Migratory whales and ‘passive’ bycatch
While small cetaceans, including Cephalorhynchus hectori māui (Māui Dolphin) and Phocoena sinus (Vaquita) are vulnerable to incidental capture (see Bycatch & Incidental Capture of Cetaceans under Impacts), large migratory baleen whale species are particularly prone to entanglement in fishing gear.
Humpback whales, gray whales and right whales utilise shallow, inshore areas to breed, seek shelter and give birth. Large migratory whale species often frequent locations where they are more likely to encounter, and become entangled in, discarded fishing gear, than are other species found in deeper, offshore waters (DAWE 2021).
Entanglement in fishing gear is potentially fatal due to complications from infection, starvation or drowning. If the whale survives, it may experience changes in energy budgets. Entangled whales require more energy to swim (van der Hoop et al. 2017), leaving less energy available for other requirements.
Entanglements in fishing gear is one of many threats facing large baleen whale species, with no single threat being solely responsible for a species’ expected demise or hampered recovery.
Migratory whales in Australian waters
Two species of migratory baleen whales inhabit Australian waters – Eubalaena australis (Southern Right Whale) and Megaptera novaeangliae (Humpback Whale). Both species experienced a severe reduction in numbers due to the impacts of commercial whaling, but face new threats in the recovery phase, including increased fishing activity, aquaculture, entanglements in discarded fishing gear and other non-fishing-related marine activity that occurs within their migratory routes. Reported incidence of entanglements in fishing ropes and nets are increasing in Australia (DAWE 2021).
The conservation status of E. australis (Southern Right Whale) was changed from Critically Endangered in 2013 to Endangered in 2020, under the Environment, Protection, Biodiversity and Conservation (EPBC) Act however, despite some evidence of population increase, current abundance estimates are below historical estimates (DSEWPC 2012).
The conservation status of M. novaeangliae (Humpback Whale) is currently being re-assessed. Evidence provided in a government submission supporting the removal of the species from the EPBC’s Threatened Species List indicates that Australia’s East and West coast humpback whale populations have recovered beyond the original size of their pre-whaling populations, increasing 10-11% annually over the past decade, but this data has been rejected by whale researchers (Whales & Climate Research Program 2021).
The North Atlantic Right Whale (Eubalaena glacialis)
E. glacialis (North Atlantic Right Whale) may be at risk of extinction due to increased mortality from a combination of threats, including entanglements in fishing gear, ship strikes and low reproductive rates. Although the species’ southern counterparts, the humpback whales and southern right whales in Australian waters, may not be as severely at risk from entanglements, it is accepted that a leading driver of death and possible extinction of the North Atlantic Right Whale is entanglement in fishing gear.
The conservation status of E. glacialis (North Atlantic Right Whale) has been upgraded from Endangered to Critically Endangered on the IUCN Red List, with a decreasing population trend, and only 200 – 250 mature individuals remaining (IUCN 2020). In 2020, the IUCN reported that between 2012 and 2016, 26 out of the 30 deaths or injuries to North Atlantic Right Whales caused by human activity were due to entanglements in fishing gear.
The North Atlantic Right Whale Consortium (NARWC) Annual Report Cards provide the ‘Best Right Whale Population Estimate’ for the North Atlantic Right Whale population each year. Previous population estimates indicated 451 individuals were alive at the end of 2016, 411 at the end of 2017, 409 at the end of 2018 (Pettis et al. 2019), and 356 at the end of 2019, with only 77 reproductively mature females (Pettis et al. 2020).
A recent study using high-resolution aerial photogrammetry examined trends in the size and body condition of 129 E. glacialis (North Atlantic Right Whale) individuals to determine current size compared to historical size (Stewart et al. 2021).
The results of this study showed North Atlantic Right Whales that had experienced severe entanglement in fishing gear are shorter than those whales without any documented entanglement. Body lengths have decreased over the last 40 years, with a fully grown right whale today measuring one metre shorter than its 1980 counterparts. Female right whales also produce smaller calves (ibid.)
The researchers indicated the primary reason for the stunted growth was entanglement in rope and fishing gear however, it was acknowledged other factors may have contributed, including climate change, ship strikes, acoustic disturbance and changes in prey availability (ibid.)
Another study examined 626 photographic images of North Atlantic Right Whales between 1980 and 2009 and found evidence of 1032 unique instances of entanglement with fisheries gear (presence of rope or netting or visible scars from rope or netting). Of these whales, 82.9% were found to have been entangled at least once and 59% were found to have been entangled more than once (Knowlton et al. 2012).
Australian Government Department of Agriculture, Water and the Environment (DAWE), 2021, ‘Entanglements’, https://www.environment.gov.au/marine/marine-species/cetaceans/entanglements, accessed 17.07.2021
Australian Government Department of Sustainability, Environment, Water, Population and Communities (DSEWPC), 2021, Conservation Management Plan for the Southern Right Whale: A Recovery Plan under the Environment Protection and Biodiversity Conservation Act 1999, 2011–2021, https://www.environment.gov.au/system/files/resources/4b8c7f35-e132-401c-85be-6a34c61471dc/files/e-australis-2011-2021.pdf, accessed 17.07.2021
Cooke, J.G. 2020. Eubalaena glacialis (errata version published in 2020). The IUCN Red List of Threatened Species 2020: e.T41712A178589687. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T41712A178589687.en. Downloaded on 17 July 2021.
Knowlton, A., Hamilton, P., Marx, M.K., Pettis, H.M., & Kraus, S. (2012). Monitoring North Atlantic right whale Eubalaena glacialis entanglement rates: a 30 yr retrospective. Marine Ecology Progress Series, 466, 293-302. https://doi.org/10.3354/meps09923
Pettis, H.M. et al. 2020. North Atlantic Right Whale Consortium 2019 Annual Report Card. Report to the North Atlantic Right Whale Consortium. https://www.narwc.org/uploads/1/1/6/6/116623219/2019reportfinal.pdf, accessed 26.07.2021.
Pettis, H.M., Pace, R.M. III, Hamilton, P.K. 2021. North Atlantic Right Whale Consortium 2020 Annual Report Card. Report to the North Atlantic Right Whale Consortium. https://www.narwc.org/uploads/1/1/6/6/116623219/2020narwcreport_cardfinal.pdf, accessed 26.07.2021.
Stewart et al., Decreasing body lengths in North Atlantic right whales, Current Biology (2021), https://doi.org/10.1016/j.cub.2021.04.067
van der Hoop, J., Corkeron, P. and Moore, M. (2017), Entanglement is a costly life-history stage in large whales. Ecology and Evolution, 7: 92–106, https://doi.org/10.1002/ece3.2615
Whales & Climate Research Program, Griffith University, 2021, Statement in response to the proposed delisting of humpback whales (Megaptera novaeangliae) from the Threatened Species List in Australia, https://whalesandclimate.org/statement-in-response-to-the-proposed-delisting-of-humpback-whales-megaptera-novaeangliae-from-the-threatened-species-list-in-australia/, accessed 17.07.2021