Bringing Ecologists and Statisticians Together for the Conservation of Endangered Species

Post provided by Cecilia Pinto and Luigi Spezia

The Benefits of High Frequency Data

One of the tagged flapper skates showing the three different kinds of tags. ©Cecilia Pinto

One of the tagged flapper skates showing the three different kinds of tags. ©Cecilia Pinto

High frequency data, like those obtained from individual electronic tags, carries the potential of giving us detailed information on the behaviour of species at the individual level. Such data are particularly useful for marine species, as we can’t observe them directly for long periods of time.

Understanding how individuals use water columns – both at daily and seasonal scales – can help define conservation measures such as restricting fishing activity to reduce by-catch or defining protected areas to help recovering populations or protect spawning and nursery areas. High frequency data have become popular as they give insight to detailed individual foraging behaviour and therefore the specific energetic needs that are linked to reproduction and fitness.

The potential of high frequency data is extremely high. But how do we get the best out of these complex new generation data? In order to obtain all the information mentioned above we need to be able to analyse these complex data and draw out the detailed information they contain. Therefore, the development and application of methods that can account for such complexity is necessary.

Another equally important question is: can the development and application of complex analytical tools be useful when it comes to conservation? New analytical tools that are considered complex don’t always receive the warmest of welcomes from ecologists. They are sometimes seen as methods developed to push statistical and mathematical theory, lacking general applications aimed at improving ecological understanding and species conservation.

Complex Data and Endangered Species

A flapper skate caught by the Scottish Sea Anglers Conservation Network (SSACN) in the Sound of Jura. ©Cecilia Pinto

A flapper skate caught by the Scottish Sea Anglers Conservation Network (SSACN) in the Sound of Jura. ©Cecilia Pinto

Developing methods that can explore complex data to obtain as much information as possible at the individual level is particularly useful for endangered species as data are often lacking or sparse. The flapper skate (Dipturus intermedia) is an endangered species, whose population is now restricted to a number of small populations off the west coast of Scotland. This species, which was only genetically identified in 2010, used to be commercially exploited. It is now prohibited to land the species and a protected area was designated in 2014.

This was the first step towards implementing appropriate conservation measures for this little-known endangered species whose population declined by 90% in the last 40 years. Hopes are that this new protected area and future conservation decisions will help the flapper skate’s population to increase and allow the species to recolonize its former range.

Working with Statisticians

The bringing together of ecologists and statisticians has been encouraged recently in order to enhance the quality and applicability of model development. Our work on the endangered flapper skate is the product of one such collaboration.

We brought complementary approaches together to pursue the development of a new method to analyse high frequency vertical movement data obtained from individual tags. Existing methods used to infer behaviour from individual vertical movement data failed to fully account for the intrinsic statistical violations (such as non-Normality, non-stationarity, non-linearity and long memory) in our data sets. To account for these we applied Markov switching autoregressive models borrowed from econometrics and not yet well-known among ecologists.

An example of the data sent back from one of the Data Storage Tags

An example of the data sent back from one of the Data Storage Tags

Influencing Conservation Decisions

A Data Storage Tag which we attached to the skates to record depth every two minutes. © Cecilia Pinto

A Data Storage Tag which we attached to the skates to record depth every two minutes. © Cecilia Pinto

Applying such models to our data we were able to observe that skates behaviour can be summarized by periods of high and low vertical activity. Such variation in their vertical activity does not seem to be related to the speed they move at or the depths they are exploring. It does seem to be related to their activity near the seabed though. When skates are at the seabed, they tend to move around more horizontally. As they move towards the surface though, their horizontal movement decreases. Our study was limited by the number of individuals that we were able to recapture (only four in total, one female and three males). Therefore it was essential to make the most of what detailed data we had.

As the level of individual variability was really high among the four individuals we analysed, we are still lacking information on which environmental factors cause higher or lower vertical activity, at both daily and seasonal scales. However, the development of our model has paved the way for analysing the behaviour of flapper skates. As more tags are returned in the future it will hopefully allow us to make wider ecological inference at the population level and apply this to conservation plans. The model could also easily be applied to other endangered species and we hope that many research groups will find it useful.

A fundamental step in studies on endangered species should be updating of the existing information and collecting additional data to improve the understanding of their populations. The development of models is also vitally important when data are sparse. Our hope is that the existing models will be improved by future monitoring and tagging programs and that these will help to improve conservation activities around the world.

To find out more about ecology and statistics for endangered species conservation, read our Methods in Ecology and Evolution article
Markov switching autoregressive models for interpreting vertical movement data with application to an endangered marine apex predator’.

This article is part of our Virtual Issue on Endangered Species. All articles in this Virtual Issue are freely available for a limited time.

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