and hence probably more hazardous, habitat outside the structures, this study suggests that mortality due to intra‐cohort cannibalism may occur in an indirect as well as a direct way.     

Radioactive strontium (85Sr) in marking newly hatched pike and success of stocking

Immersion of newly hatched pike fry in an aqueous solution of 1·85 MBq ml⁻¹⁸⁵Sr did not affect their growth or survival over 3 weeks. Cannibal pike fry retained only l.2–3·3% of the ⁸⁵Sr from their labelled prey. Newly hatched ⁸⁵Sr-marked fry stocked into two lakes in 3 years were distinguishable from wild fish 4–6 weeks later. Stocked and wild fry grew equally well, and stocked pike survived best where density of wild pike was highest. There was no evidence of increase in density as a result of Stocking.     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

Post-stocking survival of 0+ year pike in ponds as a function of water transparency, habitat complexity, prey availability and size heterogeneity

Survival of 0+ year pike Esox lucius (20–31 mm L _T) was evaluated over the first week following stocking in ponds (16 m²) depending on water transparencies (low and high), habitat complexity (low and high) and food availability (zooplankton). A multiple regression analysis showed that survival, essentially as a result of cannibalism, decreased with increasing size heterogeneity of pike, and the decrease was steeper when no food was available. Survival was equal in clear water and water containing copper chlorophyllin (chlorophyll), and slightly higher in complex than in simple habitats, but only when alternative prey availability was low. Conversely, growth in water containing chlorophyll was slightly faster than in clear water. This suggests that initial size heterogeneity is the prevailing factor controlling mortality when stocking 0+ year pike almost irrespective of the stocking environment.     

Sibling cannibalism among juvenile vundu under controlled conditions. II. Effect of body weight and environmental variables on the periodicity and intensity of type II cannibalism

Cannibalism among starved groups of juvenile (19–48 days old) vundu catfish Heterobranchus longifilis was 66·5% nocturnal, and its impact under modified day length was proportional to the duration of the dark phase. Shallow depth and high population density decreased the intensity of cannibalism, whereas low density and deeper environments had an opposite effect. The presence of refuges had no significant effect on cannibalism. The maintenance ( R _maint) and maximum ( R _max) daily food rations (% day⁻¹) of cannibals feeding on live prey were modelled as R _maint=3·899 W _C^0·327 ( r ²=0·684; d.f.=31), and R _max=49.545 W _C^0·321 ( r ²=0·999; d.f.=5), where W _C was the body weight of the cannibal (g). The latter model indicated that the impact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vundu would become insignificant for cannibals heavier than 30 g. The significance of these findings is discussed within the contexts of vundu aquaculture and of general, conceptual models of the dynamics of cannibalism among fishes.     

Gastric evacuation rates and daily ration of piscivorous coho salmon, Oncorhynchus kisutch Walbaum

Effects of temperature and meal size on gastric evacuation rates of juvenile coho salmon, Oncorhynchus kisutch , consuming sockeye salmon, O. nerka , fry were examined and used in the estimation of daily meal, daily ration and number of fry consumed by coho in Chignik Lake, Alaska. Evacuation of fry by coho was best described by a negative exponential model (average R² = 0.93). A square root model also provided a good fit (average R² = 0·93), but the y-intercepts deviated more from the expected value than did the y-intercepts of the exponential model. The effect of temperature ( T , 5–13° C) and meal size (MS, 0·166–0·367 g) on the exponential evacuation rate (r_e, h^-1) could be described as
In the lake, coho fed continuously during the 24-h period in early June 1986 and 1987. Estimates of daily meal and ration of coho calculated by the Eggers method and the geometric mean of prey weight ranged from 0·224 to 0·435 g (2.1–4.4% body wt) depending on location and year. The Elliott & Persson method provided similar estimates of food consumption, whereas estimates based on the Pennington method and square root evacuation of prey differed from the exponential models. Sockeye fry represented 93% of the total prey weight. The average number of sockeye fry consumed per coho per 24 h, based on the arithmetic mean of prey weight, was 3·0–3·9 fry.     

