ESSAY

Bycatch mitigation strategies in pelagic longline fisheries: an aid to the welfare of the loggerhead turtle (Caretta caretta)

Introduction

Although described as a “rare event” in many fisheries (Gilman et al., 2010), sea turtle bycatch is asignificant issue in trawl, set-net and pelagic longline fisheries operating in regions that overlap with sea turtle distribution. International trade of sea turtles is prohibited, with six out of seven species listed as endangered or critically endangered by the International Union for the Conservation of Nature (IUCN) (2003). Bycatch mortality from pelagic longline fisheries poses a significant anthropogenic threat to the welfare of the endangered loggerhead sea turtle (Carreta caretta)(Echwikhi et al., 2010). Recently, numerous bycatch mitigation strategies have been devised to reduce incidental sea-turtle capture while avoiding negative impacts on local fishermen (Gilman et al., 2010).

Discussion

Hook shape, bait choice and catch area have proved to significantly affect numbers of loggerhead turtles caught by pelagic longline fisheries (Gilman et al., 2010). Sales et al. (2010) compared the effects of circle hooks and J-shaped hooks on sea turtle bycatch rates and post-release survival. Data were collected on 22 trips by four different vessels from 2004 to 2008 in the south-western Atlantic Ocean. Hook type and location of insertion were recorded with lighthooking indicating attachment to the mouth, and deep-hooking signifying oesophageal or deeper attachment. Results showed a total of 200 sea turtles captured, 85 per cent of which were loggerheads. Capture rate increased by a factor of 2.2 when J hooks were used, and deep-hooking was more frequent than with circle hooks. Furthermore, capture rates of four of the target species, including blue sharks and tuna (42.2 per cent and 14.6 per cent, respectively), were significantly increased when using circle hooks. Only swordfish had significantly decreased capture rates with circle hooks.

The benefits of circle hooks on the welfare of loggerhead turtles are twofold: these hooks decreased loggerhead capturerates and deep-hooking frequency. Additionally, greater catch rates of targeted species with circle hooks may result in boosted economic return for pelagic fisheries, increasing the likelihood of the acceptance of circle hooks by local fishermen (Sales et al., 2010).

Deep hooking by J hooks is likely to increase mortality in loggerhead turtles in comparison to light hooking; deeper hooks cannot be removed as easily and attached branchlines may induce strangulation and traction, resulting in delayed mortality in the loggerhead turtles (Valente et al., 2007). Alimitation to this study could be seen in the use of different shipping vessels, since managerial procedures could alter turtle catch numbers and affect post-release survival rates. Similarly, it is unclear whether increased capture of sharks and tuna with circle hooks would adequately negate the loss due to reduced swordfish catch.

Bait variations used in pelagic longline fisheries can further alter bycatch frequencies in loggerhead turtles. Echwikhi et al. (2010) studied the effect of bait type on 21 fishing trips (48 sets) from July to September over two years, using onboard surveyors. Mackerel was used by 29 fishing sets and 19 used stingray fragments, with the aim of catching sandbar sharks (Carcharhinus plumbeus)and swordfish (Xiphias gladius). Of the 29 loggerheads that were caught, 26 wereoffhooks baited with mackerel, while only three were caught off stingray-baited hooks, showing loggerheads’ strong preference for mackerel. Furthermore, sandbar shark catch rate was significantly greater with stingray-baited hooks. Thus, while improving the catch rate of targeted species, turtle interactions with longline fisheries can be strongly mitigated by altering the type of bait used. This is supported by a similar study performed by Yokota et al. (2009) demonstrating that loggerheads have a higher tendency to feed on squid than on mackerel. Bait alterations can therefore be seen as a second economically viable option to pelagic fisheries to reduce loggerhead .

Limitations to the study conducted by Echwikhi et al. (2010) principally lie in the use of only one fishery; bycatch mitigation techniques are likely to be influenced by numerous factors, and may not work as well in alternate fisheries, especially when using a sensory-based incentive such as bait. Seasonal variations, time of day, age of interacting turtles and oceanographic region are all likely to play a role in sensory capabilities (Gilman et al., 2010). The importance of oceanographic regions in loggerhead distribution, and subsequent bycatch frequency, isfurther demonstrated by Howell et al. (2010). In the study, 17 juvenile loggerheads were tagged with satellite-linked depth recorders (SDRs) and released back into the central North Pacific Ocean, from which they had come. The SDRs recognised individual dive events, and collected raw time-and-dive data for morethan 50 days, with some tags (n=6) transmitting data for more than one year.

