Marine Disturbance in Parts of the Australian Exclusive Economic Zone
Australia: State of the Environment Second Technical Paper Series (Coasts and Oceans), Series 2
David Barratt, John Garvey and Jean Chesson
Bureau of Resource Sciences, Australia
Department of the Environment and Heritage, 2001
ISBN 0 6425 4745 9
Indicator 3 - Line and Net Fishing
"The extent (area and intensity) of fishing conducted by longlining, droplining, gillnet and meshing operations"
(see indicator 4.6; Ward et al. 1998, p46)
Introduction
This indicator is one of a group of 6 indicators on Renewable Products (Class 4: Ward et al. 1998, p42), which document aspects of the harvesting and production of living resources from marine and estuarine systems. Other indicators in this group are aquaculture effort, aquaculture production, fish stocks, seafood quality and trawl fishing area. These are used as crude indicators of the condition of the marine and estuarine ecosystems from which the products were derived.
Fishing operations may have a significant effect on top-level predators in marine and estuarine ecosystems due to the capture and removal of large fish and other animals (see Harris and Ward 1999, and BRS 1998 for reviews on the effects of fishing on non-target species and the marine environment). The magnitude of the effect will be dependent on a range of factors, including the intensity of fishing, and the fish assemblage. This indicator documents the extent and intensity of four line and net fishing methods in Australian marine and estuarine waters, longline, dropline, gillnet and meshing operations. Meshing includes all types of seining (beach, estuarine, Danish, purse) and other encircling or surrounding gears. While the effects of these gears is not fully understood, these fishing methods often target larger more mobile species. The catch from these fishing operations also includes a range of non-target species, including some protected species. As most of the catch data currently collected is about the targeted species, the data concurrently collected on fishing effort may help to assess pressure on non-target as well as targeted species.
Most fisheries management agencies collect information on the area and intensity of fishing operations in order to measure fishing effort for stock assessment and management purposes. This information is usually collected using logbooks or fishing returns. The types of information collected depends on the gear used and often differs between management agencies. It can also differ over time as logbooks change, or changes occur to the jurisdiction of fisheries. Because of this it is necessary to review the types of data collected by State and Commonwealth fisheries in order to make recommendations on the spatial and temporal granularity with which this indicator can be presented nationally.
Methods
Commonwealth and State marine and estuarine fisheries that use longline, dropline, gillnet, and meshing gears were identified (see Appendix I). Information about these fisheries was available from reports and statistical documents published by Commonwealth, State and Territory fisheries agencies, and confirmed by interview with the general manager of commercial fisheries (or equivalent) of each fisheries management agency.
Fishing effort data collected by the Commonwealth and State fisheries logbook and fisheries return programs for marine fisheries relevant to this indicator were reviewed to determine whether the data needed to implement this indicator were currently being collected. The logbooks and forms used were identified and their ability to provide the appropriate spatial, temporal and effort data was determined using the criteria described in the General Methods section of this report.
More general documentation was available from the current update of the Collection of Commercial Fisheries Statistics in Australia by the Fisheries Statistics Working Group of the Standing Committee on Fisheries and Aquaculture (FSWG in prep). This document was used to determine the time frame of the data collected by each agency.
The longline and gillnetting categories under this indicator were subdivided into pelagic and demersal activity as their impacts on marine species and ecosystems are likely to be different. For this report, the Commonwealth managed Southern Shark and South East Non-trawl Fisheries were selected as case studies to examine the extent and intensity of demersal longline, demersal gillnet and dropline fishing. Data for these methods were only available for the years 1997 and 1998. Consequently, temporal trends in fishing effort and intensity were not analysed. Data for 1998 only were spatially analysed owing to significant improvements in data quality (spatial accuracy and precision) between 1997 and 1998. No pelagic gillnetting occurs in south eastern Australian waters.
The Commonwealth's Southern Bluefin Tuna and East Coast Tuna Fisheries were selected as case studies to examine the extent and intensity of pelagic longline fishing effort in south-eastern Australian waters between 1989 and 1998.
The Danish seine sector of the Commonwealth South East Trawl Fishery and the Victorian Danish Seine Fishery were selected as case studies to illustrate the extent intensity of mesh fishing effort in south-eastern Australian waters between 1989 and 1998. However, owing to delays in negotiating access to data from the Victorian State Fisheries, the Victorian Danish seine logbook data has only been superficially analysed here to illustrate the type and quality of available data in comparison to Commonwealth fisheries logbook data.
Results
A total of 28 logbooks and catch and effort forms were identified that collect information on longline, dropline, gillnet and meshing fishing effort (Table 6.1). Appendix III contains the spatial, temporal and effort details collected by these logbooks and forms. Table 6.2 shows the number of logbooks and forms for each fishing method, and the number that meet the spatial, temporal and effort criteria required for effective mapping of each fishing method as an indicator of marine disturbance. The criteria are described in the General Methods section of this report.
There were five Commonwealth (AFMA) logbooks identified for longline, dropline, gillnet and meshing gears. Most of these logbooks collect latitude/longitude information for each operation. The exceptions to this are GN01, which gives fishers the option to report location of fishing activities using a 30'x30' grid; and the TPB02 and TPB03, which collect information on a daily basis rather than by operation. The use of a grid system by some fishers limits the extent to which questions about area fished may be answered.
