Sea lion population status and demography

Sea Lion Island shelters a small colony of souther sea lions, which current productivity is about one hundred pups. Southern sea lion suffered an impressive population crash, due to unknown reasons. Although in recent years the total number of sea lion pups has been gradually increasing, the total size of the population is very small compared to the historical size, and most colonies are still small. Therefore, it is important to carry out a regular monitoring of this species, and Sea Lion Island is an ideal place for that because the breeding colony is quite accessible, being just a short walk from the settlement.

The sea lion colony

The southern sea lion colony at Sea Lion Island, from the top of the cliffs

One of the main problems of estimating breeding success and productivity of sea lions at Sea Lion Island is that the colony is located on flat rock below a steep and high cliffs, and, therefore, counting is not easy, because sea lions, and pups in particular, can be out of view. Depending on the tide and weather conditions, counts from the top of the cliffs, even when carried out by experienced observers, can be definitely low. Repeated counts and observations of pup movements in and out of view showed that counting error can be up to 25%. A solution to that problem is to take aerial photos from a drone, and then count the sea lions in the the photos. We are doing exactly that using a Phantom 3 drone, with very good results.

Pup groups

Groups of sea lions under the cliffs, visible only in drone pictures

Sea lion count in drone photos

Counting sea lions in photos taken from a drone

We observed a notable increase in number of pups counted in recent years compared to the available counts of the past. This is very likely the result of a real increase in the number of pups, buut we think that also the improvement in the quality of counts (repeated counts, at least weekly, insted of occasional spot counts) may have played a role.

Pup groups

Graph of maximum pup counts

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