The word ‘lines’ in the title of this ingenious wordless picturebook by Brazilian-born Clayton Junior means many things.

First the word refers directly to the various fishing lines that form the subject of the book. These include both the individual line that the protagonist Cat uses to catch a fish for supper, and the thicker rope line that connects an industrial trawler to a fishing net that’s scraping the ocean floor to catch vast quantities of fish.

Second it refers to the book’s use of graphic line, which is a masterclass in how to create a range of illustrations using line alone. These lines can be straight, curved, wavy, zig-zag or circular. They can be thick or thin; far apart or close together; on their own or overlapping. In each combination they create a different meaning.

For instance in one picture a thin line extends across the lower half of the page to form the horizon, while a thick jagged line going vertically from the top of the page to sea level represents a bolt of lightning. In the same illustration, multiple thin diagonal lines indicate rain, and wavy overlapping lines thunder clouds. Meanwhile Cat’s boat, which sits securely on the horizon, is drawn in thick white lines against a blue background.

The blue background is made of intense flat colour, and represents both sea and sky. Night is indicated by a slightly darker shade of the same blue. But it’s the use of black or white against this strong blue that gives the book its drama. The trawler, for example, is shown as a solid oppressive block of black and its polluting smoke an angry mass of swirling lines. While the rich variety of ocean life, from a huge spouting whale to shoals of tiny fish, is portrayed in delicate white lines.

The ecological message about sustainable fishing comes across loud and clear, and is made explicit by the title Free the Lines. But it is Cat’s personal campaign to ensure there are always plenty of fish in the sea for supper that really grabs our attention. The David and Goliath story of a plucky little creature battling the powerful forces of industrial food production has us rooting for the cute feline. Clue… the key to Cat’s success involves a large pair of scissors!