Food habits of the otter (Lutra lutra) in two habitats of the Doñana National Park, SW Spain

Food habits of otters Lutra lutra were studied in two localities of the Doñana National Park (SW Spain) 16 km apart. These were the lowest stretch of Arroyo Rocina, a eutrophic stream where American red-swamp-crayfish were introduced in 1976, and at Lucio Bolín, an artificial pond 150 m in diameter, situated on the border of the Guadalquivir marshes. In all, 598 spraints were analysed between 1979 and 1984. Crayfish, occurring in 80% of the spraints, was the dominant food item in Arroyo Rocina, where other common foods were fish (63%), insects (55%) and amphibians (18%). Fish, occurring in 94% of the spraints, were by far the most abundant food item in Lucio Bolin, followed by insects (32%) and amphibians (28%). Seasonal differences in diet were small but interesting: reptiles were eaten more often in the dry season (April-September) and insects and crayfish in the rainy season (October-March). Among fish, eels were more commonly eaten in the rainy period and the remaining species in the dry period. This pattern of seasonal variation is opposite to the usual in temperate Europe. Mean size of the captured eels was statistically higher in Lucio Bolin than in Arroyo Rocina. A large amount of very small fish such as Gambusia was eaten. A comparison of prey consumed with estimates of prey abundance reveals a strong preference for eels. The diet of Mediterranean European otters seems to be more diverse than that of northern European ones, including more insects, amphibians and reptiles.     

Trophic flexibility of the otter (Lutra lutra) in southern Italy

Diet composition of otters (Lutra lutra) was investigated in 2001 by spraints analysis (N=1323) on five rivers of southern Italy, with the aim of assessing the influence of fish availability, elevation and discharge on the consumption of food resources alternative to fish. Data were expressed as per cent frequency of occurrence (%FO) and per cent volume (%V). The study confirmed the great feeding adaptability of the otter that, in rivers partially interconnected and flowing on a small area, showed a strong fish eating habit in some rivers (Sinni and Mercure-Lao) and a diet mainly constituted by alternative resources in other ones (amphibians in the rivers Cogliandrino and Frido, crustaceans in the River Battendiero). Fish consumption for the five rivers was significantly correlated with fish biomass and with mean summer discharge, while it was inversely correlated with the mean altitude of the five rivers. The lack of a clear seasonality in the consumption of food sources alternative to fish together with the correlation between fish use and fish biomass for each river indicated fish availability as the main factor affecting otter relying to non-fish preys. Otter diet seemed influenced by the characteristics of river habitats (altitude, discharge and consequently fish biomass) more than by summer drought, typical of Mediterranean regions. The %FO and the %V allowed to drawn a similar picture of otter diet. Nonetheless the %V was useful for better illustrating diet variation among the different rivers and we argue that it could be useful in habitats where the otter feeds on preys with different proportions of indigestible remains.     

Predation by marine-feeding otters (Lutra lutra) in south-west Portugal in relation to fluctuating food resources

Patterns of predation by otters ( Lutra lutra ) inhabiting the Portuguese south-west rocky coast, were inferred from the analysis of 757 spraints collected along a 5-km stretch of shore, from November 1990 to October 1993. Undigested remains were identified, counted and measured; the length and weight of ingested prey was estimated from regression equations. Monthly fluctuations in diet were compared to changes in the abundance of the primary prey species along the coast. The most commonly taken fish species had median lengths between 6.7cm and 15.0cm, and median weights between 3.5 g and 34.2g. Corkwing wrasse dominated the diet in terms of biomass (51.6%), and was the most important prey in terms of numbers (22.6%). Gobies (19.4%), Valenciennes' blennies (15.0%), shannies (1 1.4%), crayfish (7.2%), and shore rocklings (4.1%) were other numerically important prey. The contribution in biomass of gobies (14.5%), shore rocklings (6.7%) and conger eels (5.5%) was also significant. The dominant prey species and sizes in the diet were consistent over the years. From late winter to early spring the diet was numerically dominated by corkwing wrasse and gobies, whereas for the rest of the year shannies, Valenciennes' blennies and crayfish were also important. The contribution of these last species in biomass was small at all times of the year, and the corkwing wrasse was always the dominant prey. Prey was twice as heavy in winter as in spring. There was close correspondence between seasonal variation in diet and fluctuations in the abundance of the primary prey along the coast, but most dietary variation could be accounted for simply by fluctuations in the abundance of corkwing wrasse. In south-west Portugal, the most important food resource for otters seems to be the corkwing wrasse, probably because they are large and easy to catch. Corkwing wrasse are also exploited by local fishermen, and the possibility of competition between otters and humans should be investigated.     

