Vessel Strike Risk to Bowhead Whales - North American Arctic

Vessel traffic is increasing throughout the Arctic as sea ice is declining, leading to increased vessel strike risk for large whales. Vessel strikes are a leading cause of serious injury and mortality for baleen whales in areas of high traffic, but have rarely been studied in the Arctic. We examined vessel strike risk for two populations of bowhead whales, the Bering-Chukchi Beaufort (BCB) and Eastern Canada-West Greenland (ECWG), during the July-October open water shipping season.

This story map has been designed to accompany our recent paper in the journal Biological Conservation, "Overlap between bowhead whales (Balaena mysticetus) and vessel traffic in the North American Arctic and implications for conservation and management", which can be viewed  here . The goal of this story map is to provide more interactive maps, allowing readers to explore the data in more detail.

This study identifies areas of elevated vessel strike risk for BCB and ECWG bowhead whales during July-October, providing important information that can be used to further evaluate and minimize or mitigate this threat. Although vessel strike risk is presently lower for these populations than for other temperate large cetacean populations, bowhead whale behaviour and projected increases in traffic elevates their risk in the Arctic. Our study provides information about potential hotspots for vessel strike risk, allowing wildlife managers to monitor these sites in more detail.

The vessel strike risk hotspots identified in this study may also be candidates for further management measures. For example, only two of the hotspots currently have vessel management measures in place. The area near Tuktoyaktuk is within a voluntary slowdown zone, and the area near Isabella Bay includes the Ninginganiq National Wildlife Area, which strictly manages and limits ship traffic within that area. However, the offshore portion at Isabella Bay outside the National Wildlife Area remains unprotected. The other hotspots that our study identified, including Cumberland Sound, Gulf of Boothia, and Utqiaġvik, currently have no additional vessel management measures in places. Management measures such as shipping corridors or vessel slowdowns could be useful tools to reduce strike risk for bowhead whales.

To get right to the results and interactive maps, click on either of the Vessel Strike Risk links in the header, or scroll down.

This study focuses on the North American Arctic, from Baffin Bay in the east to the Chukchi Sea in the west. It encompasses the ranges of two populations of bowhead whales, the Bering-Chukchi-Beaufort (BCB) bowheads and the Eastern Canada-West Greenland (ECWG) bowheads. We used satellite telemetry and aerial survey data to calculate average monthly relative density of both whale populations, and satellite automatic identification system vessel tracking data to calculate average monthly vessel density and speed. The map below outlines the study area, showing the locations where the four datasets used to estimate bowhead density are located.

An example of the steps to calculate vessel strike risk is shown with BCB telemetry data from August.

• Interact with the map below to examine all of the data used to calculate vessel strike risk and the outputs in each stage of the calculation.
• This example uses data from August, specifically bowhead whale relative density from satellite telemetry data, and bulk carrier density and speed. The processing follows these steps:

1. First, we multiply bowhead density by vessel density for one class of vessels to obtain vessel x bowhead overlap.
2. Second, we correct vessel x bowhead overlap by vessel speed for that vessel class to obtain vessel strike risk for that vessel class.
3. Third, we repeat those first two steps for every class of vessels.
4. Finally, we add up the vessel strike risk for all classes to obtain the strike risk for all vessels.

These interactive maps display the vessel strike risk results for both BCB and ECWG bowhead whales based on satellite telemetry data. Interact with the maps to zoom in and out on the range of each population of bowhead whale, or zoom in further on specific areas of interest. Hit the right and left arrows to switch between months (July to October).

Vessel strike risk as a function of vessel class

The largest vessels, which are bulk carriers, container ships, and tanker ships, are the most likely to cause lethal strikes due to their size and the speeds at which they travel. When we restricted our analysis to just these large vessels, the general hotspots remained the same, but hypothetical strike risk decreased, since these vessel classes are much less common within the BCB range.

Similarly, we excluded just the smallest vessels (recreational class) from the analysis, and the hotspot remained the same and at roughly the same hypothetical risk level, since these vessels often travel slower and did not add much to the overall strike risk.

These interactive maps display the vessel strike risk results for both BCB and ECWG bowhead whales based on aerial survey data. General results from the aerial surveys were similar to results from satellite telemetry, but in a restricted area. Zoom in further on specific areas of interest. Hit the right and left arrows to switch between BCB and ECWG data. For BCB data, switch the month by clicking on the text at the left.

Click on the red rectangles on the map below to see the composition of vessel classes specific to the vessel strike risk hotspots. The average number of vessel tracks across years within each vessel class in September that contributed to the vessel strike risk hotspots were extracted (values > 0.3) for each 10 km cell, and then summed as the number of vessel tracks per class across cells.

This study on vessel strike risk is part of our large research program that focuses on the impacts of vessel traffic on Arctic marine mammals. Much of our research focuses on underwater noise and passive acoustic monitoring. To read more about our larger research program, go to  http://www.arcticnoise.ca/ .