Size dependent predation in piscivorous larval stages of three tuna species

Abstract

The bluefin tuna (Thunnus thynnus) is a heavily fished temperate tuna that spawns in the Mediterranean Sea; the area off the Balearic Islands is a key spawning area. Other abundant tunas, including albacore (Thunnus alalunga) and the small bullet tuna (Auxis rochei) spawn in the same area. The three species temporally overlap during the summer spawning period of the adults. Because they are clearly piscivorous already at very early larval stages, we expect strong interactions both in terms of a direct predator–prey relationship and as competitors for food resources. In this study, we focus on understanding the size dependent trophic interactions among the three species at the different developmental larval stages. First, we describe the environmental and biological scenarios where different size stages of the three species co-occur through the application of generalized additive model (GAM) analyses to field data collected during cruise surveys in 2004–2005. We then develop an individual_based model (IBM) to evaluate inter- and intraspecific predation rates considering size structured prey and predator fields in the framework of piscivorous behaviour. The results demonstrate how predation mortality rates influence the spawning location of the three specie