December 2020 Student of the Month – James Robbins
Marine mammals are a diverse category, including whales, dolphins, porpoises, seals, sea lions, walrus, manatees, dugong and even sea otters and polar bears. Their classification is unique, in that they are grouped based on their shared aquatic environment rather than shared evolutionary origins. Marine mammals are also special in that they are often dubbed ‘charismatic megafauna’ due to capturing the affection of the public. Despite this popularity, these animals face a multitude of human threats.
If you were asked what the biggest threats are to marine mammals, you may think of well-publicised issues like commercial whaling, plastic consumption, or even entanglement in fishing gear. Animals being hit by ships (‘ship strikes’) may not be high up on that list, or even on it. Many may assume that ships are so big and loud that animals would notice them and get out of the way, and wonder how likely a collision is to happen in such a big ocean environment.
These are the questions that I’m challenged with answering during my PhD project at the University of Portsmouth. We already know from other studies that large whales are likely the most frequently hit marine mammals globally1. Some species are particularly at risk including the North Atlantic right whale, which was once widespread but was decimated by historic commercial whaling and although that has ceased across its range, it continues to be unsustainably killed by entanglement in fishing gear and collisions with vessels. While this species is well-studied, there are huge gaps in our knowledge about the risk ship strikes pose to other species outside of a handful of well-studied areas.
My focus is on the waters of north-west Europe, where little research has been conducted on this issue. There have been several dead cetaceans (the taxonomic order that includes whales, dolphins and porpoises) washing ashore in the region with signs of being hit by vessels2, including in the UK. In October 2019, a humpback whale was killed in the Thames (https://theconversation.com/thames-humpback-whale-killed-by-ship-the-casualty-of-a-global-problem-125284), and a fin whale was brought into Portsmouth on the bow of a vessel in December 2019. These are not new occurrences, but are they happening more frequently?
While we know that shipping is on the rise globally3, we don’t know the state of affairs in this region, or how vessels overlap with whales. The first step in investigating this is to analyse vessel traffic, using Automatic Identification System (AIS) data, which transmits the location of large vessels. I’m using a dataset spanning from Portugal to Iceland across three years, which amounts to an impressive half a billion records. Working with such a large dataset is challenging, but has allowed vessel densities to be calculated for ten different vessel categories. The analysis of patterns is still ongoing; however, preliminary results suggest that shipping is on the rise in the north-east Atlantic too. Not only does this mean greater risk for marine mammals and other animals from collisions, but also potentially more noise being produced, which can have additional negative effects on marine life, from damaging hearing and disrupting behaviour to masking communications4.
Using our newfound knowledge about shipping patterns in the north-east Atlantic, we can also look at the overlap between vessels and cetaceans. A simple way to look at this is as straight-forward as multiplying published densities of animals by calculated densities of vessels, resulting in an index of overlap which changes across time and space. We will be doing this for twelve species, including dolphins and porpoises, which are often overlooked with regards to ship strike risk, but certainly are affected. The below poster was presented at the International Marine Conservation Congress conference earlier this year and outlines our methodology and preliminary results. We will be furthering this work by also looking at vessel speeds in the area, as there is a higher risk of mortality at higher vessel speeds5.
PDF of poster available to download here.
Once we know the spatial overlap of whales and vessels, we’ll be able to go a bit “deeper”. One of the interesting aspects of marine mammals is that they occupy a 3D environment – as well as moving around horizontally, they can also dive to great depths. So although animals may spatially overlap with vessels, are they also occupying ‘safer’ depths beyond the reach of ships or are they in the ‘danger zone’ of surface waters? To answer this, I will be focusing on the Bay of Biscay where shipping lanes overlap with an abundance of fin whales in the summer months. Using data collected from tags temporarily attached to the back of whales studied in the Azores, we will look at how they spend their time and even see how much time they spend within the reach of vessel hulls and propellers to quantify the proportion of time at risk vertically in the water column.
Using a combination of the above methods, we can even estimate the number of whales hit per year, and the proportion of those that likely die. We still have a little work to do before sharing those results, but can say that provisional numbers are slightly worrying. The final part of my PhD will be to combine all of our findings to suggest appropriate measures to limit ship strike events in the north-east Atlantic. This could include seasonal speed restrictions, re-routing, or new procedures for bridge crews in higher risk areas and times of year.
For now, I have a bit more work to do, but I look forward to sharing final results, which will hopefully help to identify areas and times of concern – vital information to make appropriate conservation management decisions to minimize the risk to these animals.
- Schoeman, R. P., Patterson-Abrolat, C. & Plön, S. A Global Review of Vessel Collisions With Marine Animals. Frontiers in Marine Science 7, 292 (2020).
- Peltier, H. et al. Monitoring of Marine Mammal Strandings Along French Coasts Reveals the Importance of Ship Strikes on Large Cetaceans: A Challenge for the European Marine Strategy Framework Directive. Frontiers in Marine Science 6, 486 (2019).
- Pirotta, V., Grech, A., Jonsen, I. D., Laurance, W. F. & Harcourt, R. G. Consequences of global shipping traffic for marine giants. Front. Ecol. Environ. 17, 39–47 (2019).
- Erbe, C. et al. The Effects of Ship Noise on Marine Mammals—A Review. Frontiers in Marine Science 6, 606 (2019).
- Vanderlaan, A. S. M. & Taggart, C. T. Vessel collisions with whales: The probability of lethal injury based on vessel speed. Mar. Mamm. Sci. 23, 144–156 (2007).