Dive-depth distributions showed 80 per cent of dives were to depths of less than 5 metres and 90 per cent to depths shallower than 15 metres. Moreover, 99 per cent of the turtles’ time was recorded to be in waters warmer than 15°C, with seasonal migration following warmer temperatures. This is supported by Sales et al. (2010), who reported seasonal changes in loggerhead capture. Such information can greatly benefit bycatch mitigation strategies; longline fishing in depths below 25metres is likely to circumvent shallower regions of the water column where turtles spend 99 per cent of their time. By analysing loggerhead distribution and feeding patterns, probability of fisheryinteractions with turtles can be determined and consequently, loggerhead bycatch could be significantly reduced. However, a limitation to this study is that the reasoning behind the turtle distribution is unclear as thermal limitations and prey distributions are unknown. Similarly, only juvenile loggerheads were used, and as such the study is restricted to an age class that might display different foraging behaviours to other classes.

Conclusion

In conclusion, altered bait type and use of circle hooks can be used in conjunction with oceanographic data to reduce bycatch mortality in loggerhead turtles. However, while empirical evidence has shown bycatch mortality solutions may benefit the welfareof loggerhead turtles, it is probable that solutions are fishery-specific. Additional reviews are required to enhance understanding of the risk posed by pelagic longline fisheries on loggerhead populations, in order to prioritise limited conservation resources and ascertain appropriate mitigation opportunities.

■ LOUISESCHAFFER

References

Echwikhi, K., Jribi, I., Bradai, M.N., Bouain, A. (2010) Effect of type of bait on pelagic longline fishery–loggerhead turtle interaction in the Gulf of Gabes (Tunisia). Aquatic Conservation: Marine and Freshwater Ecosystems 20:5, 525-530. Gilman, E. Gearhart, J., Price, B., Eckert, S., Milliken, H., Wang, J., Swimmer, Y., Shiode, D., Abe, O., Peckham, S.H., Chaloupka, M., Hall, M., Mangel, J., Alfaro-Shigueto, J., Dalzell, P., Ishizaki, A. (2010) Mitigating sea turtle by-catch in coastal passive net fisheries. Fish and Fisheries 11:1, 57-88. Howell, E.A., Dutton, P.H., Polovina, J.J., Bailey, H., Parker, D.M., Balazs, G.H. (2010) Oceanographic influences on the dive behavior of juvenile loggerhead turtles (Caretta caretta) in the North Pacific Ocean. Marine Biology 157:5, 1011-1026. IUCN (2003) IUCN Redlist of Threatened Species. International Union of Conservation of Nature and Natural Resources, Cambridge, UK. Sales, G., Giffoni, B., Fiedler, F., Azevedo, V., Kotas, J., Swimmer, Y., Bugoni, L. (2010) Circle hook effectiveness for the mitigation of sea turtle bycatch and capture of target species in a Brazilian pelagic longline fishery. Aquatic Conservation: Marine and Freshwater Ecosystems 20:4, 428-436. Valente, A.L.S., Parga, M.L., Velarde, R., Marco, I., Lavin, S., Alegre, F., Cuenca, R. (2007) Fishhook lesions in Loggerhead Sea Turtles. Journal of Wildlife Diseases 43:4, 737-741. Yokota (2009)

This essay is one of a number selected for The Veterinarian magazine Prize for Written Communication for Sydney University third-year veterinaryscience students.

Emergency animal disease bulletin: Japanese encephalitis

Rhyll Vallis, Nicole Byrne and Jarrad Sanderson, Department of Agriculture, Water and the Environment

Japanese encephalitis (JE) is an acute mosquitoborne viral disease of humans and animals which occurs throughout much of Asia. Infections are mainly subclinical, but can be associated with abortion in pigs and encephalitis in humans and horses. Although an effective vaccine is available, the World Health Organisation estimates approximately 68,000 human cases occur annually predominantly in South-east Asia (WHO 2019).

