441 



Abstract — Management of coastal 

 species of small cetaceans is often 

 impeded by a lack of robust estimates 

 of their abundance. In the Austral 

 summers of 1997-98, 1998-99, and 

 1999-2000 we conducted line-transect 

 surveys of Hector's dolphin iCepha- 

 lorhynchus hectori) abundance off the 

 north, east, and south coasts of the 

 South Island of New Zealand. Survey 

 methods were modified for the use of 

 a 15-m sailing catamaran, which was 

 equipped with a collapsible sighting 

 platform giving observers an eye- 

 height of 6 m. Eighty-six percent of 

 2061 km of survey effort was allo- 

 cated to inshore waters (4 nautical 

 miles [nmi] or 7.4 km from shore), 

 and the remainder to offshore waters 

 (4-10 nmi or 7.4-18.5 km from shore). 

 Transects were placed at 45° to the 

 shore and spaced apart by 1, 2, 4, or 8 

 nmi according to pre-existing data on 

 dolphin density. Survey effort within 

 strata was uniform. Detection func- 

 tions for sheltered waters and open 

 coasts were fitted separately for each 

 survey. The effect of attraction of dol- 

 phins to the survey vessel and the 

 fraction of dolphins missed on the 

 trackline were assessed with simul- 

 taneous boat and helicopter surveys 

 in January 1999. Hector's dolphin 

 abundance in the coastal zone to 4 

 nmi offshore was calculated at 1880 

 individuals (CV=15.7%, log-normal 

 95% 01 = 1384-2554). These surveys 

 are the first line-transect surveys for 

 cetaceans in New Zealand's coastal 

 waters. 



Small-boat surveys for coastal dolphins: 

 line-transect surveys for Hector's dolphins 

 (Cephalorhynchus hectori) 



Stephen Dawson 1 

 Elisabeth Slooten 2 

 Sam DuFresne' 

 Paul Wade 3 

 Deanna Clement 2 



1 Department of Marine Science 

 University of Otago 

 340 Castle Street 

 Dunedm, New Zealand 

 E-mail address stevedawsoofastonebow otago acnz 



•"Zoology Department 

 University of Otago 

 340 Castle Street 

 Dunedm, New Zealand 



3 National Marine Mammal Laboratory 

 National Marine Fisheries Service 

 7600 Sand Point Way NE 

 Seattle, Washington 98115 



Manuscript submitted 27 April 2003 

 to Scientific Editor's Office. 



Manuscript approved for publication 

 3 March 2004 by the Scientific Editor. 



Fish. Bull. 201:441-451 (2004). 



Several international workshops on 

 cetacean bycatch problems have stated 

 that a key impediment to the conser- 

 vation of coastal and riverine small 

 cetaceans is the lack of quantitative 

 data on abundance (e.g., IWC, 1994). 

 An important reason for this lack of 

 data is that line-transect surveys are 

 often conducted from large (>50 m) 

 vessels (e.g. Barlow, 1988) and hence 

 are extremely expensive ($US 10,000/ 

 day). Such costs usually put high-qual- 

 ity surveys such as those conducted 

 for harbor porpoise in the U.S. (e.g., 

 Carretta et al„ 2001) beyond the reach 

 of less affluent nations. The need for 

 abundance estimates is especially 

 great for the coastal and riverine spe- 

 cies found in Asia, Africa, Australasia, 

 and South America (Table 1). Several 

 of these species have apparently small 

 populations and restricted distribu- 

 tions, and all suffer from being taken 

 as bycatch in fishing gear, principally 

 in gill nets (IWC, 1994). In addition, it 

 is difficult or impossible for large ves- 

 sels to work close to shore, in shallow 

 waters, where some of these species 

 are most common. 



The work described in this contri- 

 bution had two aims: 1) to adapt ship- 

 based line-transect methods (e.g., 

 Barlow, 1988) to a 15-m catamaran, 

 and 2 ) to provide an updated estimate 

 of the abundance of Hector's dolphin 

 (Cephalorhynchus hectori). Hector's 

 dolphin, a small delphinid found 

 only in the inshore waters of New 

 Zealand, is subject to bycatch in gill 

 nets throughout its range (Dawson et 

 al., 2001). At least in the Canterbury 

 region, and off the North Island west 

 coast, recent catch levels are clearly 

 unsustainable (Dawson and Slooten, 

 1993; Martien et al., 1999; Slooten et 

 al., 2000; Dawson et al.. 2001). Stud- 

 ies of mt-DNA indicate that the very 

 small North Island population is dis- 

 tinct and that there are at least three 

 separate populations in South Island 

 waters (Pichler et al., 1998; Pichler 

 and Baker, 2000; see also Baker et 

 al., 2002). At the time of the present 

 study the only quantitative population 

 estimate was from a strip-transect 

 survey conducted in 1984-85 (Daw- 

 son and Slooten, 1988), in which the 

 offshore distribution, as well as the 



