Evaluation of changes to dusky flathead catch limits in Mallacoota Inlet
Recreational Fishing Grant Program – Research report
PROJECT NUMBER: 11/03/04R
MAY 2010
Table of Contents
Executive Summary
Introduction
Purpose of this report
Methods
Data collection
Data analysis
Age composition
Results
Characteristics of the Mallacoota Inlet recreational fishery Targeting preferences
Bait vs lure preference for dusky flathead fishing
Dusky flathead catch rates
Dusky flathead catch rates
Size composition of dusky flathead catches
Age composition
Impacts of the 2003 dusky flathead catch limits
Reasons for releasing/discarding dusky flathead
Angler perceptions of dusky flathead size and catch limits
Comparison of recreational fishing surveys undertaken in Mallacoota Inlet during 2003/04–2007/08 and 1981/82–1984/85 16
Predicted impacts of future changes to catch limits
DiscussionConclusionsAcknowledgementsReferences
Appendix 1
Executive Summary
In December 2003, Fisheries Victoria introduced new recreational catch limit regulations for dusky flathead (daily bag limit and possession limit of five fish per person, including no more than one fish ≥ 60 cm Total Length, TL). These stricter catch limits were a precautionary measure in response to concerns over a substantial increase in targeted recreational fishing for dusky flathead in eastern Victorian estuaries, accompanied by an increasing use by anglers of highly effective soft plastic lures and other types of lures.
The access point creel survey (December 2003 to October 2008) and attitudinal survey (September 2004 to May 2006) undertaken in Mallacoota Inlet provided valuable data to assess the impacts of new catch limit regulations on dusky flathead fishing in Mallacoota Inlet. It confirms that since a survey undertaken in the 1980s there has been increased targeting of dusky flathead and anglers are now commonly using lures such as soft plastics, instead of bait, to catch them.
In recent years the Mallacoota Inlet recreational dusky flathead fishery has exhibited the following characteristics:
- The dusky flathead fishery is seasonal, with the highest targeted effort and catch rates occurring in summer and the lowest in winter
- The retained catch rates of dusky flathead were higher than for released fish and have increased in recent years compared with catch rates in the 1980s
- The majority (70%) of dusky flathead caught have been retained. Few retained dusky flathead are below 30 cm TL despite the Legal Minimum Length (LML) being set at 25 cm TL (27 cm TL since March 2009)
- The majority of the retained dusky flathead catch both in the 2000s and the early 1980s was in the length range 35–45 cm TL
- The proportion of larger (≥ 50 cm TL) fish in Mallacoota Inlet dusky flathead catches has declined considerably since 2003/04, and few fish ≥ 60 cm have been recorded in catches since 2005/06.
While growth of Mallacoota Inlet dusky flathead is similar for the first three years, females subsequently grow at a faster rate and reach a larger size than males. Dusky flathead are currently 1+ to 2+ when recruited to the fishery. Further research into sexual maturity and egg production of female dusky flathead in eastern Victorian estuaries is needed to better understand the potential effects of either existing or proposed alternative fishery management measures.
During the 2000s relatively few Mallacoota Inlet anglers caught their daily bag limit of five dusky flathead. Reducing the daily bag limit to four fish is likely to reduce fishing mortality by only 6–8%. The majority of anglers agreed with the current dusky flathead daily bag limit.
Few dusky flathead ≥ 60 cm TL have been caught by anglers since 2004/05, and these were most likely to be females. Assuming a similar maturation size for female dusky flathead as that found in NSW (56 cm TL), it is likely that in Mallacoota Inlet most of the catch of female dusky flathead consists of immature fish. Further investigation is needed on the potential effects of this catch profile on reproductive capacity, and on the most effective ways to control fishing impacts to mitigate these effects if necessary.
The majority of anglers felt the then dusky flathead LML of 25 cm TL should be increased to at least 30 cm TL and a third wanted the LML increased to at least 35 cm TL. Increasing the LML to 30 cm TL is predicted to have little effect on reducing the retained catch (0–2%) while increasing the LML to 40 cm TL is likely to initially reduce the retained catch by 19–39%.
Most anglers were satisfied with the overall quality of fishing in Mallacoota Inlet. Of those not satisfied the main reason given was poor catches. Strategically applying catch limits or other management measures to this recreational fishery in the future has the potential to minimise the impacts of fishing on stock abundance and thus to maintain or improve the quality of fishing.
Introduction
Flatheads (Family Platycephalidae) are the most common finfish group caught by recreational fishers in Australia (Henry and Lyle2003). Dusky flathead, Platycephalus fuscus, are caught in New South Wales and Queensland waters andare a key component of recreational fisheries in east Victorian estuaries. Dusky flathead are one of the two most important recreational target species in the Mallacoota Inlet and Lake Tyers Fisheries Reserves. Anglers also target dusky flathead in the Gippsland Lakes and other East Gippsland estuaries.