Clinical disease occurs most commonly in pigs, horses (and donkeys) and humans. Reports of disease in other species are rare. JE has been reported in cattle, and chicks and ducks less than 6 weeks old.

In pigs, the most common clinical signs are mummified, stillborn or weak piglets, some with neurological signs. Many cases in horses are asymptomatic and most clinical disease is mild. However, severe encephalitis can occur, which may be fatal. Reports of clinical disease in donkeys is less common.

Aetiology

The virus that causes JE is a single-stranded, enveloped ribonucleic acid (RNA) virus belonging to the genus Flavivirus genus in the family Flaviviridae. The virus replicates in various tissues, with tropism for neurological and lymphoid tissues.

There is one serotype of JEV and five reported genotypes. Substantial strain variation has been reported among JEV isolates. While JEV strains vary in virulence and clinical signs, all are readily inactivated by heat, photochemical treatment, pasteurisation, treatment with detergents and low pH.

Distribution Global

Japanese encephalitis is widely dispersed throughout Asia, and its geographic range extends from maritime areas of the north-east Russia, China and Philippines in the east, to India and Pakistan at its western limits, and throughout South-East Asia.

Outbreaks of Japanese encephalitis have been reported in Papua New Guinea (PNG) and northern Australia, as well as in the Western Pacific islands of Guam and Saipan.

For the latest information on the distribution of JE, refer to the WAHIS information database website of the World Organisation for Animal Health (OIE) (wahis.oie.int/#/dashboards/ country-or-disease-dashboard) or theFAO EMPRESi Global Animal Disease Information System (empres-i.review.fao.org).

Australia

Japanese encephalitis emerged in the Torres Strait in 1995. A human case was reported on mainland Australia in northern Queensland in 1998. Although serological evidence of pig infection was also detected, a transmission cycle was not established.

On the Australian mainland, a human case was reported from the Mitchell River area of western Cape York in 1998. Serological evidence of pig infection was detected in the Mitchell River area and in the Northern Peninsula area of Cape York at that time, but there was no further evidence of human infections in residents of nearby communities, and JEV did not establish a transmission cycle (Hanna et al 1999). Periodically,overseasacquired human cases of JE are detected; however,there have been no reports of associated viral transmission in Australia.

The disease was not detected in mainland Australia again until 25 February 2022. Initially the disease was confirmed by laboratory diagnosis in three eastern states – in one piggery in Victoria, 6 piggeries in NSW and in one piggery in Queensland. At the time there had been alarge amount of rain across eastern Australia with high numbers of mosquitoes reported.

Vaccination

Effective JE vaccines are available for use in people. The Australian immunisation handbook (ATAGI 2018) provides recommendations on vaccination of humans.

In some Asian countries, pigs are vaccinated as part of control efforts, and horses in endemic areas are vaccinated to protect against disease and for international travel.

Transmission

The primary mode of transmission for JEV between hosts is through the bite of infected mosquito vectors.

The virus has been isolated from over 30 mosquito species. JEV vectors are opportunistic feeders and are zoophilic, preferring animals to humans. The principal competent Australian vector mosquito is Cx.annulirostris. This vector species has been primarily responsible for JEV in the Torres Strait islands. As host availability is an important factor influencing feeding, Cx.annulirostris preferentially feed on cattle and marsupials.

JEV has also been isolated in two vector mosquito species found in Torres Strait. They are, C. gelidus and Ochlerotatus vigilax.C. gelidus was introduced into northern Queensland and is now believed to be widely distribributed throughout northern Australia.

Maintenance of the virus is believed to occur in mosquito – waterbird, or mosquito – waterbird – pig cycles. Pigs and waterbirds are important amplifying hosts.

Water birds, particularly herons and egrets, are the main natural reservoir hosts of JE. Waterbirds and pigs are amplifying hosts of JEV and can act as maintenance hosts in endemic areas. Following natural infection, pigs develop a high level viraemia for 4-5 days capable of infecting mosquito vectors. The high birth rate and rapid turnover of pigs in commercial production systems provide a continual source of susceptible hosts, and large epidemics of Japanese encephalitis have occurred when JEV spreads to new areas where susceptible hosts and suitable vectors co-exist.