Determinants of Eurasian otter (Lutra lutra) diet in a seasonally changing reservoir

Otter diet in reservoirs is known to experience seasonal changes. We selected a reservoir with a large population of exclusively wintering great cormorants and seasonal changes in stored water volume to test the relative influence of abiotic and biotic factors on otter foraging ecology. DNA metabarcoding of otter spraints revealed a dietary change from autumn to winter. Otters had a diet dominated by the exotic goldfish in autumn, but predated intensively on the native northern straight-mouth nase in winter. This change was likely caused by predation of cormorants on goldfish and to fish biology. Secondly, macroscopic analysis of spraints revealed that otters shifted from a diet dominated by fish (in terms of biomass) to a diet dominated by red swamp crayfish during spring–summer, when the latter became overabundant. As revealed by modelling, this second shift was most likely influenced by the sudden increase in stored water volume in spring, but also by the cumulative effect of cormorant predation on fish during autumn–winter. Macroscopic analyses of otter spraints collected in a second reservoir with no cormorants revealed a lack of seasonality. Hence, the combined influence of both biotic and abiotic factors explained otter diet seasonality in a lentic-water novel ecosystem.

     

Feeding habits of the otter and the American mink in Bialowieza Primeval Forest (Poland) compared to other Eurasian populations

Diets of the otter Lutra lutra and the American mink Mustela vison were studied by scat analysis on five woodland rivers and streams in eastern Poland. Fish constituted 51% of food biomass consumed by otters in spring‐summer and 40% in autumn‐winter, with common fish (perch Perca fluviatilis, pike Esox lucius, and roach Rutilus rutilus) being captured most frequently by the otters. Amphibians (mainly Rana temporaria, which also dominated in the living community) made up 34% of otters’ food biomass in spring‐summer and 58% in autumn‐winter. American mink relied on three prey groups: fish (40% in spring‐summer, and 10% in autumn‐winter), frogs (32% and 51%, respectively), and small mammals (21% and 36%). Out of available Micromammalia, mink strongly selected the root vole Microtus oeconomus. The cold season diet of both otter and mink depended on river size. On small rivers with forested valleys, otters and mink fed nearly exclusively on amphibians (72–90% of food biomass). With size of a river increasing and riverside habitat becoming more open (sedge and reed marshes instead of forests), otters shifted to catching predominantly fish (up to 76% in diet) and mink to preying on small mammals (up to 65% in diet).
Review of literature on otter and mink in Eurasia showed that their diets did not change with latitude (as indicators of climate severity and duration of water freezing) but they depended on habitats. In otter diet, the mean share of fish declined from 94% (SE 1.7) on sea shores, to 71% (SE 2.9) on lakes and fish ponds, to 64% (SE 2.8) on rivers and streams. The roles of amphibians and crustaceans increased in the same gradient (from 0 to 15%, and from 3 to 7%, respectively). On inland waters, the abundance of crayfish was the essential factor differentiating otters’ diet composition. In Eurasia, the staple food types of American mink on rivers and streams were fish (on average, 27% in diet, SE 3.9), mammals (30%, SE 5.0), and amphibians (17%, SE 4.8), whereas on lakes and ponds mink fed predominantly on birds (on average, 33% in diet, SE 10.1) and fish (28%, SE 9.5). In the Palaearctic region, over a wide gradient of habitats, otters appeared strongly specialised on prey taken from water, whereas American mink was a typical generalist capable of utilising several prey groups originating from both water and land.     

