Stock–Recruitment Dynamics and the Maximum Population Growth Rate of the Barndoor Skate on Georges Bank

Abstract

In 1998, the barndoor skate Dipturus laevis was reported to have been locally extirpated in parts of its northern range and to be potentially on the brink of extinction. Managers were faced with assessing the species with virtually no information other than a limited number of individuals observed in annual groundfish surveys. Since that time, a number of the primary life history parameters have been estimated, but the population dynamics of the species remain largely unexplored. In this study, we use information from the National Marine Fisheries Service (NMFS) annual groundfish surveys to investigate two critical components of barndoor skate population dynamics: the relationship of recruitment to spawner abundance and the maximum population growth rate. A strong stock–recruitment relationship was found in the fall survey data, suggesting that recruitment is closely tied to spawner abundance. The Ricker and Beverton–Holt stock–recruit models were fitted to the survey data, and estimates of the slope at the origin was generated. These parameters provided an estimate of the maximum annual reproductive rate, which was then converted to an estimate of the instantaneous maximum population growth rate of 0.37–0.38 per year. A second analysis was also conducted using a Leslie matrix and data from the NMFS survey. Observed rates of population change were used to estimate early life history parameters and incorporate density dependence into the density-independent framework of a Leslie matrix demographic model. From this method, the instantaneous maximum population growth for the barndoor skate was estimated to be 0.36–0.48 per year. Our results suggest that the species is more resilient to fishing pressure than previously believed and is capable of growing at an instantaneous rate in excess of 35% at low population sizes.