Two Families in the Order Pinnipedia are found in Australian waters: the Otariidae (eared seals; fur-seals and sea-lions) and the Phocidae (true or earless seals). Otariid species found in Australian waters are the Australian fur-seal (Arctocephalus pusillus), the New Zealand fur-seal (Arctocephalus forsteri), the Australian sea-lion (Neophoca cinerea), the subantarctic fur-seal (Arctocephalus tropicalis) and the Antarctic fur-seal (Arctocephalus gazella). The southern phocids include the leopard seal (Hydrurga leptonyx), southern elephant seal (Mirounga leonina), Weddell seal (Leptonychotes weddellii), crab-eater seal (Lobodon carcinophaga) and Ross seal (Ommatophoca rossii). Southern elephant seals and leopard seals are seen frequently in Tasmanian waters and occur less frequently in other states. Weddell, crab-eater and Ross seals, Antarctic and subantarctic fur-seals and Hooker’s sea-lions (Phocarctos hookeri) are only occasional visitors to the Australian coast.

Typical lengths and weights of Australian pinnipeds are presented in Table 17.1. Figure 17.1 displays the approximate range of Australian and New Zealand fur-seals in Australian waters, the Australian sea-lion and Antarctic and subantarctic fur-seals, with details on their breeding range.

The southern elephant seal has a circumpolar distribution with a non-breeding range extending from the Antarctic continent to the tropics (Carrick & Ingham 1962). Most breeding occurs on islands on either side of the Antarctic convergence (Bonner 1994). It is not uncommon for healthy individuals to haul out in Australia, particularly on the Tasmanian coast, and New Zealand.

The leopard seal is the most widely distributed of the Antarctic pinnipeds, ranging between 50–80°S (Hofman et al. 1977). Although primarily a resident of the pack ice where breeding occurs (Siniff & Stone 1985), there is some movement of individuals to the subantarctic islands and the southern continents including southeastern Australia and frequently Tasmania (Gwynn 1953; Rounsevell 1988; Bonner 1994). Individuals hauling out in more northerly locations are commonly debilitated. Weddell, crab-eater and Ross seals also have a circumpolar distribution and are generally found south of the Antarctic convergence.

2 ANATOMY AND PHYSIOLOGY

2.1 Anatomy

Otariids and phocids differ anatomically. For example, otariids have prominent external pinnae, large fore flippers and smaller hind flippers that can be rotated forwards under the body to enable them to walk quadripedally, assisting in terrestrial locomotion. Propulsion through water is primarily from the long fore flippers, while the hind flippers control direction. In contrast, phocids are unable to rotate the hind flippers under the body and therefore have a less agile, slug-like terrestrial locomotion. They employ lateral undulating movements of the hind flippers and lower body for aquatic locomotion, steering with the fore flippers. Phocids lack external pinnae and the opening of the ear canal is barely visible just behind the eyes.

Table 17.1 Lengths and weights of Australian pinniped species

Figure 17.1 Approximate ranges a) Australian and New Zealand fur-seals in Australian waters; b) Australian sea-lions; c) Antarctic and subantarctic fur-seals and southern phocids. (Source: Csordas & Ingham (1965); Warneke (1982); Ling (1987); Shaughnessy & Warneke (1987); Brothers & Pemberton (1990); Goldsworthy et al. (1997);Irvine et al. (1997))

The flexible cartilaginous ribcage of pinnipeds extends more caudally than that of terrestrial mammals, so surgical access to some abdominal organs can be difficult. The skeletal muscle is dark red, almost black, because of the relatively high myoglobin concentration. Pinnipeds have a simple stomach and considerably longer intestinal tract than terrestrial mammals. The large intestine is relatively short, the small intestine can be up to 20 times longer than the large intestine (Richardson & Gales 1987; Rommell & Lowenstein 2001) and the caecum is vestigial (Rommel & Lowenstein 2001). The liver is large and multi-lobed and lies mostly to the left of the midline (Rommel & Lowenstein 2001). The kidneys are multi-lobed and venous drainage forms a superficial stellate plexus, visible on the kidney surface (Harrison & Tomlinson 1956).

The anatomy of the reproductive tracts is generally similar to that of terrestrial carnivores (Boyd et al. 1999). The male urogenital opening is found on the ventral abdomen caudal to the umbilicus and the female urogenital opening is found underneath the tail just ventral to the anus. Male pinnipeds have a baculum or os penis. The testes are scrotal in otariids, but are para-abdominal (deep to the blubber in the inguinal area) in phocids (Bryden 1967; Harrison 1969). The uterus is bicornuate.

The anatomical adaptations of the pinniped eye maximise visual sensitivity and visual acuity in air and in water at low light intensity. The eye is characterised by a large globe, high density of photoreceptors, well-developed tapetum, large rounded lens and a slit-like pupil, which is generally vertical in orientation (Wartzok & Ketten 1999). There is a central circular fattening of the cornea, which should not be mistaken for a lesion. Tear production is constant and copious, typically producing a wet area below the eye when the animal is dry.

2.2 Integument and thermoregulation

Fur-seals have highly developed compound hair follicles consisting of a single guard hair follicle and several intermediate and underfur follicles creating an undercoat of dense fur which, by trapping air, has excellent insulating and water-repelling qualities (Scheffer 1964; Ling 1970). The blubber layer is comparatively thin in fur-seals with the pelage providing most of the insulative capacity of the integument (Rommel & Lowenstein 2001). In contrast, phocids have few or no secondary or underfur fibres (Scheffer 1964) and rely on a thick blubber layer for insulation (Ling 1965a). Sea-lions generally have a small number (1–4) of secondary or underfur fibres (Scheffer 1964) and, like phocids, rely on blubber for their primary insulation (Pabst et al. 1999). Moulting of the pelage occurs annually, generally during summer and autumn, except in the Australian sea-lion which moults on a 17–18 mo cycle; females moult approximately 4 mo after parturition (Higgins 1993). For most species, the moult involves the regeneration of the pelage only; in otariids, the moult can take several weeks to months (Rommel & Lowenstein 2001). Some phocids, including the southern elephant seal, undergo an extensive moult (Ling 1965b; Laws & Sinha 1993) in which large areas of the stratum corneum are shed with the hair. Southern elephant seals spend 4–7 wk ashore and fast during the annual moult (Ling 1965b), using blubber reserves for energy. The timing of the moult must be considered when remote monitoring devices are deployed on free-ranging pinnipeds, as the instruments are most commonly glued to the pelage and will be shed with the pelage during the moult.

