Examining cannibalism in relation to recruitment of silver hake Merluccius bilinearis in the U.S. northwest Atlantic

Abstract Cannibalismcan be an important feature for several fish species. From an ecological perspective, studying cannibalismin the northwest Atlantic fish community usually results in examining silver hake Merlucciusbilinearis population dynamics. From a population dynamics(and hence fisheries assessment) perspective, silver hakepose some unique challenges and have defied easy, standardized approaches for evaluation of stock dynamics. Thus, here we propose to examine one facet of silver hakedynamics in light of their known cannibalistic propensity. We show for the two U.S. northwest Atlantic stocks that the percent diet composition of silver hakein silver hakeis quite high and has been quite consistent over time. We also explore the size composition of cannibalizedindividuals as well, noting that the 0–10 cm grouping is largely cannibalizedby the 20–40 cm group, which is itself cannibalizedby 40–60 cm group. From this, we fit stock-recruitment models (both Ricker and Beverton–Holt) that were typical and excluded cannibalism, that included cannibalismas an additional factor, and that changed the definition of the spawning stock biomass (SSB) from 20+ to those fish that are >40 cm. This latter shift resulted from the observed offset of recruitment production versus copious cannibalismas seen in the middle size group. Our results show that either the inclusion of cannibalismdirectly, or accounting for cannibalismindirectly by using a larger cutoff for the definition of SSB, are better model fits for both stocks than ignoring cannibalismfor this species. We discuss the broader implications of including cannibalismfor this species, for other cannibalistic species, for changes in how we consider recruitment—particularly those species managed with recruitment-based reference points— and for how these might alter perceptions of stock dynamics.