Tasmanian Salmonid Growers Association

“I have seen the changes first hand “- perceptions of a changing environment

September 13, 2016

Perceived changes in the environment are often identified by comparing current observations to unique past events that serve as a baseline for future reference.  Often referred to as sliding or shifting baselines, they can change between individuals and generations depending on differing experiences. What is believed to be ‘natural’ is subconsciously viewed as the state of the environment from one’s earliest memory.  Therefore, the expectation of what the environment should look like depends on the remembered observations within one’s lifetime, changing with each generation.[1] When reconstructing historical circumstances, often the most significant or outstanding events triumph the non-memorable occasions.[2] Therefore, sliding baselines can provide an inadequate measurement for long term, system wide change. This is particularly evident in the marine environment which the vast majority of people only view from above or through a limited exposure. This places unduly increased weighting on marine cues visible from the surface, such as the decline in giant kelp forests.

Giant kelp (Macrocystis pyrifera) was once a commonly visible aspect of Tasmanian coastal ecology, in quantities sufficient to support a commercial harvest. Reliant on cold nutrient rich waters, the giant kelp has been in a long term decline on the east and south coasts of Tasmania aligning with the increased influence of the East Australian Current over the past 30 years. This change has been increasingly evident on the east coast and has moved further south as the East Australian Current has influenced further south and persisted in southern regions.  While the decline in giant kelp has therefore been observed in parallel with increased fish farming activity over the past 30 years, there has been no scientific evidence that salmonid farming is the cause of the decline in giant kelp and considerable evidence that it is the result of changes in the East Australian Current.

So clearly there has been some big changes on the east coast in recent years with Macrocystis loss and increased densities of long spined sea urchins, but for some communities there does appear to be stability. Although there’s a heavy bias in the scientific literature towards papers that demonstrate change, it’s much harder to sell the story of no change! The following link (stuart-smith2010) takes you to a paper that does demonstrate marine ecosystem stability in the face of warming water currents.

[1] Hobday, A.J 2011, Sliding baselines and shuffling species: implications of climate change for marine conservation, Marine Ecology, vol. 32, No. 3, pp. 392-403

[2]  Bulleri, F, Underwood, A.J, Benedetti-Cecchi, L 2007, The assessment and interpretation of ecological impacts in human-dominated environments, Environmental Conservation, Vol. 34, No. 3, pp. 181-182


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