2.3 Diving adaptations

Several anatomical and physiological adaptations contribute to the diving ability of pinnipeds. Foraging behaviour, and therefore diving strategy, differs between species. Fur-seals generally undertake short shallow dives (Gentry et al. 1986), whereas Australian sea-lions are benthic, foragers and dive to greater depths to forage on or near the sea floor (Gales & Mattlin 1997 and references therein; Costa et al. 2001). Phocids, especially Weddell and elephant seals, generally dive deeper and for longer than otariids, which is reflected in their degree of adaptation. A post-moult female southern elephant seal from Macquarie Island recorded a maximum dive depth of 1256 m and dive duration of 120 min (Hindell et al. 1991).

Diving adaptations increase transport, storage and conservation of oxygen, and aid thermoregulation in the aquatic environment. Physiological adaptations associated with the dive response (see 6.2.3) are reviewed by Lynch et al. (1999). Anatomical adaptations include a distensible dilatation of the ascending aorta, which facilitates the maintenance of mean arterial blood pressure and perfusion of the brain and heart during diving bradycardia (Elsner 1969; Drabek 1975). A sphincter surrounding the caudal vena cava cranial to the diaphragm, an enlarged caudal vena cava and the large venous reservoir of the hepatic sinus caudal to the diaphragm allow massive pooling of blood in the venous system and control venous return to the heart, preventing volume overload of the heart during diving (Harrison & Tomlinson 1956, 1963). Venous plexuses in the cervical, lumbar and renal regions may also have a blood storage function (Harrison & Tomlinson 1956). A pericardial retia and a duplicated caudal vena cava have been reported in some species (Harrison & Tomlinson 1956, 1963). Arteriovenous anastomoses, a network of intertwining arteries and veins, create vascular counter-current heat exchange systems that dissipate and conserve heat, particularly from the flippers, to control core body temperature (Riedman 1990). The intravertebral extradural vein provides a large alternative venous pathway from the brain and spinal cord (dural sinuses) that eventually empties into the caudal vena cava (Harrison & Tomlinson 1956, 1963).

Haematological adaptations include larger erythrocytes, lower erythrocyte counts, greater haematocrit and haemoglobin concentrations (Lenfant 1969; Ridgway 1972) and greater blood volume (Bryden & Lim 1969; Ridgway 1972) than in terrestrial mammals. Among the pinnipeds, greater haematocrit and haemoglobin values are seen in phocid seals (Lenfant et al. 1970; Horning & Trillmich 1997).

There are a few adaptive features of note in the respiratory system. Pinnipeds have a flexible ribcage which enables the thoracic cavity to compress during diving (Ridgway 1972; Pabst et al. 1999 and references therein; Rommell & Lowenstein 2001). Depending on species, the cartilaginous support of the trachea varies from complete cartilaginous rings to dorsally incomplete cartilage rings to only small ventral bars (King 1983), permitting its collapse during diving and, sometimes, anaesthesia. Last, the terminal airways are reinforced with muscle in phocids and cartilage in otariids (Denison & Kooyman 1973). Under compression during diving, the alveoli collapse and air can be forced into the reinforced upper airways of the bronchial tree; reducing exposure to nitrogen during diving (Pabst et al. 1999 and references therein).

2.4 Physiological data

The normal adult heart and respiratory rates are 60–120 beats and 3–6 breaths per minute respectively, but both vary considerably during stress or physical restraint. Body temperature is also variable (35.0–38.0°C) and is most reliably measured with a deep rectal thermometer.

3 REPRODUCTION

Pinniped reproduction is characterised by synchronised annual parturition and postpartum mating within a few days or weeks of parturition (Stirling 1983). The Australian sea-lion is an exception as it has a 17–18 mo non-seasonal breeding cycle (Ling & Walker 1978; Gales et al. 1992) and the breeding season is asynchronous between colony sites (Gales et al. 1992). Southern phocids give birth on ice or land and have a 3–6 wk lactation period, during which females fast (southern elephant seal and leopard seal) or partially fast (Weddell seal) (Laws & Sinha 1993). Females remain near the pupping site and weaning is generally abrupt (Oftedal et al. 1987), resulting in a post-weaning fast of the young until they learn to forage on their own (Atkinson 1997). In contrast, otariids give birth on land and have a prolonged lactation, characterised by an initial intense nursing period followed by alternating periods of foraging at sea for 2–10 d (depending on species and individual) with terrestrial nursing. Weaning is more gradual in otariids (Oftedal et al. 1987) as pups begin to accompany their mothers on foraging trips to sea during the latter part of lactation.

Embryonic diapause is thought to be an obligate part of the reproductive cycle of all pinnipeds (Daniel 1981). The synchronicity of the seasonal pattern relies on this feature (Boyd 1991a) as mating occurs close to parturition and in most pinnipeds the period of active gestation is approximately 8 mo (Daniel 1981; Boyd 1991a). The Australian sea-lion, however, is thought to have an active gestation period of up to 14 mo (Gales et al. 1997). Embryonic diapause occurs when the embryo reaches the blastocyst stage; cell division slows and there is a delay of 2–4 mo, depending on gestation length, before the blastocyst reactivates and implants (Daniel 1981).