Prey selection in coastal Eurasian otters Lutra Iutra

Prey preferences and dietary differences between sex and age categories of Eurasian otters were studied in coastal Norwegian habitats Relative to their trapping frequency potential prey species with hard, spiny exoskeletons (crabs and sea urchins) or otherwise tough, spiny integuments (Labridae) were much less frequently found in spraints than fish species with soft integuments Spines did not protect fish with otherwise soft integuments from otter predation The number of non-fish taxa per otter stomach did not vary significantly between otter age categories despite presumed differences in hunting abilities (small cubs large cubs and subadults, adults) Relative frequency of occurrence of crabs and sea urchins was < 5% in the stomachs in each of these otter categories Anadromous, katadromous and freshwater fish species were infrequently eaten The coastal otter population during the study period probably had access to an adequate, and preferred, supply of marine fish prey
At the otter population level no prey size selection was conclusively demonstrated within the range of fish sizes sampled However, fish sizes eaten differed significantly between otter sex and age categories The fish sizes per stomach were on average larger in males than in females, regardless of age Adult males tended to eat the largest fishes Among the self provisioning age categories (subadult and adult otters) fish lengths differed significantly between otter males and females, but not between the otter age categories, and did not covary significantly with otter body length Fish eaten by females with old placental scars (potential mothers of fisheating cubs) were significantly smaller than those eaten by small cubs, provisioned by their mothers     

Estimates of daily food intake by an inshore population of Pleuronectes platessa L. off eastern Anglesey, North Wales

A sequence of trawl surveys showed that the diet of plaice off eastern Anglesey was dominated by Abra alba in spring and summer, and by Pectinaria koreni in early spring and autumn. Plaice ate little food in winter. Despite the relatively small stomach in this species, plaice were able to achieve high rates of daily food intake during bouts of heavy feeding by rapidly transferring newly-ingested prey items into the anterior intestine without full gastric digestion. Seasonal daily feeding rates (percentage body weight) varied between 5 and 10% for small fish (15–20 cm total length), 3 and 12% for medium fish (20–25 cm) and 2.8 and 4.4% for large fish (30–35 cm).     

Meiofauna as food source for small-sized demersal fish in the southern North Sea

Meiofauna play an essential role in the diet of small and juvenile fish. However, it is less well documented which meiofaunal prey groups in the sediment are eaten by fish. Trophic relationships between five demersal fish species (solenette, goby, scaldfish, dab <20 cm and plaice <20 cm) and meiofaunal prey were investigated by means of comparing sediment samples and fish stomach contents collected seasonally between January 2009 and January 2010 in the German Bight. In all seasons, meiofauna in the sediment was numerically dominated by nematodes, whereas harpacticoids dominated in terms of occurrence and biomass. Between autumn and spring, the harpacticoid community was characterized by Pseudobradya minor and Halectinosoma canaliculatum, and in summer by Longipedia coronata. Meiofaunal prey dominated the diets of solenette and gobies in all seasons, occurred only seasonally in the diet of scaldfish and dab, and was completely absent in the diet of plaice. For all fish species (excluding plaice) and in each season, harpacticoids were the most important meiofauna prey group in terms of occurrence, abundance and biomass. High values of Ivlev’s index of selectivity for Pseudobradya spp. in winter and Longipedia spp. in summer provided evidence that predation on harpacticoids was species-selective, even though both harpacticoids co-occurred in high densities in the sediments. Most surficial feeding strategies of the studied fish species and emergent behaviours of Pseudobradya spp. and Longipedia spp. might have caused this prey selection. With increasing fish sizes, harpacticoid prey densities decreased in the fish stomachs, indicating a diet change towards larger benthic prey during the ontogeny of all fish species investigated.     

