island, Gozo. Out of these 2,251 craft, only 77 are considered as large commercial vessels (i.e. over 15m in length) (NSO, 2007). These are mainly trawlers and.
Reliability of data collected from questionnaires administered to fishers Marija Sciberras1, Mark Dimech1,2, Philip Smith3 & Patrick J. Schembri1 1 - Department of Biology, University of Malta, Msida, Malta. 2 - Malta Centre for Fisheries Sciences (MCFS), Fort San Lucjan Marsaxlokk, Malta. 3 - University Marine Biological Station Millport, Isle of Cumbrae, Scotland UK.
Introduction and Aim Effective management of Marine Protected Areas (MPAs) requires good quality data. Socio-economic data may not be readily available and need to be collected, most often through questionnaire surveys. This was the case for the 25-NM Fisheries Management Zone (FMZ) around the Maltese Islands, where such data were required as part of the EMPAFISH project (http://www.um.es/empafish). However, the information collected in questionnaire surveys may be inaccurate as personal perception can be influenced by cultural beliefs, or by the respondents’ inaccurate memory; additionally respondents may be selective in their response. Therefore, to test the reliability of questionnaire data collected from Maltese fishers, questionnaire replies received in 2005 were cross-checked against official records, including the fleet register and official fish market landings for 2005, available from the Maltese Government’s Veterinary Affairs and Fisheries Division. Background information on the fishing industry in Malta The fishing industry in Malta is relatively small and mainly artisanal, but its social significance far outweighs its economic importance (0.1% of GDP). It is in fact a traditional activity that operates on a small scale producing small volumes of a valuable product. In 2005, the Maltese fishing fleet consisted of 2,251 registered fishing craft, of which 84% were based in the main island of Malta, and the other 16% in the second largest island, Gozo. Out of these 2,251 craft, only 77 are considered as large commercial vessels (i.e. over 15m in length) (NSO, 2007). These are mainly trawlers and longliners. The rest are multi-purpose vessels (MPVs), since these use several types of fishing gear including trammel and gill nets, traps, and Fish Aggregating Devices (FADs) combined with a purse seine (for the dolphinfish fishery). The MPVs are owned by some full-time, but mostly by part-time and recreational fishers. These craft differ substantially in size, gear utilized and in the hours spent in fishing activities. In 2005, there were 432 persons registered as professional full-time fishers, 993 registered as professional part-time fishers and 826 as recreational fishers (NSO, 2007). ‘Full-time’ is the term used for fishers whose main income is derived solely from fishing. Both professional and recreational fishers are involved in coastal inshore and deep water offshore fisheries.
700
Number of vessels
600
500
400
300
Licence type 200 MFA 100
MFB
0
MFC 1-4
5-9
10-14
15+
Vessel length (m)
Figure 1. Composition of the Maltese fishing fleet by vessel length and licence type in 2005 (adapted from NSO report, 2007). MFA indicates full-time commercial fishing vessels, MFB indicates part-time commercial fishing vessels, MFC indicates recreational fishing vessels. According to fisheries regulations, all fish caught by local fishers have to be sold through the wholesale fish market in Valletta, where catches are sold by public auction through a middleman to retailers and fish hawkers. All dealers in fish are registered with the Fisheries Department. Statistical data for total landings are collected through the daily returns of sales submitted by middlemen at the Valletta fish market (NSO, 2005). The total annual volume and annual wholesale value of landings at the official market for 2005 were 1,337 tonnes and Lm 2.478 million (€5.776 million), respectively (NSO, 2007).
Methods •
• •
In 2005, telephone interviews were conducted as part of the EMPAFISH project, to collect basic socio-economic data from Maltese fishers. The interviewer asked the respondent a number of predetermined questions and noted the response, after asking the respondent for clarification as necessary. The professional fishing fleet was divided into full-time (MFA) and part-time (MFB) fishers and interviews were made with 112 and 69 persons from these two categories, respectively. The questionnaire replies were then cross-checked against official records on the main technical features of vessels - length (m), Gross Tonnage (GT) and engine power (kW) - as well as on details of annual fishing activity (the total annual number of trips at sea inside the FMZ), and the total annual landings
(kg) (i.e. all species, including invertebrates such as crustaceans and cephalopods).
Results Figure 2. Boxplots summarizing the frequency distributions of the positive and negative deviations of questionnaire responses (R) from the official record (S) expressed as Log-Discrepancy index (Log10(R/S)), for each measure (vessel length (m), Gross Tonnage (GT), engine power (kW), annual total landings (kg/yr), annual fishing trips (no./yr), in each licence category, by showing the median, first (25%) and third (75%) quartiles, and outliers. MFA indicates full-time commercial fishers and MFB indicates part-time commercial fishers. Note: total annual landings data were not available for part-time fishers.