Three Queensland logbooks were identified. These logbooks currently give fishers the option of reporting location of greatest catch by GPS position or a grid (6'x6') reference. Most logbooks collect daily fishing details. The line and net/crab catch and effort databases kept by Queensland both contain data from 1988 to the present. The current Queensland Fisheries Act came into effect in 1995. The current logbooks are therefore no more than four years old, although the previous logbooks collected similar information.
| Jurisdiction | Logbook or catch and effort form |
|---|---|
| Commonwealth | Australian General Confidential Daily Fishing Logbook (GN01) Australian Pelagic Daily Fishing Logbook (AL04) Australian Purse Seine and Pole Daily Fishing Log (TPB02, TPB03) Coral Sea Line, Trawl and Collector Fishery Log (CO01) South East Fishery - Trawl Sector Daily Catch Log (SEF1B) |
| Qld | Logbook for Gulf Set Net Fishery (GB01) Queensland Net and Crab Fishery (NC03) Reef Line Fishery Logbook (RL03) |
| NSW | Ocean Hauling (OH02) Trap and Line (TL02) |
| Vic | Ocean General Purse Seine - Ocean Trawl - Inshore |
| Tas | General Fishing Log Purse Seine Fishing Logbook |
| SA | Commercial Fishing Daily Log Marine Scalefish Blue Swimmer Crab Daily Log Pilchard Fishery Research Logbook |
| WA | Netting Trap and Line |
| NT | Bait Net Fishery Coastal Line Fishery Demersal Fishery Daily Log Sheet Development Coast Net: Daily Log Sheet Restricted Bait Entitlement Shark Fishery Daily Log Sheet (longline) Shark Fishery Daily Log Sheet (Pelagic net) Timor Reef Fishery Daily Log Sheet |
Two New South Wales catch and effort forms were identified. NSW has used a system of Zones since 1977 for the collection of spatial information on marine fishing. Each zone is 1 degree of latitude wide with no longitudinal delineation. There is some refinement of these zones in each logbook. Use of such a coarse zoning system severely limits the extent to which questions about area fished may be answered. All NSW forms are monthly returns. Detailed effort data, other than days fished, for the New South Wales commercial wild fisheries has only been collected since 1997, however the particulars of effort information being collected are currently being reviewed.
|
No. of logbooks | Meeting spatial criteria | Meeting temporal criteria | Meeting effort criteria | Meeting all criteria |
|---|---|---|---|---|---|
| Pelagic longline | 3 | 67% (2) | 33% (1) | 100% (3) | 33% (1) |
| Demersal longline | 8 | 38% (3) | 75% (6) | 100% (8) | 38% (3) |
| Dropline | 11 | 55% (6) | 82% (9) | 91% (10) | 45% (5) |
| Gillnet | 8 | 50% (4) | 88% (7) | 100% (8) | 50% (4) |
| Meshing/seining | 18 | 56% (10) | 72% (13) | 89% (16) | 50% (9) |
Victoria has three logbooks that collect catch and effort information from its marine non-trawl fisheries. Victoria currently uses a 10 n mile grid system for the collection of all spatial data. All logbooks collect information for each day fished. The Victorian Catch and Effort database contains data from 1978 to the present. However, logbooks have changed in that time. Prior to 1998, for example, Danish seining data was referenced to a 15 n mile grid, while general fishing logbooks used a one degree reference grid.
Two Tasmanian logbooks were identified. Tasmania's General Fishing Logbook is used to collect information on all fishing methods except purse seining. A block system is used for the collection of spatial data by all relevant logbooks. The General Fishing Logbook uses 30'x30' blocks and the Purse Seine Fishing Logbook uses 7.5'x7.5' blocks. For the General Fishing Logbook, details are usually recorded for each day's fishing, however for some gears information is given for each operation. The Purse Seine Fishing Logbook only requires information for each trip. The current General Fishing Logbook has been in use since 1995. It replaced the General Fishery Return, which did not collect the same detail of effort information nor at the same spatial resolution. Data collected by the General Fishing Logbook are stored in a database called Seals (Pisces). Catch and effort data from 1969/70 onwards is stored electronically, however not all of it is in Seals (Pisces). The Purse Seine Fishing Logbook data is stored in electronic form and contains information from 1984/85 onwards.
Three logbooks were identified for South Australian marine non-trawl fisheries. South Australia currently uses a grid/block system for the collection of most spatial data. There is some limited use of latitude/longitude positions. These grids/blocks vary in size depending on the region and logbook in question. Most logbooks require details of each day's catch, however effort information is collected on a monthly basis (eg. average number of hooks per day). Catch and effort data has been collected in South Australia since 1976/77. However, GARFIS, the main catch and effort database only contains data from 1983/84. The Pilchards database contains data from 1993 to the present.