Food habits of the American mink Mustela vison in the Mazurian Lakeland, Northeastern Poland

Food habits of the American mink Mustela vison were studied based on the analysis of 2364 scat samples, collected at three lakes in Northeastern Poland. The mink preyed on a wide range of prey, but two types of prey, amphibians and fish, dominated in the diet of the mink during all the seasons. Frogs, and first and foremost, the common frog Rana temporaria, were hunted by the mink, mainly from the late autumn until the early spring, and comprised up to 83.9% of the prey biomass (the multiannual average for November–December at the Majcz Wielki Lake). The most frequently eaten fish were cyprinids and percids. Seasonality of fish consumption by mink was not as well pronounced as in the case of amphibians. At the first two lakes, fish were hunted mainly in the winter and in the early spring, whereas at the third lake in the summer. The highest multiannual average share of fish in the diet of the mink was recorded in March–April at Lake Tuchlin (69.2% of the prey biomass). Crayfish, which were recorded in the diet mainly in the late spring and in the summer, comprised up to 59.6% of the prey biomass for May–June at the Majcz Wielki Lake. Birds, mammals and insects were supplementary food for the mink. During the breeding season, mink predation on waterfowl and their broods was correlated with the abundance of crested grebe Podiceps cristatus and coot Fulica atra nests in the area. The diet of individual mink varied considerably and the share of birds in the diet of the mink was related to the distance from individual mink dens to the colonies of waterfowl. In May–June, adult birds, chicks and eggs comprised up to 73.6% of the prey biomass of a female mink that inhabited a den located 100 m from the colony's edge. At all three lakes, the diet of the mink was the most diverse in the late spring and in the summer. In May–August, the values of the mink food niche breadths were about twice those noted in winter months.     

Diet of otters (Lutra lutra) in closely associated freshwater, brackish and marine habitats in south-west Portugal

The diet of otters was studied in closely associated freshwater, brackish and marine habitats, from spraints collected on the Portuguese south-west coast over an 18-month period. In areas where marine prey was the only available resource, diet was dominated by blennies, wrasses and gobies, but other prey was taken in areas near coastal lagoons, marshes and estuaries. Eels and amphibians were considered the typical prey of freshwater habitats, and grey mullet the typical prey of brackish water habitats. If the inland habitats near the coast were large enough, otters preferred to forage there rather than in the sea. In one area where otters alternatively used marine and inland habitats, the former were used most extensively in autumn and winter, and the latter in spring and summer. It is suggested that otters prefer to forage inland rather than in the sea.     

Spatial distribution and diet of the Neotropical otter<Emphasis Type="Italic">Lontra longicaudis</Emphasis> in the Ibera Lake (northern Argentina)

The seasonal spatial distribution and diet of the Neotropical otterLontra longicaudis (Olfers, 1818) were studied on Ibera Lake within the Esteros del Ibera, an important wetland of NE Argentina (Ramsar site no. 1162). Twelve lake perimeter sites were regularly checked for otter tracks and signs. The amount of signs was compared to environmental parameters to test their influence on otter presence and movements. A positive correlation was found between the amount of signs and the physical structure of the littoral areas, as well as vegetation structure. Lakeside otter presence decreased during the summer sampling throughout all sites. In order to determine otter diet, 205 spraints were examined. Otters fed mainly on fish (mostly Cichlidae), but also on crustaceans and molluscs. Other fish consumed were Characidae, Synbranchidae, Loricariidae and Erythrinidae. Seasonal variation was observed in diet composition: in summer, diet crustaceans and vertebrates other than fish increased. A higher percentage of benthic fish species was also observed in summer, while pelagic and benthopelagic species increased in winter. Such dietary changes may be explained by the different habitat use of otters in different seasons, from the lake coast (winter) towards more internal marshy areas of the wetland (summer).     

Seasonal and area-related variations in the diet of otters Lutra lutra on Mull

The diet of otters Lurra lutrn living in a sea loch on the Isle of Mull was described by means of spraint analysis. Seasonal and spatial differences in the spraint composition were explored in the context of fluctuations in prey availability, as revealed by trapping. Butterfish Pholis gunnellus and the cottids Myoxocephalus scorpius and Taurulus bubalis were the most commonly occurring prey in spraints. In the winter, the proportion of rocklings ( Ciliata spp. and Gaidropsarus spp.) and non-rockling gadoids (Gadidae) in the diet increased. Their relatively large size makes these latter species an important constituent of the winter diet. Seasonal and spatial variation in fish consumption largely reflected fluctuations in availability. The mean size of principal prey fishes in spraints was similar to that observed in the traps. These observations suggest that otters were not strongly selective with regard to fish species and size. Shore crabs, in contrast, were not taken in proportion to availability. The findings are discussed in the light of other studies of the diet of coastal otters. It is suggested that the lack of selectivity demonstrated in this study, compared with previous studies, may be explained by area-related variations in prey availability.     

