Central Great Barrier Reef shark nursery area survey (NERP TE 6.2, JCU)

This dataset contains the catch data from seasonal gillnet and longline surveys of shark nursery areas in the Central Section of the Great Barrier Reef Marine Park (2011-2014). 

Methods:

Sampling occurred seasonally in nine bays along ~ 400 km of the tropical north Queensland coastline: Rockingham, Halifax, Cleveland, Bowling Green, Upstart, Abbott, Edgecumbe, Woodwark/Double and Repulse Bays. Of these nine bays, five were sampled regularly, the others (in italics) were sampled only once as part of a broader survey. Sampling sites were dominated by silty substrates, and mudflat and/or mangrove-lined foreshores. Between October 2011 and November 2013 eight rounds of fisheries-independent surveys were undertaken to collect data on the shark community across the study region. Within each bay sampling occurred randomly within sixteen 0.9 km wide strips running perpendicular to the shore. Two groups of eight strips were placed within each bay to spread the sampling across different habitat types and management zones (i.e. gill-net fishing allowed and gill-net fishing prohibited) where possible. During each round, each bay was sampled over four days allowing for two days of sampling in each group of strips. The bays vary in size and so the relative proportion of area sampled varied between bays.

Two methods were used to sample across a broad range of shark sizes. During a total of 183 days of sampling, 453 longline shots and 343 gill-net shots were deployed totaling 370 and 310 h, respectively. Bottom-set gill-nets, comprised of 11-cm-stretched mesh, were deployed for ~ 1 h and checked every 15 min to facilitate tagging and release. In accordance with the Great Barrier Reef Marine Park Authority’s Dugong Protection Areas, multiple panels of net were joined to create a total net length of either 200 m or 400 m. In addition, some 100-m gill-nets were used during the Jan/Feb round in 2012. Bottom-set longlines were comprised of 800 m of 6-mm nylon mainline with an anchor and float at both ends. Gangions were attached to the mainline ~ 8–10 m apart; and were comprised of 1 m of 4-mm nylon cord, 1 m of 1.5-mm wire leader, and a baited 14/0 Mustad tuna circle hook. A variety of fresh and frozen baits were used including butterfly bream (Nemipterus sp.), squid (Loligo sp.), blue threadfin (Eleutheronema tetradactylum) and mullet (Mugil cephalus). Up to two longlines were deployed simultaneously for 40–90 min sets. Environmental data (water temperature, salinity, depth, turbidity and oxygen saturation) were recorded for all sets.

Captured sharks were identified to species level, tagged on the first dorsal fin (Rototag or Superflex tag; Dalton, Oxfordshire, UK), measured, sexed, assessed for clasper calcification, examined for umbilical scar condition, and released at their capture site. Stretch total length was determined according to Compagno (1984). Small sharks (? 1 m) were placed ventral side down on a measuring board and measured to the nearest mm with the upper lobe of the caudal fin depressed in line with the body axis. Larger sharks were secured beside the boat and measured to the nearest cm using a measuring tape. Additional measurements of fork length and pre-caudal length were recorded.

Format:

CSV File, 4432 rows (~1MB), Shapefiles (4409 Points)

Each line of data represents the catch of an individual shark, ray, fish, etc. Multiple lines exist per shot if more than one animal was caught. 

The shapefile was created by the eAtlas for visualisation purposes. It retains most of the information in the CSV as a point shapefile. The point shapefile was created from the CSV using the Start_Lat and Start_Long as the coordinate for points. If rows which did not have a valid Start_Lat or Start_Long (29 rows) then the End_Lat and End_Long were used instead (6 rows). If neither of these were available then the row was ignored. This removed 23 rows. Attributes Lat and Long were added to contain the coordinates used in the shapefile, leaving the original start and end coordinates untouched.

Data Dictionary:

Note: The attribute names in rounded brackets () correspond to the name in the shapefile version of the data. These names were adjusted to fit within the 10 character limit of shapefile attributes.



Shot_Code: Unique identifier for each gear shot.

Bay_Code: Bay identifier (AB – Abbott Bay; BG – Bowling Green Bay; CB – Cleveland Bay; ED – Edgcombe Bay; HB – Halifax Bay; RE – Repulse Bay; RO – Rockingham Bay; UP – Upstart Bay; WD – Woodwark/Double Bay)

Round: Round identifier. A combination of the year and a sequential letter unique to the round in that year.

Trip_Start_Date (Trip_Date): sampling date

Fishing_Start (Fish_Start): start time of set (24 hour time)

NERP_Grid: code of the sampling strip used (randomly selected)

Gear_Type: type of gear used (Long-Line or type of gill-net [mesh sizes])

Number_Hooks (Num_Hooks): If long-line number of hooks. If gill-net then blank.

Gear Length (Gear_Len): length of gear deployed

Mesh size (Mesh_Size): gill-net mesh size (in inches stretched mesh), if long-line then blank

Soak_Hours: time gear was fishing (in hours)

Net_Fishing (Net_Fishin): whether the set was in an area open or closed to net fishing

Lunar Stage (Lunar_Stge): lunar stage on day of sampling (derived from date of set)

Season: season of year (derived from date of set)

Start_Lat: latitude at start of deployment (decimal degrees) (WSG84)

Start_Long: longitude at start of deployment (decimal degrees) (WSG84)

End_Lat: latitude at end of deployment (decimal degrees) (WSG84)

End_Long: longitude at end of deployment (decimal degrees) (WSG84)

Depth: depth of deployment (metres)

Temp: water temperature at deployment (degrees centigrade)

Salinity: salinity at deployment (unitless)

DO: dissolved oxygen level (mgO2)

Secchi_Depth (Secchi_Dep): turbidity as measured by the secchi depth (metres, blank if unmeasured or if secchi disk visible on bottom)

Species_ID: three letter species code of individual (full species name is in Name field)

Species_ID_ElasmosOnly (Sp_ID_Elas): three letter code if an elasmobranch, non-elasmobranchs denoted by dash.

Functional Group (Func_Group): broad taxonomic group of individual (shark, ray, fish)

Maturity stage 3 levels (Mat_stge_3): three stage index of maturity of individual (YOY – young of the year; IM – immature; MAT – mature; UNK – unknown)

Maturity stage 2 levels (Mat_stge_2): two stage index of maturity of individual (IM – immature; MAT – mature; UNK – unknown)

Tag_ID: tag number if individual tagged and released. Tag numbers starting with U designated individuals not fitted with tags (code represents location biological data)

TL: stretched total length of individual (millimetres)

Sex: sex of individual (M – male; F- female; U – unknown)

Fate_ID: fate of the individual (RT – released tagged; RELA – released alive; DD – dead at capture and discarded; RES – retained as a research sample)

Name: species name of individual

Family: family name of individual

Trip_ID: unique identifier for trip


Data Location:

This dataset is filed in the eAtlas enduring data repository at: data\NERP-TE\6.2_Juvenile-sharks

Tags: marine
Organization: Australian Ocean Data Network