Fisheries long term monitoring program : Syngnathids in the East Coast Trawl Fishery: a review and trawl survey

Abstract

The Department of Primary Industries and Fisheries (DPI&F), Queensland, manages the state’s fish, mollusc and crustacean species and the habitats in which they live. Inherent in this responsibility is a commitment to monitor the condition of, and trends in, fish populations and their associated habitats. This information is used to assess the effectiveness of fisheries management strategies and contributes to ensuring that the fisheries remain ecologically sustainable.
The family Syngnathidae (seahorses, seadragons, pipefish and pipehorses) are harvested incidentally in the Queensland East Coast Trawl Fishery (ECTF) and as a target species in the Marine Aquarium Fish Fishery (MAFF), due to their value as curios, aquarium fish and traditional Asian medicines (Dunning et al., 2001; Vincent, 1996). There is very little information available on the biology or ecology of syngnathid species and as such many are listed as a worldwide conservation concern.
The objectives of this project were to carry out a fishery-independent trawl survey to:
• improve our understanding of the distribution and abundance of syngnathids in shallow water eastern king prawn (EKP) trawl grounds
• collect basic biological information on the syngnathid species within the shallow water EKP trawl grounds
• compare the patterns of syngnathid distribution and abundance using the fisheryindependent data collected from the trawl survey to the patterns using fishery-dependent commercial logbook data from the Commerical Fisheries Information System (CFISH)
• investigate the relationship between syngnathid distribution and abundance, and assemblages and habitat characteristics.
During this fishery-independent assessment, 87 trawl shots were undertaken over a 10 night stratified survey in the shallow water EKP trawl grounds. Information was collected on the syngnathids and the entire community composition collected from the trawls. The information collected was statistically compared against the current syngnathid monitoring information.
Over 90% of the total syngnathid catch comprised of pipehorses, S. dunckeri and S. hardwickii. In addition, there were two species of seahorse and one pipefish collected in the survey area. The highest density of all syngnathids was collected in the ‘low effort, zero reported catch’ grid east of Noosa. The shallowest depth where pipehorses were caught in the survey area was 50 m, however no trawls were conducted deeper than 85 m and therefore no maximum depth limit was indicated.
There was little correlation in terms of syngnathid abundance between the information gathered from the survey and the daily commercial fishery logbook data used to currently monitor syngnathids. This result indicates that the logbook data alone is not an accurate or comprehensive monitoring tool for fine scale areas of syngnathid distribution and abundance along the Queensland coast. The survey showed that the highest mean abundance of syngnathids occurs in the low trawl effort grids, signifying that syngnathids either prefer habitats not targeted by trawlers or that syngnathid populations in high effort trawl grounds have been reduced due to fishing mortality. Further investigation is required on the biology and preferred habitat of syngnathids to further support either of these potential causal mechanisms.
The data presented in this report is limited to providing information on the first three objectives of the study. The final objective is to be assessed at a later date as the data become available, and will be the subject of a future report.