810 Conservation news
Hope for an apex predator: giant otters rediscovered in Argentina
The giant otter Pteronura brasiliensis, categorized as Endangered on the IUCN Red List, is an apex predator in Neotropical freshwater systems with the potential to regu- late food webs through density-mediated trophic cascades (Quéméré et al., 2021, Environmental DNA, in press). The giant otter has been extirpated in some countries and extant populations are declining. Giant otters were once abundant in Argentina but heavy
Microlight piloted by a foster parent leading northern bald ibises to the wintering site in southern Tuscany, Italy. Photo: Waldrappteam Conservation & Research.
by human foster parents. After fledging the birds undergo a training programme to follow two microlights co-piloted by the foster parents. From mid August this migration leads in flight stages of c. 220 km per day from the breeding sites north of the Alps over c. 1,000 km to the wintering site in southern Tuscany, where the birds are released. During 2014–2019 a total of 154 birds were released. No release occurred in 2020 because of the COVID-19 pandemic. First-year survival of the released juveniles is 0.73, significantly higher than the 0.31 first-year survival of re- leased juveniles in the Spanish Proyecto Eremita (Böhm et al., 2020, Oryx, 55, 934–946). We attribute the high sur- vival rate of released birds in our project to the complex pre- release training and low loss during the human-led migra- tion. Reproduction in the released population has increased steadily. During 2014–2020, 151 birds in 61 nests fledged in the wild, amean fledging rate of 2.47 per nest. This is double the fledging rate of 1.23 per nest in the last remaining wild population inMorocco. The high fledging rate in the LIFE+ project reflects the high-quality feeding habitats in the breed- ing areas north of the Alps. A recent population viability analysis indicates that the
reintroduced population is close to sustainability but that further releases and management will be needed. This will be under a second European LIFE project, run by Zoo Vienna with partners from Germany, Austria, Italy and Switzerland, aiming to establish further migratory colonies in Austria, Switzerland and northern Italy, and a total popu- lation size of .350 individuals.
JOHANNES FRITZ (
orcid.org/0000-0003-4691-2892) Waldrappteam Conservation & Research, Mutters, Austria, and IUCN Species Survival Commission, Stork, Ibis and Spoonbill Specialist Group. E-mail
jfritz@waldrapp.eu
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence CC BY 4.0.
Giant otter photographed in El Impenetrable National Park, Argentina, in May 2021. Photo: Sebastián Di Martino.
Oryx, 2021, 55(6), 809–817 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001071
hunting, habitat loss and degradation resulted in their dra- matic decline. The last known population disappeared in the 1980s. Since then, records of solitary individuals have been reported in the Iguazú and Paraná River basins, the most re- cent from 2010, but these records lack supporting evidence such as images or signs. In the Bermejo River basin, in the Chaco region, the last sightings of giant otters date from the late 1800s. El ImpenetrableNational Park, created in 2017, protects
the declining dry forests of the Chaco region. To the north, the Park is bounded by the Bermejo River. On 16 May 2021 in El Breal, one of several ponds formed by old meanders of this river, SDM observed an adult giant otter and se- cured a photograph. Surveys later that day revealed two fresh latrines and two recently dug dens on the shore. El Breal pond has steep clayey shorelines 2–3 m above the highest water level and a total surface water area of 0.37 km2. Water depth is c. 10 m and potential giant otter prey in the pond include abundant fish, macroinverte- brates and caimans. A mature dry forest surrounds the pond. The origin of this individual is unknown. The closest
giant otter population is in the Jejuí River in Paraguay, close to its confluence with the Paraguay River (Cartes et al., 2013, Paraquaria Natural, 1, 8–11). But an animal dis- persing from there would have to travel c. 1,000kmof water- ways to reach El Impenetrable National Park. Alternatively,
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