Errors associated with otter Lutra lutra faecal analysis. II. Estimating prey size distribution from bones recovered in spraints

New methods of estimating the size of salmonids Salmo spp. and eels Anguilla anguilla consumed by otters Lutra lutra are presented, based on feeding trials involving captive, tame otters. These methods involve modelling the size-related differential recovery of key fish bones recovered in faeces (spraints) and avoid two sources of errors that may have occurred using previous techniques which relied solely on a series of correlations between fish length and the length of individual vertebrae. Sources of errors avoided are: (a) that vertebrae recovered in spraints could not always be assigned to the correct correlation equation for mean, maximum, or minimumsized bones; and (b) that the number of fish represented in a spraint was assumed to be one, in the case of similarly-sized vertebrae, and two in the case of bones varying considerably in size. We tested the use of salmonid atlas vertebrae to determine the largest minimal numbers estimate, the length frequency distribution of salmonids consumed, and to estimate the proportions of trout and salmon in the diet. Eels do not contain an atlas which is resistant to digestion and so equivalent estimates of the minimum numbers of fish represented in spraints are not possible. A model was therefore developed to estimate the distribution of lengths of fish consumed from the lengths of thoracic vertebrae recovered in the spraints using a series of equations. For each type of prey (salmonids or eels), the proportions of identifiable bones recorded in spraints were related to the original size of ingested fish. Such models greatly enhance the value of otter spraint analyses, particularly for size-selection studies.     

Seasonal and spatial differences in food selection by otters (Lutra lutra) in Shetland

Otters Lutra lutra in Shetland feed almost exclusively in the sea. Their diet was assessed from direct observations of 13, 313 dives, of which 27% were successful, and 2028 prey could be identified. The results are compared with published data on the availability offish for different seasons, time of day, state of tide, and different types of coast. The most frequently taken prey was eelpout Zoarces viviparus (34%), but they were relatively small, and rocklings Ciliata mustela dominated the diet in terms of biomass (18%, against eelpout 15%). Small eel-shaped, bottom-living species dominated in the diet at all times, but of those, otters took the larger fishes in the populations (median weight of prey 28 g). The size and species composition of prey of males was the same as that of females with cubs, but females without cubs took smaller fish.
In spring, prey was smaller than at other times, and otters were least successful when diving. Diving success and mean prey weight was highest in winter, although prey availability was highest in summer.
Eelpout were caught mostly along sheltered coasts, rocklings in more exposed areas. It is argued that for optimal exploitation of the seasonal availability of different species of prey, otters need to use different types of coast, and the size of their ranges would be related to the spacing of coastal types.
Most fishes were caught in daytime, and around high tide otters fed less than at other times; hunting therefore took place during periods of inactivity of prey. For the main prey species, Ciliata mustela , it was estimated that otters took a substantial part of the total population.     

