Oil and gas exploration and production activities can have a wide range of impacts on biodiversity, both positive and negative. These impacts, which can be defined as changes in the quality and quantity of biodiversity in a physical environment, will vary in scale and significance, depending on the activities and environmental conditions involved. Impacts to biodiversity can be broadly divided into two types: primary and secondary (see Box 1). This document focuses on the specific challenge of negative secondary impacts, beginning with a discussion of how secondary impacts differ from primary impacts and then examining the difficulties of understanding and addressing the negative effects of secondary impacts. 1. PRIMARY VS. SECONDARY IMPACTS Ultimately, both primary and secondary negative impacts to biodiversity may mean habitat conversion, degradation and fragmentation; wildlife disturbance and loss of species; air, water and soil pollution; deforestation; soil erosion and sedimentation of waterways; soil compaction; contamination from improper waste disposal or oil spills; and loss of productive capacity and degradation of ecosystem functions – both onshore and offshore. Where the two types of impacts differ is in cause, scope, scale, intensity and boundaries of responsibilities. This can sometimes make it difficult to definitively label environmental degradation as either primary or secondary (see Box 2 for an example of one cause of both primary and secondary negative impacts). In general, primary impacts are changes to biodiversity that result specifically from project activities. These impacts, which will be most familiar to project managers, are normally associated with the geographic area relatively near to project activities. Primary impacts usually become apparent within the lifetime of a project, and often their effect is immediate. For example, clearing areas of a dense-canopy forest to build project infrastructure will result in immediate deforestation and loss of habitat, and may lead to soil erosion over the longer term that will contaminate a waterway. Most primary impacts can be relatively easily predicted with a standard Environmental and Social Impact Assessment (ESIA) process, based on the proposed activity and an understanding of the surrounding ecosystem. Primary impacts can usually be minimized or avoided by incorporating sound biodiversity conservation objectives, impact mitigation and operational management practices into company Environmental Management Systems and project-level assessment, design and execution, from the very start of an operation.