Effects of off‐bottom shellfish aquaculture on winter habitat use by molluscivorous sea ducks

Abstract

ABSTRACT1. Shellfish farming is an expanding segment of marine aquaculture, but environmental effects of this industry are only beginning to be considered.2. The interaction between off-bottom, suspended oyster farming and wintering sea ducks in coastal British Columbia was studied. Specifically, the habitat use of surf scoters (Melanitta perspicillata) and Barrow's goldeneyes (Bucephala islandica), the most abundant sea duck species in the study area, was evaluated in relation to natural environmental attributes and shellfish aquaculture.3. The extent of shellfish farming was the best-supported habitat variable explaining variation in surf scoter densities, and the only habitat attribute from the considered set that was a strong predictor of Barrow's goldeneye densities. In both cases, the findings indicated strong positive relationships between densities of sea ducks and shellfish aquaculture operations. These relationships are presumably the result of large numbers of wild mussels (Mytilus trossulus) that settle and grow on aquaculture structures and are preferred prey of these sea ducks.4. Previous work has shown that aquaculture structures provide good conditions for recruiting and growing mussels, including refuge from invertebrate predators, which in turn provides higher densities of higher quality prey for sea ducks than available in intertidal areas. This offers a rare example in which introduction of an industry leads to positive effects on wildlife populations, which is particularly important given persistent declines in numbers of many sea ducks.

Sea ducks and aquaculture: the cadmium connection

“…2a, b) (1981), (1982), and Vermeer and Ydenberg (1989) note that the primary food of surf scoters in wintering areas with rocky shoreline (i.e., limited intertidal area), such as Desolation Sound, is the blue mussel. For those sea ducks foraging within Desolation Sound, direct observation has demonstrated their preference for mussels associated with aquaculture structures rather than mussels within the nearby intertidal region (Kirk et al 2007;Ž ydelisa et al 2009). Indeed the strong positive relationships between densities of sea ducks and shellfish aquaculture operations lead Ž ydelisa et al (2009) to conclude that such structures provide higher quality prey for sea ducks than available in intertidal areas and thus provides an example of a possible positive interaction between an industry and wildlife populations.…”

“…Strong positive relationships between densities of sea ducks and shellfish aquaculture as a result of the high numbers of wild mussels that grow on aquaculture structures and are preferred prey of these sea ducks have been reported (Kirk et al 2007;Ž ydelisa et al 2009). Mussels associated with aquaculture structures possess a number of morphological traits such as weaker byssal thread attachments and thinner shells as compared to mussels on intertidal regions (Kirk et al 2007;Ž ydelisa et al 2009) making them attractive forage choices for sea ducks.…”

“…Mussels associated with aquaculture structures possess a number of morphological traits such as weaker byssal thread attachments and thinner shells as compared to mussels on intertidal regions (Kirk et al 2007;Ž ydelisa et al 2009) making them attractive forage choices for sea ducks. Kirk et al (2007) for example reported that densities of wild mussels on shellfish farming structures were reduced by 97% during the winter, with this decrease almost certainly attributable to sea duck predation.…”

Ethical Issues in Aquaculture Production

“…Natural habitat alterations are often a result of either aquaculture constructions (e.g., exclusion of migrating fish passages) or of biological processes of the cultured species (e.g., changing of flow and composition of waters, local extinction of flora and fauna species from feeding) (Cole et al 2009). On the other hand, aquaculture installations often provide new niches for wild populations of aquatic organisms or seabirds that tend to use them as habitats, and relate their living and their feeding to them (Roycroft et al 2004;Fernandez-Jover et al 2009;Ž ydelis et al 2009). Although, this may be seen as a positive influence, the environmental autonomy is still changed, since trophic relations, or feeding habits or even nutrition of wild species, are disturbed.…”

“…The large concentrations of organisms occurring in the intensive aquaculture, or wild fish gathered around farms, attract predators like seals (Güçlüsoy and Savas 2003;Sepúlveda and Oliva 2005), dolphins Shirai 2007, 2008), and seabirds (Melotti et al 1993;Roycroft et al 2004;Ž ydelis et al 2009). These predators are often trapped in aquaculture nets or other human construction (Güçlüsoy and Savas 2003;Díaz López and Shirai 2007), or annoyed by the antipredator measures, or, in some cases, even killed by the farmers.…”