Field methods

TheHG (Latitude 36° 10’ to 37° 10’ S, Longitude 174° 40’ to 175° 30’ E; Figure 2.1) is a relatively shallow (<60 metres (m) depth; Manighetti and Carter 1999; Black et al. 2000), semi-enclosed coastal body of temperate water located on the north-eastern coastline of the North Island, New Zealand. The Gulf is situated adjacent to Auckland city (Latitude 36° 50’ S, Longitude 174° 44’ E; Figure 2.1), New Zealand’s largest urban area. A line between Takatu Point on the mainland and Kaiiti Point on the Coromandel Peninsula was been used to delineate between the inner and outer HG (IHG and OHG; Wiseman et al. 2011; Figure 2.1). Surveys were only conducted in the IHG (hereafter referred to as the HG), which covers an area of 3,480 kilometres squared (km2_{) (Dwyer 2014). Delphinus}

59 in the HG primarily inhabit waters >30 m and are rarely observed within inshore bays of the IHG (e.g. Stockin et al. 2008a; Dwyer 2014). Considering this, surveys were primarily conducted in the central IHG, defined as the area between the 30 m isobath and the boundary line of the OHG (Figure 2.1).

Figure 2.1: Study area, the Hauraki Gulf (HG), New Zealand. The solid black line (from Takatu Point to Kaiiti Point) indicates the boundary between the inner and outer HG (IGH and OHG). The white and yellow lines indicate the 30 m and 100 m isobaths, respectively. The area between the 30 m isobath and the boundary to the OHG represents the central IHG (the primary area surveyed). Bathymetry is indicated by darker shades of blue, which represent deeper waters (Source: NIWA; et al. 2012 Mackay). Inset shows the location of the HG and North Island, relative to New Zealand. Source: Dwyer 2014.

60 2.2.1.2 Field methodologies

Opportunistic photo-id surveys were undertaken from February 2002 to December 2009. In addition, dedicated photo-id surveys were conducted inclusively from January 2010 to December 2013. Dedicated observations were conducted from two vessel types: Aihe II, a 5.5 m research vessel, fitted with a 120-horse-power (hp) four-stroke outboard engine, and; Dolphin Explorer, a 20.0 m commercial catamaran, powered by twin 350-hp engines. Both vessels focussed on surveying the central IHG region to identify the maximum number of dolphin groups per day. Non-systematic sampling was used by both vessels: a) due to the study area being too large to cover within a day, and; b) as systematic sampling of all regions of the IHG (e.g. inner bays) would have reduced the number of animals detected, therefore limiting the number of photo-ids obtained. Two vessels were used in an effort to increase the spatial coverage of the study area. When both vessels surveyed the same focal group, pseudo-replication was removed by pooling photographs captured on the same day. Only one photograph was used for each individual captured, regardless of the vessel it was photographed from.

Observer eye height for the research vessel and commercial platform was 0.5 m and 2.0 m, respectively. Given the known detectability issues associated with visual surveys for cetaceans (Hammond et al. 2011), survey conditions were adapted depending on platform type. Surveys on the research vessel were conducted in good visibility (≥1.0 kilometre; km), swell <1.0 m, and Beaufort Sea State (BSS) ≤3 (Stockin et al. 2008a). However, when on-board the commercial platform, surveys were conducted in similar visibility and swell, but up to BSS ≤4. The direction of travel was based upon the sea state and wind direction, with vessel speed maintained at 11.0 and 19.0 knots (kts) for the research vessel and tour platform, respectively. During surveys, vessels would move towards animals at a slow speed (~5.0 kts), travelling on a parallel course, and approaching from the rear (Stockin et al. 2008a). For each encounter with a dolphin group, the following data were collected: time; Global positioning system (GPS) location (using a Garmin Dakota GPS); group composition, and; group size. Individuals were classified as either immature (including neonates, calves, and juveniles) or adult (Appendix 2.1).

61 2.2.1.3 Photo-identification

A team of two to five trained observers, including the principle investigator, conducted concurrent photo-id sessions, following standardised methods (Würsig and Jefferson 1990). Dolphins located within a 100 m radius were considered to be part of the same group, with animals observed moving in the same direction and (usually) engaged in the same activity (e.g. Stockin et al. 2009a). Multiple images were taken at a 90° angle (Würsig and Jefferson 1990) when dolphins surfaced within 25 m of either vessel (Tyne et al. 2014). Only one side of the dorsal fin (left) was photographed following photo-id procedures outlined in Chapter 3 (Section 3.1.1.4). In summary, Chapter 3 focussed on capturing nicks and notches, which were defined as cut-like incisions (or lacerations) resulting in a tear of the epidermis on either the leading or the trailing edge of the dorsal fin (adapted from Luksenberg 2014). As as some individuals exhibited only minor nicks and notches, which were deemed not recognisable from both sides, only the left side of the dorsal fin was photographed. Photo-id was randomly collected for each individual in a group without bias towards marked or unmarked individuals (Würsig and Jefferson 1990). Regardless of group size, an attempt was made to photo-id as many individuals within the group as possible.

2.2.1.4 Grading and sorting of photo-identification images

Grading and sorting of photo-id images were undertaken using strict protocols. Images were compared manually, as per Tyne et al. (2014). All images were graded according to photographic quality (PQ) criteria (following Urian et al. 1999, 2014; Tyne et al. 2014), and only individuals with good or excellent quality images were used for analysis (for detailed information refer to Section 3.2.1.5 in Chapter 3). Individuals were identified by pigmentation patterns. Here, a pigmentation pattern-derived feature was defined as a dorsal fin exhibiting contrasting grey or white patterns (e.g. edge outlines and/or clusters of pigment), which allowed observers to identify distinctive corresponding sections of pigmentation between individuals (Figure 2.2). While both white and grey patterns are considered pigments, here, a dorsal fin possessing pigmentation was defined as the presence of white patterning. Each new prospective individual was carefully examined and all matches scrutinized by at least two independent experienced observers before being assigned a unique identification code. Each

62 photograph was date stamped to assess changes in pigmentation patterns over time.

Figure 2.2: Examples of distinguishable pigmentation patterns for two adult common dolphins (Delphinus sp.) (Dd_0328 and Dd_0953) photographed in the Hauraki Gulf, New Zealand. Red circles indicate distinctive corresponding sections of pigmentation.