Sexual maturity in pinnipeds occurs at 2–7 yr of age and is dependent on species, sex and environmental factors affecting growth rate (Atkinson 1997; Boyd et al. 1999). The age of sexual maturity in males is more variable and, although often capable of spermatogenesis at 3–6 yr of age, many are not behaviourally capable of breeding until 8–10 yr of age (Atkinson 1997).

Table 17.2 Reproductive parameters for Australian pinniped species

Otariids and southern elephant seals are highly gregarious, polygynous and sexually dimorphic; bulls defend individual terrestrial territories. Slight reverse sexual dimorphism is seen in the Antarctic ice breeding seals, which generally maintain aquatic territories (Stirling 1983).

Table 17.2 outlines reproductive parameters for each species.

4 HUSBANDRY

The housing and husbandry requirements of pinnipeds are specialised.

4.1 Housing

Captive pinnipeds should have access to dry resting areas and at least one pool of sufficient depth and size to allow the animals to perform their natural behaviours. Otariids are good climbers and high fencing is required for these species. Pools with gentle sloping sides are best for all phocids and otariid pups, allowing them easy access into and out of pools and a place to rest in shallow water. The substrate should not contain objects that can be worked loose, such as rocks, as pinnipeds often ingest foreign objects. Air and water temperature should be maintained within a range that is consistent with the natural geographical range of the species. Sweeney and Samansky (1995) recommend the following guidelines for water temperature for pinnipeds: 0–24°C for polar species, 7–27°C for temperate species and 13–29°C for tropical species. Pinnipeds are much more tolerant of cold than of high temperatures, but extremes of both should be avoided. Ambient temperatures of 26–28°C approach the upper thermal limit for most pinnipeds and they should have access to water (pools, hosing, sprinklers) under such conditions to avoid heat stress. Outdoor facilities should have a shaded area to protect from direct sunlight and heat. Lighting should mimic the natural photoperiod for the species as closely as possible and natural lighting is preferable. Ideally, off-exhibit holding areas should have a large flat dry area that can be isolated from pools. This can be used for veterinary procedures, isolation/quarantine and to isolate mothers and pups. A sloped shallow depression at one end of the dry area that can be filled with water is useful for young pups or debilitated animals. Pools should be cleaned regularly – the cleaning interval is usually determined by the number of animals, type of pool and type of life-support system used to maintain water quality.

Social species should not be housed alone unless there are specific reasons for doing so, e.g. isolation due to illness, medical treatment or quarantine. Interspecific and intraspecific aggression, sex ratios and individual compatibility also need to be considered when housing pinnipeds together. Non-social phocid species, such as the leopard seal, should not be housed with other species due to territorial aggression. They often require individual housing, however, compatible females can sometimes be housed in pairs if provided sufficient space.

Although a relatively small number of wild southern phocid species, such as the leopard seal and southern elephant seal, have been held in captivity, they traditionally have had poor long-term survivorship, most likely resulting from inadequate husbandry and poor acclimatisation. Consequently the suitability of these species, particularly the southern elephant seal, for captivity is questionable. Leopard seals have been maintained successfully for several years but few have survived long-term in captivity. Survivorship of southern elephant seals in captivity has been very poor. A thorough understanding of biology and husbandry requirements, and the ability to provide adequately sized enclosures with appropriate air and water temperatures, is critical for their health and survival in captivity.

4.2 Hospital and quarantine housing

Pinnipeds undergoing veterinary care, quarantine or rehabilitation can be held in pens for several weeks without access to water for swimming. However, they are more content if they have free access to water and ideally should be provided with a pool, at least large enough for the animal to immerse itself. The water must be changed daily or turned over by placing a slow-running hose in the pool, such that it constantly overflows. Pools must be cleaned regularly. Water does not need to be salinated for short-term holding. Where animals have no access to water, drinking water must be provided. These animals also enjoy being hosed. Pens should have non-abrasive washable floors, be well-ventilated and large enough for the animal to move around freely. A slightly raised, preferably slatted, platform should be provided as a dry resting area. Pups sometimes like to hide or sleep in a roomy pet-pack or crate within the holding area.

Salt water is preferred, although pinnipeds can be housed long-term in fresh water. Oral sodium chloride supplementation is required for all pinnipeds held in fresh water to ensure general well-being (see 5.4). When the use of natural seawater is not possible, some institutions use artificial seawater salts. Good water quality is essential for the health of captive pinnipeds. Some pools are maintained as an open seawater system, with minimal to no filtration. Semi-closed and closed systems require filtration, or pools need to be emptied and filled regularly. Chlorine, ozone and ultraviolet irradiation are commonly used for disinfection of water in marine mammal pools. Chlorine, ozone and, less frequently, copper are used to remove algae. Monitoring levels of oxidative compounds such as chlorine and ozone is critical as excessive amounts may result in corneal damage (Stoskopf et al. 1983). Bromide, a component of fresh water, seawater and organic matter, is oxidised to bromine when exposed to chlorine or ozone, and bromine in excessive amounts is irritating to tissues. Water should be tested regularly for temperature, pH, salinity, chlorine, bromine (if oxidants such as chlorine or ozone are used), any added chemicals, and bacteria. Daily water testing is preferred, although weekly testing may be adequate for established life-support systems. Pinnipeds can be maintained safely in water of pH 7.2–8.4, salinity 20–36 ppt and total chlorine below 1.0–1.5 ppm. Free chlorine should be maintained at approximately 50% of total chlorine, and combined bromine below 1.0 ppm. Total coliform bacterial counts are recommended to be less than 500 MPN (most probable number) per 100 mL of water (NSW DPI unpub), although less than 1000 MPN per 100 mL water is a commonly accepted international standard (APHIS 2002). Arkush (2001) provides more detail on water quality for marine mammal pools.

Figure 17.2 (a) An Australian sea-lion and (b) a leopard seal trained for dental examination.

