Small-boat surveys for coastal dolphins: line-transect surveys for Hector's dolphins

Fishery Bulletin, July, 2004 by Stephen Dawson, Elisabeth Slooten, Sam DuFresne, Paul Wade, Deanna Clement

Table 1
Examples of coastal and riverine species of special conservation
concern.

Common name               Scientific name

Vaquita                   Phocoena sinus
Chilean dolphin           Cephalorhynchus eutropia
Hector's dolphin          Cephalorhynchus hectori
Commerson's dolphin       Cephalorhynchus Commersoni
Heaviside's dolphin       Cephalorhynchus heavisidii
Peale's dolphin           Lagenorhynchus australis
Finless porpoise          Neophocoena phocaenoides
Indo-Pacific humpbacked   Sousa chinensis
dolphins
Burmeister's porpoise     Phocoena spinipinnis
Franciscana               Pontoporia blainvillei
Indus river dolphin       Platanista minor
Ganges river dolphin      Platanista gangetica
Boto                      Inia geoffrensis
Tucuxi                    Sotalia fluviatilus

Common name               Habitat

Vaquita                   Northern Gulf of California
Chilean dolphin           Inshore coastal Chile
Hector's dolphin          Inshore coastal New Zealand
Commerson's dolphin       Inshore coastal Chile, Argentina, Falkland
                            Is, Kerguelen Is.
Heaviside's dolphin       Inshore coastal South Africa and Namibia
Peale's dolphin           Coastal Chile, Argentina, Falkland Is.
Finless porpoise          Coastal and riverine Asia and Indonesia
Indo-Pacific humpbacked   Inshore tropical and estuarine habitats in
  dolphins                western Pacific and Indo Pacific
Burmeister's porpoise     Coastal Chile, Argentina, Uruguay, Brazil
Franciscana               Coastal Brazil and Argentina
Indus river dolphin       Indus River
Ganges river dolphin      Ganges, Bramaputra, Karnphuli, Meghna rivers
Boto                      Amazon River
Tucuxi                    Coastal and estuarine Atlantic Central and
                            South America

Table 2
Survey effort by stratum. Number of sightings is the total number made
before truncation and quality auditing (see "Vessel choice and field
methods").

Survey zone                Stratum

Motunau to Timaru          Banks Peninsula harbors and bays
(1997-98)                  Banks Peninsula Marine Mammal Sanctuary
                             (BPMMS) (excluding open coasts)
                           <4 nmi offshore, to the north and south of
                             BPMMS
                           Offshore (4-10 nmi)
Timaru to Long Point       Timaru-Long Point (excluding Te Waewae Bay)
(1998-99)                  Te Waewae Bay
                           Offshore (4-10 nmi)
Motunau to Farewell Spit   Farewell Spit-Stephens Island
(1999-2000)                Marlborough Sounds (including Queen
                             Charlotte Sound)
                           Cape Koamaru-Port Underwood
                           Cloudy Bay and Clifford Bay
                           Cape Campbell-Motunau
                           Offshore (4-10 nmi)

Survey zone                 Survey     No. of    Sightings
                          effort(km)  sightings   per km
Motunau to Timaru            223         89        0.399
(1997-98)                    265         66        0.249

                             174         21        0.121
                              89          4        0.045
Timaru to Long Point         336         13        0.04
(1998-99)                    101         14        0.14
                             106          0        0
Motunau to Farewell Spit     120          0        0
(1999-2000)                  205          3        0.015
                              68          0        0
                              89         13        0.146
                             192          5        0.026
                              93          2        0.022

Table 3
Summary of variables required for correction factor
(boat-and-helicopter trials)

Parameter                                        Estimate

Length of transect, L (km)                           308
Truncation distance, w (km)                          1.0
Number of helicopter detections, [n.sub.h]            58
Number of ship detections, [n.sub.s]                 126
Number of duplicate detections, [n.sub.hs]            33
ESW of helicopter (km)                             0.532
ESW for duplicates (km)                            0.342
Apparent ESW of boat (km)                          0.268
Apparent density estimate (groups/[km.sup.2])     0.7631
Corrected density estimate (groups/[km.sup.2])    0.3839
Boat detection probability "near" trackline       0.8861
Correction factor (c)                             0.5032
Standard error, SE(c)                             0.0912

Table 4
Corrected abundance estimates (only strata with sightings are listed).
Number of sightings represents only those made in that stratum and
used for density estimation. The number used for estimating effective
half strip width. (ESW) differs because it includes sightings from
extra transects in areas of similar exposure and transects repeated
on the same day (and hence not true replicates for the purposes of
estimating density).

                                                 No. of       ESW (m)
Survey zone         Stratum                    sightings     (n, CV%)

Motunau to Timaru   Akaroa harbor                  56           275
  (1997-98)                                                 (71, 22.6)

                    Other harbors and bays          8           275
                                                            (71, 22.6)

                    Banks Peninsula Marine         62           261
                    Mammal Sanctuary (BPMMS)                (75, 10.3)
                    (excluding harbors and
                    bays)

                    <4 arm offshore, to the        19           261
                    north and south of BPMMS                (75, 10.3)

Timaru to Long      Timaru-Lung Point              13           268
  Point (1998-99)   (excluding Te Waewae                    (121, 10.5)
                    Bay)

                    Te Waewae Bay                  14           268
                                                            (121, 10.5)

Motunau to          Queen Charlotte Sound           3           214
  Farewell Spit                                             (70, 20.2)
  (1999-2000)
                    Cloudy and Clifford Bay        13           277
                                                             (89, 6.1)

                    Cape Campbell-Motunau           5           277
                                                             (89, 6.1)

Total

                                               [N.sub.(c)      Lower
Survey zone         Stratum                      (CV%)        95%n CI

Motunau to Timaru   Akaroa harbor                  62            32
  (1997-98)                                      (33.9)

                    Other harbors and bays         14             3
                                                 (67.5)

                    Banks Peninsula Marine        821           535
                    Mammal Sanctuary (BPMMS)     (22.1)
                    (excluding harbors and
                    bays)

                    <4 arm offshore, to the       300           133
                    north and south of BPMMS     (36.5)

Timaru to Long      Timaru-Lung Point             310           201
  Point (1998-99)   (excluding Te Waewae         (28.4)
                    Bay)

                    Te Waewae Bay                  89            36
                                                 (32.4)

Motunau to          Queen Charlotte Sound          20             4
  Farewell Spit                                 (100.5)
  (1999-2000)
                    Cloudy and Clifford Bay       162            56
                                                 (55.4)

                    Cape Campbell-Motunau         102            34
                                                 (55.2)

Total                                             1880         1246
                                                 (21.3)

                                                 Upper
Survey zone         Stratum                      95% CI

Motunau to Timaru   Akaroa harbor                  121
  (1997-98)
                    Other harbors and bays          79

                    Banks Peninsula Marine        1258
                    Mammal Sanctuary (BPMMS)
                    (excluding harbors and
                    bays)

                    <4 arm offshore, to the        679
                    north and south of BPMMS

Timaru to Long      Timaru-Lung Point              478
  Point (1998-99)   (excluding Te Waewae
                    Bay)

                    Te Waewae Bay                  218

Motunau to          Queen Charlotte Sound          110
  Farewell Spit
  (1999-2000)       Cloudy and Clifford Bay        474

                    Cape Campbell-Motunau          305

Total                                             2843