Changes in collision risk index in the regional seas for whales between 2017 and 2022

Units

Index value change (no units)

Additional information

Source for animal species selection and strike frequency factors: Schoeman RP, Patterson-Abrolat C and Plön S (2020) A Global Review of Vessel Collisions With Marine Animals. Front. Mar. Sci. 7:292. doi: 10.3389/fmars.2020.00292

Methodology

The collision risk index is designed as a spatial overlay of the animal species distribution and vessel density. In areas where marine species are present (i.e. high occurrence probability) and the density of marine traffic is high, the collision risk index is also high. 23 whales (cetaceans) species and 3 turtle species were included in the calculation of the index. Each species was assigned (weighted by) a strike frequency factor, which indicates the level of susceptibility of the species to collisions with vessels. The factors were developed based on the frequency of a species observed stricken by a ship (Schoeman et al., 2020). Weighted species occurrence probability layers were summed to get the species group (whales, turtles) occurrence probability layer.

The vessel density values over 100 were first truncated to 100 to remove the high value cells due to ships idling in ports or anchoring sites with their AIS transponders turned on. Additionally, the vessel density data was log transformed (ln+1).

Then, the weighted and summed species group occurrence probability layer was multiplied by the truncated and log transformed vessel density layer for the 2017-2022 period. The results are raster datasets:

• Collision risk index for whales in period 2017-2022

• Collision risk index for turtles in period 2017-2022

Datasets are providing information on collision risk index value for whales and turtles for each year.

Additionally, two raster datasets were created:

• Changes in collision risk index for whales between 2017 and 2022

• Changes in collision risk index for turtles between 2017 and 2022

which provide the difference between 2022 and 2017 collision risk index values.

The resulting map shows the difference between 2022 and 2017 collision risk index values for whales (2022 minus 2017).