Diel activity otter

Observation of Eurasian otter’s diel activity using camera trapping in Central-eastern Romania BOUROȘ GEORGE, DAN TRAIAN IONESCU, CĂLIN HODOR

Introduction 

Which is the diel activity of otters, are they nocturnal animals, or active in daytime?

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It might be both of them, but mainly nocturnal.

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Why are they nocturnal?

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Not because of the disturbance from people, as is often thought, the nocturnal behaviour is primarily related to the availability of prey and fish behaviour.

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How to study the behaviour of Eurasian otters (Lutra lutra) which are largely nocturnal, solitary and elusive?

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Using camera traps it was possible to study the diel activity of the otters in Romania by analysing the capturing date and time of the images and videos of the otters captured by the cameras.

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The need for such studies arises not only from a necessity to understand the behaviour of this endangered aquatic carnivore, for finding the factors that determine its behaviour (human disturbance, prey availability), but also to meet a need for knowledge to establish best measures for otter’s conservation management.

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Materials & Methods 

10 monitoring sites from all three protected areas were selected and monitored for 1356 days & nights between March 2011 to April 2016.

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2 cameras have been installed in Lower Siret Valley NATURA 2000 Site (C1 & C2), four cameras have been placed in Putna Vrancea Natural Park (C3, C4, C5 & C6) and other four in Ramsar Site Dumbravița Fishpond Complex (C7, C8, C9, C10).

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It wasn’t used bait in order to not change or influence otter’s behaviour and activity.

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Information from each camera were look for temporal detection patterns.

analyzed to

Traping succes in the study areas

Results 

The camera traps have recorded a total of 222 otter visits at all 10 monitoring sites.

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Camera traps were functional for 97.2 % of the study period due to technical issues.

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Eurasian otters were strongly nocturnal. Most of the otters were recorded during the night (86.5 %) and only 6.3 % of the otters were crossing the monitoring sites during the day.

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Otters have been also active during the Civil Twilight (7.2 %), more active during the dusk (5 %) than during the dawn (2.3 %).

General diel activity of otters

Results

Results 

Otters were more diurnal during late winter (February) and early spring (March and beginning of April) than in the summer or autumn, 78.6 % of the otter diurnal activity recordings are from February to April.

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Otter’s main activity period was variable according to the season, and strongly correlated with the darkness time: spring (6:30 pm - 7:00 am), summer (8:00 pm – 6:00 am), autumn (6:30 pm – 6:30 am) and in winter (4:30 pm – 7:30 am).

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All this indicated that the otters were strongly nocturnal in their behaviour.

Results

Discussions The night activity is common for otters in Romania, followed by crepuscular activity, and continued with diurnal activity, wich is much less common.

There are some factors that influence the activity patterns of the mammalian carnivores and some of them are: 

diel temperature variation;

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climatic conditions of the area;

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interference from competitors;

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the types of habitats in which they live;

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limitations of the visual system;

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risk of predation;

synchrony in diel activity between predator and their prey;

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social behaviour;

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the degree of human interference;

The disturbance and persecution from humans is not the main factor of otters nocturnal activity.

Otter nocturnal behaviour is primarily related to the accessibility to prey species.

Discussions 

Some freshwater fish species are often inactive during the night, waiting motionless on the bottom of the water and are presumed to be more vulnerable to otter predation then.

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fish predation during twilight is higher, when neither diurnal nor nocturnal fishes are truly active. Then is a time of major activity for predatory fishes and also for Eurasian otter, according the results of this study 7.2 % of otter recordings occured during twilight.

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The changing levels of light during twilight, and the increased activity of predators at that time, suggests a direct link between vision and predation during crepuscular periods. The otter senses function better than either a diurnal (photopic) fish eye or a nocturnal (scotopic)fish eye, during twilight.

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The seasonal activity of otters in this study appears very similar to the results of other studies from UK freshwater habitats, all of this studies showing an activity typically peaking in the cold season (late autumn, winter and early spring) and decreasing thereafter.

Conclusions 

Since there are so many factors that might influence the activity patterns of the otters, it is difficult to determine which are the main factors that influence otter’s activity.

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Human disturbance is not likely to be the main factor influencing otter’s activity.

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The otter nocturnal behaviour is primarily related to prey behaviour.

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In order to make more correlations between otter activity and prey species activity, there is necessary extensive research on the behavior of this prey species, which seems to influence the behavior of the predator.

Acknowledgements For Support:

For training: For advices & coordination: m.c. Acad. Dr. Dumitru Murariu Dr. Silviu Chiriac

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