Bycatch Reduction Devices

Research on BRDs in prawn fisheries has been conducted in NSW since 1989 and in the NPF, TSPF and ECTF since about mid-2000. The aim of BRDs is to provide escape opportunities for fish and other animals, which are captured in the net. To date, a range of devices has been tested (Figure 15). These devices either reduce mesh selectivity for bycatch (through altered mesh size/design) or create physical escape holes in the funnel of the net.

The Trawl Plan currently specifies five recognised BRD types, although it makes provisions for the use of alternate devices provided they meet the purpose of a BRD. The QFS, through a Technical Working Group of Trawl MAC, is in the process of reviewing and amending the BRD provisions. However, progress has been slow to date as discussed in Section 7.3.6.

Figure 16: BRDs in use in the ECTF and other tropical penaeid fisheries.

No more than 100

meshes Square Mesh Panel

No less than 7

5 meshes

Minim um m esh size of 45m m

Square Mesh Codend

(a) Square Mesh Panel

N o m o re t h a n 1 0 0 m e s he s F is h e y e No more t han 100 m eshes No more than 5 m eshes No less than 35cm No m ore than 50cm (e) Bigeye (f) V-Cut or Flapper

These BRD drawings were provided courtesy of Gary Day (former Australian Maritime College). N o m o

r e t ha n 2 0 0 me s h e

s (c) Fisheye

Note: 1. The minimum mesh distances from the cod end indicated above reflect the proposals suggested by

industry to improve the performance of the BRDs.

2. All devices except for the V-Cut BRD currently are specified under the Trawl Plan. 3. According to a QFS survey, the Bigeye is the most popular BRD design in the ETCF.

Based on BRD trials in the northern penaeid fisheries (Brewer et al., 1997) and preliminary results from the “BRD Evaluation Study”, several observations can be made about BRD performance. Firstly, given the range of species that needs to be excluded from the net, one BRD type will not exclude all forms of bycatch successfully. How fish and other animals respond to a trawl net and its escape device(s) depends on their swimming ability and innate behaviour. In other words, what may be a good BRD for one bycatch species may not necessarily work for another species. Secondly, the type of terrain trawled may impact on the efficiency of BRDs. Some devices perform better on “clean grounds” than in areas containing rubble, seaweed, sponges and starfish. High product loss can result when escape openings become jammed with debris. Thirdly, the correct installation of a BRD is crucial to its performance. For example, the distance of the device from the cod end, its orientation and the design of the escape opening, all impact on a BRD’s efficiency. The incorrect “tuning” of a BRD may either render the device useless or result in severe product loss (Day, 2001).

Consequently the effectiveness of BRDs varies with net design, BRD design, bycatch profile (i.e. species types and catch composition), benthic habitat type and the time when fishing occurs. Some preliminary results from the “BRD Evaluation Study” are presented in Table 21.

Table 21: Preliminary results on bycatch reduction in the major sectors of the ECOTF

[Data Source: At-Sea Observer Coverage].

Fishery and Treatment Effect on Target Species Effect on Bycatch Species

Tiger/Endeavour Prawn Fishery

1. V Slit < Standard -17.3% -15.4%

2. Square mesh panel < Standard -9.0% -7.9%

3. Modified fisheye < Standard NS -12.9%

4. Radial escape section + TED < Standard -17.0% NS 5. Modified fisheye + TED< Standard -13.3% -10.0%

Scallop Fishery

7. Bigeye + TED < Bigeye NS -22.3%

7. TED < Standard NS -48.3%

8. TED 15cm < Standard NS -44.7%

9. Bigeye + TED < TED NS NS

10. Fisheye + TED < Standard -12.4% -62.6%

Eastern King Prawn (Shallow) Fishery

11. Bigeye < Standard NS NS

12. Fisheye + TED < TED NS -28.1%

13. Bigeye < Standard NS -14.1%

14. TED + V cut + Bigeye < Standard NS -9.8%

15. Square mesh panel + TED < Standard NS NS

Eastern King Prawn (Deep) Fishery

17. Square mesh window < Standard NS NS

18. Square mesh panel < Standard NS NS

19. Bigeye + TED < Standard NS NS

Note:

1. Table 21 was provided courtesy of Dr Tony Courtney (QDPI, AFFS) based on the preliminary results from the “BRD Evaluation Study”.