Animals should be weighed monthly to monitor body condition and health. If there are health concerns animals should be weighed more frequently. Captive pinnipeds can and, where possible, should be trained to facilitate veterinary examination and procedures, including blood collection (Fig. 17.2). Behavioural enrichment is also important for pinnipeds and can be achieved through socialisation, training and enrichment activities such as toys and feeding activities.

4.5 Transport

Cages or crates are ideal for transporting pinnipeds. They must be well-ventilated and large enough to allow an animal to stretch full length, raise its head and turn around. Openings must be small enough to prevent the animal biting anyone through them, but large enough to allow the animal to be cooled by wetting. Internal plywood panelling can prevent the animal from damaging its teeth on cage mesh, but ventilation must not be compromised. An adequate number of handholds should be placed around the outside of the cage or crate so that it can be kept reasonably level when lifted and moved, and to prevent handlers from being bitten.

Fish fed to pinnipeds should be of a quality suitable for human consumption. To retain its nutritive value and quality, fish should be quick-frozen, packed in containers that are impervious to air and moisture, labelled with the date of packaging and stored at or below –23°C (Chrissey 1998; Geraci 2000a). Storage time should not exceed 6 mo as, even under optimum freezing conditions, fats become rancid due to lipid peroxidation. High-fat fish, such as mackerel and herring, deteriorate more rapidly and should be stored for a maximum of 4 mo.

To minimise nutrient loss, dehydration, lipid peroxidation and rancidity, microbial contamination and loss of palatability, the preferred method of thawing is in a refrigerator at 4–6°C (Chrissey 1998; Geraci 2000a). Fish can be thawed in cool potable water (21°C or below), preferably under running water, but this method results in increased leaching of nutrients (Chrissey 1998). Fish should not be thawed at room temperature or left soaking in water as this will reduce quality and lead to increased microbial contamination. Once thawed, fish should be refrigerated or kept on ice. Unused fish should be discarded after 24 hr. Fish should not be thawed and refrozen.

Fish are the intermediate hosts for many parasites of marine mammals, particularly helminths. Freezing is one of the most effective means of killing these parasites and the effectiveness of this method depends on several factors: temperature of the freezer, length of time the fish is held frozen, type of parasite and mass of fish in the container/box. Cestodes are more susceptible to freezing than nematodes and trematodes appear to be more resistant than nematodes. Thus the freezing time required to kill different parasitic species varies and all parts of the fish must be frozen at a low enough temperature for long enough that all parasitic larvae are killed. The lower the freezing temperature, the less time is needed to kill the parasites. The US Food and Drug Administration recommends that freezing and storing of fish at –20°C or below for 7 d, or freezing and storing at –35°C or below (commercial blast-freezing) for 15 hr, is sufficient to kill parasites (FDA 2001). All parts of the fish must reach these freezer temperatures for the recommended duration. Some bacterial pathogens found in fish can survive freezing temperatures and resume growth when thawed. This highlights the importance of using thawing techniques that do not create conditions favourable for pathogen growth. In most cases pathogen growth is very slow below 10°C, and 4.4°C is below the minimum growth temperature of most pathogens. Pathogen growth is relatively fast at temperatures above 21.1°C (FDA 2001).

5.3 Feeding

When formulating diets for pinnipeds, age, species, climatic conditions and body condition of the animal need to be considered. The optimal daily intake for young growing animals is 8–15% of body weight and for adults 4–8% of body weight, depending on the fat content of the fish. Whole fish should be fed whenever possible, as cut or eviscerated fish have lower nutritional value. The total daily ration is better tolerated if spread over the course of a day, preferably divided into three feeds. Occasional reduced intake or refusal of one or two meals is not a concern. In fact, well-blubbered animals can safely go without food for several days, or reduced food intake for several weeks. It is normal for food intake to decrease significantly during moult or the breeding season; some species, e.g. the southern elephant seal, fast during moult. Fasting also occurs during lactation in some species, e.g. leopard seals and southern elephant seals. It is very important that food type, amount eaten and feeding behaviour are recorded daily for each individual. The amount of fish eaten per feeding session is calculated by subtracting the weight of leftover fish from the total amount in the bucket prior to feeding.

Most pinnipeds eat more readily in water than on land. Captive pinnipeds are accustomed to frozen-thawed fish fed by hand, but free-living pinnipeds brought into captivity will rarely feed voluntarily. Whole fish can be thrown or offered by hand to the animal. If this is unsuccessful, fish can be left on the enclosure floor or in the pool but must be removed within 12 hr. It is common for one to several days to pass before newly captive pinnipeds voluntarily take fish. Animals that do not begin to take fish voluntarily after several days, or are severely debilitated, will require force-feeding (see 5.5). Live fish can be used to initiate feeding if an animal refuses to accept frozen-thawed fish and is considered too dangerous to force-feed. However, this method is not commonly employed due to a lack of consistent supply of appropriately sized fish.

5.4 Nutritional supplementation

Some species of fish commonly fed to captive pinnipeds contain endogenous thiaminases that destroy thiamine (vitamin B1). Vitamin E is depleted in fish by oxidation of polyunsaturated fatty acids during frozen storage. Therefore, pinnipeds fed frozen fish diets should be supplemented with 25–30 mg thiamine per kg of fish fed and 100 IU vitamin E per kg of fish fed (Geraci 2000a). Thawing of fish, particularly in water, results in leaching of vitamins, minerals and salts. Commercially available (Aquatic Mammal Chewables, Vetafarm; Vita-Zu mammal tablets, Mazuri) or compounded multivitamin-mineral supplements 2–3 times per week will typically compensate for vitamin and mineral losses in a frozen-thawed fish diet (Geraci 2000a). In addition, pinnipeds housed in fresh water must be supplemented daily with 2–3 g sodium chloride/kg of fish fed to prevent hyponatraemia (Geraci 2000a). All of these supplements are available in tablet or capsule form and can be inserted into the fish via the gill flaps. Put the daily supplement requirement, based on expected total food intake, into one or two fish and offer the medicated fish prior to the main feed.