In recent years concern over increased targeting of this species in Victorian waters by anglers, particularly using soft plastics and other types of lures, has led to the implementation of stricter dusky flathead recreational catch limits. In December 2003, Fisheries Victoria introduced a daily bag limit and a possession limit of five dusky flathead per person, including no more than one fish ≥ 60 cm Total Length (TL). Prior to this a daily bag limit and possession limit of 30 fish, including no more than 2 fish ≥ 60 cm TL applied.
The Legal Minimum Length (LML) of 25 cm TL for taking of dusky flathead and all other flathead species from Victorian waters remained unchanged in 2003 but was subsequently increased to 27 cm TL in March 2009.
In the absence of any detailed information on recreational fishery trends or the status of dusky flathead stocks, the stricter 2003 catch limits were introduced as a precautionary measure against excessive fishing pressure. This new management measure highlighted the need to better understand dusky flathead recreational fishery characteristics and stock status in East Gippsland estuaries. Funding was sought from the Recreational Fishing Licence Trust Fund and Fisheries Victoria to undertake access point surveys of recreational fishing to provide this type of information. The focus of these surveys to date has been Mallacoota Inlet, which contains the State's most popular dusky flathead recreational fishery.
Mallacoota Inlet, located approximately 520 km from Melbourne, is the eastern-most estuary in Victoria and only 5 km from the New South Wales border (Hall et al. 1985). The peak recreational fishing effort in this estuary occurs during January, April and September, coinciding with public and/or school holiday periods (DPI 2006).
The results reported here came from several projects funded by the Recreational Fishing Licence Trust Fund (Project numbers 11/03/04R, R/06/07/04, R/05/06/06) and Fisheries Victoria.
Purpose of this report
This report presents recreational catch and effort data obtained from access point creel surveys undertaken in Mallacoota Inlet from December 2003 to October 2008 to:
- Determine the characteristics of the Mallacoota Inlet dusky flathead fishery
- Assess the impacts (if any) of the stricter dusky flathead daily bag and possession limits introduced in December 2003 on the profile of retained and released recreational catches of dusky flathead in Mallacoota Inlet
- Determine angler awareness of, support for, and perceptions of the impact of the new dusky flathead catch limits
- Compare the recreational fishery profile, catch rates and size composition data of the Mallacoota Inlet dusky flathead fishery after the introduction of the stricter catch limits, with previous surveys undertaken in Mallacoota Inlet before December 2003
- Assess the capacity to predict the likely impacts of any proposed future changes to recreational dusky flathead fishery management arrangements.
Methods
Data collection
Information on angling effort, the species composition of catches, and the size and age composition of dusky flathead, was obtained from access point creel surveys (Pollock et al. 1994) of boat and shore-based fishing parties in Mallacoota Inlet between December 2003 and October 2008. Information recorded as part of these surveys included:
- Time spent fishing
- Fishing location
- Target species
- Fishing gear used
- Species retained
- Length of each fish retained
- Species released
- Reason for releasing fish.
An attitudinal survey was added to interviews from September 2004 to May 2006. Anglers were asked if they were aware of current size and bag limits for dusky flathead and whether they agreed with these regulations.
Data analysis
Data from access point creel surveys were entered into an ACCESS database and used to generate data for dusky flathead in Mallacoota Inlet including catch rates, length composition, targeting preference, catch composition, bait preference and reasons for discarding fish.
Sampling was more intensive in 2004/05 and 2005/06 than in other years (2003/04, 2006/07, 2007/08, 2008/09).
Mean catch rates were calculated for dusky flathead from targeted fishing trips using the ratio-of-means estimator (Jones et al. 1995). Confidence limits were calculated using the survey means procedure in SAS version 9.1 (SAS Institute Inc. 2004) on log-transformed data and then back transformed.
Catch data obtained from completed fishing trips where anglers had caught (kept and/or released) dusky flathead were analysed to determine the proportion of trips restricted by the new dusky flathead catch limits (either five fish in total or one fish ≥ 60 cm TL per angler). When there was more than one angler in the fishing group interviewed, it was assumed that anglers had pooled their retained catch until the combined catch limit for the fishing party was reached. Retained catches that exceeded the catch limits, and fishing parties who released dusky flathead before the combined catch limit for the fishing party was reached, were also identified.
Results presented by financial year were considered the best representation of a single dusky flathead fishing season.
Age composition
The age distribution of dusky flathead in Mallacoota Inlet recreational catches was determined from otoliths (ear bones) removed from 262 dusky flathead sampled from 2002 to 2009. The majority of samples were from 2008 (n=254).
One otolith from each pair was prepared and aged following standard procedures in the Central Ageing Laboratory at Fisheries Research Branch (Morison et al. 1998).
Transversely sectioned otoliths were examined and aged under transmitted light using a Leitz Wild M3C binocular microscope, usually between 10–16 times magnification.
Results
Characteristics of the Mallacoota Inlet recreational fishery
TARGETING PREFERENCES
From May 1998 to October 2008, 4372 interviews were conducted with anglers fishing in Mallacoota Inlet over 626 separate survey days (Table 1). Anglers caught 27,588 fish, of which 52% were kept.
