Indirect effects and prey behavior mediate interactions between an endangered prey and recovering predator

Abstract

. 2016. Indirect effects and prey behavior mediate interactions between an endangered prey and recovering predator. Ecosphere 7(12):e01604. 10. 1002/ecs2.1604 Abstract. Managing for simultaneous recovery of interacting species, particularly top predators and their prey, is a longstanding challenge in applied ecology and conservation. The effects of sea otters (Enhydra lutris kenyoni) on abalone (Haliotis spp.) is a salient example along North America's west coast where sea otters are recovering from 18th-and 19th-century fur trade while efforts are being made to recover abalone from more recent overfishing. To understand the direct and indirect effects of sea otters on northern abalone (H. kamtschatkana) and the relative influence of biotic and abiotic conditions, we surveyed subtidal rocky reef sites varying in otter occupation time in three regions of British Columbia, Canada. . Abalone densities were greater in deeper vs. shallower habitats at sites with sea otters compared to sites without otters. Sea otter effects on exposed abalone density were three times greater in magnitude than those of any other factor, whereas substrate and wave exposure effects on cryptic abalone were six times greater than those of sea otters. While higher substrate complexity may benefit abalone by providing refugia from sea otter predation, laboratory experiments revealed that it may also lead to higher capture efficiency by sunflower stars (Pycnopodia helianthoides), a ubiquitous mesopredator, compared to habitat with lower complexity. Sea otter recovery indirectly benefitted abalone by decreasing biomass of predatory sunflower stars and competitive grazing sea urchins, while increasing stipe density and depth of kelp that provides food and protective habitat. Importantly, abalone persisted in the face of sea otter recovery, albeit at lower densities of smaller and more cryptic individuals. We provide empirical evidence of how complex ecological interactions influence the effects of recovering predators on their recovering prey. This ecosystem-based understanding can inform conservation trade-offs when balancing multifaceted ecological, cultural, and socio-economic objectives for species at risk.

Unveiling the Ecological Applications of Ancient DNA From Mollusk Shells

“…H. cracherodii experienced critical population declines following intensive fishing in the 1850-1900s and then again after the peak in abalone farming of the 1950-1960s, which severely affected all abalone populations in the Pacific, including H. rufescens (Rogers-Bennett et al, 2002). Abalone population declines were aggravated by the recovery of sea otters (Enhydra lutris nereis and E. l. kenyoni) in the 20th century, abalone predators that had nearly gone extinct following overexploitation by the historical fur trade (Lee et al, 2016). High mortalities due to infections by the bacterium Candidatus xenohaliotis responsible for the Withering syndrome devastated abalone populations (Crosson et al, 2014) and contributed to the low genetic diversities and population differentiations observed in H. cracherodii and H. rufescens today (Gaffney et al, 1996;Burton and Tegner, 2000;Hamm and Burton, 2000).…”

Diverse knowledge systems reveal social–ecological dynamics that inform species conservation status

“…In areas reoccupied by sea otters, abalone and urchin densities declined by >75% within 1-5 years, then persisted at low densities. Kelp stipe density increased for ∼6 years after otters arrived, then declined and stabilized at densities higher than reefs without otters (Figure 1b,c; Lee et al, 2016;Watson & Estes, 2011). Abalone and urchin densities stabilized by 10 years of sea otter occupation, representing site conditions at high otter abundance.…”

Reconciling social justice and ecosystem-based management in the wake of a successful predator reintroduction

“…The complexity of this question can be illustrated by considering the following. Recovery of sea otters in BC has been shown to cause a 16-fold decline in the SARA-listed abalone (Haliotis kamtschatkana), part of their shellfish diet (Lee et al 2016). Although sea otters and abalone can co-exist (Lee at al.…”

“…In Alaska, these cascading indirect effects of sea otters enhance the abundance of at least one kelp forest fish (Reisewitz et al 2006), increase the amount of particulate organic carbon, thereby doubling the growth rates of filter-feeding mussels (Duggins et al 1989), and alter the diets of Glaucous-winged gulls (Larus glaucescens; Irons et al 1986) and bald eagles (Haliaeetus leucocephalus; Anthony et al 2008). They also cause a reduction in commercially (Larson et al 2013) and culturally important shellfish (Kvitek et al 1992;Salomon et al 2007) -a socioecological story foretold in Alaska (Salomon et al 2007(Salomon et al , 2011, which is currently playing out on the west coast of Vancouver Island (Watson and Estes 2011;Singh et al 2013;Markel and Shurin 2015) and British Columbia's central mainland coast (Stevenson et al 2016;Lee et al 2016).…”