Here is the sixth instalment in our series of blogs all about prions! This is in preparation for our upcoming Science Live event on Oct 22nd at 1:50 pm NZ time when you can accompany us into the lab via live streaming (a permanent link to the YouTube video can be found below). For more details please see: http://www.tepapa.govt.nz/WhatsOn/allevents/Pages/ScienceLiveWhalebirds.aspx
Today’s blog was written by Jean-Claude Stahl, an Imaging Supervisor at Te Papa. He has worked on seabirds for over 26 years, including a 16 month long stint on the Crozet Archipelago and often spent 2-3 months at sea at a time! JC has a lot to tell you about prions!
A prion’s view of marine habitats
If the high seas look boringly uniform to us terrestrials (unless one enjoys a floating casino), it certainly isn’t the case for marine animals like prions. Marine habitats heterogeneity comes at many scales that seabirds can and do exploit. At the largest scale, world oceans are composed of distinct surface or deep water masses associated with different temperatures, salinities and marine faunas. Travelling from north to south in Australasia, the sequence of surface water masses ranges from warm saline subtropical waters (home of Fairy Prions in summer, all prion species in winter), to cooler less saline subantarctic waters (summer home of Fulmar Prions, also of Antarctic Prions around the Auckland Is), to downright cold and even fresher Antarctic surface waters (home to Antarctic and Thin-billed Prions in summer, pack-ice in winter).
Oceanic fronts between those water masses are often quite sharp, as is the case of the Subtropical Front (aka Subtropical Convergence) which curls from Fiordland to the south of Stewart island before veering north-eastwards along the along the Canterbury Bight and Chatham Rise. At this front, northward travelling subantarctic water sinks below warmer lighter subtropical water in a turbulent rather than linear fashion, with cold or warm water eddies pinging off regularly on both sides of the front. Plankton often concentrates at such fronts, firstly because primary production tends to be higher there, and also because plankton resists being “dragged” below the water depths of their liking. I have crossed this front more than a dozen times in the south Indian Ocean, and in most instances feeding flocks of Salvin’s Prions were seen right over the slope of maximum water sinking (identified by expendable bathythermograph soundings undertaken at the same time as bird counts), and nowhere else until reaching the vicinity of their Crozet Island breeding grounds. It is also perhaps no mere coincidence that Broad-billed Prions all breed within 200km or so of the Subtropical Front, possibly because specializing in tiny prey like copepods needs a reliable supply of concentrated prey.
At smaller scales, marine faunas also change when travelling from coastal waters to the continental shelf then deep oceanic waters. Thus the favourite prey of Fairy Prions from the Poor Knights and Cook Strait (11-16mm euphausiid Nyctiphanes australis) is a sure indicator that chick-feeding adults do not venture beyond the shelf. On the other hand, Antarctic krill taken by Antarctic and Thin-billed Prions are normally associated with oceanic waters.
At smaller scales still, flocks of prions have been observed feeding over turbulences caused by wind (Langmuir cells), tides (tidal rips or currents), subsurface reefs, whales, seals and propeller trails in the wake of a ship. Floating kelp rafts also attract the attention of at least Antarctic Prions, which may alight and peck at them. Such rafts would be the most likely source of adult barnacles (invariably needing a support to attach to) taken by Fulmar Prions around the Chathams. In a nice twist, barnacle larvae have been recorded settling on even freshly dead seabirds recovered after the Rena oilspill.
Jean-Claude Stahl, Te Papa
Video of the Oct 22 Science Live event can be watched by clicking below.