Almost half of all interviewed Mallacoota Inlet anglers (2155) reported dusky flathead as a primary target species for their fishing trip (Table 2, Figure 1). Dusky flathead were strongly targeted in the early to mid 2000s, but the popularity of this species appears to have declined somewhat in the last few years. The data for 1998/99 suggest that dusky flathead was a far less popular target species in Mallacoota Inlet that year, although there is less confidence in this estimate because of the small sample size.
During those trips when dusky flathead were targeted, anglers caught a total of 12,500 fish including 8703 dusky flathead (Table 2). The majority of dusky flathead were kept (70%). From December 2003 to October 2008, 4015 dusky flathead were measured.
The next most popular recreational target species in Mallacoota Inlet in recent years has been bream (mostly black bream but also including yellowfin bream and hybrids) which has been targeted during about a third of all angling trips (Figure 1). A significant proportion of anglers (9%) fished for anything, and trips were also undertaken targeting luderick (2%) and tailor (2%). Other species were also targeted on occasion.
Dusky flathead have been the dominant recreational target species in Mallacoota Inlet over the 5-year period 2003/04 to 2007/08, being targeted in 33–55% of trips undertaken annually (Table 2, Figure 2). During this period bream were targeted in 19–38% of trips.
Table 1. Summary of fishing trips and catch details reported by anglers interviewed in Mallacoota Inlet (May 1998 to October 2008).
|
Financial year |
No. Interviews (fishing trips) |
All fish |
||
|---|---|---|---|---|
|
No. fish kept |
No. released (%) |
Total caught |
||
|
1997/98 |
2 |
40 |
8 (17%) |
48 |
|
1998/99 |
77 |
302 |
226 (43%) |
528 |
|
1999/00 |
6 |
85 |
9 (10%) |
94 |
|
2003/04 |
228 |
446 |
522 (54%) |
968 |
|
2004/05 |
1316 |
4395 |
3924 (47%) |
8319 |
|
2005/06 |
1757 |
6476 |
5727 (47%) |
12203 |
|
2006/07 |
589 |
1810 |
1701 (48%) |
3511 |
|
2007/08 |
268 |
707 |
677 (49%) |
1384 |
|
2008/09 |
129 |
153 |
380 (71%) |
533 |
|
Total |
4372 |
14414 |
13174 (48%) |
27588 |
Table 2. Summary of fishing trips and catch details reported by anglers interviewed who were targeting dusky flathead in Mallacoota Inlet (April 1999 to October 2008).
|
Financial year |
No. interviews (% of all interviews) |
All fish |
Dusky flathead |
|||||
|---|---|---|---|---|---|---|---|---|
|
No. kept |
No. released |
Total caught |
No. kept |
No. released (%) |
Total caught |
No. measured |
||
|
1997/98 |
||||||||
|
1998/99 |
3 (4%) |
9 |
5 |
14 |
7 |
0 |
7 |
|
|
1999/00 |
||||||||
|
2003/04 |
115 (50%) |
250 |
241 |
491 |
197 |
110 (36%) |
307 |
190 |
|
2004/05 |
727 (55%) |
2355 |
1355 |
3710 |
1881 |
635 (25%) |
2516 |
1533 |
|
2005/06 |
912 (52%) |
3280 |
2521 |
5801 |
2916 |
1322 (31%) |
4238 |
2079 |
|
2006/07 |
281 (48%) |
941 |
804 |
1745 |
761 |
358 (32%) |
1119 |
60 |
|
2007/08 |
88 (33%) |
349 |
327 |
676 |
272 |
186 (41%) |
458 |
132 |
|
2008/09 |
29 (23%) |
44 |
19 |
63 |
44 |
14 (24%) |
58 |
21 |
|
Total |
2155 (49%) |
7228 |
5272 |
12500 |
6078 |
2625 (30%) |
8703 |
4015 |
Figure 1. Primary target species as specified by interviewed anglers in Mallacoota Inlet from 1998–2008 (n=4372).
Figure 2. Proportion of trips undertaken by anglers targeting dusky flathead or bream as the primary target species in Mallacoota Inlet from 2003/04–2007/08.
BAIT VS LURE PREFERENCE FOR DUSKY FLATHEAD FISHING
Anglers used lures, particularly soft plastics, during 41% of reported fishing events when targeting dusky flathead in Mallacoota Inlet from December 2003 to October 2008 (Figure 3). Despite increased interest in soft plastics and other types of lures, bait fishing (59% of all reported fishing events) during 2003–2008 was still the most popular way of fishing for dusky flathead, with prawn (22%) and mullet (17%) the most common bait types used. A variety of other baits were also used on occasion (Figure 3).
The proportion of anglers using lures to target dusky flathead in Mallacoota Inlet fluctuated over the five year period (2003/04–2007/08) from 36% in 2005/06 to 57% in 2003/04 and 2007/08 (Figure 4). The majority of anglers used bait when targeting dusky flathead during the 3-year period (2004/05–2006/07).
Figure 3. Frequency of tackle type (lure or bait) used by anglers targeting dusky flathead in Mallacoota Inlet during 2003–2008 (n=2,139).
