Harbour porpoises Phocoena phocoena are protected under the Habitats and Species Directive (92/43/EEC) and listed as a priority species in the City and County of Swansea’s Biodiversity Action Plan (BAP). Increased coastal pressures demand better governance and this study adopted a dimensional analysis to produce a local management framework for harbour porpoise populations. Having established basic behavioural dynamics and identified critical habitats, a coastal zone use model was developed. This highlighted porpoise and coastal user interaction from a species perspective. Evidence was determined from observations and published research, and an Environmental Risk Assessment (ERA) was undertaken. An estimation of consequence probability was determined and revealed that continued coastal use, without mitigation, is likely to have significant local impacts on porpoise populations. A strengths, weaknesses, opportunities and threats (SWOT) analysis and legislative appraisal highlighted potential opportunities and deficiencies. Mitigation refers principally to industry, fisheries and recreation and suggestions include flexible zoning; speed and vessel restrictions; engineering solutions to noise intrusion and fisheries monitoring. A mixture of formal and informal regulations is recommended, together with educational projects and industry-funded research opportunities.