4.8 Recreational Fishery Surveys
4.8.2 Results
Mail survey response rate
Between the 1986/87 and the 1994/95 seasons, when the Department of Fisheries licensing section was responsible for including survey forms in the licence reminders sent out, there is some uncertainty as to exactly how many surveys were dispatched. As a result, there is therefore no way to determine response rates. However, the 1988/89 survey, which was sent to all licence holders, had a response rate of 36%. This figure is assumed to be typical of all surveys before 1995/96 (Figure 4.8–2). Various inducements or reminders have been used successfully to increase survey returns (Figure 4.8–2).
0 5000 10000 15000 20000 25000
1986/87 1987/88 1988/89 1989/90 1990/91 1991/92 1992/93 1993/94 1994/95 1995/96 1996/97 1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12
Season
Fishers surveyed (n)
0 10 20 30 40 50 60 70 80
Response Rate (%)
Number surveyed % response
Incentive Reminder
Figure 4.8–2 Return rates of recreational lobster fisher mail surveys. Thick line indicates the period
Fisheries Research Report [Western Australia] No. 217, 2012 91 The non-response bias is standard throughout the duration of the Thomson & Melville-Smith (2005) study and not influenced by inducements.
Comparison of survey techniques
The dedicated phone diary survey and the mail survey are the two main survey techniques that have been used to examine recreational catch and effort. The catch and effort results of the methods have shown major discrepancies. For the four seasons in which the phone diary was used, a direct comparison with the mail survey was possible (Table 4.8–2) (IFAAC 2007).
Table 4.8–2 Comparison of variables estimated from phone diary and mail surveys, for the seasons in which both methods were used. Adapted from IFAAC (2007)
Variable 2000/01 2001/02 2004/05 2005/06
Diary Mail Diary Mail Diary Mail Diary Mail
Response Rate 83% 51% 78% 51% 82% 43% 84% 43%
Effort (days) 15.5 26 14.4 27 10.3 29 10.3 25
Total Recreational Catch (t) 332 560 235 545 201 721 131 408
CPUE (lobsters/day) 1.81 1.5 1.63 1.5 1.95 1.6 1.64 1.3
The mail survey has two inherent biases that may result in the different catch estimates of the recreational sector:
1. It requires respondents to recall their catch and effort over a 7.5 month period. In contrast, the phone diary survey requires fishers to record fishing activity in a diary after each fishing event, combined with monthly telephone contact.
2. The mail survey is affected by non-response bias, where the fishing activity of those who return the questionnaire is different from those who do not respond. The mail survey had response rates of around 40 – 50%, whereas the phone diary survey had response rates of around 80% (Table 4.8–2).
The phone diary survey minimises both non-response and recall bias and is therefore likely to produce a more accurate estimate of recreational catch and effort than the mail survey.
As mail and phone diary surveys produced very different catch estimates, a conversion factor was developed to adjust the results of the mail survey to those of the more accurate phone diary survey, using only the four seasons in which phone diary surveys were made. The conversion ratios are shown in Table 4.6 (IFAAC 2007).
Table 4.8–3 Ratios for converting estimated total catch from diary survey to mail survey. Ratios have been determined with a linear model with no intercept, using data for different seasons (indicated with a tick) (IFAAC 2007).
Model 2000/01 2001/02 2004/05 2005/06 Ratio (s.e)
I 1.90 (0.30)
II 2.20 (0.84)
III 2.85 (0.62)
IV 2.23 (0.50)
V 2.29 (0.42)
The conversion factors range vary between 1.9 and 2.9 (Table 4.8–3). However, to maintain some consistency over the next few years, it was decided to use the 1.9 conversion ratio for
the 2000/01 and 2001/02 seasons (Table 4.8–3). When the conversion factor is applied to catch rates since the inception of the mail survey (1986), it demonstrates a much reduced recreational catch (Figure 4.8–3).
The Department of Fisheries’ current position on recreational catch is:
“… the best estimates of the recreational catch of western rock lobster over the last 17 years are obtained by using the mail survey data which has been suitably adjusted using the calculated level of bias.”
However further comparison of mail survey and phone-diary survey is required to refine this adjustment and this is currently underway.
0 100 200 300 400 500 600 700 800 900 1000
1986/87 1988/89 1990/91 1992/93 1994/95 1996/97 1998/99 2000/01 2002/03 2004/05 2006/07 2008/09 2010/11 2012/13
Season
Catch (tonnes)
Mail Survey (raw data) Adjusted catch
Figure 4.8–3 Recreational catch estimates based on “raw estimates” from the mail surveys (black) and the adjusted estimates calculated from the “phone diary-based” correction factor (red), with forecasted recreational catches (open red squares) based on puerulus settlement (updated from IFAAC 2007).
Effort
Most of the effort in the recreational sector is focused on just a few months near the start of the season, declining as the season progresses (Figure 4.8–4). The low number of days fished in November is a reflection of the season opening only in the middle of the month rather than a lower overall fishing effort (Melville-Smith & Anderton 2000). Similar results were also shown by phone diary surveys (Figure 4.8–5)
Fisheries Research Report [Western Australia] No. 217, 2012 93
Potting
Diving
Figure 4.8–4 Average number of days fished per month by recreational lobster pot and dive fishers who reported fishing in the 1998/99 survey (Melville-Smith & Anderton 2000).
Figure 4.8–5 Number of days fished by month from the phone diary survey for the six seasons
surveyed (Updated from IFAAC 2007).
Most of the fishing effort is focused in Geraldton (Zone B), Jurien Bay (Zone C) or the Perth and surrounding areas (Mandurah–Lancelin; Zone C), with most licence holders residing in the Metropolitan Region (Figure 4.8–6) (Melville-Smith & Anderton 2000).
Figure 4.8–6 Location of residence and fishing for lobster licence holders (Melville-Smith &
Anderton 2000)
Fisheries Research Report [Western Australia] No. 217, 2012 95 1 – 2% while there are fluctuations in Zone C, with an overall increasing trend (Figure 4.8–7) (IFAAC 2007). Recently, due to a nominal TAC for the commercial sector, the recreational proportion of the catch in both northern and southern zones has increased, with further increases predicted due to capping of commercial catch in up future seasons. This however, is predicted to fall as the two poor recruitment seasons (Figure 4.1–4) begin to enter the fishery.
0 1 2 3 4 5 6 7 8
1986/87 1987/88 1988/89 1989/90 1990/91 1991/92 1992/93 1993/94 1994/95 1995/96 1996/97 1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11
Season
Proportion of Total Catch (%)
Zones A&B Zone C
Figure 4.8–7 The proportion (%) of recreational catch in a zone compared with the total lobster catch in that zone (zones A and B and Zone C; using adjusted recreational catch estimates). Note the recreational catch in Zone A is minimal (IFAAC 2007).