Estimating survival of rock lobsters from long-term tagging programmes: how survey number and interval influence estimates

A long-term tagging dataset on southern rock lobster (Jasus edwardsii) conducted at the Crayfish Point Scientific Reserve near Hobart, Tasmania, Australia, was used to determine how survey number and survey duration affected the precision of survival estimates of male and female lobsters to ensure sustainable exploitation of the population. Tagging surveys were undertaken twice yearly during 2000-2003 with unequal time-intervals between surveys and then once a year with equal time-intervals during 2004-2012 during the January-February period. The most parsimonious Cormack-Jolly-Seber model for estimating survival of lobsters was dependent on (i) timing of the tagging and recapture surveys, (ii) time between consecutive recapture surveys, and (iii) gender. The number of surveys required to provide a precise survival probability varied with gender and time between recapture surveys. For surveys where there was unequal time between recapture surveys, seven and five surveys were required for female and male lobsters, respectively, whereas only five surveys were required when annual surveys were undertaken. Thus, lobster tagging projects using annual surveys should ideally extend to at least 5 years, which is beyond the 3-year project duration common in marine science.