Density estimates of Spotted Handfish (Brachionichthys hirsutus) - GPS Underwater Visual Census. 2015-2016

Brief description

Dive surveys were conducted in 2015 and 2016 to establish a baseline and monitor the status of the critically endangered spotted handfish (Brachionichthys hirsutus) population. This dataset contains track records of variable length, GPS tracked underwater visual census transects conducted within 11 sites across the Derwent Estuary (n=9) and D'Entrecasteaux Channel (n=2).

Records illustrated search effort (transect length, swathed area) and total fish sighted along each transect. Data were also presented in a standardised unit, with density estimates (fish per hectare [Ha]) extrapolated for each transect. In addition, this dataset also included information for each sighting of individual fish. This dataset contains size measurement (total length) and location (depth, latitude, longitude) records for each sighted fish.
Lineage: Population surveys of spotted handfish (Brachionichthys hirsutus) were conducted during the non-breeding season (March – August) of 2015 and 2016. Surveys were conducted at 9 different location within the Derwent Estuary and 2 additional location in D'Entrecasteaux Channel. Data were collected using a variable length, GPS tracked underwater visual census method. Divers swam abreast approximately 0.5m-1m above the sediment to search for fish while towing a surface float with GPS housed onboard. The GPS tracked the position of the divers in real time and allowed extraction of spatial data post-hoc to determine searched distance to parameterise each transect. When B. hirsutus were located along the transect a series of photographs were taken to record the time of the sighting for cross-referencing with GPS spatial logs to determine the location of each sighting. The total length of each fish was measured to the nearest millimetre using a ruler placed laterally adjacent to the fish.