A Q U A T I C E X H I B I T S 157

an adult Black-footed penguin and 800-900 g for a Humboldt penguin; in summer each species eats 3040% less.

Since the Wave Cove provides the animals with an almost natural habitat in which to live, successful births are expected each year. So far two Californian sealions, three South African fur seals and one Steller’s sealion born at Ocean Park are still alive. Newborn pups are not kept in the cove but are moved with their mothers to the Veterinary Hospital until they have been weaned. If at all possible the mother and young are kept together even if the mother refuses, or is unable, to nurse. When aged one- and-a-half to two years some of the pups are transferred to the Ocean Theatre where they are trained to perform in the marine mammal show which takes place three or four times a day. Occasionally they are returned to the Wave Cove after having performed in the theatre for two or three years; we have experienced no problems with such reintroductions.

Int. Zoo Yb. (1987) 2 6 157-163

To increase their resistance to disease all pinnipeds receive regular inoculations of the erysipelas and Pseudomonas pseudomallei vaccines.

In order to improve and strengthen the existing Wave Cove exhibit a renovation project is now under way, due to be completed in mid-1987. At that time the exhibit will have become part of an exhibition centre combining marine life display with educational exhibitions on themes such as ‘seashores’, ‘stories of marine mammals and penguins’ and ‘wave and tide’. The tank will also have been redecorated to simulate an Antarctic habitat and it is intended that even more varieties of marine mammals will be expressing their welcome to our visitors.

PRODUCTS MENTIONED IN THE TEX?

Isoeal: milk-replacement formula, manufactured by Mead Johnson & Co., Nutritional Division, Evansville, IN 47721, USA.

Manuscript submitted 30 September 1986; revised January 1987

0 The Zoological Society of London

Breeding European otters

in the new otter exhibit at Krefeld Zoo Lutra 1 . lutra

PAUL VOGT Assistant Director, Krefelder Zoo, Uerdinger Strasse 377, 4150 Krefeld 1, West Germany

The European otter Lutra 1. lutra is an attractive but delicate animal which needs a carefully planned enclosure (Duplaix- Hall, 1972). At Krefeld Zoo plans for an otter exhibit were started in 1980; it was to form part of a complex also containing Servals Felis serval and Aardwolves Proteles cristatus. The design was

influenced by the layouts of existing successful exhibits especially those at the Norfolk Wildlife Park (Wayre, 1972) and Innsbruck Zoo (Pechlaner, 1980), although additional features were incorporated. In particular we hoped to build a natural-looking enclosure in which breeding and rearing could occur

I58 A Q U A T I C E X H I H I T S

t : : : : : I 5m 10m

Fig. I . Plan of the enclosure for European otters Lurrci 1. lutrtr at Krefeld Zoo showing the location of the two underground tunnels (dotted lines) leading to the den normally used for sleeping and in which the 9 gives birth.

without the need for separation of the 5 'it any stage.

EXHIBIT 'The enclosure (Fig. 1) lies on a flat open ;ires 250 m2 and receives shade from three birch and some larger trees about 15 m to the west. Half the area consists of an irregularly shaped pool 90-95 cm deep while the other half is comprised mainly o f earth planted with grass and small tmshes. The pool is fed by a small waterfall 90 cm high and water flows out by way of a pipe, the mouth of which is

protected by a metal grating; it is then filtered through 3 m3 of coke and pumped back into the pool via the waterfall. A supply of fresh water, but no chemicals, is added to the recirculated water continuously. Surplus water overflows onto three shallow, planted swamp areas (Fig. 1). The water never freezes over completely in winter, owing to the action of the waterfall, the constant swimming of the otters and the use of additional water pumps when necessary.

Three large natural rocks, with hollows beneath them, form islands in the pool.

AQUATIC E X H I B I T S 159

Fig. 2. Cross section through the otter exhibit to show the slope of the pool base from the bottom of the enclosure wall to the land area, and the inclined electric fence.

The hollows are much used by the otters as feeding areas and for play. The outer edge of the pool is formed by a 90-95 cm vertical wall, the top of which is level with the ground, and the floor slopes up from the base of the wall to meet the land area. Both floor and wall are made of natural- looking concrete.

Otters are particularly expert at escaping from their enclosures, so all fencing has to be strong and inspected regularly (Duplaix-Hall, 1972). At Krefeld escape over the edge of the pool is prevented by a wiremesh fence (50 x 100 mm gauge), 50 cm high and strong enough the resist otter bites, which has been mounted at an oblique angle on the top of the outer wall; two electrified wires (18 OOOV) run along its length, one 10 cm above the water and the other near the top (Fig. 2). Most of the land area is surrounded by a 200 cm high wiremesh fence, the top 50 cm of which is angled inwards and has two electrified wires running along its length. Concrete foundations 50 cm deep lie beneath the fence to prevent the otters from digging their way out. A 50 cm angled wiremesh fence with electrified wires attached is mounted on an 80 cm high wall to form the back of the enclosure, extending over the pool as part of the waterfall (Fig. 3; Plate 1).

