Sitting Duck is is a variation on the classic (and oft-adapted) short story "The Most Dangerous Game" by author Richard Connell. Game being a play on words to mean a game one plays and the game that is hunted: man! It was a very popular TV theme in that era, and many TV shows had at least one episode revolving around it, such as The Snare (1979) and Angel Hunt (1979). In fact, the very pilot for this show had already recreated it, with Pilot (1977).
Strangely enough, both love interests for Suzi Swann are look-alikes! George Maharis---who is himself a look-alike for his namesake George Chakiris---looked a lot like James Darren here. It however wasn't part of the storyline but they are a bit hard to tell apart, being that they're the same height, same dark hair color, same dark eyes, cheekbones and general facial structure. It is unclear why the casting department chose them, as they could have easily played brothers---if not twins.
It appears Los Angeles was very overcast the day they filmed this. It makes for a rather gloomy "island" in most scenes. One "outdoors" set was an evidently artificially (if brightly) lit indoors studio: the actors all had 4 shadows going in all directions, revealing that it was spotlights and not a sunny day.
Sitting Duck: A person or thing with no protection against an attack or other source of danger.
Burlap, also known as Hessian fabric is woven out of the skin of the jute plant. It's a dense and coarse woven fabric that is useful in various contexts such as gardening, landscaping, crafting, and shipping.