It may surprise you to know that I don’t have textbooks about aquatic mammals lying around the house, so I was hard-pushed to find an index from which to write today’s NaPoWriMo poem. Fortunately, Newcastle Library had a magnificently arcane handbook for commercial fishermen, from which I gleaned these wise words…(which should have been heeded by this fishing boat in Shetland)
The Trawlerman’s Handbook, p.89-91
Otter Boards divert water flow into your nets.
Keep your Otter Boards well-adjusted, don’t spoil them.
They are boards for water, but not waterboards.
Please do not waterboard your otter,
they can hold their breath for four minutes,
at best you will merely annoy them, and then
you must quickly calculate the Angle Of Attack,
which is the distance between your Otter Board
and the Direction of Flow calculated in degrees,
multiplied by your otter’s annoyance.
If your otter shows a V-shape when sideways on,
it is a British otter and remembers Agincourt.
If a piratical otter boards your vessel, repel!
Protect your salmon! Otters may become unstable
in the presence of large quantities of salmon.
Stop your otter tilting by shortening, or lengthening
their upper and lower backstrops accordingly.
Careful of your fingers!! They may strop back!
Always keeping in mind that a little tilt
is a good thing for some bottom conditions.
If you see your otter heeling inwards, and then
heeling outwards, he has begun his ritual dance
of Saluting The Salmon, and your catch is lost to you.
You should have repelled him when I told you to.
Kirsten Luckins 
Very nice. You probably already know this but for other readers: Otter boards and otter trawling have nothing to do with otters.