How Much Does a Swimming, Underweight, Entangled Right Whale Weigh? Calculating the Weight of Right Whales (Eubalaena glacialis) at Sea, to Facilitate Accurate Dosing of Sedatives, to Enable Disentanglement from Fishing Gear
Fishing gear entanglement represents a significant source of anthropogenic mortality in North Atlantic right whales (Eubalaena glacialis).1 The current methods of photo identification and postmortem examination of stranded carcasses give a good indication of the prevalence of entanglements. Consistent monitoring of the trends in entanglements has demonstrated a rise in the number of whales affected.2 The implications of this trend are of serious concern in an already endangered species. Mortality as a result of entanglement can be a chronic process with the average time entangled lasting six months and the maximum known extending to eighteen months.3 The persistence of terminal entanglements demonstrates the urgent need to improve individual entanglement mitigation.3 Additional insight as to why large right whales become severely entangled will depend on continued monitoring.4
Disentanglement of whales from fishing gear is one potential mitigation option; however, approaching a distressed right whale is challenging. North Atlantic right whales are the least tractable species to disentangle due to their persistent and successful avoidance of close-approaching vessels.5 Due to their increased muscle strength compared to other species right whales have actually been shown to be less tolerant to the additional drag placed upon them during a disentanglement effort, thrashing even more.4 Effective sedation methods are therefore even more applicable to this species to facilitate approach.
Accurate sedative dosing is therefore paramount to reduce the risk of fatalities in an already compromised individual. Overdosing an entangled animal could increase the anesthetic risk of loss of consciousness, potentially resulting in a failure to locomote in the aquatic species ultimately leading to apnea due to the inability to remain at the surface. Accurate body weight estimation is therefore required to facilitate calculating the correct dose. We hypothesise that if the width and length of right whales are linearly related, then the use of an allometric model to determine the weight at sea of right whales could be established.
We successfully created an allometric formula relating length and circumference measurements obtained from carcasses to facilitate accurate weight estimate from photogrammetry images of entangled North Atlantic right whales at sea.
Weight = 6044.79 – 17.88 x L - 9.14 x C + 0.05 x (L x C)
L = snout to tail notch length and C = circumference at 40% of body length
Despite there being extensive morphometric data available for the right whale, accurate body weights still remain extremely sparse. We have shown that weight estimations can be obtained from morphometric data for both mesomorphic and underweight right whales. By focusing our research on underweight right whales we aim to increase the accuracy of dosing already compromised individuals. However, no matter how well the disentanglement process is developed, the only lasting solution to the entanglement problem is avoidance of entanglement in the first place. Further research into the prevention of entanglements will be necessary to mitigate this anthropogenic cause of mortality in North Atlantic right whales.
This study was carried out in fulfillment of the Wild Animal Health MSc degree at the Royal Veterinary College and the Zoological Society of London. We gratefully acknowledge the Right Whale Consortium (RWC) particularly H. M. Pettis for access to the RWC database. We would also like to acknowledge Katie Jackson, Julie van der Hoop, Wayne Perryman, Victoria Starczak and Yu-Mei Chang. This project was made possible through funding from the IAAAM Medway Scholarship, UFAW Animal Welfare Student Scholarship, The Zebra Foundation and the North Pond Foundation.
* Presenting author
+ Student presenter
1. Glass AH, Cole TVN, Garron M, Merrick RL, Pace RM. Mortality and serious injury determinations for baleen whale stocks along the United States eastern seaboard and adjacent Canadian maritimes. Fisheries Science. 2008;1:2002–2006. US Department of Commerce.
2. Knowlton A, Hamilton P, Marx M, Pettis H, Kraus S. Monitoring North Atlantic right whale Eubalaena glacialis entanglement rates: a 30 yr retrospective. Marine Ecology Progress Series. 2012;466:293–302.
3. Moore MJ, Van Der Hoop JM. The painful side of trap and fixed net fisheries: chronic entanglement of large whales. Journal of Marine Biology. 2012:1–4.
4. Johnson A, Salvador G, Kenney J, Robbins J, Kraus S, Landry S, Clapham P. Fishing gear involved in entanglements of right and humpback whales. Marine Mammal Science. 2005;21(4):635–645.
5. Moore M, Walsh M, Bailey J, et al. Sedation at sea of entangled North Atlantic right whales (Eubalaena glacialis) to enhance disentanglement. PloS One. 2010;5(3):e9597.