Figure 4. Frequency of tackle type (lure or bait) used by anglers targeting dusky flathead in Mallacoota Inlet, presented by financial year (2003/04–2007/08) (n=2,111).
DUSKY FLATHEAD CATCH RATES
Mean targeted catch rates (fish per angler hour) of dusky flathead caught and retained in Mallacoota Inlet ranged from 0.28 (2003/04) to 0.52 (2005/06) (Figure 5). Catch rates of retained dusky flathead were highest during summer (0.56) and lowest during winter (0.18). Catch rates were similar during the spring (0.34) and autumn (0.37) periods.
Monthly retained catch rates were high from November to February, peaking in February at 0.68 fish per angler hour. Catch rates decreased and were lowest in August (0.06).
Figure 5. Estimated mean targeted catch rates (± 95% confidence limits) of dusky flathead retained by anglers in Mallacoota Inlet from 2003/04–2007/08 presented by financial year, season and month.
Mean targeted catch rates (fish per angler hour) of dusky flathead released in Mallacoota Inlet were similar for the five year period, ranging from 0.13 (2004/05) to 0.19 (2005/06) (Figure 6). Catch rates of discarded dusky flathead were similar for all seasons and months of the year (Figure 6).
Annual targeted catch rates of retained dusky flathead were higher compared with catch rates of released fish (Figures 5 & 6). Catch rates of retained fish were higher during summer, spring and autumn but similar to released catch rates during the winter period.
Figure 6. Estimated mean targeted catch rates (± 95% confidence limits) of dusky flathead released by anglers in Mallacoota Inlet from 2003/04–2007/08 presented by financial year, season and month.
Size composition of dusky flathead catches
Dusky flathead sampled in Mallacoota Inlet from 2003/04 to 2007/08 ranged in length from 24 to 80 cm TL (Figure 7).
Few dusky flathead retained by anglers (0-2% of annual catches) were less than 30 cm TL (Table 3). Of all dusky flathead measured (3994), only one fish was undersize (24 cm TL).
There was a higher proportion of larger fish measured in 2003/04, compared with the other years sampled (2004/05–2007/08). Nearly a third of all dusky flathead caught in 2003/04 were ≥ 50 cm TL, and 11% were ≥ 60 cm TL. In comparison, only 7–15% of annual catches in 2004/05–2007/08 were ≥ 50 cm TL and only 0–3% were ≥ 60 cm TL (Figure 7, Table 3).
The majority of flathead caught in 2004/05–2007/08 were 35–45 cm TL, accounting for between 56 and 80% of the catch sampled annually (Table 3).
The maximum length recorded for dusky flathead is 120 cm TL (Morison and Conron 2003).
Figure 7. Length distribution of dusky flathead caught by anglers fishing in Mallacoota Inlet from 2003/04–2007/08 (n=number of fish measured). Fish ≥ 60 cm TL are indicated by black bars.
Table 3. Summary of the length distribution of dusky flathead caught by anglers fishing in Mallacoota Inlet from 2003/04–2007/08.
|
Financial year |
|||||
|---|---|---|---|---|---|
|
2003/04 |
2004/05 |
2005/06 |
2006/07 |
2007/08 |
|
|
No. fish measured |
190 |
1533 |
2079 |
60 |
132 |
|
Proportion of fish: |
|||||
|
< 30 cm |
1% |
2% |
1% |
0 % |
1% |
|
35-45 |
37% |
56% |
75% |
80 % |
67 % |
|
≥ 50 cm |
32% |
15% |
10% |
7% |
14% |
|
≥ 60 cm |
11% |
3% |
1% |
0 % |
1% |
|
Min length |
27 cm |
26 cm |
24 cm |
30 cm |
29 cm |
|
Max length |
73 cm |
80 cm |
77 cm |
55 cm |
62 cm |
|
Mean size |
47 cm |
41 cm |
41 cm |
41 cm |
42 cm |
AGE COMPOSITION
The age composition of dusky flathead caught by recreational fishers in Mallacoota Inlet was determined by ageing otoliths of 262 dusky flathead sampled from 2002 to 2009. The majority of otoliths aged were from fish sampled in 2008 (n=254).
The age-length distribution of dusky flathead caught in Mallacoota Inlet ranged from 0+ to 15+ years (Figure 8). Von Bertalanffy growth parameters estimated for male and female dusky flathead are shown in Table 4.
Female dusky flathead ranged in length from 26 to 91 cm TL and in age from 1+ to 15+ years. Male dusky flathead ranged in length from 26 to 56 cm TL and in age from 1+ to 9+ years.
Male and female growth rates were similar for the first three years of life. Females then grow at a faster rate than males and reach a larger size compared with males of the same age (Figure 8).
There were no males measured that were more than 60 cm TL or older than 9+ years in the aged sample. Dusky flathead were 1+ years old when they reached the previous LML of 25 cm TL.
