A comparison of image and observer based aerial surveys of narwhal Author Bröker, Koen C. A. Shell Global Solutions International B. V., Kesslerpark 1, 2288 GS, Rijswijk, the Netherlands and Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, the Netherlands; koen.broker@shell.com Author Hansen, Rikke G. Greenland Institute of Natural Resources, ℅ Greenland Representation, Strandgade 91, 2, DK- 1401 KØbenhavn K, Denmark; Author Leonard, Kathleen E. LGL Alaska Research Associates, Inc., 2000 West International Airport Road, STE C- 1, Anchorage, Alaska 99502, U. S. A.; Author Koski, William R. LGL Limited environmental research associates, 22 Fisher Street, PO Box 280, King City, Ontario L 7 B 1 A 6, Canada; Author Heide-Jørgensen, Mads Peter Greenland Institute of Natural Resources, ℅ Greenland Representation, Strandgade 91, 2, DK- 1401 KØbenhavn K, Denmark. text Marine Mammal Science 2019 2019-01-31 35 4 1253 1279 http://dx.doi.org/10.1111/mms.12586 journal article 10.1111/mms.12586 1748-7692 13221822

Table 3. AIC values after fitting explanatory variables to the DS and MR models. The final model chosen, Model 1, is given in bold and ΔAIC indicates the difference between the chosen model and the specified model. HN indicates a half-normal form and HR indicates a hazard-rate form for the DS model. The explanatory variables are perpendicular distance (D), group size (S), group size as a factor with three classes (1, 2–5, and ≥ 6 narwhals) (S3), Beaufort (BF), side of airplane (SP), observer pair (O), and time to next observation ≤ 10 s (T). Appendix S3 provides an overview of all the models that were developed.

Model	DS model	MR model	No. of parameters	AIC	ΔAIC
1	HN: D + BF	D + O + S 3	5	1,330.91	0
2	HN: D + BF	D + O + S	5	1,332.81	1.90
3	HN: D + BF + S3	D + O + T	6	1,333.10	2.19
4	HN: D + BF	D + O	4	1,333.50	2.59
5	HN: D + BF + S3	D + O	5	1,335.08	4.17
6	HR: D + BF	D + O + S3	5	1,336.97	6.06