Two catch and effort forms were identified for Western Australia. Fishers use whichever of the forms (Netting or Trap and Line) pertains to their primary fishing activity. Each form, however, contains a generic section for collection of information on other fishing activities. Western Australia currently uses a 1 degree block system for the collection of most spatial data. Separate codes have been assigned to estuaries and marine embayments, and special blocks have been defined for the Abrolhos Islands, Shark Bay, Geographe Bay, Cockburn Sound and King George Sound areas. These special blocks are smaller in area than the 1 degree blocks used elsewhere. However, the block system limits the extent to which questions about area fished may be answered. These data are collected for each month's fishing. Effort data for the Western Australian commercial fisheries has been collected since 1965, however it has only been stored electronically since 1975. Western Australia also has a system of research logbooks that collect more detailed information on fishing operations.
The Northern Territory monitors net and line fishing gears with eight logbooks. Northern Territory currently uses either latitude/longitudes or a 1 degree grid system for the collection of spatial data. Where used, the grid system limits the extent to which questions about area fished may be answered. Most information is collected by operation or by day, however some effort information is collected for each month, and some logbooks collect information for each trip. FISHDAT is the database used to store the Northern Territory's catch and effort, and licensing information. It contains data from 1993 to the present. A separate database exists that contains data collected from earlier logbooks for the period from 1984 to 1992.
Victorian Danish seine data analysis
The Victorian non-trawl logbook data are now of a spatial resolution that will allow informative gridded analyses of the distribution of fishing effort, and the reporting of effort by IMCRA regions, to be conducted in combination with Commonwealth (AFMA) logbook data. However, problems arise in relation to changes in the spatial resolution of the data over time and also with regard to duplication of data between State and Commonwealth logbooks. For example, the Victorian General Fishing logbook required records to be referenced to a one degree grid until 1997 when a 10 n mile grid system was introduced. The resolution of Danish seine records only changed from 15 n miles to 10 n miles in 1997, but Victorian and Commonwealth management authorities currently appear uncertain as to the degree of overlap of Danish seine operations reported in the Commonwealth (GN01) and State (otter trawl and Danish seine) logbook databases.
The extent and intensity of Danish seining between 1989 and 1997 based on Victorian Fisheries Management logbook records is shown in Figure VIC_DS 1. The intensity of fishing by IMCRA regions is shown in Figure VIC_DS 2. The distribution of effort closely reflects that described from analyses of Commonwealth Danish seine records in the Danish Seine Fishery case study described later in this chapter. Integration of these State data and Commonwealth logbook records is currently feasible, but would be inappropriate until the level of duplication of records between State and Commonwealth logbooks is both understood and resolved.
Case Study 1 - Southern Non-trawl Demersal Fisheries
Methods
Logbook records for 1998 in the Southern Shark and South East Non-Trawl Fisheries database were analysed. This database holds catch and effort details collected from operators in the Southern Shark and South East Non-Trawl fisheries using the GN01 logbook. This logbook was introduced in 1997, but complete coverage was not obtained until 1998. This is a newly developed database, which is held and maintained by AFMA. Previously the data for the Southern Shark fishery were collected and maintained by the Victorian Marine and Freshwater Resources Institute (MAFRI) on behalf of AFMA. MAFRI still hold these data in the Southern Shark Fishery Monitoring Database (SSFMDB). MAFRI is also contracted to obtain the recent GN01 data from AFMA to keep the SSFMDB up to date in order to provide complete data summaries and to maintain consistency with the earlier data. Data for droplining and demersal longlining north of the NSW-Victorian border are collected and held by NSW Fisheries. Gillnetting is not allowed in marine waters under NSW jurisdiction.
Each record in this dataset holds information on each fishing operation for gillnetting, demersal longlining and trotlining, or for each day's fishing for droplining. Records with geocode errors (i.e., where geocode co-ordinates were missing, or the reported position was beyond the EEZ or on land) were removed from the dataset prior to analysis. Records where fishing operations were not conducted were also removed. Finally, if records were lacking data on gear units (length of net, number of line lifts), then the average of all records where these data were recorded was applied to these missing data. Similarly, if records were lacking data on gear sub-units (soak time, hooks per line), then the average of all records where these data were recorded was applied to these missing data.
Analyses were carried out on data for the following types of operations; demersal gillnetting, demersal long-lining and drop-lining. The following analyses were conducted to quantify and illustrate the spatial extent and intensity of operations within the fishery in 1998:
- Gridded fishing intensity (net-hours / hooks in 30 n miles2)
- Fishing intensity (net-hours, hooks) by IMCRA region (standardised by area)
The techniques used to generate a smoothed gridded representation of the relative intensity of operations throughout the fishery in 1998 are described in the General Methods chapter. To help remove random geocoding errors and to better define the main body of the fishery, cells having less than 3 operations within a 30x30 minute neighbourhood were masked. Fishery area figures are coarse approximations, owing to the poor spatial resolution of much of the data and the spatial analytical methods applied.
Results
In 1998, demersal longline operations in these fisheries were conducted over an area of approximately 31,000 n miles2 extending from south of St Vincents Gulf in the west, to Cape Howe in the east and south to south-east of Hobart (Figure DLL 1). Fishing occurred in 13 IMCRA regions. Core fishing areas (defined as areas in the 30-100 percentile range of fishing intensity values and shown on maps as moderate or greater fishing intensity) covered approximately 3,400 n miles2 and were located off the north-west coast of Tasmania in the Otway IMCRA region (Figure DLL 1). The Franklin region had the highest intensity of fishing, when calculated by IMCRA region (Figure DLL 2). This was due to very high fishing effort in the north of the region relative to other parts of the fishery (Figure DLL 1).