Analysis of sibling cannibalism among pike,Esox lucius,juveniles reared under semi-natural conditions

Synopsis Sibling cannibalism in pike, Esox lucius, larvae and juveniles living in outdoor rearing ponds was studied using stomach contents analysis. For the two initial densities tested (6 and 18 larvae m^–2, equivalent to 12 and 36 larvae m^–3), cannibalism was non-existent during the larval period (13 to 35 mm total length) and was observed only during the juvenile stages. Initial density of larvae influenced both the date of first detection of cannibalistic individuals and the rate of development of cannibalism in the population. At initial stocking densities of 18 larvae m^–2 (36 larvae m^–3), cannibalism was observed from 21 days after the start of exogenous feeding (mean total length: 60 mm) onwards. At a mean total length of 100 mm and for initial stocking densities of 6 and 18 larvae m^–2, (12 and 36 larvae m^–3), the average proportions of cannibals in the populations of juveniles were 7.8% and 41.3% and the cannibals accounted for 15.5% and 65.9% of the total pike biomass, respectively. In stomachs of cannibals, young pike were the dominant prey in terms of weight. Dry weights of invertebrate-prey were lower in cannibals than in non-cannibals of similar size. Cannibalism among pike juveniles was characterized by the prey being swallowed whole and head first in the vast majority of cases. There was a strong positive correlation between predator and prey size and the mouth size of a cannibal was found to be an important constraint determining maximum victim size. The overall mean ratio of pike prey length to pike cannibal length was 66.2% and the average ratio of prey head depth to predator mouth width amounted to 87.6%. Prey size selection could be demonstrated for several length-groups of cannibals. These results are compared with the characteristics of early cannibalism in other fish species.     

Functional response of juvenile pink and chum salmon: effects of consumer size and two types of zooplankton prey

Feeding rate experiments were conducted for pink salmon Oncorhynchus gorbuscha fry [mean fork length ( L _F) 39 mm], juveniles (103–104 mm L _F) and juvenile chum salmon Oncorhynchus keta (106–107 mm L _F). Fishes were presented with small copepod ( Tisbi sp.) or larger mysid shrimp ( Mysidopsis bahia ) prey at varying densities ranging from 1 to 235 prey l⁻¹ in feeding rate experiments conducted at water temperatures ranging from 10·5 to 12·0° C under high light levels and low turbidity conditions. Juvenile pink and chum salmon demonstrated a type II functional response to mysid and copepod prey. Mysid prey was readily selected by both species whereas the smaller bodied copepod prey was not. When offered copepods, pink salmon fry fed at a higher maximum consumption rate (2·5 copepods min⁻¹) than larger juvenile pink salmon (0·4 copepods min⁻¹), whereas larger juvenile chum salmon exhibited the highest feeding rate (3·8 copepods min⁻¹). When feeding on mysids, the maximum feeding rate for larger juvenile pink (12·3 mysids min⁻¹) and chum (11·5 mysids min⁻¹) salmon were similar in magnitude, and higher than feeding rates on copepods. Functional response models parameterized for specific sizes of juvenile salmon and zooplankton prey provide an important tool for linking feeding rates to ambient foraging conditions in marine environments, and can enable mechanistic predictions for how feeding and growth should respond to spatial-temporal variability in biological and physical conditions during early marine life stages.     

Prey size selection and cannibalistic behaviour of juvenile barramundi Lates calcarifer

This study assessed the cannibalistic behaviour of juvenile barramundi Lates calcarifer and examined the relationship between prey size selection and energy gain of cannibals. Prey handling time and capture success by cannibals were used to estimate the ratio of energy gain to energy cost in prey selection. Cannibals selected smaller prey despite its capability of ingesting larger prey individuals. In behavioural analysis, prey handling time significantly increased with prey size, but it was not significantly affected by cannibal size. Conversely, capture success significantly decreased with the increase of both prey and cannibal sizes. The profitability indices showed that the smaller prey provides the most energy return for cannibals of all size classes. These results indicate that L. calcarifer cannibals select smaller prey for more profitable return. The behavioural analysis, however, indicates that L. calcarifer cannibals attack prey of all size at a similar rate but ingest smaller prey more often, suggesting that prey size selection is passively orientated rather than at the predator's choice. The increase of prey escape ability and morphological constraint contribute to the reduction of intracohort cannibalism as fish grow larger. This study contributes to the understanding of intracohort cannibalism and development of strategies to reduce fish cannibalistic mortalities.     

Downstream migration and critical water velocities in stream channels for fry of four salmonid species

Fry of brown trout, Atlantic salmon, brook trout and lake trout were tested for downstream migration and critical velocities with a method of stepwise increasing water velocities. Each velocity was tested for 15 min before increase to the next step. Critical velocities for fry entering the free-feeding stage, defined as the stage when the fry has resorbed its yolk sac and will have to ascend from the bottom gravel to catch food, were between 0.10 and 0.25 m s⁻¹, varying among individuals and depending on species and water temperature. Downstream displacement started at lower velocities. Lake trout had the lowest critical velocity. Temperature influenced swimming performance considerably. On average, a 7°C increase in temperature resulted in a 0.05 m s⁻¹ increase in critical velocity. The fry actively searched out the low-velocity niches in the channels. Flow-sensivity gradually decreases with fry development; when the fry had reached a length of 40–50 mm they were able to tolerate water velocities higher than 0.50 m s⁻¹.     

