Examples of approach used for modelling of marine species distributions around Australia for "Bioregionalisation" Project
CMR scientists have quantified the ranges of c.3000 marine fish species around Australia according to four basic parameters - start point around the coast; stop point around the coast; minimum water depth in which the species occurs; maximum water depth in which the species occurs. (In some cases, there may be multiple start/stop points, for example, a species with a discontinuous distribution).
"Start" and "stop" points are according to a set of 281 radiating sectors arranged similarly to the face of a clock, measured off as incremental distances around the 500m continental slope contour. These sectors are then extended inwards towards the coast and outwards towards deep water. For example, point 0 is off Cape York (extreme NE point of Australia), point 52 is off Brisbane, and point 66 is off Sydney. This allows a quick and convenient notation for, say, a species which occurs between Brisbane and Sydney, in water depths between 50 and 500m.
Scientists are currently examining distribution ranges entered during a previous compilation of data and are currently comparing selected species with the latest available data from voucher specimens, literature records, and in-house agency observations, to improve the reliability which can be assigned to these "modelled" distributions prior to undertaking statistical analyses for the purpose of designating "bioregions" on which management planning decisions can be based.
The CMR Data Centre has created a tool (data entry form and web mapping application) by which scientists can enter values to designate a "modelled" distribution range, then click a button to visualise the resulting range on a map. The ranges are displayed as sets of 0.5 x 0.5 degree squares which have attributes fitting the user's defined criteria or depth and sector number ("string position").
An example distribution record from the last (1996) study is given below for the species Centrophorus uyato (southern dogfish), for which the entered values were start point 63; stop point 139; min depth 225m; max. depth 660m (NB, the start/stop points have been translated from original "inshore" values of the previous study, to the current "slope" notation). Two further examples are given (for demonstration purposes only) of what changes would result if first, the "minimum depth" value were altered to 70m, and second, if then, the "maximum depth" value were also altered - e.g. to 3000m. (These are not real values, but are included to demonstrate the working of the system). Similarly, the user can alter the stored start and stop points, and on refreshing, the maps will adjust to include or exclude as many new squares as required.
(1) Actual research catch data distribution - as held in Divisional "Data Warehouse" as at March 2003
(2a) Current modelled distribution - start point 63; stop point 139; min depth 225m; max. depth 660m
(2b) Example adjusted modelled distribution (b) - start point 63; stop point 139; min depth 70m (adjusted from 225); max. depth 660m
(2c) Example adjusted modelled distribution (c) - start point 63; stop point 139; min depth 70m (adjusted from 225); max. depth 3000m (adjusted from 660)