Physical restraint can be hazardous to handlers as pinnipeds are quick and agile and inflict severe bites. Therefore, the capture and restraint of any pinniped should be undertaken with extreme care and only by experienced handlers. Additional restraint can be achieved by placing a head bag, which is a hessian or ventilated canvas bag on a net hoop, over the head to reduce vision and, if deep enough, to pin the pectoral flippers against the body (Fig. 17.3). The head and neck can be briefly restrained further by pinning with the net hoop or a concave handlebar attachment on a pole, though care must be taken not to impede respiration.

Figure 17.3 Capture of a southern elephant seal using a head bag. Photo: Corey Bradshaw.

Chemical restraint demands as much planning as physical restraint. Pinnipeds can be expected to flee or attack following drug administration, risking entry to the water or misadventure on cliffs, ledges, pool edges or abrasive substrates. For more aggressive species or individuals, pursuit of handlers can sometimes be used to lure animals away from such threats. Pinnipeds can be blocked from hazards by herding boards, or they may be physically restrained for drug administration. Pools should be emptied and covered or fenced off, or the procedure performed in the bottom of the pool. When physical restraint is not used, the risk of fight can be reduced by not crowding close to the animal, keeping a low profile, avoiding eye contact and using low-impact light-weight gas injection darting systems (Lynch et al. 1999; Higgins et al. 2002). In general, fur-seals are more easily disturbed than sea-lions and phocids. Interaction by conspecifics, especially during the breeding season, can pose a threat to the animal and to handlers, and can impede anaesthetic induction by stimulating the patient.

6.2.2 Drug administration

Inhalation agents offer the best control of anaesthetic depth but require physical restraint if used as induction agents. IV induction of southern elephant seals is routinely performed with highly reproducible results; during manual restraint the agent is administered into the intravertebral extradural vein (see 7.1.2). IM injections are generally administered into the lumbar or gluteal muscles. Long needles are required to penetrate the blubber; minimum needle lengths of 3.8 cm are needed for smaller pinnipeds and up to 10 cm for large southern phocids. Hand injection can be performed using a needle attached to a pre-loaded 1.2 m extension tube. The needle is placed, the operator then retreats and injects the drug swiftly and flushes the tubing with saline to ensure the entire dose has been administered. This useful technique can often be performed with only herding boards for restraint. Administration by dart is the least reliable method, but has the advantage of not requiring physical restraint. It is therefore useful with intractable animals, when insufficient skilled handlers are available or if physical restraint poses a risk to the seal or handlers due to heat stress or other physical hazards. Darts should generally be fired into the lumbar or gluteal musculature, as the skin and blubber are thinner in this area. They should hit perpendicular to the body surface to avoid ricochet or deposition of drug into the blubber, and gun pressure should be moderated to prevent the dart from rebounding. Light-weight air-pressurised plastic darts elicit least response from the animal (Higgins et al. 2002).

Cardiorespiratory emergencies can occur in any species, although predispositions vary depending on the species and chemical restraint method used. Although adaptations allow pinnipeds to survive periods of apnoea during diving (see 2.3), they should not be relied upon to function normally under the influence of anaesthetic agents. The pharmacokinetics of anaesthetic agents may also be affected by apnoea (Woods 1994). The degree of anatomical and physiological adaptation varies considerably between species—anaesthetised southern elephant seals commonly tolerate 8–20 min periods of apnoea during anaesthesia (Slip & Woods 1996; Woods et al. 1996), while shorter-diving leopard seals, crab-eater seals and otariids appear no more tolerant than terrestrial mammals. However, any apnoea should be cause for concern and increased diligence, as in terrestrial mammals. As movement of the nares and thoracic wall sometimes occur without sufficient inspiratory volume, diligent monitoring of blood oxygen saturation (pulse oximetry), end tidal CO₂ (capnography) and expired air volume is essential (Lynch et al. 1999; D Higgins pers. obs.).

The ability of the phocine trachea to collapse dorsoventrally often predisposes these species to inspiratory obstruction, especially when the cervical musculature is relaxed. In addition, large or male phocids and otariids are prone to respiratory obstruction by pharyngeal and palatine soft tissue. The flexible thoracic structure and elastic pulmonary interstitium of pinnipeds makes larger animals particularly susceptible to progressive pulmonary collapse and ventilation–perfusion mismatch and, although the literature is equivocal, Robin et al. (1963) suggest that phocid respiration is poorly stimulated by hypercapnoea. This, and observations that end tidal CO₂ readings of otariids and phocids tend to rise throughout extended procedures despite regular respiratory rates (J Barnes, M Lynch & D Higgins, unpub), suggest that positive pressure ventilation should be seriously considered where procedures exceed 20–30 min (i.e. where the improvement of ventilation outweighs the disadvantages of prolonging the procedure by intubation, the greater depth of anaesthesia required for intubation and the risk of stimulating vomition in non-fasted free-ranging pinnipeds). In addition, end tidal CO₂ readings (without associated tachypnoea) of Australian sea-lions immediately after gaseous induction appeared to be higher in animals that had been physically restrained for longer before induction (D Higgins pers. obs.). Capnography and positive pressure ventilation should be considered for anaesthetised pinnipeds where manual restraint has been vigorous or prolonged.

The possible influence of physiological adaptations for diving in the management of pinniped anaesthesia remains poorly defined. These adaptations, known collectively as the dive response, are most developed in the deep-diving phocids. Literature on the phenomenon is reviewed by Lynch et al. (1999). The response comprises apnoea, bradycardia, peripheral vasoconstriction and redistribution of blood flow so that circulating blood is mostly limited to vital organs such as the heart and brain and pooling of blood in the caudal vena cava and hepatic sinus. Although bradycardia is vagally mediated and several authors have suggested the use of the parasympatheticolytic drug atropine as a preventative, its efficacy has not been formally assessed and the authors found no apparent disadvantage to omitting it. The dive response is often reported to be a cause of death during anaesthesia, however, without detailed monitoring equipment the presentation of apnoea and bradycardia is often difficult to distinguish from that of cardiorespiratory depression from other causes, e.g. profound anoxia or pharmacological depression.