Figure 8. Age–length data for dusky flathead caught in Mallacoota Inlet, fitted with von Bertalanffy growth curves (n=262). Female fish are indicated in pink, male fish are indicated in blue. Fish whose sex was unknown are indicated by black crosses. Dashed lines are included at 25 and 60 cm TL for reference to the size limit and 2nd tier catch limit regulations.
Table 4. Von Bertalanffy growth parameters for male and female dusky flathead caught in Mallacoota Inlet (n=262).
|
Male |
Female |
|
|---|---|---|
|
L∞ |
49.4 |
76.1 |
|
k |
0.433 |
0.204 |
|
T0 |
–0.290 |
–0.440 |
Impacts of the 2003 dusky flathead catch limits
Little information is available on whether, and to what extent, flathead catch limits prior to December 2003 (30 fish per person including no more than two fish ≥60 cm TL) constrained recreational catches of dusky flathead.
The two-tiered nature of the stricter recreational daily bag limit and possession limit for dusky flathead introduced in December 2003 (five fish including no more than one fish ≥60 cm TL) means that retained catches can be restricted in various ways or fish can be released for a variety of reasons (Table 5). The extent to which these catch limits may have constrained dusky flathead retained catches is best measured by identifying the proportion of completed fishing trips where some aspect of the catch limits has been reached.
From 2003/04 to 2008/09, 4,287 interviews were conducted with fishing parties in Mallacoota Inlet. Of these interviews, 1206 represented completed trips where dusky flathead had been caught and/or released (Table 5). Due to a low sample size, data from 2008/09 were excluded from further analysis (6 completed dusky flathead fishing trips).
Only a small proportion of anglers reached their daily bag limit of 5 dusky flathead (with all fish below 60 cm TL). A higher proportion reached this bag limit from 2003/04 to 2005/06, ranging from 10% to 13% of completed trips, compared with the following two years (3–6% of completed trips) (Table 5).
In 2003/04, a higher proportion of anglers reached the upper bag limit (i.e. one fish ≥60 cm TL) (8%) than in all other years sampled (Table 5). A small proportion of anglers caught the upper bag limit in 2004/05 and 2005/06. No anglers surveyed caught any fish ≥ 60 cm TL in 2006/07 and 2007/08.
Few anglers (≤2% overall) reached both 1st and 2nd tier dusky flathead catch limits in a single trip. Fishing parties that reached their limits of 5 fish per person including 1 fish ≥ 60 cm TL for all party members declined from 5% of trips in 2003/04 to <1% in 2005/06. No anglers surveyed reached both tiers of the dusky flathead catch limits in 2006/07 or 2007/08 (Table 5).
Of the completed fishing trips, 132 anglers reported releasing dusky flathead because they had exceeded the catch limit even though they had not reached either of the catch limits based on the number of anglers in the fishing party.
Only 13 of 1206 fishing parties surveyed were found to have exceeded the catch limit, indicating a high level of compliance with regulations.
Table 5. Proportion of completed angling trips where anglers reached the dusky flathead bag limit regulations in Mallacoota Inlet during 2003/04–2007/08
|
2003/04 |
2004/05 |
2005/06 |
2006/07 |
2007/08 |
n |
|
|---|---|---|---|---|---|---|
|
Percentage of trips where the following limits were reached: |
||||||
|
Bag limit (5 fish/person - all fish <60cmTL) |
12% |
10% |
13% |
6% |
3% |
|
|
Upper tier bag limit (One fish ≥60cmTL) |
8% |
2% |
1% |
0% |
0% |
|
|
Bag limit (5 fish including 1 ≥60cmTL per person) |
2% |
1% |
<1% |
0% |
0% |
|
|
Bag limit (5 fish per person including at least 1 ≥60 cm TL) reached for all members of the fishing party interviewed) |
5% |
1% |
<1% |
0% |
0% |
|
|
No. completed fishing trips sampled |
59 |
447 |
541 |
120 |
33 |
1200 |
REASONS FOR RELEASING/DISCARDING DUSKY FLATHEAD
Anglers interviewed in Mallacoota Inlet caught a total of 8703 dusky flathead, 30% of which were released or discarded. During the period, 2003/04–2007/08, anglers released dusky flathead because they were in excess of catch limits (37%), undersize (26%), unwanted – even though within catch limits (13%), they practised catch and release (23%) or the fish was tagged (<1%) (Figure 9).
The reasons anglers released or discarded dusky flathead changed over the 5-year period. During the first three years (2003/04–2005/06) a higher proportion of anglers (24–57%) released dusky flathead as they were in excess of catch limits, compared with 0–6% during 2006/07 and 2007/08. Most dusky flathead released during 2006/07 and 2007/08 were undersize (51–56%) or anglers were practising catch and release (29–38%).
Anglers could provide more than one reason for discarding (i.e. the discarded catch could comprise some dusky flathead that were undersize and some that were surplus to the bag limit).
Figure 9. Angler reasons for releasing dusky flathead in Mallacoota Inlet by financial year, 2003/04–2007/08 and for all years combined (n=755).
Angler perceptions of dusky flathead size and catch limits
From September 2004 to May 2006, 404 anglers fishing in Mallacoota Inlet were asked if they were aware of current size and daily bag limits for dusky flathead and whether they agreed with these regulations.
