Versatility is an important need when choosing a lens to use for making nature and wildlife photographs from a kayak. Trying to make lens changes in one of these little boats isn’t really a practical option. After all you’re surrounded by water… potential death for a lens… and vulnerable to currents, winds and waves. That makes a zoom lens with a healthy range a good choice. You just never know how close or how far away from subjects you may find yourself. I’d suggest a maximum reach of at least 400mm. Though if using a “fast” lens you might consider a maximum focal length of 200mm or 300mm combined with a teleconverter to increase reach. Minimum reach is somewhat dependent upon your photographic style. A 100mm or 200mm might be perfect, or you may need one of the “super-zooms” like Sigma’s 50-500mm to allow even a wider minimum focal length.
As a general rule you can expect lenses from camera manufacturers such as Canon & Nikon to be of a higher quality than those by after-market suppliers like Sigma, Tamron and Tokina. However, from a cost versus return point of view the after-market lens makers offer some wonderful products. Don’t expect a zoom lens to match the performance of a prime (fixed focal length) lens. It simply isn’t going to happen. Convenience is the main attraction here. Plan on stopping down one or two stops when using a zoom lens in order to milk the maximum sharpness and resolution out of it. This may mean using a bit higher ISO setting in order to keep your shutter speed up for hand-held shooting. Since you’ll be hand-holding the lens image stabilization, sometimes called optical stabilization or vibration reduction depending on the manufacturer, can be a plus.
Below are a few images of some suitable zooms. Pictured are the Canon 100-400mm EF f/4.5-5.6L IS USM Telephoto Zoom Lens, the Tamron 200-500mm SP AF F/5-6.3 Di LD (IF) Zoom Lens for Canon EOS, the Nikon 80-400mm f/4.5-5.6D ED Vibration Reduction Nikkor Lens , and the Tamron 200-500mm SP AF F/5-6.3 Di LD (IF) Zoom Lens for Nikon D-Series. Clicking on the photos will take you to the Ritz Camera product information page for that lens. Of course there are many other lens choices that are suitable for use when making photographs from a kayak.