All pinnipeds have low surface area to mass ratios and either subcutaneous blubber or dense fur coats. They rely on active peripheral vasodilation for cooling and anaesthetic agents can interfere with these mechanisms. Therefore, pinnipeds are susceptible to hyperthermia during anaesthesia and body temperature should be monitored by feeling the skin, especially the flippers, for hot areas. Ideally a rectal thermometer should be used to measure body temperature; in larger animals a long probe may be required for accurate measurement of core body temperature. Animals can be cooled by application of cold packs to the extremities and axillae, wetting the animal and using a fan. Extremes of cold can induce hypothermia (Gales et al. 2005), so thermal blankets and windbreaks should be kept on hand in cold environments.

6.2.4 Cardiopulmonary support and resuscitation

As apnoea and tracheal collapse are common causes of respiratory failure, particularly in phocids, in the authors’ experience endotracheal intubation alone is often inadequate to restore ventilation. Interestingly, endotracheal intubation has induced apnoea in southern elephant seals (Woods et al. 1996). Essential equipment for chemical restraint should include a method for positive pressure ventilation, e.g. an endotracheal tube and breathing bag or oxygen demand valve. Ideally, oxygen should be available for emergencies.

Visual endotracheal intubation is often impeded by the location of the larynx, which is caudal relative to many carnivores and is obscured by the soft palate and pharyngeal folds. Manual placement of the tube by feeling the laryngeal opening with the hand is the most efficient means in all but small pinnipeds, although for safety the animal must be completely anaesthetised and a gag firmly placed. In otariids, the tracheal bifurcation into the primary bronchi is more cranial compared to other mammals (King 1983), occurring at the thoracic inlet and not at the pulmonary hilus, as occurs in phocids (Rommel & Lowenstein 2001 and references therein). Therefore, in otariids the endotracheal tube should be placed just beyond the larynx, the cuff inflated and bilateral ventilation confirmed by thoracic auscultation. In the authors’ experience, ideal tube placement varies among phocids. In leopard seals, the collapsible nature of the trachea makes caudal placement desirable to bypass tracheal collapse during spontaneous inhalation. However, where an airtight seal is needed for positive pressure ventilation, the large tracheal diameter, relative to that of the larynx, makes placement of the inflatable cuff immediately behind the larynx more effective unless the cuff is very large.

Reports describing the use of cardiac and respiratory stimulants are uncommon and equivocal. The authors and Gales et al. (2005) have successfully stimulated respiration by administration of doxapram (1–2 mg/kg) IV in pinnipeds with adequate cardiac function. Peripheral venous access is often difficult to obtain during an emergency, particularly in otariids, and a jugular cut-down may be necessary to obtain reliable IV access. Peripheral administration of cardiac and respiratory stimulants to pinnipeds during cardiorespiratory collapse is often ineffective, although it is difficult to determine whether poor drug distribution is due to the dive response or simply to anoxic or pharmacological reduction of cardiac function. In such animals, Woods et al. (1996) and Higgins et al. (2002) report improved efficacy with intratracheal administration of doxapram (1–4 mg/kg) and adrenaline (1:1000, 0.02–0.06 mL/kg). Management of cardiopulmonary emergencies in southern elephant seals under field conditions has been described by Woods (1994).

It is not uncommon for phocids and otariids to become apnoeic during recovery. These animals generally respond well to stimulation, rocking, or intubation and ventilation provided the problem is detected before cardiac function is compromised. Close monitoring should be continued through the entire recovery phase, and extubation should be performed as late as safely practical.

6.2.5 Inhalation anaesthesia

Mask induction of anaesthesia with isoflurane in oxygen is becoming the method of choice for chemical restraint of pinnipeds that can be safely physically restrained, or sedated then physically restrained. Females of all ages and juvenile to subadult male otariids are commonly anaesthetised by this method and recent studies report induction of crab-eater seals (Gales et al. 2005), subadult leopard seals (J Barnes unpub) and Weddell seals (Bodley et al. 2005) with isoflurane 5% in oxygen 10–15 L/min. Typically, isoflurane 1.5–3% via mask or endotracheal tube is suitable for maintenance. Prior to induction, both phocids and otariids can be sedated with midazolam (0.25–0.5 mg/kg IM) to facilitate physical restraint. Significantly fewer complications are seen than in most studies using injectable agents alone. They include transient apnoea, which can be remedied by physical stimulation, and hypothermia in Antarctic conditions.

Field procedures necessitate equipment that is robust and portable and, in Antarctic conditions, heated (Gales et al. 2005). However, in the controlled environment of a zoo or rehabilitation facility, it is fleasible to use a standard vaporiser and closed circuit of appropriate capacity. Although pinnipeds use a greater percentage of their tidal volume at rest than do other mammals, their tidal volume is similar to that of other mammals (10–20 mL/kg).

6.2.6 Injectable agents: phocids

Tiletamine/zolazepam has been used for anaesthesia of thousands of southern elephant seals with few complications. IV administration into the intravertebral extradural vein (0.54 mg/kg) to over 1000 seals immobilised them within 1 min and lasted 20 min without fatality and without apnoea exceeding 5 min (Field et al. 2002). Thinner seals had longer recovery times. IM administration (1 mg/kg) to 15 seals produced heavy sedation in approximately 10 min, lasting approximately 10–50 min without fatality (Woods et al. 1994b).

Adult female Weddell seals have been effectively immobilised with IV tiletamine/zolazepam (0.50–0.65 mg/kg) without fatality or pronounced apnoea, whereas there was a 25% mortality rate with IM administration. A starting dose of 0.50 mg/kg IV is recommended for other age classes of Weddell seal and other phocid species (Wheatley et al. 2006).