The majority of anglers surveyed were targeting dusky flathead (54%) (Figure 10). Anglers also targeted black bream (12%) and other species less frequently. Over a fifth of anglers were fishing for anything (21%).
About half of all anglers interviewed were aware of the LML for dusky flathead (49%) and a further 39% were aware when aided (e.g. "The size limit is 25 cm; can you recall ever seeing or hearing anything about this?"); 12% were not aware of the size limit at all (Figure 11). A higher proportion of anglers targeting dusky flathead were aware (59%) of the LML; 7% were not aware at all.
While 36% of anglers agreed with the LML for dusky flathead, the majority of anglers (61%) thought the LML should be higher than 25 cm TL (Figure 12). Less than 1% of anglers felt the LML should be lowered. Some anglers were unsure (2%) while no anglers felt the LML should be removed completely.
Of the 224 anglers that disagreed with the current size limit of 25 cm TL, 49% felt the LML should be increased to 30cm TL (Figure 13) and nearly all of them (93%) thought the LML should be at least 30cm TL. A third of these anglers (33%) wanted the LML to be ≥ 35 cm TL, an increase of 10cm or greater on the then LML of 25 cm TL. Only one angler wanted the LML reduced.
The majority of anglers were aware of the daily bag limit for dusky flathead (61%) and a further 25% were aware when aided; 15% were not aware of the daily bag limit (Figure 14). A higher proportion of anglers targeting dusky flathead (70%) were aware of the daily bag limit; 11% were not aware at all.
Most anglers interviewed agreed with the daily bag limit for dusky flathead (89%) (Figure 15). Some anglers (8%) felt the daily bag limit should be higher (i.e. more lenient) while a few anglers were unsure (2%), thought the bag limit should be lower (1%), or supported no bag limit at all (<1%).
Of the 32 anglers that disagreed with the current dusky flathead daily bag limit, 66% felt the limit should be 10 fish per person rather than 5 (Figure 16).
Anglers were provided the opportunity to make further comment. Some anglers felt all dusky flathead over 60 cm TL should be released, others were worried about multi-tripping (i.e. anglers undertaking more than one trip per day) and members of the Mallacoota Angling club stated that club members apply a LML of 36 cm TL.
Figure 10. Targeting preference of anglers surveyed about size and bag limits of dusky flathead in Mallacoota Inlet from September 2004 to May 2006 (n=404).
Figure 11. Awareness of the dusky flathead Legal Minimum Length (LML) by anglers interviewed in Mallacoota Inlet from September 2004 to May 2006 (n=403). Anglers targeting dusky flathead are indicated by white bars (n=217).
Figure 12. Angler opinion of the dusky flathead Legal Minimum Length (25 cm TL). Anglers were interviewed in Mallacoota Inlet from September 2004 to May 2006 (n=359). Anglers targeting dusky flathead are indicated by white bars (n=202).
Figure 13. Suggested dusky flathead Legal Minimum Length (LML) by anglers who disagreed with the existing LML. Anglers were interviewed in Mallacoota Inlet from September 2004 to May 2006(n=224). Anglers targeting dusky flathead are indicated by white bars (n=136).
Figure 14.Awareness of the dusky flathead daily bag limit by anglers interviewed in Mallacoota Inlet from September 2004 to May 2006 (n=400). Anglers targeting dusky flathead are indicated by white bars (n=215).
Figure 15. Angler opinion of the dusky flathead daily bag limit. Anglers were interviewed in Mallacoota Inlet from September 2004 to May 2006 (n=347). Anglers targeting dusky flathead are indicated by white bars (n=195).
Figure 16. Suggested dusky flathead daily bag limit by anglers who disagreed with the existing limit. Anglers were interviewed in Mallacoota Inlet from September 2004 to May 2006 (n=32). Anglers targeting dusky flathead are indicated by white bars (n=21).
Comparison of recreational fishing surveys undertaken in Mallacoota Inlet during 2003/04–2007/08 and 1981/82–1984/85
A roving intercept and access point survey of recreational fishing was undertaken in Mallacoota Inlet during the period 1981/82–1984/85 (Hall et al. 1985). During this period 265 interviews were conducted with anglers fishing in Mallacoota Inlet. A total of 152 dusky flathead were caught, of which 10 were released. Results from this report are presented in Appendix 1.
The size distribution of dusky flathead measured during the 1981–84 and 2003–08 surveys were similar, although the sample size was much smaller in the 1980s survey (n=142) compared with the recent survey (n=3994). There was a higher proportion of fish <30 cm TL in 1981/82–1984/85 (4%) compared with the recent survey (1%). The majority of fish were 35–45 cm TL in both surveys (1981–84 60%, 2003–2008 65%) (Table 6).
The targeting preference of anglers and the type of fishing tackle used to target dusky flathead has changed markedly between the two time periods. During 1981/82–1984/85, the majority of Mallacoota Inlet anglers targeted bream (38%) or 'anything' (35%); dusky flathead were targeted on 22% of trips. In the recent survey (2003/04–2007/08) anglers predominately targeted dusky flathead (50%) rather than bream (31%) or 'anything' (9%).
