Biomass estimates of New Zealand orange roughy in June and July 2013 using a net attached acoustic optical system: Mid East Coast and Chatham Rise

[摘要] In the months of June and July 2013 orange roughy biomass surveys of three spawning regions on New Zealand's east coast were carried out. These were (1) Mid East Coast region, primarily focussed on a region known as The Valley but also with excursions to other nearby potential spawning sites, (2) North West Chatham Rise focussed on The Morgue and Graveyard features and (3) North East Chatham Rise with surveys at the Chatham Rise Spawning Box, nearby Mt Muck and Rekohu.The objectives were to provide snapshot acoustic biomass estimates at these locations and to compare estimates obtained from vessel-based acoustics and those from a newly developed Acoustic Optical System (AOS). During this survey program 115 operations were conducted which included vessel and AOS acoustic survey as well as biological sampling using the vessel’s demersal trawl net. A common thread in our observations were that orange roughy behaviour at each of the spawning grounds was dynamic whether they were conical features (e.g. Morgue, Graveyard or Mt Muck), relatively flat and featureless seafloor (e.g. Spawning Plume or Rekohu) or basin like features (e.g. Mid-East Coast - The Valley). As a consequence multiple operations were necessary to establish understanding of the temporal and spatial dynamic. High resolution AOS surveys were complemented by observations of the vessel's echosounder during formal surveys or ad-hoc movements. Demersal trawls and AOS acoustics and optics provided further information that aided understanding. Key outcomes are summarised as follows with biomass estimates given for the above acoustic bottom biomass unless otherwise stated.Mid-East CoastSubstantial and relatively stable orange roughy aggregations surveyed at The Valley spawning ground with biomass estimates made from three AOS surveys. Orange roughy were readily distinguished from surrounding backscatter using AOS multi-frequency acoustics and it is expect that results will have low species identification error. Biomass estimates at 38 kHz ranged from 2348 tonnes to 4142 tonnes, or 2698 to 5348 tonnes if a deadzone estimate is included. Biomass estimates at 120 kHz were within 10% of the 38 kHz estimates at this location. Other orange roughy were observed at a conical feature known as the Rock Wall but this location was not identified as a priority for analysis in the first instance....

[发布日期] 2014-12-17 [发布机构] CSIRO

[学科分类] 地球科学(综合)