Dawson et al.: Line-transect surveys of Cepha/orhynchus hectori 



443 



every 30 minutes to avoid fatigue. Although Hector's 

 dolphins are easily identified from other species, and 

 group size is typically small (usually 2-8; Dawson and 

 Slooten, 1988), in order to maintain even sighting effort 

 on both sides of the trackline, observers did not confer 

 during a sighting. Sighting information was entered into 

 a custom-written program on a Hewlett-Packard 200LX 

 palmtop computer on the sighting platform. Data record- 

 ed included horizontal sighting angle, downward angle 

 to sighting (in reticles), species, group size, orientation 

 of the animals when first sighted, depth, Beaufort sea 

 state, swell height, glare, GPS fix, date, and time. The 

 program also recorded survey effort by storing a GPS fix 

 every 60 seconds. Weather conditions were recorded at 

 the start of field effort, and whenever they changed. 



Observers used reticle- and compass-equipped Fujinon 

 7x50 (WPC-XL) binoculars to make sightings and to 

 measure the downward angle from the land, or horizon, 

 to the sighting. If the former, the corresponding dis- 

 tance to land was measured with RADAR (Furuno 1720 

 model), or, if within a few hundred meters of shore, 

 with a Bushnell lightspeed laser rangefinder (tested 

 accuracy ±1 m from 12 to 800 m). We calibrated the ac- 

 curacy of the RADAR by comparison with transit fixes 

 and laser rangefinder measurements. Sighting angles 

 were recorded by using angle boards (see Buckland et 

 al., 1993) in the first season, and thereafter with the 

 compasses in the binoculars. There were no ferrous 

 metals or significant electrical fields within 6 m of the 

 sighting platform. 



Navigation was facilitated by the use of a Cetrek 343 GPS 

 chartplotter with digitized C-MAP charts onto which 

 transect waypoints were plotted. Depths were measured 

 with a JRC JFV-850 echosounder (at 200 kHz). 



At the start of each survey, several days were spent 

 training observers at Banks Peninsula, where sighting 

 rates are high. Training continued until we gained 

 about 100 sightings (data gathered in this period were 

 not used in the analyses). An observer manual (avail- 

 able from authors) specified scanning behavior and 

 recording methods. To ensure a wide shoulder on the 

 histograms of perpendicular sighting distances, observ- 

 ers were instructed to concentrate their effort within 

 45° of the trackline and to spend less time searching 

 out to 90°. Observers spent about 85% of the time scan- 

 ning with binoculars. Regular scans with the naked eye 

 minimized fatigue and reduced the chance of missing 

 groups close to the boat. To promote consistency, observ- 

 ers were asked to re-read the manual at least once a 

 week throughout the survey. 



While the survey was underway, exploratory data 

 analyses were undertaken to assess data quality. These 

 analyses showed that in the early stages of the first sur- 

 vey, observers were rounding angles of sightings close to 

 the trackline to zero. The use of the angle boards was 

 modified to minimize this problem, and they were not 

 used in subsequent surveys. The data from these early 

 lines were discarded and the survey lines repeated. 



Survey effort was restricted to sea conditions of Beau- 

 fort 3 or less and swell heights of <2 meters. Transect 



lines were run down-swell and down-sun to minimize 

 pitching and effects of glare. Deviations of up to 10° from 

 the intended course were made if needed to further re- 

 duce pitching or glare. The inshore end of each line was 

 surveyed to just outside the surf zone on open coasts, 

 or until a 2 m depth was reached, or to within 50 m 

 of rocky shores. All surveys were conducted in passing 

 mode to minimize the extent of vessel attraction. 



Line-transect data were collected in three surveys in 

 three consecutive summer seasons, each focussing on 

 a particular coastal area (Fig 2; Motunau to Timaru, 

 5 January-21 February 1998; Timaru to Long Point, 

 9 December 1998-16 February 1999; Farewell Spit to 

 Motunau, 17 December 1999-28 January 2000). 



Survey design 



In order to obtain a clear picture of density and to mini- 

 mize variance in encounter rate, Buckland et al. (1993) 

 recommend placing transects across known density 

 gradients. Because short-distance, alongshore move- 

 ments are well-known for Hector's dolphins (Slooten and 

 Dawson, 1994: Brager et al., 2002) and the dolphins' 

 density declines sharply with distance offshore (Dawson 

 and Slooten, 1988), transects were placed at 45° to the 

 coast. On curved coastlines (within strata) we divided 

 the coastline into blocks, drew an imaginary baseline 

 along the coast, and placed lines at 45° to that baseline. 

 The starting point of the first line along the baseline 

 was decided randomly; thereafter lines were spaced at 

 regular intervals according to the sampling intensity 

 required in that stratum (Fig. 2). Within harbors we 

 placed lines at 45° to an imaginary line down the center 

 of the harbor (Fig. 3). The aim of this scheme was to 

 ensure that, within a stratum, any one point had the 

 same chance of being sampled as any other. 



Survey effort was stratified according to existing data 

 on distribution, obvious habitat differences, and areas 

 of intrinsic management interest. In summer, very few 

 Hector's dolphins are seen beyond four nmi from shore 

 (Dawson and Slooten, 1988); therefore most sampling 

 effort was placed in this inshore zone (i.e. 45° lines at 

 2-, 4-, or 8-nmi spacings, approximately proportional to 

 density as determined from previous surveys). Within 

 harbors, transect spacings were either one or two nau- 

 tical miles. In the offshore zone (from 4 to 10 nmi) we 

 expected very low densities, and therefore used sparse 

 transect spacing (-30 nmi apart). It was not our inten- 

 tion to estimate density in this offshore zone. A subse- 

 quent aerial survey was found to be better suited for 

 this purpose (Rayment et al. 1 ). 



Our goal was to estimate effective half strip width 

 (ESW) separately for strata with different exposure 

 to wind and swell. Hence, in each survey we aimed to 

 gain sufficient sightings to estimate ESW separately for 

 harbors or protected waters, and open coasts. To reach 



1 Rayment, W., E. Slooten, and S. M. Dawson. 2003. Unpubl. 

 data. Department of Marine Science, Univ. Otago, P.O. Box 

 56, Dunedin, New Zealand. 



