Quantifying non-target seahorse fisheries in central Vietnam

Tropical shrimp trawling results in large amounts of highly diverse, non-target bycatch. We assessed the incidental catch of seahorses from shrimp trawls in central Vietnam to investigate the effects of fishing on an example group of small fishes that are potentially vulnerable and economically important. We used logbooks and catch landings surveys to quantify seahorse catches from 1996 to 2000. The majority of the seahorse catch consisted of two species, Hippocampus spinosissimus and Hippocampus trimaculatus, whose proportions varied by season and year. We found no consistent, directional patterns across years in key biological and fisheries parameters including seahorse size, sex ratio, reproductive state, life-history stage or catch-per-unit-effort but we had no information on distribution of trawl effort. However, there were strong seasonal patterns in reproductive state and catch-per-unit-effort. Overall, we calculated that the total catch was 36,000–55,000 seahorses year ‑1 from a fleet of 150–170 trawlers (a small part of the total Vietnamese fleet), even though the catch was only 0.9–1.6 seahorses boat ‑1 night ‑1. Other aspects of the trawling process, such as displacement or injury of seahorses, community disruption, and/or habitat damage may still pose a threat to the seahorses, particularly as Vietnam's fisheries intensify.