Role of egg predation by haddock in the decline of an Atlantic herring population

Abstract

Theoretical studies suggest that the abrupt and substantial changes in the productivity of some fisheries species may be explained by predation-driven alternate stable states in their population levels. With this hypothesis, an increase in fishing or a natural perturbation can drive a population from an upper to a lower stable-equilibrium population level. After fishing is reduced or the perturbation ended, this low population level can persist due to the regulatory effect of the predator. Although established in theoretical studies, there is limited empirical support for predation-driven alternate stable states in exploited marine fish populations. We present evidence that egg predation by haddock (Melanogrammus aeglefinus) can cause alternate stable population levels in Georges Bank Atlantic herring (Clupea harengus). Egg predation by haddock explains a substantial decoupling of herring spawning stock biomass (an index of egg production) from observed larval herring abundance (an index of egg hatching). Estimated egg survival rates ranged from <2-70% from 1971 to 2005. A population model incorporating egg predation and herring fishing explains the major population trends of Georges Bank herring over four decades and predicts that, when the haddock population is high, seemingly conservative levels of fishing can still precipitate a severe decline in the herring population. These findings illustrate how efforts to rebuild fisheries can be undermined by not incorporating ecological interactions into fisheries models and management plans.depensation | predator pit | population dynamics | fish recruitment C lassic single-species fishery models, which assume that changes in population abundance are largely a function of fishing mortality and density-dependent population responses, cannot account for the rapid and persistent shifts in abundance observed in some marine fish populations (1, 2). This lack of agreement between model predictions and observed trends may be explained by the inability of single-species models to resolve alternate stable states in population levels caused by species interactions (1, 3). In the simplest form, a population with alternate stable states has three equilibrium levels: an upper and lower stable equilibrium and an intermediate unstable equilibrium, above which population growth is positive and below which it is negative. This contrasts with the single upper stable equilibrium, or carrying capacity, of classic population models, including most single-species fisheries models. One mechanism that can generate alternate stable states in a population is consumption by a predator that becomes satiated at high prey abundances (1,(4)(5)(6). With this mechanism, per capita mortality from predation increases as the prey population declines. Below the unstable equilibrium, predation mortality is sufficient to cause negative population growth. At very low population abundances, prey switching by the predator or the existence of a predation refuge results in the lower stable equilibrium; this low...

A real-time PCR assay to estimate invertebrate and fish predation on anchovy eggs in the Bay of Biscay

“…In this sense, changes in the predator community and/or in prey abundance have the potential to impact the recruitment success (e.g. Koster and Mollmann, 2000;Lynam et al, 2005;Richardson et al, 2011;Irigoien and de Roos, 2011).…”

Population‐level effects of egg predation on a native planktivore in a large freshwater lake

“…For example, a model that included Atlantic herring Clupea harengus biomass (which are known to prey on eggs and larvae) and the abundance of copepod prey best explained variation in the recruitment of Atlantic cod Gadus morhua in the North Sea over a 44-year time series (Fauchald 2010). Similarly, the population dynamics of Atlantic herring in Georges Bank were explained by a model that included egg predation by haddock Melanogrammus aeglefinus and fishing mortality (Richardson et al 2011) and an approach similar to ours that coupled empirical diet information, daily ration, and population modelling revealed substantial egg predation by two clupeid species on Baltic cod eggs (K€ oster & M€ ollmann 2000). In freshwater ecosystems, predation on eggs, but not larvae, likely regulated recruitment of lake sturgeon Acipenser fulvescens in the Peshtigo River (a tributary to Lake Michigan in Wisconsin, United States, Caroffino et al 2010) and the abundance of invasive common carp Cyprinus carpio in a series of interconnected lakes in the Upper Mississippi River basin (Bajer et al 2012).…”

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

“…Complex interactions between life stages, however, are not unique to pelagic fish preying upon the pelagic early life stages of benthic fishes, as the opposite interactions between benthic and pelagic fishes have also recently been documented, with implications for population management. In the Northwest Atlantic, the dominant benthic fish, haddock Melanogrammus aeglefinus, has been implicated in the decline of Atlantic herring recruitment, due to its overlapping with, and preying upon, benthic herring eggs (Richardson et al 2011). These complex interactions in other areas serve to highlight the need to consider spatial and stage-specific interactions, and the consequences of pelagic × benthic interactions influencing population dynamics via more than a single life stage.…”

“…A high biomass of adult predators keeps down species that may be predators/competitors of its eggs and larvae in size-structured ecosystems; this has been termed the 'cultivation effect' (Swain & Sinclair 2000, Walters & Kitchell 2001. When harvesting reduces the abundance of predators, natural mortality of its young life stages may increase, leading to a feedback loop that may hamper or delay recovery of fish stocks after overfishing (de Roos et al 2003, Frank et al 2011, Richardson et al 2011.…”