Fish-eating birds in Western Port: long-term trends. Peter Dann, Richard Loyn, Peter Menkhorst, Canran Liu, Birgita Hansen & Moragh Mackay

Transcription

1 Fish-eating birds in Western Port: long-term trends Peter Dann, Richard Loyn, Peter Menkhorst, Canran Liu, Birgita Hansen & Moragh Mackay

2 The most important science gaps Number 12. Examine the trends in abundance of fish-eating birds in Western Port. Understanding the Western Port Environment A summary of current knowledge and priorities for future research Hansen, B., Menkhorst, P. and Loyn, R. (2011) Western Port Welcomes Waterbirds: Waterbird usage of Western Port. Arthur Rylah Institute for Environmental Research Technical Report Series. No.222. Department of Sustainability and Environment, Heidelberg, Victoria.

3 Hansen et al (2011) 17/37 species have declined in Western Port since 1974 Shorebirds - mudflat reclamation in the Yellow Sea? Waterbirds 10 years of drought? Fish-eating birds mostly residents, local causes? (Dennett & Loyn 2009)

4 Approach Our approach involved two key steps: 1. An analysis of the trends in abundance for fish-eating birds over the past 25 years ( ) for Western Port and Corner Inlet. 2. An analysis of the declines in relation to the foraging guilds, diets and sizes of the birds, and the timing of any observed change.

5 Locations of two study areas Essential differences in character are coarser sediments, dominance of Posidonia (seagrass), less developed catchment, reduced freshwater inputs & reduced shoreline in Corner Inlet

6 Survey methods Western Port Hansen et al. 2011

7 Survey methods West Corner Inlet

8 Fish-eating birds Surface seizers Australian Pelican Underwater pursuit Great Cormorant Pied Cormorant Little Pied Cormorant Little Black Cormorant Black-faced Cormorant Pursuit divers Crested Tern Caspian Tern Fairy/Little Terns Gull-billed Tern Visual jabbing Eastern Great Egret Little Egret White-faced Heron Filterers Royal Spoonbill 14 species (13 spp. ate >40% fish in their diets) 9 species breed in Western Port, other 5 species recorded breeding in Victoria Fall into 5 feeding guilds

9 NUMBER OF FISH-EATING BIRDS Fish-eating birds (14 species) Total fish-eating birds in summer (Western Port) TOTAL (Western Port) R² =

10 NUMBER OF FISH-EATING BIRDS Fish-eating birds (14 species) Total fish-eating birds in summer (Corner Inlet) Total (Corner Inlet) Linear (Total (Corner Inlet) ) R² = 0.62

11 NUMBER OF FISH-EATING BIRDS Fish-eating birds in summer (Western Port & Corner Inlet) TOTAL (Western Port) R² = Total (Corner Inlet) R² = 0.62

12 NUMBER OF FISH-EATING BIRDS Fish-eating birds in winter (Western Port & Corner Inlet) Total (Corner Inlet) Winter Total (Western Port) Winter Linear (Total (Western Port) Winter) R² =

13 Trends & guild type Pelican- no significant trend Cormorants no significant trend Herons & egrets no significant trend Terns significant decline in numbers Royal Spoonbills - significant decline in numbers

14 NUMBER OF TERNS Trends in tern numbers in Western Port (summer) CRESTED TERN TRENDLINE R² = 0.29 CASPIAN TERN FAIRY/LITTLE TERN CRESTED TERN Linear (FAIRY/LITTLE TERN) Linear (CRESTED TERN) FAIRY/LITTLE TERN TRENDLINE R² = 0.18

15 Crested Terns in summer and annual commercial catch

16 Numbers of breeding Royal Spoonbills in Western Port & Corner Inlet WESTERN PORT CORNER INLET R² = 0.36 Linear (WESTERN PORT) Linear (CORNER INLET) R² =

17 What do Crested & Fairy/Little Terns eat? Crested Tern Fairy/Little Tern Main fish in diet Anchovy Engraulis australis Jack Mackerel Trachurus declivis Barracouta Thyrsites atun Pilchard Sardinops sagax Anchovy Blue sprat Spratelloides robustus % fish in diet 93% frequency of occurrence brought to chicks at Nobbies, Phillip Island Chiaradia et al. (2002) Mostly fish Taylor & Roe (2004) Royal Spoonbill Bridled Goby Arenigobius bifrenatus 23% wet weight of prey in Western Port Lowe (1982)

18 Summary: Crested Terns Pursuit diving guild has declined significantly, mainly Crested Terns and Fairy/Little Terns Crested Terns have decreased in number inside Western Port but breeding numbers have increased greatly at the western entrance. Crested Terns numbers have increased in Corner Inlet in summer. Conclusion: Crested Terns use of Western Port for feeding has declined. while the local breeding populations of Crested Terns has increased. Management actions required: Develop abundance measures for monitoring key fish species in Western Port

19 Summary: Fairy/Little Terns Little/Fairy Terns numbers vary widely and appear to have decreased both in number feeding in Western Port & Corner Inlet and probably breeding locally. Conclusion: Fairy/Little Terns use of Western Port & Corner Inlet for feeding have declined. Management actions required: The decline of this species appears more widespread and a review of current trends and management across Victoria is required. Develop abundance measures for monitoring key fish species in Western Port

20 Summary: Royal Spoonbills Royal Spoonbills have declined significantly in Western Port in summer and have increased in Corner Inlet in summer. Likely that they haven t bred very successfully in Western Port over the last decade due to drought affecting breeding sites. Conclusion: Numbers in Western Port have declined for reasons that haven t operated in Corner Inlet. Management actions required: Continue to monitor numbers at high-tide roosts Monitor numbers and productivity of breeding colonies in Western Port

21 Acknowledgements Rhys Coleman of Melbourne Water for commissioning us to do this work, with funding from the Port Phillip and Westernport Catchment Management Authority through the Victorian Government s Natural Resources Investment Program (NRIP). BOCA (now Birdlife Australia) Western Port count volunteers since DSE- Fisheries & Wildlife & Parks Victoria & many volunteers who have helped in Corner Inlet since Rhys Coleman & Will Steele for comments on this analysis. Jeff Lacey for use of his Fairy Tern counts. Phillip Island Nature Parks and Victorian Wader Study Group for data on breeding Crested Tern numbers at the Nobbies.