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 1. Summary of survey effort in the four strata during aerial surveys conducted in Melville Bay from 25 to 30 August 2014.

											Aerial observers
a Including 180 off-effort images that were not used in the analysis. b Ind. = individuals.
						Image		Aerial observers			(truncated 500 m)
		Planned/	Length of
	Area	completed	surveyed	Analyzed	No. of	No.	Ave. group	No. of	No.	Ave. group	No. of	No.	Ave. group
Stratum	(km2)	transects (no.)	transects (km)	images a	sightings	of ind.b	size n (CV)	sightings	of ind.	size n (CV)	sightings	of ind.	size n (CV)
NW	6,376	5 / 4	226	2,066	0	0	0 (0)	0	0	0 (0)	0	0	0 (0)
NE	2,076	11 / 12	468	6,572	23	49	2.1 (0.95)	15	39	2.6 (0.77)	13	32.5	2.5 (0.76)
C	2,621	9 / 18	663	8,193	39	86	2.2 (0.73)	48	188	3.9 (0.69)	23	93.5	4.1 (0.61)
S	3,748	13 / 10	575	4,105	0	0	0 (0)	0	0	0	0	0	0
All strata	14,821	38 / 44	1,932	20,936	62	135	2.2 (0.77)	63	227	3.6 (0.72)	36	126	3.5 (0.69)