Distribution Of Trawling Effort Research Articles

Patterns in the Local Distribution of the Sea Whip, Halipteris willemoesi, in an Area Impacted by Mobile Fishing Gear

While conducting a larger project along the continental shelf off central California in June 2006, we encountered a large patch of sea whips (Halipteris willemoesi) in an area that was actively fished by vessels using otter trawls. A total of 10 transects were conducted using a remotely operated vehicle (ROV) to collect video imagery of seafloor communities. Video records allowed us to quantify sea whip density and to calculate the densities of upright and damaged or broken sea whips. Though the transects were sited within a dense aggregation of trawl tracks, we recorded significant variability in sea whip densities across transects. While subtle differences in water depth among transects may have contributed to the variability in sea whip density, we suggest that the distribution of trawling effort is a more likely explanation.

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.

Effects of otter trawling on macrobenthos and management of demersal scalefish fisheries on the continental shelf of north-western Australia

The effects of two types of otter trawl on macrobenthos (mainly sponges, soft corals, and gorgonians) were measured in an experiment involving repeated trawling of a marked area interspersed with video transects to estimate density of benthos. The gears tested were a demersal otter trawl and a semi-pelagic trawl fished approximately 15 cm above the seabed. Fishing with the semi-pelagic trawl had no measurable effect, whereas the standard demersal trawl reduced benthos density by 15.5% on each tow through the site. Only 4% of the benthos detached was actually retained in the net. Comparison with other studies indicates that macrobenthos mortality can vary greatly depending on how an otter trawl is rigged. The experimental estimate of one-pass mortality was combined with the frequency and distribution of commercial trawling to estimate patterns of annual mortality of macrobenthos in 6-min square blocks throughout the area where the fishery operates. The management response to the problem of benthos mortality in the trawl fishery has been to limit trawling for scalefish to a small proportion of the area of the continental shelf and to control the level and distribution of trawling effort. 2000 International Council for the Exploration of the Sea