Scattered around the land area are large rocks and stones which the otters use for scent marking, and close to the pool is a sandy beach c.10 m2 (Fig. 1). A hollow log and a shallow indentation beneath one of the rocks are used for hiding and, especially, play activities.

Fig. 3. Sketch plan of the waterfall and fence forming part of the back of the otter enclosure.

The main sleeping and breeding den is located near the centre of the exhibit, hidden under a concrete mound which is covered with planted earth (Fig. 4). The den consists of a bottomless wooden box 50-75 cm high with three compartments, one measuring 150 x 75 cm and each of the other two measuring 75 x 75 cm, connected via circular openings 20 cm in diameter. The floor of the den is concrete and is electrically heated from underneath, the temperature of the interior being kept at about 20°C by a thermostatic control. An infra-red bulb provides additional heat when necessary. A thick layer of hay is provided as bedding and this has to be replaced regularly because moisture and algae are carried into the den on the animals’ fur. The otters obtain access to the den via two curved tunnels, 3 m and 6 m long and measuring 20 cm in diameter; the longer tunnel is entered from under water at the pool’s edge while the other has its entrance by the beach (Fig. 1). The length of the tunnels helps to prevent cold air from entering the den, and the small diameter ensures that much of the excess water on the fur is squeezed off as the otter runs towards the den. Although the diameter is within the range of 15-20 cm suggested by Duplaix-Hall (1972), some water is still brought into the den.

I 60 A Q U A T I C E X H I B I T S

Plate I. General view of the exhibit for European otters Lu/rn I lurra at Krefeld Zoo. The electric wire which runs above the fence hy the pool, the waterfall, the main den and the tall fencing at the back of the enclosure are all clearly bisible. B. Enckc~

Schmidt (1972) reports that European otters at Zurich Zoo were quite dry by the Lime they reached their dens because they first had to pass through a series of four 16 cm apertures. A relatively long tunnel of this diameter would, however, be a somewhat narrow space for the animals 10 manoeuvre easily so the tunnels at Krefeld were made slightly wider. A second den of almost the same size as the central one lies at one end of the exhibit And connects to a small isolation enclosure measuring 25 m2. This den is

not normally used except by the S and older cubs when the 9 is giving birth, and for some weeks after.

The exhibit was completed in 1981 and in June of that year a captive-bred pair of European otters was obtained from the Norfolk Wildlife Park. They were released into the enclosure in August and quickly adapted to their new surroundings. They are fed once a day in the afternoon on a diet of freshly killed chicken, pullets and beef, with each animal receiving r.750 g of food. In

A O I J A T I C E X H I H I T S 161

1

l m

-l- I

Fig. 4. The main den seen in cross section (top) and from above (bottom). c. concrete; h. heating system; i. insulation; ir. infra-red lamp. In the top diagram the entrance ways from the tunnels are shown as open dotted circles.

addition live freshwater fish, mostly trout Salmo trutta, are provided every second day. When cubs are being reared cod-liver oil is added to the diet and food is given twice a day, at 0900 and 1600 hours.

BREEDING The pair bred for the first time in the summer of 1982 and, with the exception of 1984, have produced and reared young each year since then. Litters from this

pair have consisted of 0.2 cubs in July 1982, 1.3 in June 1983, 2.1 in September 1985 and three in July 1986. In addition one of the 99 born in 1983 bred for the first time in July 1986, producing two young 12 days after her mother had given birth. Mating has been observed only in 1986, on 14, 16 and 17 April, but it was not possible to see clearly which of the 09 was involved on each occasion. Obviously these observations have not allowed us to

A Q U A T I C E X H I B I T S

make any accurate calculation of the gestation period, but Nowak & Paradiso ( 1 983) note that i t has been measured at 60-63 days in this species.

About four to five weeks before she is due to give birth the y will start to carry hay, algae, twigs and other materials into the den; physical signs of pregnancy are an increase both in the size of the abdomen and in the visibility of the nipples. About two weeks before giving birth she practically stops coming out of the den at all during the day and prevents other otters from entering. In 1983, for example. the two 1 I-month-old @ from the 1982 litter, which had until then shared the enclosure without problems, were seen on several occasions trying to enter the den from the water, only to back out again immediately. The 2, however. was tolerated for a few days longer. When the new litter was born the mother accepted no individuals into the den. The 3 and young 99 slept in the other den or outside since the weather was warm. Two weeks after giving birth the older 2 started to chase the juvenile fl; aggressively and after two months they had to be removed. At the same time as this aggressive behaviour started the adult 'I was seen swimming with the 3, but physical contact and play behaviour did not resume for a number of weeks. Three months after birth had occurred the 3 was seen to be sleeping in the same den as the 2 and young.

