Annual production of New Zealand sea lion

Data for monitoring the annual production of New Zealand sea lion were obtained by estimating the number of pups born in each year. These estimates were derived from direct counts of live and dead pups carried out at the sea lion colonies towards the end of the breeding season. The counts were performed when pupping was complete, but before the pups began to disperse. At the larger sites, a mark-recapture methodology was also used to obtain an estimate of the number of sea lion pups. The methodology used for the pup production estimates, and the rational for these methods, is described in Chilvers (2010).

The data presented here were obtained from a spreadsheet provided by the Department of Conservation, and by extracting the results from research reports. Where avalailable, individual counts made within each season are provided.


For information about the New Zealand sea lion tagging pup production estimation programme please contact the Conservation Services Programme ( For queries about the data grooming and preparation, please contact Finlay Thompson ( To report any technical problems with the website please email

Breeding sites

There are two pupping areas (Northern Auckland Islands and Figure of Eight Island) made up of four pupping sites at the Auckland Islands.

The four pupping sites, Sandy Bay (50°30'S, 166°17'E) and South East Point (SEP, 50°30'S, 166°19'E) on Enderby Island, Dundas Island (50°35'S, 166°19'E) and Figure of Eight Island (50°46'S, 166°01'E) were monitored each season.

Mark-recapture estimation

Mark-recapture experiments are a way of estimating the pup population at a breeding site when the size of the colony precludes direct counts of the pups.

A single M-R experiment was conducted each year at Sandy Bay on the 15th and 16th January and at Dundas Island on the 20th and 21st January. A fixed number of pups are marked with 6cm vinyl disks on their heads. The following day a series of recapture counts of both marked and unmarked pups is performed. The ratio of marked to unmarked pups is used as the basis for estimating the entire pup population.

Direct count estimation

Direct count estimates of pup production are carrying out that at the breeding sites where the number of pups is low enough to make this practical.

At the continuous monitored sites the direct count can be cumulative as the every birth and death during the pupping season is noted and so the population on any given day is always known accurately. At the larger or less frequently observed breeding sites several direct counts are performed and averaged.

Dead counts

Counts of dead pups are needed in order know the total pup production in a season.

At the larger or infrequently monitored sites the dead count is estimated by several surveys of the site on the given day in which the number of visible dead pups is counted. At the smaller continuously monitored sites each pup death is observed and the number of deaths that is occured by the day nominated for the population estimation experiments is known.