Spring cannibalism on 1 year walleye pollock in the Doto area,northern Japan: is it density dependent?

Cannibalism in walleye pollock off the eastern coast of the Hokkaido Island, Japan was important only during spring (April to June), and its importance increased from 0% in dry mass for <200 mm L _S fish to 48·9% for >400 mm L _S fish. Most of the prey was represented by age 1 year fish, showing a unimodal body size distribution with a mode at 121–130 mm. Although cannibal body size was larger in deeper (>150 m) water, there was no difference in prey size by depth, suggesting impingement of the predators inhabiting deeper water into the shallow areas to cannibalize 1 year fish. The minimum ratio cannibal: prey size was 1·74. There was a positive but non-significant correlation between the contribution of cannibalism to a potential predator's (>300 mm) diet and an estimate of the previous year's recruitment. This was due to an extremely high contribution of cannibalism during 1992, when a distinctly larger size of predators seemed to bias the contribution. When the 1992 data were removed from the analysis, a significant correlation was obtained ( r ²=0·77, P <0·01), showing that Pollock cannibalism is rather density dependent. Based on the results, it is hypothesized that the'overflow' of 1 year fish from the shelf waters due to their high abundance and the weak stratification in the spring water column results in increased co-occurrence with adult fish and consequent cannibalism.     

Early life characteristics of pike, Esox lucius, in rearing ponds: temporal survival pattern and ontogenetic diet shifts

Survival, biomass and diet of pike, Esox lucius , larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m⁻² in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mm t.l .) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mm t.l .). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha⁻¹) and 121 mm T.L. (181.8 kg ha⁻¹) and stabilized between 121 and 139 mm t.l . Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mm t.l .) and between 74 and 121 mm t.l . (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mm t.l . juveniles. Average-sized pike exhibited a sequence of size-dependent shifts from a diet composed primarily (in terms of weight) of micro-crustaceans (at 13 mm t.l .), to chironomid larvae (at 74 to 99 mm t.l .), and finally macrocrustaceans (at 121 to 139 mm t.l .). Cannibalism was detected first among the largest fish at the 74 mm t.l . stage. Between-year diet similarity at various developmental stages was consistently high. In 70 mm t.l . fish harvested from different ponds, we found significant among-pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquaculture practices.     

Growth performance, mortality and carotenoid pigmentation of fry offspring as affected by dietary supplementation of astaxanthin to female rainbow trout (Oncorhynchus mykiss) broodstock

Growth performance, mortality and carotenoid pigmentation were studied in triplicate groups each with 1000 swim-up larvae of rainbow trout ( Oncorhynchus mykiss ), derived from five groups of female broodstock fed diets with 0.07, 12.5, 33.3, 65.1 or 92.9 mg astaxanthin kg⁻¹, respectively. The first feeding fry (initial weight range from 113 to 148 mg) were fed a diet not supplemented with carotenoids in an experiment lasting 45 days. Fry were initially sampled for astaxanthin content and initial weight, and in subsequent 15-day intervals to determine weights, condition factors (CF), specific growth rates (SGR) and thermal growth coefficients (TGC). Total carotenoid concentration of the larvae was highly linearly correlated to that of the eggs ( r ² = 0.97, P = 0.002). About 59–67% of fry carotenoids consisted of esterified astaxanthin, and on average 39.7% of the egg carotenoids were recovered in the fry. Overall (0–45 days) SGRs and TGCs were significantly higher (P < 0.05) in the offspring of the four groups of females fed supplemented diets (12.5–92.9 mg astaxanthin kg⁻¹) than in offspring of females fed the non-supplemented diet. TGCs (0–45 days) within groups derived from broodstock supplemented with astaxanthin were similar (P > 0.05), but higher than in the group derived from females fed the diet not supplemented with astaxanthin (P < 0.05). Mortality (average 0.76%) was not significantly affected by treatment. The study indicates that dietary supplement of astaxanthin (>12.5 mg kg⁻¹) to maternal broodstock diets improves offspring SGR and TGC with up to 33 and 38%, respectively.     

The population dynamics of young trout (Salmo trutta L.) in a Danish brook

The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout ( Salmo trutta L.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m² and 18.6 g/m² in the 2 years.     

