Hi Misha,
Pages 3 includes Show Word count as a menu item in the View menu:
The count appears at the bottom left of the page, and shows more options when you click on it. Unfortunately, "line count" is not included in the available options:
If you had Pages '09 on your Mac, and did not intentionally remove it when you installed Pages 5, it will still be there, in a folder named iWork '09, in your Applications folder.
Copy your document, Open Pages '09, and paste the contents of your document into a new word processing document in Pages '09.
Check that the end of the document comes on the same page (number) and about the same position on that page as in the original, and make small changes to the margins to adjust this if necessary.
Then go Edit > Writing Tools > Statistics to see this more complete report:
Note that if you need to submit the journal article in a format other than a Pages file, the line count may change due to formatting changes in conversion to the new format.
If you do not have Pages '09, you can get a line count using Tools > Line Numbers in Apache OpenOffice or LibreOffice. Both are open source applications, free to download and use (although you may be asked for a donation to assist with future development of the application). The links will take you to their respective websites.
Oh...One more thing (as Steve jobs was wont to say at times): in Pages (3), go Pages (menu) > Provide pages Feedback, and make a feature request to have line count (and line numbering) added to the capabilities of Pages 3.
Regards,
Barry