Many legacy codes written in FORTRAN exist and must be maintained. In the past, FORTRAN was used for almost all subjects.
My main domain is nuclear reactor accident simulation, which covers for instance neutronics, thermics, mechanics, chemistry (equilibrium and kinetics), thermal-hydraulics, aerosol behavior, fusion of materials, debris bed and molten pool studies, lava/concrete interaction, hydrogen explosions, fires... All the integrated codes in that domain are written in FORTRAN like MAAP, MELCOR or ASTEC, even if these complicated codes often contain parts written in other languages like C or JAVA.
Most codes about quantum chemistry are also written in FORTRAN. Ditto for climate simulation.
Large finite element mechanical codes are also written in FORTRAN because these projects have started during seventies (look into NASTRAN for instance developed for NASA and used by most countries in the aeronautics and space area).
But the part of new FORTRAN codes has reduced strongly. Many scientific codes written in C or C++ have been developed during nineties because FORTRAN-77, without dynamic memory management, was outdated.
From my point of view, if C is clearly better than FORTRAN-77, I consider that FORTRAN-95 is better than C : cleaner, more robust, with better checking and more powerful when implementing mathematical algorithms (vectorized language and array indexes starting at any position). Anyway, I continue to program in C too but for very specific things.
I find C++ too complicated and not well suited for the mind of scientists who are not computer science experts. A physicist or a chemist is able to modify a FORTRAN code to implement a particular model. Such task is much more complicated in a C++ code : if the logic of FORTRAN and C are similar and easy to understand, the one of C++ is totally different.
As object oriented languages, JAVA or C# are much simpler to learn than C++.
The last norm FORTRAN-2008 designed for // computing seems very promising even if OpenMP is easier to introduce in existing codes. I don't think that the GPU programming will be successful, even if FORTRAN for CUDA is already available : it is too difficult and too expensive to adapt an existing large code to that technology which will be perhaps replaced by a better one in a near future.
François Jacq