Sightings of southern right whales around mainland New Zealand 1976-2002

Study Extent

Around the main islands of New Zealand (the 'mainland')

Sampling

Southern right whale sightings and photographs were obtained by contacting selected individuals, the Department of Conservation (DOC) and other organisations. These included DOC Regional Offices and Conservancies, whale-and dolphin-watching tour operators, members of the public, vessel logs from fishers, marine mammal researchers, DOC sighting sheets (forwarded by A.N.Baker), the printed press, television archives, and a sighting list collated opportunistically over the past seven years.

Method steps

1. Southern right whale sighting information collected included, when available: date, location, group size and group composition, observed behaviour, the person that first reported the sighting, estimated length of the whales, and whether or not photographs were taken. Although southern right whales are easily identifiable (black, lack of dorsal fin, v-shaped blow), it was impossible to confirm that some sightings were of right whales. These sightings were listed as‘unconfirmed’ and not included in the analysis.
2. Determining group composition, in particular if an animal was a calf, can be difficult for an observer who is not familiar with right whales. Generally, a calf is defined as an animal whose body when visible at the surface is less than half of the length of an accompanying adult, and the accompanying adult is assumed to be the cow. From this author’s experience, members of the public often call a calf an animal that is smaller in size than the companion whale (e.g. juvenile). In this study, sightings considered as definite cow/calf pairs were confirmed by at least one of the following: sighting by an experienced observer; photographs; or when the estimated length of the animal was reported to be between 4.5 and 6 m. Instances when the person reporting indicated that an animal may have been a calf, but status was not confirmed, were listed as such and excluded from analysis pertaining to cows and calves.
3. Instances when two or more reported sightings were on the same days or within a few days of each other, and in the same location or within a few n.m. of each other, were considered likely resightings if the group size and group composition were similar. This subjective method of grouping sightings is based on right whale behaviour and movement at other southern right whale grounds. The grouping of sightings may downward-bias the number of true unique sightings. However, some ‘unique’ sightings may have been duplicate sightings of the same whales seen several days apart. This will upward-bias the true number of unique sightings. Without individual photo-identification records of each sighting, the extent of these biases are impossible to resolve.
4. Positions are recorded to the nearest minute of degree. These positions are then checked in a GIS to see if they match the location description. Where there is a gross mis-match, positions are re-located to match the written locations.

Southern right whale

1. Eubalaena australis
   rank: species

The mainland of New Zealand (North, South, and Stewart Islands)