Dropline operations in 1998 were conducted over an area of approximately 37,000 n miles2 extending from south of Kangaroo Island in the west, to Eden in the east and south around Tasmania to approximately 45°south (Figure DL 1). Fishing occurred in 10 IMCRA regions. Core fishing areas covered approximately 2,400 n miles2 and were located to the east of Flinders Island; off the northern parts of the Tasmanian east coast and to the south-east of Hobart, in the Flinders, Freycinet and Bruny IMCRA regions (Figure DL 1). The Freycinet region had the highest intensity of fishing when calculated by IMCRA regions (Figure DL 2). Fishing intensity in northern parts of this region was very high relative to the rest of the fishery. Although overall fishing intensity in the Flinders region was low, moderate fishing intensities were recorded in the south east of the region (Figure DL 1).
Gillnet operations in 1998 were conducted over an area of approximately 165,000 n miles2 extending from the Great Australian Bight in the west, to Cape Howe in the east and south around Tasmania to approximately 44°south (Figure GN 1). Fishing occurred in 17 IMCRA regions. Core fishing areas covered approximately 24,000 n miles2. They were located to the south and east of Kangaroo Island in the Eyre and Coroong IMCRA regions; south of Warrnambool in the Otway region; between King Island and the north-west coast of Tasmania in the Otway, Boags and Central Bass Strait regions; and between the north-east Tasmanian coast and Ninety Mile Beach in the Freycinet, Boags Flinders and Twofold Shelf IMCRA regions (Figure GN 1). Fishing intensity was highest in the Coroong region at both the 30" grid and IMCRA region level of analysis (Figure GN 1 and GN 2). An area of high fishing intensity was recorded in the south-west of the Twofold Shelf region, though the region as a whole was classified as having a moderate intensity of fishing. Similarly, although overall fishing intensity in the Eyre and Central Bass Strait regions was low, areas of moderate fishing intensity were recorded in the east of the Eyre region and west of the Central Bass Strait region.
Discussion
The area of gillnetting operations is around five times greater than demersal longlining or dropline fishing. The highest intensity of gillnetting currently occurs to the south-east of Kangaroo Island and to the south-east of Wilson's Promontory. These are areas of good shark fishing that are close to home ports. Demersal longlining is greatest to the west of the north-west Tasmanian coast while droplining is currently greatest to the east of the north-east Tasmanian coast. These are ling and blue-eye fishing grounds respectively. Areas of relatively high fishing effort are small and localised for all three fishing methods. Core fishing areas (as defined in results section) comprise less than 15% of the total area of the gillnetting fishery, while for demersal longlining and dropline fishing, core fishing areas total only 11% and 6% respectively of the area of those fisheries.
Approximately 50% of demersal longlining operations and around 75% of dropline operations occur on the upper continental slope. These areas include regions of relatively high intensity fishing. Consequently, IMCRA regions are inappropriate to use as analytical units for spatial studies of these fisheries or for monitoring temporal trends. Gillnetting on the other hand is conducted entirely on the continental shelf within IMCRA region boundaries. It is not currently possible to calculate trends in the area and intensity of gillnetting, demersal longlining and droplining in the southern Australian fisheries as the GN01 logbook in which these data are recorded has only been in existence since 1997.
Case Study 2 - Australian Pelagic Longline Fishery
Methods
Logbook records in the Australian Pelagic Longline Fishery database from 1989 to 1998 were analysed. This database holds catch and effort details collected from Australian pelagic longline fishers operating in the Eastern Tuna and Billfish Fishery. Catch and effort data from this fishery has been collected since 1985 by a series of logbooks. The current logbook (AL04) was introduced in 1997, in conjunction with a new database design and data entry system. A description of the logbook data collection practices for Tuna fishing can be found in Caton and Robins (1998).
Each record in this dataset holds information on an individual fishing operation. Records with geocode errors (i.e., where geocode co-ordinates were missing, or the reported position was beyond the EEZ or on land) were removed from the dataset prior to analysis. Records where fishing operations were not conducted were also removed.
The following analyses were conducted to quantify and illustrate the spatial extent and intensity of pelagic longlining operations within the fishery and changes in the spatial extent and intensity of operations between 1989 and 1998:
- Gridded fishing intensity (hooks in 15 n miles2) for years 1989-1998
- Gridded trend in fishing intensity between 1989 and 1998 (change/SD)
- Total fishing intensity (hooks) by IMCRA region (standardised by area) for years 1989-1998
- Trend in fishing intensity between 1989 and 1998 (change/SD) by IMCRA region
The techniques used to generate a smoothed gridded representation of the relative intensity of operations throughout the fishery in each year from 1989 to 1998 are described in the General Methods chapter. To help remove random geocoding errors and to better define the main body of the fishery, cells having less than 2 operations within a 15x15 minute neighbourhood over 10 years were masked.