Tiletamine/zolazepam IM (1.2–1.4 mg/kg) has been used successfully in approximately 50 leopard seals. Higgins et al. (2002) describe much more reliable induction and better airway maintenance than during chemical restraint with midazolam/pethidine. Induction is smooth, taking 19 min, anaesthesia lasts approximately 20–30 min and recovery is smooth, with mobility returning after cognitive function—an advantage in avoiding misadventure. The authors have used tiletamine/zolazepam (1–1.25 mg/kg IM) six times for induction of captive leopard seals prior to maintenance by inhalation anaesthesia (isoflurane) for up to 3 hr with one mortality occurring during an apparently normal recovery. Mortalities in free-ranging leopard seals associated with the use of tiletamine/zolazepam alone were two during apparently normal recoveries and one following accidental IV administration. All three seals that died during recovery were partially mobile and apparently breathing well, before apnoea occurred and was followed swiftly by cardiac arrest. The three seals had moderate to marked pulmonary congestion with interlobular oedema at necropsy. The findings concur with reports of resistance to positive pressure ventilation in these animals. We speculate that signs might be due to pulmonary hypertension but the cause of this is unknown and further investigation is needed to understand the pathophysiology during anaesthesia. Accidental IV administration induces rapid anaesthesia and profound apnoea; intubation and ventilation is sufficient to maintain the animal, but must be instituted rapidly. Differentiating induction and inappropriate apnoea from sleep and normal apnoea respectively can be difficult, and it is sometimes necessary to lightly rouse the animal to determine the difference.

Midazolam/pethidine combination has been used to chemically restrain southern elephant (0.04 and 4 mg/kg IM respectively), leopard (0.22 and 1.15 mg/kg IM) and crab-eater seals (0.25–0.4 and 2.4 mg/kg IM) (Woods et al. 1994a; Higgins et al. 2002; Tahmindjis et al. 2003). Response is variable, induction is inhibited by stimulation and the margin of safety appears to be small. In leopard seals, and to a lesser extent crab-eater seals, profound relaxation of the cervical musculature often causes partial to complete airway obstruction, even in animals that are insufficiently anaesthetised to be intubated. Compulsive locomotion is not uncommon and mobility can occur beyond loss of cognition, increasing potential for misadventure during induction and recovery.

A common problem encountered when using IM agents, especially when administered by dart, is incomplete induction. Presumably this results from deposition of some of the drug between muscle planes or, in the case of darts, deposition of drug into blubber as the dart transits this layer or fails to reach muscle. Fatalities have occurred when animals are given supplemental doses IM, presumably because agent deposited in tissues is absorbed later, leading to subsequent overdose. To deepen or maintain anaesthesia a different and more controllable agent, e.g. isoflurane in oxygen, is ideal. IV ketamine (1–3 mg/kg to effect) has been successfully used in a range of phocids, albeit in small numbers (Baker et al. 1988; Woods et al. 1994a; Tahmindjis et al. 2003; J Barnes unpub). Some mortalities have occurred during maintenance of anaesthesia with incremental IV tiletamine/zolazepam, but this has not been studied thoroughly.

Midazolam alone (0.25–0.5 mg/kg IM) is used commonly to facilitate physical restraint for minor procedures, or prior to induction with inhalation agents. Major determinants of the extent of sedation are the completeness and accurate placement of the injection and the seal’s degree of excitement prior to and during induction. Once restrained, if the level of sedation is insufficient, supplemental IV doses (0.1–0.2 mg/kg) have been used effectively to increase the depth of sedation (J Barnes unpub). Diazepam 0.1–0.5 mg/kg IM or IV can be used for mild sedation. Oral diazepam (0.2 mg/kg) has been used with unpredictable efficacy for light sedation in captive phocids (Gales 1989).

Benzodiazepines (midazolam and diazepam) can be antagonised with flumazenil 0.002–0.01 mg/kg IV or IM. More precise doses are yet to be investigated and determined. Opiates can be antagonised with naloxone 0.012 mg/kg or naltrexone 0.05–0.12 mg/kg IM. These drugs hasten recovery but reversal can be incomplete, restoring physical mobility without full return of cognitive function and thus increasing the potential for misadventure (Higgins et al. 2002; Tahmindjis et al. 2003). The duration of action of these compounds in pinnipeds is unknown. These antagonists are therefore best suited to hastening recovery in animals that are stable and well-oxygenated and can be observed beyond the expected recovery time for non-reversed animals, or for reversal of specific drug effects where anaesthetic control can be maintained by other means (e.g. inhalation agents or IV ketamine).

6.2.7 Injectable agents: otariids

Tiletamine/zolazepam (1.2–2.0 mg/kg IM) has been the most commonly used injectable induction agent in Australian otariids, producing reliable chemical restraint for approximately 20 min. All animals, but especially large animals, should be observed closely for pharyngeal obstruction during induction and are best intubated as soon as possible.

In recent years, medetomidine/ketamine combinations have been commonly used for induction of otariids. The authors have successfully used medetomidine (70–100 μg/kg) and ketamine (2 mg/kg) IM in Australian and New Zealand fur-seals, with successful reversal following administration of atipamezole (350 μg/kg IM). Medetomidine (140 μg/kg) and ketamine (2.5 mg/kg) IM (Haulena et al. 2000) and medetomidine (70 μg/kg) and tiletamine/zolazepam (1 mg/kg) IM (Haulena & Gulland 2001) have been used successfully in northern otariid species, using atipamezole (200 μg/kg IM) for reversal. A combination of medetomidine (13 μg/kg), midazolam (0.25 mg/kg) and butorphanol (0.4 mg/kg) administered IM produced light anaesthesia in aged California sea-lions and was effectively reversed with atipamezole (0.06 mg/kg), flumazenil (0.002 mg/kg) and naltrexone (0.1 mg/kg) IM (Spelman 2004). Although there are no reports of use of this combination in Australian otariids, it may merit consideration.

