Experimental analyses of the mechanisms leading to American lobster (Homarus americanus) ventless trap saturation

Ventless lobster traps are now widely used to assess the abundance of American lobsters (Homarus americanus). However, catch in ventless traps plateaus after 24 h (trap saturation), possibly influencing abundance estimates. This study addressed 3 mechanisms that may cause ventless trap saturation: 1) traps retain so many lobsters that, over time, fewer lobsters are available to catch; 2) as lobsters accumulate in traps, they inhibit entry of additional lobsters and; 3) bait quality deteriorates over time and loses its attractiveness. We found that 1) the number of lobsters in the vicinity of traps did not change after a 24-h soak; 2) stocking traps with lobsters before deployment lowered subsequent catch, while removing the lobsters captured after 24 h led to an increase in catch after 48 h; 3) when fresh bait was added to traps that had been fished for 24 h, entry rate immediately increased; 4) if "old" bait was used, catch after 24 h was less than in traps fished with fresh bait; and 5) amino acid attractants in bait declined after the first 6-24 h. Thus, ventless traps appear to saturate due to a combination of loss of bait attractiveness and the interactions between lobsters as they accumulate in traps.