Since all the cubs born have been reared by the parents without problems, few observations on birth or the development of young have been possible. They start to leave the den at the age of about eight to ten weeks, at first only during the evenings and at night. The adult 3 usually appears interested in the cubs when they emerge. and will approach to investigate, but the 0 always chases him away. When the young are about ten weeks old the mother has been observed to carry them one at a time into the water and release them, whereupon they immediately swim back to shore or

to the tunnel entrance. From the age of 12 weeks they will appear for short periods during the day, and are seen playing with both their parents. They are usually removed from the exhibit at between the ages of six and 12 months and sent to other collections. In the wild, young usually remain with their parents for about a year and reach sexual maturity at between two and three years of age (Nowak & Paradiso, 1983).

The 3 has never initiated aggressivc encounters with the young but in 1983, when the cubs born that year were about six months old, they and the adult 5) began to show increased aggression towards him. He received several bite wounds and during one of the attacks succeeded in escaping from the enclosure. Eventually 1.2 of the juveniles were removed, leaving a single immature y. and the attacks stopped.

When two litters were born within a few days of each other in 1986, each of the $)$ gave birth in different dens; the 8 remained in the enclosure but had to sleep outside for the first few weeks. A certain amount of aggression has been observed between the two 99 following the emergence of the young from the dens, and sometimes a cub has been 'stolen' and carried to the wrong den, but on the whole the relationship between the animals is amicable.

Within the past four years 14 European otters have been born at Krefeld Zoo; all have been reared successfully by their captive-bred mothers and on no occasion has the adult 8 had to be removed. Only two of the young have died, one at the age of four months and the other at 14 months. The exhibit currently holds eight otters, three adults and five young, with six individuals having been sent to other collections. These active and charming animals have been a successful and popular addition to the zoo.

REFERENCES D ~ ~ P L A I X - H A L L . N (1972): Notes on maintaining river otters in captivity. inr. Zoo Yb. 12: 178-181.

A Q U A T I C E X H I B I T S 163

NOWAK, R. M. & PARADISO, J. L. (1983): Wa/kef"s mammals of lhe world (4th edn). Baltimore & London: The Johns Hopkins University Press. PECHLANER, H. (1980): Uber die Zucht des Fischotters irn Alpenzoo Innsbruck. In Der Fischotter in Europa: 255-260. Reuther, C . & Festetics, A. (Eds). St Andreasberg: Aktion Fischotterschutz.

SCHMIDT, c. R (1972): New otter exhibit at Zurich Zoo. Inr. Zoo Yb. 12: 83-85. WAYRE, P (1972): Breeding the Eurasian otter Lutro lutru at the Norfolk Wildlife Park. I n / . Zoo Yh. 12: 116-1 17.

Manuscript submitted 9 June 1986; revised December 1986

I n / . ZOO Yh. (1987) 2 6 163-170 O T h e Zoological Society of London

Observations on keeping the Pacific walrus

at Hanover Zoo Odobenus rosmarus divergens

LOTHAR DITTRICH Director, Zoo Hannover, Adenauerallee 3, 0-3000 Hannover 1, West Germany

The Walrus Odobenus rosmarus, as opposed to many species of pinnipeds, is not often maintained successfully in zoos. The usual life expectancy of three to eight years in captivity is much too short when compared with the natural life expectancy which might be up to 40 years (Nowak & Paradiso, 1983). According to the liter- ature I have researched (see Biblio- graphy), some 175 Walruses have been kept in Europe and the USA since the 17th century. All but 15-20 of these died before reaching the age of sexual maturity (five to seven years in the 8; five to six years in the 0 ) and, moreover, those few animals were all kept in this century. The Yearbook lists of animals bred in captivity show that only one collection, that at Rancho Palos Verdes in California, has had any success in breeding the species, recording births in 1975, 1978, 1981 and 1982; in addition my records show that a calf was born there prematurely in 1971. To my knowledge the opportunity for reproduction between captive Walruses has existed at only two other collections: ( 1 ) at Hagenbeck's Tierpark in Hamburg

where a pair was kept together from 1927 to 1940 (the 8 having arrived in 1923 and the 9 in 1927); (2) at Hanover Zoo where a pair has been kept since 1974, arriving as juveniles and reaching sexual maturity in captivity. Pregnancy has not been recorded at either collection, however. In all other cases where animals over the age of eight years have been kept these have been maintained as singletons or, where more than one animal has been held in the collection at one time, the sexes have been kept apart.

Four Walruses have been kept at Hanover Zoo since 1965. The first two, both 6, arrived together and were of the Atlantic subspecies 0. r. rosmarus; one died in 1967 and the other in 1970. The pair currently maintained, 'Boris' and 'Tanja' (Plate l), arrived on 28 September 1974 from Zoo-centr Moscow, their documentation showing them to originate from the Walrus population with breeding grounds on the islands and coast of the Bering Sea; they belong, therefore, to the Pacific subspecies 0. r. divergens. Both young animals were said to have