FEEDING ECOLOGY OF THE MARINE OTTER (LUTRA FELINA) IN A ROCKY SEASHORE OF THE SOUTH OF CHILE

The marine otter ( Lutra felina ) lives exclusively along exposed rocky shorelines on the South American Pacific coast from Peru (6°S), to Cape Horn, Chile (56°S), and Isla de los Estados, Argentina. L. felina diet and its relationship to prey availability and energy content was assessed by spraint and prey remains analysis, direct observation, and the use of crab pots and fish traps, at four sites on the Valdivian coast in the south of Chile, between June 1999 and June 2000. Based on spraints analysis, the diet was composed of 25 species; 52% (13/25) of the species identified were crustaceans, 40% (10/25) were fish, and 8% (2/25) were mollusks. Crustaceans were found in 78% of 475 spraints, 100% of 929 prey remains, and 90.8% of prey determined by direct observation, fish in 20% of spraints and 9.0% of prey determined by direct observation, and mollusks in 2% of spraints and 0.2% of prey determined by direct observation. Observed seasonal variation in prey availability was reflected in the otter diet. Fourteen prey species were trapped; 43% (6/14) were crustaceans and 57% (8/14) fish, crustaceans were 93% of 566 trapped individuals, fish 7%. L. felina showed opportunistic feeding behavior, selecting prey seasonally according to their availability rather than to their energy input.     

Eurasian otter (<Emphasis Type="Italic">Lutra lutra</Emphasis>) diet and prey selection in Mediterranean streams invaded by centrarchid fishes

The diet of the Iberian otter (Lutra lutra) was determined by analysing 547 spraints collected at 28 sites within a wide area invaded by centrarchid fishes (pumpkinseed sunfish, Lepomis gibbosus and largemouth bass, Micropterus salmoides): the middle Guadiana basin (South-west Iberian Peninsula). Fish was the otters’ main prey, representing more than 60% of total individuals and more than 80% of total biomass. Otters preyed on most of the fish species captured in the field; however, the consumption of centrarchids was low compared to their abundance in the streams, and Jacobs’ index of preference showed a clear rejection of both species by the otter. Consumption of native fish genera (Squalius, Barbus and Chondrostoma) by otters increased in relation to their increase in the environment. In contrast, increasing numbers of L. gibbosus in the field was not reflected in otter consumption. The general decline of native freshwater fishes in Iberian rivers, the preferred prey of otters, together with the spread of exotic fish species (centrarchids and others) could put otter populations at risk.     

Amphibians in Eurasian otter Lutra lutra diet: osteological identification unveils hidden prey richness and male‐biased predation on anurans

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Do non‐native fish as prey favour the conservation of the threatened indigenous Eurasian otter?

1. Biological invasions are considered a major threat to biodiversity. Most research has focused on the distribution, biology and impacts of non‐native species on native fauna and flora. However, few studies have explored their role as prey for native predators of conservation concern. 2. To assess the incidence and intensity of predation by the Eurasian otter Lutra lutra on established non‐native fish species, data were collated from the published literature. To be selected, studies had to cover at least 1 year, analyse more than 100 spraints and report the study period and percentage relative frequency (%RF) of all prey fish species. 3. To permit reliable, time‐related comparisons with %RF of non‐native fishes in otter diet, we also reviewed available information about both the distribution of non‐native fishes and history of their introductions to European countries, revealing a decrease with longitude in the number of naturalised non‐native fishes taken (ranging between 5 and 34) and their percentage in each fish assemblage. 4. Our selective criteria were met by 30 dietary studies from 44 study areas in 15 European countries during 1970–2010. The extent to which otters rely on non‐native fishes was almost negligible (mean %RF = 4.8), with the number of non‐native fishes preyed upon by otters decreasing with both latitude and longitude. 5. The %RF of non‐native fish in the diet increased slightly with time, with otters preying significantly more on non‐native fish in study areas where alterations of the fish assemblage had been highlighted in the reference papers. No relationship was found between otter diet breadth and the occurrence of non‐native fishes in their diet. 6. The current role of non‐native species in otter diet suggests that effective otter conservation management plans should focus on the maintenance and/or enhancement of native fish assemblages.     

The food of feral mink (Mustela vison) in Scotland

Feral American mink ( Mustela vison ) thrive in Scotland. The potential impact of the mink on the native fauna was investigated through its food. Fifty-five stomachs and 33 scats were analysed by identifying the indigestible remains. Fish formed the main prey (49% occurrence) and birds and mammals 28% and 23% respectively. Most of the fish eaten were Salmonidae (brown trout and salmon). No remains of eels were found.
Mink may compete with otters for food, but the smaller prey taken by the mink and its greater use of land separates it from the otter. Mink seem to be occupying a vacant feeding niche in Scotland.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.