Down for the count
Once again, hunters find themselves questioning whether the science of waterbird counting is really a valid mechanism for estimating the size and distribution of dynamic and transient waterbird populations — winged warriors continually searching for suita
Goose hunting in the Northern Territory has been cut for the 2017 season (which started on October 27).
NT Minister for Environment and Natural Resources, Lauren Moss said a shorter season and a daily bag limit of just three birds was based on scientific surveys indicating the resident population was seriously depleted and needed time to recover.
“The NT’S magpie goose population is the lowest on record at 725 000. This is a dramatic 45 per cent reduction on 2016 and only a quarter of the 2012 population,” Minister Moss said, adding the allegation that the previous government had ignored similar advice, which exacerbated the problem.
But talk to Territory hunters and they raise questions about transects flown, areas counted or not counted, and the simple fact that Magpie geese have wings — they fly away and may well fly back.
It echoes conversations by duck hunters in the southern states last year when faced with an Eastern Australian Waterbird Survey indicating a 34-year low in waterbird abundance generally and games species abundance: “…well below long-term averages, in many cases by an order of magnitude.”
On the ground, traditional hunters were seeing large numbers of game birds and multiple breeding events, and had no concerns about abundance.
Professor Richard Kingsford’s survey report noted a breeding index at the second highest level on record, and it was fairly evident that the lack of abundance observed from the air wouldn’t be replicated on the ground. However, NT scientists recommended a maximum take in 2017 of 15 000 geese for recreational hunting, and a maximum of 5000 geese under crop protection permits.
When combined with an estimated annual indigenous harvest of 60 000 birds, the total take for 2017 would be 80 000 geese.
The average harvest is 100 000 birds, with 40 000 for recreation and crop protection. So, the argument here is whether reducing this take to 20 000 birds (2.76 per cent of the current estimated population), is justified.
Whitehead (1998) and Brook and Whitehead (2005) indicate that a maximum sustainable harvest of 5 per cent to 14 per cent over the long term would be viable.
An Aboriginal traditional harvest of 60 000 and a non-aboriginal harvest of, say, 40 000 birds, together would be 13.81 per cent of the 725 000 estimated magpie goose population within the high range for a single season.
The permitted use of 80 000 geese is 11 per cent of the estimated population.
This brings us back to various fundamental questions: will the reduction in bag limit, season and offtake have any direct impact on dynamic populations? What is the impact of hunting: is it additive to overall mortality and population dynamics? Does hunting mortality matter to the overall population dynamics? And what are the landscape strategies to enhance breeding habitat to rebuild the population if it is needed?
Esteemed international wildlife
biologist Professor Grahame Webb believes tinkering based on partial science and intuition needs to be approached cautiously.
“Fluctuations in waterbird numbers are the end result of a multitude of interacting factors and variables, some that can be controlled to some extent (e.g. harvest rates) and others which cannot (flood or famine),” he said.
“We rarely, if ever, know the complex interactions which take place between these variables, nor the effect of ‘tinkering’ with the variables that we can control (like season length and bag limits). So, trying to apply science to the problem still comes down to wielding something of a blunt instrument, with no real idea of whether it hits the target.”
Professor Webb said a paper prepared for Field & Game Australia in 2004 in relation to game birds made a strong case for maintaining a “constant” harvest regime to determine definitively what happens, and how the population adjusts, rather than altering seasons and bag limits annually, with no idea of whether these strategies have any impact on the population at all.
Adaptive Management (AM) works by identifying the best apparent way of linking available data to decisions (generally a rule-based model), which is then applied to the managed system to allow its performance to be monitored. Through this process of trial and error, AM allows incrementally better decisions about how to manage hunting seasons to evolve.
The report notes that the application of AM requires “…absolute agreement and commitment by stakeholders to the process, and a fair degree of trust and risk taking” and the avoidance of cosmetic “precautionary measures”, which interfere with the gathering of meaningful facts and date about how the population responds to depletion.
“Risk and uncertainty are integral parts of adaptive management, and efforts to counter any possible or potential risk, on the basis of being ‘precautionary’, can be scientifically counterproductive within an adaptive management program.”
The 2017 NT Goose Season is an example of extreme caution in the face of limited science (aerial waterfowl survey), and perhaps a missed opportunity to observe how the population does respond if subjected to the same harvest regime with regard to season and bag limits. Whatever the estimated abundance in 2018, there will be no mechanism for deciding whether it was due to management interventions or not. So, there is an intellectual cost associated with tinkering with the harvest regime.
Professor Webb also made the observation that the indigenous harvest would naturally decrease in line with population decline because geese would be harder to come by but the assumed take is still 60 000 regardless of abundance.