Estimating a length-at-age relationship for an invasive bivalve with density-determined plastic growth

ABSTRACT At the base of stock assessments, used to monitor invasive aquatic species and to sustainably harvest stocks, are estimates of body growth, a key parameter regulating animal populations. However, due to lack of data, obtaining these estimates can be challenging, but analytical approaches for ‘data-poor’ situations have been developed. Currently, the Pacific oyster (Magallana gigas) is spreading in northern Europe and a need for management strategies to control the invasion is evident. Using methods developed for data-poor situations, the von Bertalanffy growth function and electronic length-frequency analysis, we analysed 17,289 length measurements of wild Pacific oysters collected between 2007 and 2018 at five sites in Sweden to estimate its growth in temperate waters. We identified two distinct growth patterns, where individuals in habitats with high bivalve density grow faster in length compared to those in less dense habitats. Additionally, we found that Pacific oyster populations in Sweden are still growing towards their asymptotic lengths and that growth is reduced but not stopped during colder months. We conclude that our analysis constitutes the basis for future stock assessment and management of the species in areas with feral populations of commercial interest.