Results
Operations in the eastern sector of the Australian Pelagic Longline Fishery were conducted over an area of approximately 260,000 n miles2 in waters off the south-east Australian coast from the Great Australian Bight to Frazer Island between 1989 and 1998 (Figure ALL 1). The total fishery is considerably more extensive, ringing the Australian continent. Fishing in south-eastern waters occurred in 10 Pelagic Zones but was significant (> 10,000 hooks set over 10 years) in only 9 zones (Table 6.3). Core fishing areas (defined as areas in the 30-100 percentile range of fishing intensity values and shown on maps as moderate or greater fishing intensity) covered approximately 850 n miles2. These areas were located off the NSW south coast, east of Bermagui (Figure ALL 1).
Pelagic Zone Group 18 (East) had the highest fishing intensity when calculated by Pelagic Zones as shown in Figure ALL 2. However, fishing intensities in the region at the 15' grid level were low to very low compared with areas to the east of Bermagui (Figure ALL 1). The Group 8 Pelagic Zone was classified as having a high intensity of fishing relative to other zones, but again only relatively low intensities were recorded at the 15' grid level (Figures ALL 1 and 2). Both these zones are relatively small and show fishing operations over most of their area, giving them relatively high fishing intensity classifications when calculated by pelagic zone. Overall fishing effort in the Group 7 Zone, on the other hand, was moderate relative to other zones, but a localised region of high to very high fishing intensity was evident east of Bermagui at the 15' grid level (Figures ALL 1 and 2). The Pelagic Zone Groups 17 and 6 and the Eastern Pelagic Biotone had relatively low intensities of fishing by Pelagic Zone. Groups 5 and 18 (west) and the Southern Pelagic Province had very low fishing intensities relative to other zones at both the Pelagic Zone and 15' grid levels (Figures ALL 1 and 2).
| Year | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | |
| Southern Pelagic Province | 1900 | 2480 | 6320 | 26790 | 12200 | 59940 | 10550 | 12610 | 18550 | 15720 |
| Group 18W | 23920 | 27623 | 0 | 53930 | 337311 | 222045 | 22209 | 16092 | 18189 | 38065 |
| Eastern Pelagic Biotone | 175767 | 211134 | 198921 | 182449 | 178436 | 96722 | 96805 | 172320 | 106720 | 88880 |
| Group 5 | 6600 | 0 | 8300 | 61554 | 68146 | 133880 | 83108 | 96517 | 16950 | 148170 |
| Group 17 | 14880 | 6650 | 77575 | 106392 | 13360 | 101225 | 70383 | 133337 | 143207 | 193971 |
| Group 18E | 75960 | 56160 | 192451 | 140858 | 100985 | 104550 | 70057 | 52200 | 207484 | 283314 |
| Group 6 | 6000 | 13200 | 102135 | 108204 | 75427 | 227330 | 335387 | 657651 | 434082 | 649671 |
| Group 7 | 369604 | 325876 | 698754 | 1071903 | 825850 | 1262015 | 1681408 | 1336969 | 1848159 | 2546573 |
| Group 8 | 81073 | 266449 | 194958 | 221945 | 141062 | 175711 | 507511 | 967530 | 2507859 | 4171451 |
| TOTAL | 755704 | 909572 | 1479414 | 1974025 | 1752777 | 2383418 | 2877418 | 3445226 | 5301200 | 8135815 |
The area over which operations were conducted in south-east Australian waters each year in the Australian Pelagic Longline fishery increased from approximately 49,000 n miles2 in 1989 to around 197,000 n miles2 in 1998 (Figure 6.1). The amount of fishing in this area also increased from 755,704 hooks in 1989 to 8,135,815 hooks in 1998. Fishery area figures for each year are approximations, owing to the poor spatial resolution of much of the data in earlier years, and the spatial analytical methods applied. A smoothed curve (3rd order polynomial) was fitted to these data to help illustrate the trend over time (Figure 6.1).
There were very large increases in fishing intensity between 1989 and 1998 in Pelagic Zone Groups 7, 8 and 17, relative to other zones (Figure ALL 3). Fishing intensity in Group 7 increased seven fold from a low in 1990, while fishing in the Group 8 zone in 1998 was approximately 50 times greater than in 1989 (Table 6.3 and Figure 6.2). Fishing intensity in Pelagic Zone Group 17 fluctuated substantially between years but peaked in 1998 and was 20 times greater in 1998 than in 1989.
Figure 6.1. Change in fishing effort (hooks) in the eastern sector of the Australian Pelagic Longline Fishery and the area of the fishery (n miles2) between 1989 and 1998.
Large increases in fishing intensity were recorded for Pelagic Zone Groups 5, 6 and 18 (East), as shown in Figure ALL 5. In Group 18 (East) fishing declined from 1991 to a 10 year low in 1996 before rising significantly again to a peak in 1998 (Table 6.3 and Figure 6.2). Fishing effort in Group 6 peaked in 1996 at more than 100 times the fishing intensity in 1989, before levelling off in 1997 and 1998. Fishing effort in Group 5 was highly variable, but peaked in 1998 after recording no fishing in 1990 (Table 6.3 and Figure 6.2).