The 1980s survey results indicated that anglers targeting dusky flathead used prawn (34%), mullet (26%), Bass yabbies (12%), whitebait (11%) and a variety of other baits when fishing in Mallacoota Inlet. Fewer than 10% of interviewed anglers indicated they were using lures to target dusky flathead or any other species.
While prawn (22%) and mullet (17%) remained the most popular dusky flathead baits during the 2003/04–2007/08 surveys, lures – including soft plastics – had become much more popular, being used by 41% of anglers targeting dusky flathead.
Catch rates of retained and released dusky flathead were higher during 2003/04–2007/08 compared with 1981/82–1984/85. Few released dusky flathead were recorded in interviews during 1981/82–1984/85.
Table 6. Summary of the length distribution of dusky flathead caught by anglers fishing in Mallacoota Inlet during 2003/04–2007/08 and 1981/82–1984/85.
|
Survey period |
||
|---|---|---|
|
2003/04–2007/08 |
1981/82–1984/85 |
|
|
No. fish measured |
3,994 |
142 |
|
Proportion of fish: |
||
|
< 30 cm |
1% |
4% |
|
35-45 |
65% |
60% |
|
≥ 50 cm |
13% |
11% |
|
≥ 60 cm |
2% |
1% |
|
Min length |
24 cm |
27 cm |
|
Max length |
80 cm |
81 cm |
|
Mean size |
41 cm |
41 cm |
Predicted impacts of future changes to catch limits
Data on the profile of the retained recreational dusky flathead catch in Mallacoota Inlet from 2003/04 to 2007/08 were used to model the likely impacts that any further reduction of the dusky flathead daily bag limit would have on retained catches and therefore on fishing mortality.
To predict the immediate effects on dusky flathead catch rates, it is assumed that stock size and effort remain constant. This method was similar to that used by Conron (2004) and Attwood and Bennett (1995) who described the relationship between the potential reduction in fishing mortality by a daily bag limit and retained catch rate by anglers. It was assumed that catch restrictions resulting from the 1 fish ≥ 60 cm TL upper bag limit were rare and therefore not included in the model.
The relationship between the dusky flathead daily bag limit and reduction in fishing mortality is shown in Figure 17. The potential reduction in fishing mortality increased as the bag limit decreased. A daily bag limit of four dusky flathead was estimated to reduce fishing mortality by 6–8%, while a reduction in the daily bag limit to only one fish would result in an estimated 50–60% reduction in fishing mortality (Figure 17 ).
A shift in the LML was also examined by investigating the reduction in fishing mortality (i.e. the change in retained catch) when increasing the LML from 25 cm TL to 30, 35, and 40 cm TL. The potential reduction in fishing mortality (F), as a result of increasing the LML, varied between years (Table 7). Increasing the LML to 30 cm TL had little effect (0–2%) while increasing the LML to 40 cm TL would reduce the retained catch by 19–39% (Table 7).
Figure 17. Relationships between the potential reduction in fishing mortality (F) resulting from the enforcement of various Daily Bag Limits for Dusky flathead caught by anglers fishing in the Mallacoota Inlet from 2003/04 to 2007/08.
Table 7. Predicted reductions in the retained catch (fishing mortality) of dusky flathead from increasing the Legal Minimum Length (LML) to 30, 35 or 40 cm TL, based on surveys conducted with anglers fishing in the Mallacoota Inlet from 2003/04 to 2007/08.
|
Financial Year |
Reduction in the proportion of dusky flathead retained by anglers |
||
|---|---|---|---|
|
LML 30 cm TL |
LML 35 cm TL |
LML 40 cm TL |
|
|
2003/04 |
1% |
3% |
19% |
|
2004/05 |
2% |
19% |
39% |
|
2005/06 |
1% |
7% |
35% |
|
2006/07 |
0% |
3% |
28% |
|
2007/08 |
1% |
8% |
32% |
Discussion
Dusky flathead, Platycephalus fuscus, are a key component of recreational fisheries in east Victorian estuaries. In recent years they have become the most popular target species in the Mallacoota Inlet Fisheries Reserve.
One of the primary objectives of fisheries management agencies is to manage fishing activities in order to maintain fishing pressure at sustainable levels. For recreational fisheries size limits and catch limits are the management measures most frequently used to control the impacts of fishing. Increasing minimum size limits or reducing daily bag limits generally reduces retained catches and increases the proportion of fish that are released. Provided a high proportion of released fish survive, stricter size or catch limits can reduce fishing mortality, providing additional protection for a proportion of the fish population (Woodward et al.2003). Size and catch limits are also generally easy for recreational fishers to understand and comply with, and as they affect all fishers equally, are seen to be fair (Hill 1990).
The effectiveness of size or catch limits (or other management measures) in controlling fishing pressure varies in different fisheries depending on the characteristics of the target fish stock and the fishing methods being used in the fishery. It is therefore important to assess the management measures used in any given fishery to determine how effective they are at controlling the impacts of fishing on target fish stocks.
