Tag Archives: Biodiversity

The Harbour Hang-Over

Recently I received a message from a Peninsula resident who had been cleaning up a section of the Otago Harbour of plastic and other rubbish. Now as a keen fisherman and diver I found their efforts impressive, but it was also depressing at the amount of plastic they removed from around the harbours edge. The prevalence of plastic in the harbour that is washed up onto the tidal bays is quite significant and has become a chief villain in the conservation of wildlife and sea fish stocks. More attention has been brought to plastic entering our waterways in recent years, but it’s not actually a new problem. As early as 1977, Gregory R. Murray from the University of Auckland found microplastics in almost all the coastal areas he surveyed.  

The White-capped Mollymawk or Shy Albatross is a regular to the Otago Coast and like most sea birds is vulnerable to ingesting plastic through surface feeding.

The problem with plastic waste when it enters the harbour ecosystem is that it fragments due to tide, waves and sunlight into microplastics that are often less than 1 mm in size. That small size enters the marine food chain in krill, crabs and shellfish and eventually makes its way into fish, birds, marine mammals and even humans. Sea birds are particularly vulnerable to eating plastic because they are largely surface feeders, diving down and scooping up pray along with plastic on the waters surface. This is particularly worrying for Dunedin and the Otago Peninsula whose populations of coastal sea birds include the Yellow-eyed Penguin, Blue Penguin, Red Billed Gull, Spotted Shag, White Fronted Tern, Southern Black Backed Gull, Sooty Shearwater, Fairy Prion, Black Shag and the iconic  Royal Albatross. In a published 2021 study of marine rubbish by Ella van Gool the Otago region had the highest mean density and the highest mean weight of marine rubbish (AMD anthropomorphic marine debris) in New Zealand. The Ministry for the Environment also published a report on the impact of plastic on marine ecosystems in the Otago Harbour. Takiharuru (Pilots Beach) on the Otago Peninsula recorded 15 items of rubbish for every 100sqm of beach, of which 23% were hard plastics and 23% were food wrappers. Its incredible to think that in the heart of one the most important biodiversity areas on the Otago Peninsula that we should see such results.

My children when they were younger after one of our clean ups. We can no longer rely on community good-will to deal with the pollution of our marine areas. Greater levels of local and national support is required through resourcing and planning.

We all must take collective responsibility for these results and must make real efforts to improve them. Local and national government including its agencies cannot continue to rely on the good will and feel good factor of community volunteers cleaning up our harbours and coastlines. The hard work of the local gentleman who contacted me recently on the Otago Peninsula should not be taken for granted. It needs more than just moral support, we actually need to have a plan to stop this issue growing any larger in Dunedin. The rising tide of waste and our ongoing consumption of plastic products needs to be seriously curtailed. Greater efforts in public rubbish collection, bin design & servicing along with stronger planning and statutory mechanisms need to be implemented to give the harbour and its biodiversity a chance. Given what we are seeing in the Otago Harbour a wider call from the community is needed to be more innovative and proactive in the control of waste entering its waters. 

Filter bags on storm-water outlets help collect plastic waste entering the ocean. This is just one initiative that could be used to protect biodiversity and the health of the Otago Harbour. With innovation we also need infrastructure, planning and support for our community at a local and national level.

The Passionfruit on the Peninsula

Passion-fruit

The Banana passion-fruit vine (Passiflora mollissima) has become a problem plant for the Otago Peninsula over recent years and has continued to occupy significant areas of roadside in Portobello and Harington Point Roads. Given its highly invasive nature and need for high light levels passion-fruit has begun to choke the life out of many  areas around the Peninsula. Its prolific fruit production has also been shown to be a suitable source of food for possums and birds distributing viable seed from the gut that can germinate. The other issue is if this plant remains widespread on roadside areas it will eventually be problematic to  conservation groups and agencies as well as private landowners who manage bush remnants on the Peninsula.

I have raised the issue of passion-fruit at our Community Board meetings and through The Star to highlight the need to look at a multi-agency approach to management of passion-fruit. That includes both the Dunedin City Council and Otago Regional Council. As a land manager one of the issues for the City Council is understanding the extent of the problem and how to tackle it on the roadside areas. With in mind Moira Parker and myself have completed a map of the roadside areas on the Peninsula using GPS waypoints. The extent of the spread of passion-fruit surprised me with 220 sites identified and mapped. This mapping exercise now gives the City Council some hard data to develop a programme of suitable control, but it won’t be easy. This has to be looked at as a long-term and constant project over the course of 6-7 years and discussions with the Council will be ongoing. In the mean time one of the most simplest things people on the Peninsula can do is eat more passion-fruit! By harvesting the fruit it reduces the opportunity for further seed dispersal. If you are eating the fruit or preparing it just remember to dispose of seed and vine material in your refuse, not your compost!

The map below shows the 220 sites identified predominantly on roadside areas. You can navigate around it within the frame by using your mouse. Click on one of the markers and you’ll see a photograph of the site. You can also view the map in a full screen view by clicking on the box icon on the top right corner.