Fisheries risks to Antipodean Albatrosses

A report by R. Francis and colleagues to New Zealand’s Ministry for Primary Industries considers the risks imposed by fisheries on ACAP-listed and Vulnerable Antipodean Albatrosses Diomedea antipodensis gibsoni which breed on Adams Island in the Auckland Island Group.

The report’s executive summary follows:

“This report attempts to assess fisheries risks to the population viability of Gibson’s wandering albatross (Diomedea gibsoni), which is endemic to the Auckland Islands and classified as Nationally Critical under the New Zealand Threat Classification System.   Three data sets covering a 21-year period (1991– 2011) were analysed: mark-recapture, nest-based, and counts of breeders. There is cause for concern about the status of this population.  Since 2005, the adult population has been declining at a rate of 5.7%/yr, because of sudden and substantial reductions in three demographic rates: adult survival (from 0.95 to 0.89), proportion breeding (from 0.53 to 0.37), and the proportion of breeding attempts that are successful (from 0.60 to 0.25).  It is now about two-thirds of its estimated size in 1991.  The breeding population dropped sharply in 2005, to 59% of its 1991 level, but has been increasing since 2005 at about 4.2% per year because of slow increases in adult survival and proportion breeding.  The current (2011) breeding population is estimated to be only 54% of the average of 5831 pairs estimated by Walker & Elliott (1999) for 1991–97.  It is difficult to assess the effect of fisheries mortality on the viability of this population.  There is some information about bycatch of Gibson’s in New Zealand waters, and of wandering albatrosses (species unknown) in Australian waters, but little is known about the effect of fisheries in international waters.  Three conclusions are possible from the available data: most fisheries mortality of this species is caused by surface longlines; mortality from fishing is now probably lower than it was; and there is no indication in the data that the sudden and substantial drops in the three above-mentioned demographic rates were caused primarily by fishing.  Forward projections showed that, of these three demographic rates, the most important to the future status of this population is adult survival.  The extent to which this species exhibits philopatry (i.e., breeds where it was born) is not known, and this compromised our ability to estimate juvenile survival.  Assuming full philopatry, the annual rate of juvenile survival was estimated to be 0.88; this will be an under-estimate if philopatry is partial.  The mean age of first breeding was estimated to be 12.4 y.”

Antipodean Albatrosses on Adams Island, photograph by Colon O'Donnell

Reference:

Francis, R.I.C.C., Elliott, G. & Walker, K. 2015.  Fisheries risk to the viability of Gibson’s wandering albatross Diomedea gibsoni.  New Zealand Aquatic Environment and Biodiversity Report No. 152.  48 pp.

John Cooper, ACAP Information Officer, 22 September 2015