Amplified recruitment pressure of biofouling organisms in commercial salmon farms: potential causes and implications for farm management

Abstract

The development of biofouling on finfish aquaculture farms presents challenges for the industry, but the factors underlying nuisance growths are still not well understood. Artificial settlement surfaces were used to examine two possible explanations for high rates of biofouling in Norwegian salmon farms: (1) increased propagule release during net cleaning operations, resulting in elevated recruitment rates; and (2) potential reservoir effects of farm surfaces. The presence of salmon farms was associated with consistently and substantially (up to 49-fold) elevated recruitment rates. Temporal patterns of recruitment were not driven by net cleaning. Resident populations of biofouling organisms were encountered on all submerged farm surfaces. Calculations indicate that a resident population of the hydroid Ectopleura larynx, a major biofouling species, could release between 0.3 × 10⁹ and 4.7 × 10⁹ larvae per farm annually. Such resident populations could form propagule reservoirs and be one explanation for the elevated recruitment pressure at salmon farms.

Keywords:

• biofouling
• salmon farming
• net cleaning
• Ectopleura larynx
• Salmo salar
• reservoirs

Acknowledgements

The authors thank Finn Victor Willumsen, Terje Bremvåg, Torleif Skatvold, Lisa Peacock, David Plew, Malte Unbehaun and all SalMar personnel at Rataren and Ørnøya for assistance with field and laboratory work and the provision of supporting information. The authors also thank Isla Fitridge (DTU Aqua, Danish Shellfish Centre) for constructive criticism on a draft of this manuscript and three anonymous reviewers for their improvement of the article.

Conflict of interest disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

The supplemental material for this paper is available online at http://dx.doi.org/10.1080/08927014.2015.1012713.

Additional information

Funding

This study was funded through a collaboration between SINTEF Fisheries and Aquaculture and ACE Aquaculture Engineering.