2. The above results were derived from opportunistic observer coverage aboard ECTF trawlers and, as a result, there is no statistical design to the treatments and coverage. Each treatment refers to paired comparisons between the performances of net types. Each treatment represents the results of a trip (about 30 shots).

2. “Standard” refers to a standard net, which has no TED and no BRD.

3. “Treatment” refers to the comparison between net types, where ”<” means “compared to” (e.g. “Bigeye < Standard” means that the catch from a net fitted with a Bigeye BRD is compared to the catch from a net that has neither a TED nor a BRD fitted).

4. Results were compared using a T-Test and “NS” means statistically “not significant”.

These preliminary results suggest a large variation in the performance of these devices, ranging from no discernible difference (i.e. statistically invalid results) to nearly 63% reduction in bycatch through the combined use of a fisheye and TED (Treatment 10). Also, results were not consistent between the same types of treatment (e.g. Treatments 11 and 13). Courtney (pers. comm.) indicated that this might relate to operational differences between vessels, such as the BRD position on the net and the hydrodynamic performance of the trawl nets and doors.

The preliminary results also show that prawn loss can be higher than bycatch reduction, which is of concern to operators and acts as a disincentive to the proper deployment of BRDs. Of the six treatments that showed statistically significant reductions for both the target and bycatch species, only two showed a higher reduction in bycatch than in prawns. Courtney (pers. comm.) reports widespread use of the Bigeye as the preferred BRD in late 2001 and 2002. This preference is not reflected in the QFS’ reports (see Tables 22 and 23), although it is noted that these data refer to early 2001. Courtney expressed concern about the effectiveness of the Bigeye, particularly in the manner with which it appears to be deployed.

It will be interesting to compare the final data from the bycatch reduction study with earlier information on the relative bycatch reduction through BRDs. Stobutzki et al. (1996) estimated a 33% bycatch reduction for the ECTF banana prawn sector and 55% reduction for the NPF banana prawn sector. Broadhurst and Kennelly (1996) reported about a 30% reduction using a square mesh net. Based on observations in the NPF, Brewer (CSIRO, pers. comm.) indicated that square mesh panels may achieve a 50% escape rate of seasnakes.

There is no verified information on current BRD usage by the ECTF fleet. Two data sources have been examined by the QFS. The first is reported BRD usage in the trawl logbooks in 2001 (Table 22) and the second is the result of a voluntary survey by the QFS in early 2002 (Table 23).

Table 22: BRD usage reported in trawl logbooks by the ECTF fleet in 2001

[Data Source: Trawl Logbooks.]

BRD Type Vessels in 2001 % of Vessels Ranking

Bigeye 33 5% 5

Fisheye 69 11% 3

Radial Escape

BRD Type Vessels in 2001 % of Vessels Ranking

Square Mesh Codend 58 9% 4

Square Mesh Panel 277 46% 1

Others 180 29% 2

Total 619 100%

Note: The logbook data indicate a higher level of BRD usage than there were operators in the

ECTF at the time (about 550). This is because some operators reported using more than one BRD.

Table 23: BRD usage reported in a QFS survey by the ECTF fleet in 2002

[Data Source: Voluntary Survey by QFS.]

BRD Type % of Vessels Ranking

Bigeye 25% 2

Fisheye 10% 4

Radial Escape Section

8% 5

Square Mesh Codend 5% 6

Square Mesh Panel 28% 1

Others 24% 3

Total 100% NA

Note: The above is based on 88 responses received (of a possible 550), which represents only

16% of the fleet.

There is a considerable difference in reported BRD usage between the two data sources. However, it is not clear to what degree this is a reflection of changing preferences in BRD design or a reflection of sampling bias. It is noted that the popularity of the Bigeye (as reported in the survey) appears to accord with field observations by researchers (Courtney, pers. comm.). Also, about one quarter of the fleet reported the usage of devices not specified in the Trawl Plan.

Recommendation 26

¾ That the further development of BRD technology be encouraged and that performance standards, which can be applied in the performance assessment of BRDs, be developed by a group of technical experts.