Midazolam (0.25–0.5 mg/kg IM) can be used to facilitate restraint for minor procedures or prior to induction of inhalation anaesthesia. It produces more reliable sedation following IM administration than diazepam and has a shorter duration of action.

7 CLINICAL PATHOLOGY

7.1 Blood collection

7.1.1 Otariids

Blood collection from otariids can be difficult due to the limited accessibility of peripheral veins. The most commonly used venipuncture sites are the caudal gluteal vein, the interdigital veins of the hind flippers, a brachial vein and the jugular vein.

The caudal gluteal vein is deep within the gluteal muscles and can be difficult to locate. It runs caudally lateral to the sacrum. To sample this vein the animal is restrained in sternal recumbency with the hind flippers spread. A needle is inserted perpendicularly, approximately one-third of the distance from the femoral trochanter to the base of the tail, just lateral to the sacral vertebrae (Geraci & Sweeney 1978) (Fig. 17.4). If the vein is not immediately found, the needle can be slightly withdrawn and ‘walked’ to either side (Clark et al. 2004). In smaller animals (<25 kg) a 20–22 G, 2.5 cm needle is used, in animals 25–100 kg an 18–20 G, 3.8 cm needle is used and in larger animals longer needles will be required.

Figure 17.4 Sites for blood collection in otariid and phocid seals. a) Intravertebral extradural vein in a phocid seal. b) Dorsal view of the left hind flipper showing interdigital veins which can be used in a phocid or otariid seal. c) Caudal gluteal vein in an otariid seal. (Source: Illustrations adapted from King (1983), Geraci & Lounsbury (1993), Sweeney (1993) and Bossart et al. (2001) and based on drawings by Bozena Jantulik.)

The interdigital veins can be visualised on the dorsal surface of the webbing of the hind flipper. Application of a tourniquet around the base of the hind flipper and warming the flipper can improve visualisation of these veins. The veins are small and the blood flow slow, so a heparinised butterfly catheter can aid blood collection (Gulland et al. 2001). An alternative site in the hind flipper is just proximal to the origin of the interdigital webbing on the dorsal surface. The needle is inserted at a shallow angle centrally in the inverted V that forms the proximal point of the interdigital webbing (junction of furred and non-furred area) in any of the interdigital spaces (K Bodley pers. comm.). Sometimes the vessel can be palpated between the index finger and thumb, which aids location of the venipuncture site, but more often the vessel is not palpable and must be attempted blindly. A better blood flow rate is obtained from this vessel than from the small vessels within the interdigital webbing. The use of a tourniquet and butterfly catheter and warming the flipper also improve the success of venipuncture at this site.

Another useful vein is the brachial vein, which is found on the medial side of the fore flipper in the loose tissue on the trailing edge of the flipper between the elbow and carpus (Fig. 17.5). It is usually an easily visualised vessel that is useful for venipuncture, catheter placement and IV drug administration in otariids. Rolling the animal onto its side or back and placing the flipper perpendicular to the body allows access to this vein. The vessel can be easily accessed in pups and physically restrained or sedated small pinnipeds, but large otariids require anaesthesia unless animals are trained for the behaviour.

Figure 17.5 Brachial vein—site for blood collection and IV catheter placement in otariid seals.

The jugular veins, which run from the angle of the jaw to the thoracic inlet, can be used for venipuncture but are smaller in pinnipeds than in other species (Harrison & Tomlinson 1963). The jugular vein is generally not palpable or visible except in pups and sometimes in adult animals in poor body condition. The vein can usually be located in the jugular groove in the mid-cervical region on a line running between the commissures of the lips and the point of the shoulder (Gage 2003). For emergency venous access in otariids, the subclavian vein can be located by inserting a needle perpendicularly into the angle between the sternum and the first rib (Gulland et al. 2001), or the cranial vena cava can be located by inserting a needle between the first two ribs close to the midline (Hubbard 1968). Both methods require dorsal recumbency and are not recommended for routine venipuncture. The intravertebral extradural vein (see 7.1.2) is generally not a recommended venipuncture site for otariids.

7.1.2 Phocids

The preferred site for venipuncture in phocids is the lumbar portion of the intravertebral extradural vein, which is a large valveless vein located dorsal to the spinal cord within the vertebral canal (Harrison & Tomlinson 1956, 1963). The seal is placed in sternal recumbency and an intervertebral space is located by palpating along the dorsal midline of the caudal lumbar vertebrae (L3-L5). A needle is inserted into the intervertebral space perpendicular to the skin until blood is observed in the hub of the needle (Fig. 17.4). For pups and smaller phocids (<50 kg) a 20 G, 2.5–3.8 cm needle is used and for larger phocids an 18 G, 8.9 cm spinal needle is used. Large Antarctic phocids may require needles that are 12.7 cm or longer. Large volumes of blood can be readily obtained.

The plantar interdigital veins of the hind flipper form a rich vascular network in the metatarsal region just proximal to the origin of the interdigital webbing (Geraci & Lounsbury 1993) and can be used for blood collection. These veins are located by inserting a 20–21 G, 2.5–3.8 cm needle at a 10–20° angle to the skin over the second digit or medial to the fourth digit, at the origin of the interdigital webbing (Geraci & Sweeney 1978) (Fig. 17.4). Interdigital veins are not visible on the surface of the webbing in phocids as the flippers are covered with fur.

7.2 Haematology and biochemistry

Reference ranges for haematology and biochemistry in pinniped species, particularly those in the southern hemisphere, are limited by sample size, especially within age or sex cohorts. Captive animals are often sampled during periods of clinical disease or abnormality, so results cannot be used to develop species-specific reference ranges and it is best that individual baseline values be obtained for captive animals (Bossart et al. 2001). Published values for haematology and biochemistry in free-ranging pinnipeds and non-published values for clinically normal captive animals are shown in Tables 17.3, 17.4 and 17.5