A small increase in fishing was evident in the Southern Pelagic Province, relative to other Zones between 1989 and 1998, though fishing effort peaked in 1994. Fishing effort in the Eastern Pelagic Biotone on the other hand, declined after peaking in 1990 (Table 6.3 and Figure 6.2). No significant change in fishing intensity between 1989 and 1998 was recorded for the Group 18 (West) region.
The direction of change in fishing intensity (increase or decrease) was spatially variable within Pelagic Zones at the 15' grid level (Figure ALL 4). Both increases and decreases in intensity were recorded in different parts of the same Pelagic Zone in all zones. However, changes were overwhelmingly positive (increases) in Groups 7, 8 and 17 (Figure ALL 4).
Figure .2. Fishing intensity (hooks per 10 n miles2) by pelagic zone in the eastern sector of the Australian Pelagic Longline Fishery between 1989 and 1998.
Discussion
The area in which pelagic longlining operations are conducted in Australian waters is increasing. The rate of this increase has itself increased notably since 1996, mainly due to an increase in vessel size and the development of a fishery for swordfish in deeper water. Larger vessels have increased the range at which the fishery can operate, and the type of weather they can stay out in. Fishing intensity (hooks per unit area) is also increasing in spite of the significant increase in the area of the fishery. The number of hooks set each year is increasing at approximately twice the rate of the area of the fishery.
The fishery has expanded to the north, east and south of the NSW coast, and to the south-east of the Tasmanian coast. Increases in fishing intensity in these areas are relatively large owing to the small amounts or absence of fishing previously, particularly to the north east of NSW. At the same time, the fishery has moved offshore from the NSW and east Victorian coasts, where fishing has declined on the continental shelf. The greatest increases in fishing intensity though, are mostly located in a small area to the east of Eden, on the upper and mid continental slope. These trends are due to increased targeting of southern bluefin tuna and swordfish, coupled with the larger boats needed for these fisheries and the larger number of hooks they can set. Advances in satellite navigation, imagery and weather prediction are also factors. However, some of the magnitude of the increases in this area can be attributed to the poor spatial precision of much data collected prior to 1992.
The increasing trends in the area and intensity of fishing are relatively consistent between years from 1989 to 1998. The observed differences in the area and intensity of fishing between 1989 and 1998 reflect these trends and are not merely a function of annual variation in fishing effort.
Case Study 3 - South-east Danish Seine Fishery
Methods
Logbook records for Danish seine vessels in the South East Trawl database from 1989 to 1998 were analysed. This database holds catch and effort details collected from otter trawl and Danish seine fishers operating in the South East Trawl Fishery. Catch and effort data from this fishery has been collected since 1995 by a series of logbooks. The current logbook (SEF1B) was introduced in 1999. A description of the logbook data collection practices for the South East Trawl fishery can be found in Garvey (1998b).
Each record in this dataset holds information on an individual fishing operation. Records with geocode errors (i.e., where geocode co-ordinates were missing, or the reported position was beyond the EEZ or on land) were removed from the dataset prior to analysis. Records where fishing operations were not conducted were also removed.
The following analyses were conducted to quantify and illustrate the spatial extent and intensity of seining operations within the fishery and changes in the spatial extent and intensity of operations between 1989 and 1998:
- Gridded fishing intensity (shots in 15 n miles2) for years 1989-1998
- Gridded trend in fishing intensity between 1989 and 1998 (change/SD)
- Fishing intensity (shots) by IMCRA region (standardised by area) for years 1989-1998
- Trend in fishing intensity between 1989 and 1998 (change/SD) by IMCRA region
The techniques used to generate a smoothed gridded representation of the relative intensity of operations throughout the fishery in each year from 1989 to 1998 are described in the General Methods chapter. To help remove random geocoding errors and to better define the main body of the fishery, cells having less than 20 shots within a 15x15 minute neighbourhood over 10 years were masked.
Results
Between 1989 and 1998, Danish seine operations in the South East Fishery were conducted over an area of approximately 14,000 n miles2. The fishery extended from Cape Otway in the west, to Jervis Bay in the north-east and to the north-west tip of Tasmania in the south (Figure DS 1). Fishing occurred in 7 IMCRA regions (Table 6.4).
Core fishing areas (defined as areas in the 30-100 percentile range of fishing intensity values, and shown on maps as moderate or greater fishing intensity) covered approximately 830 n miles2 in the Twofold Shelf IMCRA region (Figure DS 1). Fishing intensity was greater in near-shore areas of this region, east of Lakes Entrance, than in any other part of the fishery. The region also had the highest fishing intensity when calculated by IMCRA regions (Figure DS 2). Fishing intensities in the Central Victoria region were low to very low at the 15' grid level, but at the IMCRA level the region had a high intensity of fishing relative to all other regions except the Twofold Shelf (Figures DS 1 and 2).