Log-Discrepancy index
2
1
0
Licence
-1
MFA -2 N=
MFB 111
68
84
32
102
66
13
40
16
s ip Tr r) /y o. (n
) yr g/ (k
T) (G
)
) kW
e ag nn
(m
r( we po
To
h gt en
gs in nd La
ne gi En
ss ro G
l el ss Ve
Figure 3. Frequency distribution (%) of the positive and negative deviations of questionnaire responses (R) from the official record (S) expressed as Log10(R/S), for each measure: (A) Vessel length (m), (B) Gross Tonnage (GT), (C) Engine Power (kW), (D) Total annual landings (kg/yr), and (E) Annual fishing trips (no./yr), in each licence category; MFA (full-time commercial fishers; orange) and MFB (part-time commercial fishers; green). Note: total annual landings data were not available for part-time fishers. (A negative Log-Discrepancy index indicates that the value given in the questionnaire response was lower than the official record). (A) Vessel length (m) 50
50
(i) MFA
40 Frequency (%)
Frequency (%)
40
30
20
10
0
(ii) MFB
30
20
10
-0.6
-0.5
-0.4
-0.3 -0.2 -0.1 0.0 0.1 Log-Discrepancy index
0.2
0.3
0.4
0
-0.6
-0.5
-0.4
-0.3 -0.2 -0.1 0.0 0.1 Log-Discrepancy index
0.2
0.3
0.4
(B) Gross Tonnage (GT) 50
(ii) MFB
50
(i) MFA
40
30
20
Frequency (%)
Frequency (%)
40
30
20
10
10
0
0
0 45 30 15 00 15 30 45 60 75 90 05 20 35 50 . . .6 . 0. 0. 0. 0. 1. 1. 0. 0. 1. 0. 1. -0 -0 - 0 -0 Log-Discrepancy index
0 5 0 5 0 5 0 5 5 0 0 5 0 5 0 .6 0.4 0.3 0.1 0.0 0.1 0.3 0.4 0.6 0.7 0.9 1.0 1.2 1.3 1.5 -0 Log-Discrepancy index
(C) Engine power (kW) 70
70
(ii) MFB
60
60
50
50
Frequency (%)
Frequency (%)
(i) MFA
40 30
40 30
20
20
10
10 0
0 . 0 .8 .6 .4 .2 . 0 . 8 . 6 .4 . 2 . 0 . 2 . 4 . 6 . 8 .0 . 2 . 4 . 6 .8 .0 .2 -2 -1 -1 -1 -1 -1 -0 -0 -0 -0 0 0 0 0 0 1 1 1 1 1 2 2
Log-Discrepancy index
.0 . 8 . 6 . 4 . 2 . 0 .8 .6 . 4 . 2 . 0 . 2 . 4 .6 . 8 . 0 . 2 . 4 . 6 . 8 .0 . 2 -2 -1 -1 -1 -1 -1 -0 -0 -0 -0 0 0 0 0 0 1 1 1 1 1 2 2
Log-Discrepancy index
(D) Annual total landings (kg/yr)
25
(i) MFA
Frequency (%)
20
15
10
5
0
.0 .8 .6 .4 .2 .0 .8 .6 .4 .2 .0 .2 .4 .6 .8 .0 .2 .4 .6 .8 .0 -2 -1 - 1 -1 - 1 - 1 -0 - 0 -0 -0 0 0 0 0 0 1 1 1 1 1 2 Log-Discrepancy index
(E) Annual fishing trips (no./yr) 40
(i) MFA
35
40
(ii) MFB 35 30
25
Frequency (%)
Frequency (%)
30
20 15
25 20 15
10
10
5
5
0 -0.50 -0.25 0.00
0.25 0.50 0.75 1.00 1.25 Log-Discrepancy index
1.50
1.75
2.00
0 -0.50
-0.25
0.00
0.25
0.50 0.75 1.00 1.25 Log-Discrepancy index
1.50
1.75
2.00
Table 1. Results of a Wilcoxon Signed Rank Test comparing differences between questionnaire and official data for vessel length (m), Gross Tonnage (GT), engine power (kW), total landings (kg/yr) and annual fishing trips (no./yr). N = sample size. Data for annual fish landings for part-time fishers were not available. Full-time fishers
Part-time fishers
N
Z
P-value
N
Z
P-value
Vessel length (m)
111
-1.55
0.12
69
-1.38
0.17
Gross Tonnage (GT)
85
-3.32
0.001
31
-3.14
0.002
Engine power (kW)
102
-6.55
