Interactions between small pelagic fish and young cod across the North Atlantic

Abstract

Species interactions that play out over large spatial scales are difficult to observe, particularly in the oceans. The current lack of empirical evidence for biologically meaningful interaction parameters likely delays the application of holistic management procedures. Here we estimate interactions during the early life history of fish across regions. We present separate and hierarchical Bayesian models that estimate the direction and strength of interactions between Atlantic cod and dominant pelagic fishes across much of their range in the North Atlantic. We test the hypothesis that small pelagic fish may reduce survival of cod at early life stages, and thereby contribute to the delayed recovery of depleted cod populations. Significant regional variation exists between cod recruitment and Atlantic herring abundance with eight of 14 regions displaying a negative relationship, four regions displaying no relationship, and a positive relationship observed in two regions. In contrast, most regions where Atlantic mackerel co-occurs showed no relationship with cod recruitment, with the possible exception of Gulf of St. Lawrence and Celtic Sea regions. Regions with sprat or capelin as dominant pelagics also displayed weak or no relationship, although the probability of a negative interaction with sprat increased when time series autocorrelation was accounted for. Overall, the interaction between herring and young cod was found to be negative with 94% probability, while the probability of negative interactions with mackerel was only 68%. Our findings suggest that the strength of predation or competition effects on young cod varies among small pelagic species but appears consistently for Atlantic herring; this effect may need to be considered in recovery trajectories for depleted cod populations. The methods introduced here are applicable in the investigation of species interactions from time series data collected across different study systems.

Post-harvest recovery dynamics depend on predator specialization in size-selective fisheries

“…The second was that, as predatory species recovered, the smaller, faster-growing species consumed juveniles of larger species, adding further fluctuations to community size structure recovery. An analogous effect can occur when prey can consume juvenile predators, as has been demonstrated for herring and cod (Walters & Kitchell 2001, Fauchald 2010, Minto & Worm 2012. In these cases, recovery of a prey species could delay recovery of its own predator, potentially enhancing the 'delayed predation' found here.…”

The predictive potential of early life stage individual-based models (IBMs): an example for Atlantic cod Gadus morhua in the North Sea

“…This was potentially caused by extensive (over-) exploi tation of the stock, but several studies also indicate important changes in environmental factors potentially regulating the productivity (recruitment potential) of the North Sea cod stock. These include bottom-up, prey-driven changes ; changes in water temperature (Brander & Mohn 2004); and food web interactions (Kempf et al 2009, Minto & Worm 2012, Hjermann et al 2013. applied a principal component analysis to investigate the statistical relationship between cod recruitment strength and the abundance and species and size composition of dominant copepod species in the North Sea.…”

Spatial analysis of North Sea cod recruitment: concurrent effects of changes in spawning stock biomass, temperature and herring abundance

“…It is striking that the papers that suggest a substantial effect of herring predation on cod are based on modelling or statistical analyses (An dersen & Ursin 1977, Fauchald 2010, Speirs et al 2010, Minto & Worm 2012. In contrast, earlier work based on herring stomach samples (Daan et al 1985, Last 1989) concluded that herring predates on an insignificant amount of cod eggs.…”

“…The possible generality of such synergistic effects has been scrutinized by Ottersen et al (2013, this volume). A third mechanism may be that herring play a crucial role in limiting the recruitment of cod, through predation on, or competition with, cod eggs and larvae (Minto & Worm 2012). The predation mechanism has been discussed since the 1970s, as a period of exceptionally high recruitment years of cod and other gadoids (the 'gadoid outburst'), which started at approximately the same time that the stock of NS herring began to decline (Cushing 1980).…”