Japanese encephalitis predominantly affects rural areas where irrigated agriculture human habitation, waterbirds and pig rearing are in close proximity. Typically, two epidemiological patterns exist: endemic activity in tropical regions and epidemic activity in temperate and subtropical regions.

Humans and horses are dead-end hosts of JEV, because they do not produce adequate viral levels required to infect mosquitoes. However, the disease can be fatal to humans and horses.

The virus is relatively unstable in the environment and is not considered significant in transmission.

Clinical disease

The incubation period is 1–3 days in pigs, 4-14 days in horses and 5–15 days in humans. Note that less than 1% of people infected with JE virus develop clinical illness.

Clinical signs, mortality and morbidity differ by species, as shown in Table 1 below.

Species Pigs

Clinical signs Adult pigs generally show no overt signs of infection

Under experimental conditions, pigs can become pyrexic (40–41°C) after 24 hours of infection, lasting up to 5 days, with inappetence and depression

Piglets may show central nervous signs indicative of encephalitis, such as hind limb tremor

Infected boars may have oedematous, congested testicles, lowered motile spermcounts and abnormal spermatozoa

Mortality in litters of pigs can reach 100 per cent but is rarein adult pigs

Mortality rates

Horses

Subclinical infection is most common

Neurological sequelae can occur in surviving horses, and has manifested as incoordination, paraplegia, ataxia and incontinence

Transient, lethargic or hyperexcitable type syndrome

There are three clinical presentations in horses. These are:

Transient type – pyrexia of up to 40°C for 2-4 days, with anorexia, sluggish movement, congested or jaundice mucous membranes, and rapid and an uneventful recovery

Lethargic type – fluctuating pyrexia up to 41°C, with lethargy, anorexia, stupor, grinding of teeth and chewing motions, difficulty in swallowing, jaundice, petechial haemorrhages in mucous membranes, incoordination, staggering and falling, transient neck rigidity,radial paralysis, impaired vision and recovery within 1 week

Hyperexcitable type – marked pyrexia (>41°C), with aimless wandering, violent and demented behaviour, blindness, profuse sweating, muscle trembling, bruxism, collapse, coma and death

Estimated at 5–15 per cent in endemic areas and 30–40 per cent in seasonal epidemics. JE in livestock has not been accurately quantified Low (<1 per cent) and up to 1.4 per cent during epidemics

Diagnosis

JE should be suspected in disease outbreaks in pigs, with clinical disease characterised by abortion, foetal mummification or stillbirth, and encephalitis in animals up to 6 months old.

JEin horses must be differentiated from other causes of neurological diseases. In Australia, this includes infections with Hendra virus and the closely-related subtype Kunjin virus and Murray Valley encephalitis viruses, which have caused outbreaks of equine encephalitis and have very similar epidemiology to Japanese encephalitis.

Geographical and temporal clustering of pigs and horses displaying the described clinical signs should raise suspicion of JE, particularly in JE high risk areas. Where JE is suspected, samples from animals euthanised in the acute stage of the disease or from animals that have been dead for less than 12 hours should be collected. This is because viremia only lasts a few days. Virus isolation is best achieved from infected brain and post-mortem tissues as the virus is rarely cultured from blood or CSF. Samples to collect: ■ arange of tissues in formalin ■ whole blood and serum samples (paired serum samples should be collected 2–4 weeks apart) ■ placental tissues from aborted foetuses ■ cerebrospinal fluid and a range of brain tissue from animals with neurological signs A Hendra virus infection is a differential diagnosis in cases of neurological disease in horses, please consult with the relevant jurisdictional guidelines prior to commencing sample collection. Appropriate personal protective equipment should be worn if Hendra virus is suspected.

For the latest information on specimens required for JE testing, refer to the CSIRO ACDP Japanese encephalitis Virus Diagnostic Testing Factsheet. (acdp.csiro.au/resources/ documents/CSIRO_JE_Diagnostic_Testing_Fact sheet_V3.pdf)

Control

Management in endemic areas worldwide involves controlling disease in animal populations to support public health initiatives, limiting disease in livestock and protecting highvalue animals (e.g., stud and racing horses). The primary means of control are awareness raising, use of vaccination where available, and vector control.

