Endangered king shag numbers in the Marlborough Sounds are stable and the birds are foraging for food around marine farms, new reports have found.
The first report details an aerial survey done in the Sounds in February this year. Aerial surveys began in 2015 as part of a King Shag Management Plan, required as a consent condition for NZ King Salmon to establish new farms in Pelorus Sound.
The first aerial survey funded by NZ King Salmon found 834 king shags at nine roosting sites, but when repeated in 2018 only 633 birds were found at 10 sites. Last year, 789 king shags were seen from the plane and in February this year 815 birds were recorded across 13 sites.
Marlborough-based Wildlife Management International Ltd (WMIL) which oversaw the aerial flight says fluctuations in numbers may be due to several factors including annual breeding variations and counts missing some roost sites, as is suspected to have occurred in 2018.
WMIL’s Mike Bell says this year’s count is comparable to earlier counts.
“It suggests king shag numbers are stable; continuing with aerial surveys will help prove this and provide certainty around population trends.”
WMIL is also the author of an interim report from a three-year research project, funded by the Marine Farming Association (MFA) and Seafood Innovations Limited (SIL), on king shag. This included work to determine where king shags were sited, banding some birds and putting GPS tracking devices on six other birds. The focus was on the Tawhitinui and Duffers Reef colonies in Pelorus Sound. Tawhitinui is a newer colony in a relatively sheltered area and connected to the mainland (king shag nesting sites in more exposed locations are at risk from increasing strong storms linked to climate change). The Duffers Reef site is the largest king shag breeding colony, accounting for about half the total population.
Mike Bell says the GPS devices showed all six king shags tracked spent some time roosting on mussel farms; four foraged near and another in a mussel farm. One overnighted on a mussel buoy.
Further tracking of king shags is planned under the research project next month with more birds to have GPS devices attached.
Another study has also shown king shags roost or forage around mussel farms.
Wildlands Consultants were commissioned by the MFA and SIL to investigate marine farm interactions. The study says previous assessments have speculated mussel farm structures may deter foraging and their waste may make the habitat less favourable for fish species that king shag favour.
In fact, Wildlands observed king shags using three out of eight monitored mussel farms for foraging and roosting, which it said could be considered a high ‘hit rate.’ The report also noted overall bird abundance at the mussel farms sites was much greater than at the control sites.
“This is a very significant result from the pilot study,” said the Wildlands study, which recommended expanding the work to more sites.