Depredation update

The longline fishery off Vesterålen has now taken place for a bit over two weeks (started 23/5).The area where interactions between sperm whales and fishery are observed is an approximately 20 km long and 2km wide "stretch" of the continental slope around 600 m depth. This area is fished by boats leaving mainly from the harbours of Stø and Nordmela, and the fishermen staying in these harbours have proven to be valuable collaborators providing us with observations and even video- and ID images! We have also obtained ID images and other data from august 2014, when this behavior was first observed. Thank you to all skippers!!

 Photo by Jesper Persson.

 Photo by Erik Heiskanen.

Here are two images of whales identified in June feeding from a longline. We are in the process of organising and updating the long term photoidentification data set collected onboard whalesafari boats operating from Andenes (pictures dating back to 1989) and will check if these two whales have been sighted before. We know that one of the "main operators" from August 2014 is a whale that has been identified for more than a decade in these waters.

We have seven confirmed depredation events, and there are still several fishermen from Nordmela we have not interviewed yet. So yes, the whales are defnitely taking Greenland Halibut from the longlines. We have realised that fishermen are not always aware of when depredation events take place, a rather common description has been: "The whale(s) was just floating around the boat, not feeding". This is due to the fact that when the sperm whale dives under the boat and starts feeding, this is not observed other than as fish lacking from the line (there is no "tugging" or other visible behaviors). On some occasions the fishermen have filmed whales that are swimming towards the boat, lifting their head as if to "precision target" to where the boat and the fish are.

Our next step is to try to get sound recordings of the sound the boat makes when they start taking up the line. According to research done elsewhere, it is this sound that alerts the whales to presence of fish. However, several fishermen have also reported that the whales start "waiting" as soon as they have set the line and can swim around the boats for several hours, waiting that the line is being taken up, so we are thinking of recording sounds of the whole fishing operation.

Ideally we will also be able to record the sounds made by sperm whales when they are taking fish from the lines. In future, acoustic monitoring might be an additional method in getting an estimate on how often depredation takes place.