In Australia, the national policy is to control JE in pigs in order to support public health agencies. Strategies include: ■ Early recognition and laboratory confirmation of cases ■ Coordination and cooperation with public health response activities ■ Epidemiological assessment to inform decisions on appropriate control measures of mosquito vectors and reservoir host species in the transmission of JEV ■ Movement controls over pigs, pig semen and embryos, and other potential amplifying hosts ■ Tracing and surveillance of domestic and wild animals and potential mosquito vector species.

There is no effective treatment for JE in animals. Infection with JE is reportable throughout Australia. For further information see the National list of notifiable animal diseases. (www.awe.gov.au/biosecurity-trade/pestsdiseases-weeds/animal/notifiable)

For further details on Australia’s response policy, see the AUSVETPLAN Japanese encephalitis response strategy located on Animal Health Australia’s website: animalhealthaustralia.com.au/ ausvetplan/

Risk to Australia

JE is endemic in neighbouring Australian countries such as Papua New Guinea and in the Torres Strait.

In Australia, there are three main ways JEV could have been introduced: movement of infected waterbirds, dispersal of infective mosquitoes by wind, and movement by humans of viraemic pigs.

In the case of pigs, animal movement within Torres Strait is controlled, and few animals move south from the Thursday Island group of islands. In addition, live pigs are not imported into Australia.

However, control of movements of wild waterbirds and mosquitoes is not possible. Potential JE vector species (such as Culex annulirostris) are present in many parts of Australia. Australia also has significant populations of susceptible host animal species, including amplifying host species such as waterbirds and pigs (domestic and feral).

JE is a disease of public health importance. Social effects include human fatalities and the ongoing need for vaccination.

Given the February 2022 detections of JE in parts of Eastern Australia, it is important that Australian veterinarians maintain current knowledge and remain alert to the possibility of JE infection in horses and livestock, as early detection and laboratory confirmation are critical for a rapid and effective response.

Vets should:

■ immediately report suspect cases of JE to a government veterinarian or via the EAD Hotline wear appropriate personal protective equipment (coveralls and boots, gloves, mask) when examining animals, performing post-mortem examinations, or handling tissue, carcasses or abortion materials ■ isolate sick/dead animals and limit contact with the sick/dead animals perform personal decontamination when leaving infected premises, and thoroughly clean and then disinfect equipment before leaving the property ■ protect their own health through vaccination advise clients that human infections can potentially occur via needlestick and mucosal exposure, orinhalation of infected samples, or through contact with aborted foetuses, bodily fluids and tissues of infected animals

Veterinarians can also encourage clients with pigs and horses to practise good farm biosecurity and implement an effective mosquito control program. The information about controlling mosquitoes around piggeries can be found on the farm biosecurity website (www.farmbio security.com.au/livestock/pigs/controllingmosquitoes-around-piggeries).

Unusual clinical presentations, particularly when symptoms are consistent with an emergency animal disease (EAD), should be reported directly to state or territory government veterinarians or through the Emergency Animal Disease Watch Hotline (1800 675 888).

References

Animal Health Australia (2020). Response strategy: Japanese encephalitis (version 5.0). Australian Veterinary Emergency Plan (AUSVETPLAN), edition 5, Canberra, ACT. AVA (Australian Veterinary Association) (2022) Japanese Encephalitis detected in pigs in Queensland, NSW and Victoria, AVA, accessed 1March 2022. Department of Agriculture and CSIRO. 2019. Emergency animal diseases: A field guide for Australian veterinarians, Canberra, August. CC BY 4.0. Department of Agriculture and Fisheries (27 February 2022) Japanese encephalitis detected in pigs in southern Queensland [media release], Queensland government, accessed 1 March 2022. DPI (Department of Primary Industries) (2022) Japanese Encephalitis, DPI, accessed 1 March 2022. WHO (World Health Organization) (2019) www.who.int/news-room/factsheets/detail/ japanese-encephalitis

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