Estimating weight–length relationships without individual weight data: an application to the American lobster (Homarus americanus) fishery of Long Island Sound

Abstract

The estimation of weight–length relationship of fish species requires having data on individual weight and length. However, individual weight data are often not available because they are too expensive or not feasible to gather and the relationship cannot be explicitly estimated. Yet, in this paper I develop a simple methodology that allows me to estimate a weight–length relationship when only aggregate weight data are available. To show its usefulness, the methodology is applied to the American lobster (Homarus americanus) population of Long Island Sound. Results indicate the existence of isometric growth for American lobsters in this geographical location: W = 0.000924L 2.9619. The estimated relationship is used to predict individual weight of lobsters which are then used to construct biomass indexes for three size classes of lobsters for the time period 1987–2006. This analysis suggests that is not necessary to invest efforts in collecting individual weight data to be able to construct meaningful indicators of fish population.