Point to Point Distances around coastlines

[SimonPittman]

I am trying to calculate point to point distances for 125 points scattered in the sea around a Caribbean island.  Hawth's point to point tool will provide straight line distances but these paths in many cases would go over land.  I am interested in calculating the distances between points for pathways of fish that must stay in the sea and not cross over land (i.e. shortest distance but sometimes around headlands and islands etc. 
Any ideas on how I can do that?  Thanks

[DavidPetrey1]

For creating a path between 2 points:
-create a raster with all same values (values of 1)
-blank out the land (i.e. make the land all null values)
-use the Cost Distance tool with a start point and the single-value, land-masked raster created above to create a Cost Distance raster and a Backlink raster
-use the Cost Path tool with the Cost Distance and Backlink Rasters and an input end point
-Convert the Cost Path output to a polyline using the Raster to Polyline Tool.

-For multiple points I imagine you need to take each point as a start point and get the cost paths to all the other points. Creating the above procedure in ModelBuilder, python or VB/C# would help.

-Further analysis options would be to buffer the land or to eliminate shallow water from the study before performing the above analysis as the path will tend to hug the coastline. Or potentially reclassify the various water depths as weights to the cost path creation. Incorporating tidal data to the cost path analysis would add even more sophistication.

Hope that all makes sense.

David
Simply GIS Ltd
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