Bycatch of Myliobatid Rays in the Central Mediterranean Sea: the Influence of Spatiotemporal, Environmental, and Operational Factors as Determined by Generalized Additive Modeling

AbstractIdentification of the factors influencing the distribution of vulnerable species can be useful for predicting their occurrence at a local to regional scale and for identifying the most suitable measures of management and conservation. We used generalized additive models to assess the effects of spatiotemporal, environmental, and operational factors on the catches of two myliobatids: the Common Eagle Ray Myliobatis aquila and the Bull Ray Pteromylaeus bovinus. Fishing data were collected from commercial midwater trawlers operating in the north-central Adriatic Sea during 2006–2013. Presence/absence and abundance (CPUE) data were modeled separately, and each model was then validated by using a test data set. The presence/absence and abundance of Common Eagle Rays and Bull Rays were mostly influenced by spatial (haul location) and temporal predictors. The major occurrences of Common Eagle Rays and Bull Rays were observed in the upper Adriatic Sea between late spring and early autumn. During winter, a...