Keeping to A Nautical Theme,

it was not only sea shanties that sailors had to contend with,

there were the sea monsters that would prey on ships and sailors as depicted in the above illustration, Olaus Magnus's 1539 Carta Marina. From the James Ford Bell Library, University of Minnesota; courtesy of Ivy Press, Lewes, South Essex, 2013, the map of Scandinavia is littered with fantastic creatures, such as a sea unicorn and a giant worm that wraps itself around a big ship, 

 

and who better to describe them than Joseph Nigg, author of How To Tame Your Dragon,  

From Ivy Press

"Olaus Magnus’s 1539 Carta Marina can be considered the major source of Renaissance sea monster iconography and lore. The map and its voluminous commentary, History of the Northern Peoples, established Olaus as the innovative historian of the sea serpent, the giant squid and sea monsters in general.

"Sea Monsters is structured around Olaus’s map which is reproduced as a beautiful fold-out on the back of this book jacket and the charts that two pre-eminent sixteenth-century cartographers derived from it: Sebastian Münster’s Monstra Marina & Terrestria (1544) and Abraham Ortelius’s Islandia (1590). All three charts are remarkable for their identification of sea beasts in lettered keys. The keys are included in the book, enabling the reader to match corresponding beasts with each other and with the text.

"Joseph Nigg introduces readers to Olaus’s fantastic sea beasts by taking an imaginary voyage up the northern seas of the historic Carta Marina map, with Olaus himself as guide. After the Swedish cartographer has introduced each creature, it bursts forth in stunning art, followed by a discussion of its meaning and influence. Olaus’s marine beasts multiplied in natural histories, and his map inspired and influenced marine zoology and cartography for centuries thereafter.

"Sea Monsters is an enthralling tour of a world that still holds many secrets for us land dwellers, who will forever be fascinated by reports of giant squid and the real-life creatures of the deep that have proven to be as bizarre and otherworldly as we have imagined for centuries. It is a gorgeous guide for enthusiasts of maps, monsters and the mythic."

apparently only for sale in America, but it can be posted to the UK, you can buy the Sea Monsters book here.