August 2012
Read about shag interactions with commercial rock lobster pot and trap fishing methods in the Chatham Islands.

Read about shag interactions with commercial rock lobster pot and trap fishing methods in the Chatham Islands. This project was commissioned as part of the Conservation Services Programme project INT2011-02.

Pitt Island shags. Photo: Igor Debski.
Pitt Island shags at a nest


Three species of shag breed in the Chatham Islands, two of which Chatham Island Shag and Pitt Island shag are endemic. The populations of both these species have suffered significant declines in the past 15 years. Accidental bycatch of shags has been reported from the Chatham Islands rock lobster fishery, but there has been no qualitative research into the issue.

Internationally studies of seabird interactions (including shags) in pot and trap fisheries are limited, with shag interactions reported from the Chatham Islands, New Zealand, Australia, North and South America, and few studies have quantified the level of shag bycatch.

Outside of New Zealand there have been no mitigation measures developed for seabird interactions with commercial pot and trap fisheries, including shag/ cormorant interactions. This is probably as a result of the low levels of shag interactions reported. The CRA6 Industry Association has been operating a seabird interaction code of practise since the issue of shag interactions was drawn to their attention in 2010. This appears to be the first such mitigation practise developed for pot and trap fishing in relation to seabird interactions.

Between the 1979/80 – 2009/10 fishing season the annual number of pot lifts has remained relatively stable with an average of 285,300 pot lifts per season (range 163,500 – 428,000), although the number of boats has declined from around 48 to 34.Interviews were carried out with 22 past and present fishermen to determine shag interactions with commercial rock lobster pot fishing in the Chatham Islands. Nine of these fishermen reported catching between 1-5 Pitt Island shag during their entire fishing career.

Fishermen reported a total of 20 captures of Pitt Island shag, captures where widely distributed throughout the Chatham Islands although more bycatch was reported from Area 942 than other areas. All reported bycatch occurred at least 5 years ago, and most over 10 years ago. Generally fishermen could not recall precise dates of shag interactions, but related the bycatch to pot and bait type, commenting that they changed baiting methodology 10-15 years ago.
Fishermen who reported bycatch reported that shag captures occurred when they were using hanging baits and they thought shags were attracted to the bait, or small fish attracted to that bait when pots were first lowered into the water. These fishermen reported that since they moved to using snifters (bait holders) they had not caught shags.

Fishermen noted that at the time of their shag interaction they were using a different pot design than they do presently. The pots had a larger neck and were covered with large mesh, it was considered that the larger neck and mesh size of old pots provided more opportunity for shags to enter pots, either through the neck or even through the mesh. Modern pots have a narrower neck and smaller mesh size.

Publication information

Author: Mike Bell

This report was prepared by Wildlife Management International Limited for the Department of Conservation as fulfilment of Contract 4342 (INT2011-02 Shag interactions with commercial pot and trap fishing methods in New Zealand).


Conservation Services Programme
Department of Conservation
PO Box 10-420
Wellington 6143


Back to top