Changing Community Structure and Emerging By-Catch Mitigation Measures in Falkland Islands Demersal Finfish Fisheries

The southern Patagonian shelf has undergone important changes in fish community composition in recent years, including a decline in southern blue whiting Micromesistius australis stocks and increased abundance of rock cod Patagonotothen ramsayi - formerly a discard species now accounting for more than 50% of total annual catches by finfish trawlers in Falkland waters. Developing rock cod fisheries currently have substantial discards of juvenile fish. To ensure stock conservation, experimental trials were undertaken to evaluate the performance of alternate trawl configurations (increasing codend diamond mesh size and fitted square mesh panels (SMP)) for minimizing by-catch of small fish. Changes in fishery efficiency including total and species-specific catch rates, discard rates, length structure and retention probabilities were assessed and compared among gear. An increase in codend mesh size from 90 mm to 120 mm was found to reduce by-catch of undersized rock cod but also yielded reduction between 35%-72% of the total catch. A 110 mm diamond mesh codend fitted with a 40 mm SMP appears to effectively reduce discard rates while sustaining fishery efficiency. The results illustrate the importance of ongoing monitoring and evaluation of harvesting practices in changing fisheries.