Oxygen consumption in Oreochromis niloticus (L.) in relation to development, salinity, temperature and time of day

Oxygen consumption of Oreochromis niloticus at different stages of development was studied in relation to salinity, temperature and time of day, using a Warburg apparatus. The oxygen consumption of newly hatched (0–14 h) larvae was 3.40 μl O₂ larva⁻¹ h⁻¹, of older yolk sac larvae 10.09 μl O₂ larva⁻¹ h⁻¹, and of one-month-old fry 32.99 μl O₂ larva⁻¹ h⁻¹. The QO₂ values showed a decrease with development and growth, ranging from 21.2–26.0 μl O₂ mg⁻¹ h⁻¹ in newly hatched larvae to 2.97 μl mg⁻¹ h⁻¹ in one-month-old fry. Changes in oxygen consumption occurred with salinity, the highest being at 17%o. Active larvae (12-24 mm T.L.) showed a doubling of consumption with a 10° C rise in temperature, and their Q₁₀ factor increased from 2.25 to 3.43 with increasing size. Day-old yolk-sac larvae, late yolk-sac larvae (5 days old) and fry of 12 14 mm length all showed a depression in oxygen consumption at midnight followed by a dawn rise.     

The distances travelled by downstream-moving trout fry, Salmo trutta, in a Lake District stream

SUMMARY. 1. Field experiments were performed in the day and night at six modal water velocities (range 10–52cm s⁻¹), using: (i) newly- emerged fry without neutral buoyancy; (ii) older fry in poor condition (weight well below that expected for resident fry); (iii) older fry in good condition (weight similar to that of resident fry); (iv) dead fry.
2. An exponential model described the return rate of fry to the stream bottom; the mean distance travelled downstream varied considerably between the four fry categories, but always increased linearly with increasing water velocity.
3. Results were similar for dead fry and newly-emerged fry released at night; 50% of the fry returned to the bottom in 10–11 s and nearly all returned in c . 70s, the maximum distance travelled ranging from c . 7 m at 10 cm s⁻¹ to c . 37m at 52cm s⁻¹, Newly-emerged fry released in the day returned slightly faster (54s for 99% return to bottom).
4. Older fry in poor condition returned to the bottom slightly faster in the day than at night, but took about 2 min and travelled about twice the distance covered by dead fry. Older fry in good condition returned to the bottom at the fastest rate (3–6s for 50% and c . 30s for the rest), and travelled only about half (at night) or a third (in day) of the distance covered by dead fry.
5. The implications of this investigation are discussed and it is concluded that, apart from water velocity, the age and condition of the fry were the two most important factors affecting their downstream movement.     

Density-dependent predation and implications for stock enhancement with Japanese flounder

In laboratory predation trials kinsen-gani crab Matuta lunaris rarely preyed on hatchery-reared (HR) Japanese flounder Paralichthys olivaceus , even at extremely elevated prey densities ( c . 90 fish m⁻²), but fed readily on sacrificed Japanese founder. This suggests that under similar conditions in the wild predator-prey interactions between kinsen-gani and juvenile Japanese flounder are likely to be weak. Larger Japanese flounder readily cannibalized smaller conspecifics, suggesting that within-release group cannibalism may contribute considerably to post-release mortality of HR Japanese flounder when sufficient size variation exists within groups of released fish. Kinsen-gani presence had no effect on within-release group cannibalism rates of large Japanese flounder on small Japanese flounder. Within-release group cannibalism rates were significantly affected by densities of smaller (prey) fish, implying that the number of fish released (and thus post-release densities) in stock enhancement programmes may significantly affect post-release mortality rates. The probability of within-release group cannibalism increased rapidly as the cannibal-to-prey size ratio exceeded 1.6, suggesting that minimizing size variation of released HR individuals will reduce post-release cannibalism rates. These results have implications for Japanese flounder stock enhancement release strategies, and may be applicable to other finfish stock enhancement programmes.     

The effect of bladderwort (Utricularia) predation on microcrustacean prey

SUMMARY 1. The effects of the carnivorous plant Utricularia ( bladderwort) on its microcrustacean and macroinvertebrate prey were studied under seminatural and natural conditions. The results suggest that Utricularia is a strong interactor in littoral communities that influences its prey populations by direct predation and indirect facilitation.
2. In an 8-week enclosure experiment, effects on prey density were compared in three treatments with (1) U. vulgaris with intact trapbladders, (2) U. vulgaris without bladders and (3) no Utricularia present.
3. Utricularia predation caused a decrease in prey density over time, whereas presence of Utricularia without bladders increased prey density. In the controls without Utricularia , prey density was relatively constant over time.
4. Field samples were collected to quantify predation rates of three Utricularia species on two natural prey populations. Daily consumption rates on prey peaked from mid-July to mid-August for all Utricularia species, but were low in June and September. This pattern was explained mainly by a high number of trapbladders at this time, but also by a slight increase in the number of prey caught per bladder. Per capita prey mortality rates caused by Utricularia were substantial and ranged between 0.14 and 0.43 day⁻¹ for copepods, 0.1–0.27 day⁻¹ for ostracods and 0.04–0.2 day⁻¹ for chydorid cladocerans.
5. Predation and facilitation effects were observed for total prey and separately for epiphytic and benthic prey. Planktonic microcrustaceans showed no response to Utricularia presence.