Is Fishing for Squid, Fishing Down the Food Web?

Cephalopods are important prey to many high level predators including fishes, marine mammals and seabirds. Additionally, over recent decades commercial fisheries have increasingly targeted squid and other cephalopods to supplement or replace the yields lost from traditional fisheries, such as groundfish and large pelagics. This rise in global landings of cephalopods has led to concerns about sustainability. As invertebrates, cephalopods have generally been considered to occupy low trophic levels and are commonly listed as “forage fish”. However, recent studies using stable isotopes have demonstrated that cephalopods occupy a wide range of trophic positions, which in some cases, are equivalent to their predators - including tunas and marine mammals. Through diet, isotopic, and catch data this study will explore the ecological role of the northern shortfin squid, Illex illecebrosus, in offshore environments of the northwest Atlantic, and consider whether they should be viewed as occupying low, mid, or upper trophic levels.  Results demonstrate there is still much we do not understand about the trophic ecology of cephalopods, and depending on how trophic level is calculated (e.g., stable isotopes vs. diet-based food-web models) estimates of trophic levels can shift and may be highly uncertain.