| Year | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | |
| Victorian Embayments | 1 | 20 | 0 | 0 | 0 | 0 | 7 | 6 | 30 | 25 |
| Central Bass Strait | 64 | 43 | 75 | 31 | 37 | 51 | 12 | 78 | 56 | 40 |
| Batemans Shelf | 156 | 100 | 128 | 177 | 197 | 92 | 0 | 0 | 0 | 0 |
| Flinders | 173 | 442 | 299 | 189 | 173 | 388 | 476 | 489 | 594 | 908 |
| Otway | 272 | 34 | 31 | 139 | 226 | 14 | 3 | 2 | 1 | 0 |
| Central Victoria | 643 | 717 | 665 | 655 | 509 | 712 | 783 | 1072 | 1231 | 1004 |
| Miscellaneous | 1313 | 851 | 917 | 940 | 712 | 568 | 272 | 263 | 228 | 125 |
| Twofold Shelf | 5859 | 6850 | 6193 | 7074 | 7418 | 7660 | 7001 | 7690 | 7716 | 8164 |
| TOTAL | 8481 | 9057 | 8308 | 9205 | 9272 | 9485 | 8554 | 9600 | 9857 | 10266 |
The area over which Danish seine operations were conducted each year increased from approximately 9,000 n miles2 in 1989 to around 13,000nm2 in 1998 (Figure 6.3). The number of shots also increased from 8,481 in 1989 to 10,266 in 1998 mostly from fishing in the Twofold Shelf IMCRA region. Fishery area figures for each year were only indicative approximations, owing to the poor spatial resolution of much of the data in earlier years, and to the spatial analytical methods applied. Consequently, a smoothed curve (3rd order polynomial) was fitted to these data to help illustrate the trend over time (Figure 6.3). The plateau in the rate of increase of the area of the fishery after 1992 may be largely a function of increased use of GPS by skippers to record operation locations and a decline in the use of the grid system.
The greatest increases in fishing intensity were in the Flinders and Twofold Shelf regions as shown in Figure 6.4 and Figure DS 3, though significant decreases in fishing intensity were evident in some near-shore areas of the Twofold Shelf region (see Figure DS 4). The increase in fishing intensity in the Flinders IMCRA region occurred predominantly from 1993 onwards, with a particularly large increase observed in 1998 (Table 6.4 and Figure 6.4). This trend was primarily due to substantial increases in fishing operations to the east of Wilsons Promontory (see Figure DS 4).
Fishing intensity in the Central Victoria IMCRA region increased between 1989 and 1998, most notably from a low in 1993 to a peak in 1997 (Table 6.4 and Figure 6.4). Relatively low intensities of fishing in the Batemans Shelf region off the NSW south coast ended in 1994. Seining near Cape Otway in the south-east of the Otway region, predominantly ceased in the same year. The very small amount of fishing occurring each year in the Central Bass Strait region was calculated to be decreasing. However, this trend was very weak, with a peak in fishing occurring in 1996 following a low in 1995 (Table 6.4). Occasional fishing in the Victorian Embayments appeared to be increasing (Table 6.4).
Figure 6.3.Change in fishing effort (shots) in the South East Danish Seine Fishery and the area of the fishery (n miles2) between 1989 and 1998.
Figure 6.4. Danish seining intensity (shots per 10 n miles2) by IMCRA region for the South East Fishery between 1989 and 1998.
Discussion
The amount of Danish seining is increasing in south-eastern Australian waters, despite the cessation of seining on the Batemans Shelf in 1994. The increases have occurred in the Central Victoria, Flinders and Twofold Shelf IMCRA regions. The area of the fishery also appears to be increasing. However, increases in fishing area are prone to exaggeration when a 15nm2 precision buffer around fishing records is required. A small number of spatially dispersed operations in previously unfished areas can massively inflate the area of a fishery. In addition, a large proportion of the increase in the area of the fishery is due to seining records to the south-east of the Twofold Shelf on the continental slope in the late 1990's. These are likely to be geocoding errors and are responsible for significantly exaggerating the total area of the fishery in the late 1990s. In reality, the area of the fishery has probably remained relatively constant while the amount of seining has increased.
Fishing effort in the south-east Danish Seine Fishery fluctuates greatly between years. Although fishing effort increased by 12% between 1989 and 1994, the number of shots in 1991 was less than in 1989 and almost identical in 1989 and 1995. Fishing effort has increased rapidly and consistently however, from 1996 onwards, due to a range of factors including the replacement of some vessels, advances in satellite navigation technology, and increased market demand.
Fishing intensity in core fishing areas, including the Twofold Shelf, Flinders and Central Victoria IMCRA regions, is generally increasing. These areas are close to the home ports of the vessels. The decreases in intensity in certain parts of these regions are likely to be as much a function of improving spatial precision in the data as real decreases. However, there appears to be a significant increase in fishing effort to the east of Wilsons Promontory with some vessels operating out of Port Albert. The decreases in effort on the Batemans shelf are due to the loss of boats operating out of Eden in the early 1990's.
Discussion
For Commonwealth fisheries, fishing grounds are readily identifiable and annual net lengths and hook numbers are calculable. Analysis of fishing intensity by IMCRA regions is readily achievable. There are however, significant numbers of pelagic longlining, demersal longlining and demersal droplining operations conducted beyond the continental shelf in areas not represented by the IMCRA regionalisation. Also, in all fisheries where a grid, block or zone spatial location reporting system is used, the ability to accurately define fishing areas is limited. The grid and zone systems used in Western Australia, New South Wales and in the Tasmanian General Fishing Logbook are too coarse for accurate reporting by IMCRA regions.
