Application Of Generalized Additive Models To Examine Ontogenetic and Seasonal Distributions Of Spiny Dogfish (Squalus acanthias) In The Northeast (US) Shelf Large Marine Ecosystem

 Increased commercial importance of spiny dogfish combined with a debated ecological impact has warranted an investigation of the quantitative relationship between its distribution, environment, and prey abundance. Ontogenetic movements and regional fluctuations in abundance further complicate deciphering drivers behind population flux. To elucidate mechanisms behind distributional changes we modeled seasonal occurrence and abundance of neonate (total length, TL ≥26 cm), immature (male: 26 < TL < 60; female: 26 < TL < 80), and mature (male: TL ≥60 cm; female: TL ≥80 cm) spiny dogfish as functions of environmental, temporal, spatial, and ecological factors (i.e., prey abundance) using generalized additive models (GAMs) and fishery-independent data obtained from the Northeast Fisheries Science Center annual bottom trawl survey. Significant nonlinear relationships were widespread throughout dogfish stages and seasons. Inclusion of important interactions identified by boosted regression tree (BRT) analysis greatly enhanced descriptive power and validation of GAMs. Seasonal occurrence was tightly linked to depth and bottom temperature with year and Julian day influential for some dogfish stages. While these factors also influenced the abundances of most dogfish stages, ecological factors (e.g., squid abundances) significantly contributed to abundance trends for many dogfish stages. Forecasted distributions under different temperature scenarios during spring revealed lower probabilities of occurrence for all dogfish stages in northern regions during a year with below average temperatures. Our results can be used to better understand the relationship between sampling periods and movement drivers to survey catchability of the population in the Northeast US continental shelf large marine ecosystem (NES LME).