Stowaway Rats

[Moose-tache]

It seems that almost every island colonized by humans received an allotment of rats, from the Chathams to the Azores, and everywhere in between. I get that any agricultural society is going to have rats. What I don't get is why they can't de-rat a boat. Go a few hundred meters out from the dock, start at one end of the boat, and just kill every rat. If the rats are hiding, stop building rat hiding places into your boat. Some Polynesian sailing vessels had single-story 20-30 meter hulls. You could flush the whole thing from one end to the other in a couple of minutes. There's really no excuse. You can believe if I found a rat in my house, which is several times the size of a row boat, by the way, that building would be completely rodentfrei by the end of the day. Why is this simple task so impossible for boats?

[gestaltist]

What would be the benefit for the sailors to kill the rats? It would sure be a lot of work that would not only have a poor return on investment, but would also remove an alarm system from the ship. Seeing rats leave the ship was a surefire way to know you have a leak.

[Frislander]

Furthermore I think it is inappropriate to project our modern-day concerns about rats onto peoples of the past. Firstly most first colonists were not ecologists; they wouldn't have necessarily understood the ecological impact of introducing rats into an environment which before didn't have them, so that's no incentive. Additionally, in the absence of the black plague (or, heck, even with such) for most of history epidemiology has not recognised rats as a vector of disease so, particularly for a society such as that of the Polynesians, this would not have been a concern either. About the only concern a pre-modern maritime society might have with rats is them consuming food stores, and even then you could just eat the rat, as many cultures still do.

[Salmoneus]

You can believe if I found a rat in my house, which is several times the size of a row boat, by the way, that building would be completely rodentfrei by the end of the day.

I can guarantee you from experience, no it wouldn't be. [well, I've had mice. Rats are apparently even harder to get rid of, because they're smarter.] And that's with modern traps and poisons.

Rats can live in tiny spaces. Rat babies are very very small. Yes, if you have a perfectly smooth, empty outrigger cannoe, you can probably make sure to avoid rats. But if you have a ship, with bilges, and cargo, and crew quarters, and internal walls and floors made of thick wooden planks that aren't actually watertight, and corners, and pointy ends with hard-to-access areas, and masts and rigging and sails (black rats in particular loved climbing up rigging, as they're arboreal; brown rats prefer the lower decks), you're going to have rats. And you're not going to interrupt the voyage, or redesign your ship, or invest heavily in rat-traps, because who even cares if there's a rat or not anyway?

Another thing not mentioned yet: people really like rats. They keep them as pets. On a long ocean crossing, there's not a lot to do on board. If a cute little furry animal turns up, most people won't instinctively murder it, but will keep it around for entertainment. I mean, look how people treat pigeons, and they're much more disgusting than rats! Or squirrels.

Our society has a phobia of rats, partly because of the experience of the plague, and partly because of the sewer-living habits of brown rats (again, the earlier black rats lived in attics so didn't have that automatic 'filthy' association). And because large numbers of rats can be a pain if you're storing food. But even in our society, people keep rats as pets.

[mèþru]

Rat fancy was mainly an elite thing and only started in the 19th century. Ships often have cats and less often dogs or other pets to kill the rats, who spoil and steal food, spread diseases and chew the woodwork/wiring. That said, Sal's other points still stand, making rats still a danger.
BTW, the Polynesians were responsible for spreading the Polynesian rat, which led to its own ecological disasters.

[alynnidalar]

If the rats are hiding, stop building rat hiding places into your boat.

This would seem to defeat the purpose of a boat. If you're carrying any kind of cargo, if you have any sort of living space that involves people having things, if you have any sort of equipment, if you have any kind of storage or shelves or cabinets or walls, you have rat hiding places. If I have a ship and I stack a bunch of crates in the hold, the crates are not going to 100% perfectly fill the hold (and I wouldn't want them to anyway--I need to be able to enter the hold and maneuver around crates so I have access to the boat's hull in case of damage or leaks), which means there's rat hiding places between and on top of the crates. If I build some shelving to put cargo on, or even to put the equipment of sailing on, and I have, say, a coil of rope, that's a rat hiding place.