For Victoria, annual length of nets and numbers of hooks are calculable, either from the information collected in the logbooks or from the information collected on the "Operator Vessel and Gear Specification Annual Return", which describes all nets carried onboard the vessel. Estimates of annual length of nets and numbers of hooks are calculable in Western Australia, while for New South Wales, only annual numbers of hooks is calculable as no information is collected on length of nets.
The data collected using the South Australian Commercial Fishing Daily Log is adequate for estimating annual length of nets (gill nets) and numbers of hooks (longline and drop line). No data on net length is collected for meshing/seining in any of the logbooks. For Tasmania, the data collected using the General Fishing Logbook is adequate for estimating annual length of nets and numbers of hooks. The Purse Seine Fishing Logbook does not collect effort information, however the gear specification sheets do provide detailed descriptions of the gear carried.
The data collected with the relevant logbooks for Queensland fisheries is adequate for estimating annual length of nets, however no information is collected on numbers of hooks. In the Northern Territory, latitude/longitudes are used for reporting of fishing activities on the Demersal Fishery Daily Log Sheet and the Timor Reef Fishery Daily Log Sheet. Consequently, fishing grounds can be accurately identified in these fisheries. Annual length of nets and numbers of hooks are calculable.
The intensity of fishing was highly spatially variable in all of the case study fisheries examined. Core fishing areas - areas of moderate to high intensity fishing relative to other parts of a fishery - generally comprised less than 10% of the total area of a fishery. Gillnetting in the southern non-trawl fishery had the largest core fishing area relative to the total area of the fishery, comprising 15% of the fishery area. At the other end of the spectrum, the core fishing area in the eastern sector of the Australian Pelagic Longline Fishery made up less than 1% of the total area of the fishery. As well as being small in comparison to the total area of the fishery, these areas also generally comprised only a fraction of the area of the IMCRA region or regions in which they were located. Even when all fishing activity, irrespective of intensity, was taken into account, fishing areas often encompassed only relatively small proportions of IMCRA regions. Presenting fishing effort information by IMCRA regions can therefore be both inaccurate and misleading because significant areas of a region with no fishing are represented as being fished at some level.
An additional problem with the use of IMCRA regions as spatial analytical units for displaying fishing effort information lies in the fact that many Australian fisheries conduct operations over the continental slope, outside of areas defined by IMCRA region boundaries. For a marine regionalisation to be useful for analysing fishing effort data on a regional or national scale, work on further sub-regionalisation of the current IMCRA regions and incorporation of the waters above the continental slope is required.
Conclusions and recommendations
- Core fishing areas within line and net fisheries are generally small relative to the total area of a fishery. Consequently, areas of relatively high fishing intensity tend to be very small relative to the total area of a fishery. IMCRA regions are inappropriate analytical units for spatial and temporal analyses of the Southern Demersal Longline and Southern Dropline fisheries because of the significant amounts of fishing occurring beyond the continental shelf.
- The Australian Pelagic Longline fishery is increasing in both area and intensity of fishing. The intensity of Danish seining in the South East Fishery is also increasing. The geographic extent of Danish seining appears to have shifted south and west over the last decade, though the total area of the fishery is relatively stable. The case studies examined indicate the Twofold Shelf region may be the most highly disturbed of the IMCRA regions in south-eastern Australia with respect to disturbance indicator 3.
- It is not currently possible to report on the spatial extent and intensity of net and line fishing on a national scale. This is because less than half of the logbooks and forms identified as data sources for indicator 3 met the spatial, temporal and effort data quality criteria developed to filter information for analysing and mapping the indicator. Also, this indicator currently comprises both hook and net fishing methods and consequently can only be reported on by using the number of fishing operations as a surrogate for fishing effort.
- The spatial analysis of temporal trends in the area and intensity of fishing operations is currently confounded by changes in the spatial precision of logbook data over time.
Based on our investigation of this indicator we recommend that:
- The indicator should be split into the seven indicators shown in Table 6.5
- Management bodies should be encouraged to improve the accuracy and precision of information being received from fishing vessels. Logbooks should collect, as a minimum, the data listed in Table 6.6.
- Work on further sub-regionalisation of the current IMCRA regions and incorporation of the waters above the continental slope is required. The impact of fishing on marine species and communities in the Twofold Shelf IMCRA region should be examined as a priority.
| Indicator | Units |
|---|---|
| Pelagic hook operations (longlines) | Hooks per unit area |
| Pelagic meshing operations (gillnets) | Net-hours per unit area |
| Pelagic encircling operations (purse seines, lampara nets, etc) | Operations per unit area |
| Demersal hook operations (longlines, droplines, trotlines) | Hooks per unit area |
| Demersal meshing operations (gillnets) | Net-hours per unit area |
| Demersal encircling operations (beach seines, Danish seines, etc) | Operations per unit area |
| Demersal trapping operations (lobster traps, fish traps, etc) | Operations per unit area |
| Spatial | Fishing location given by latitude or longitude or by reference to a grid of 6 minutes square or less |
|---|---|
| Temporal | Fishing operations reported individually or details of fishing reported daily |
| Effort | Gillnet: length of net used Dropline: number of hooks used Longline: number of hooks used Seines: number of operations Traps: number of operations |