In December 2003, Fisheries Victoria introduced new recreational catch limit regulations for dusky flathead (daily bag limit and possession limit of five fish per person, including no more than one fish ≥ 60 cm TL). These stricter catch limits were a precautionary measure in response to concerns over a substantial increase in targeted recreational fishing for dusky flathead in eastern Victorian estuaries, accompanied by an increasing use by anglers of highly effective soft plastic lures and other types of lures.
Data from access point creel surveys (December 2003 to October 2008) and accompanying attitudinal surveys (September 2004 to May 2006) in Mallacoota Inlet were analysed and compared with survey data from the early 1980s to provide an updated profile of recreational fishing in this estuary and to assess the impacts (if any) of the new catch limits on dusky flathead catches in Mallacoota Inlet.
In recent years, the Mallacoota Inlet recreational dusky flathead fishery has exhibited the following characteristics:
- The dusky flathead fishery is seasonal, with the highest targeted effort and catch rates occurring in summer and the lowest in winter
- The majority (70%) of dusky flathead caught have been retained
- Few retained dusky flathead are below 30 cm TL despite the LML being set at 25 cm TL (27 cm TL since March 2009)
- The proportion of anglers using lures (including soft plastics) to target dusky flathead has increased substantially (41% in the 2000s compared with <10% in the early 1980s)
- Retained dusky flathead catch rates in the 2000s have been consistently higher than those recorded in the early 1980s. Reasons for this difference are not clear, but may include recent advances in the effectiveness of recreational fishing methods (eg. soft plastics and electronic fish finding equipment); differences in the survey methods used in the 1980s (roving intercept survey of incomplete fishing trips) compared with the 2000s (access point survey of completed trips); or increased abundance of dusky flathead in the estuary
- Retained dusky flathead catch rates in Mallacoota Inlet increased during the early to mid 2000s but have since been declining
- The majority of the retained dusky flathead catch both in the 2000s and the early 1980s was in the length range 35 – 45 cm TL
- The proportion of larger (≥ 50 cm TL) fish in Mallacoota Inlet dusky flathead catches has declined considerably since 2003/04, and few fish ≥ 60 cm have been recorded in catches since 2005/06. A similar trend has been observed in Lake Tyers during the same period (Conron et al. 2010).
Analysis of length and age data for Mallacoota Inlet dusky flathead indicates that the growth of male and female dusky flathead is similar for the first three years and then females grow at a faster rate and reach a larger size than males. Of the dusky flathead that were sexed, no males were above 60 cm TL, indicating that most or all of the fish at or above this size are female.
Available data indicate that some Mallacoota Inlet dusky flathead grow quickly enough to reach the LML at 1+ years old, but that nearly all 2+ year old fish are recruited to the fishery. A recent study of dusky flathead in NSW estuaries found that although females grow faster and reach a larger maximum length than males, they take longer to reach sexual maturity. In NSW, 50% of females reached maturity at approximately 56 cm TL and 4.5 years (Gray and Barnes 2008).
The size at sexual maturity of Victorian dusky flathead is unknown, but if similar to NSW it may mean that a significant proportion of female dusky flathead are being removed from Victorian fisheries before they reproduce. This reduction in large females may in turn affect the spawning capacity of dusky flathead and future recruitment to the fisheries. Further research into sexual maturity and egg production of female dusky flathead in eastern Victorian estuaries is needed to better understand the potential effects of current levels of fishing pressure.
There has been an increase in the proportion of anglers targeting dusky flathead and using lures, particularly soft plastics, since the 1980s. The application of new fishing technology has the potential to increase catch efficiency which may lead to an increase in catch rates even though stock abundance has not changed (Claramunt et al. 2009).
Interviews with Mallacoota Inlet recreational fishers during the period 2003-2008 indicated that the most frequent reason given for releasing/discarding dusky flathead was that they were in excess of the catch limits (37%).
Closer examination of the proportion of completed trips where anglers reached the dusky flathead catch limits (Table 5) and reasons for discarding (Figure 9) indicates that the impact of the catch limits on retained catches was greatest in the first three years (2003/04 to 2005/06) but has diminished considerably since then. This recent reduction in the effectiveness of the catch limits together with a decline in retained catch rates, suggests a decline in dusky flathead abundance. Few anglers have been constrained by the 2nd tier of the catch limit (maximum 1 fish ≥ 60 cm TL) since 2004/05.
Modelling of the potential impact of further reductions in the dusky flathead catch limits indicates that a reduction of the daily bag limit to 2 fish per person would reduce fishing mortality by about 30% while a reduction to 1 fish per person would reduce fishing mortality by 50 – 60%. These estimates of reduction in fishing mortality are based on an assumption that most or all released/discarded dusky flathead survive.
Release mortality can impact the effectiveness of size and catch limits. Lyle et al. (2007) found post-release survival of sand flathead was higher for fish that were shallow-hooked (i.e. hooked in the lip, mouth or eye) (~100%) compared with those that were deep-hooked (i.e. hooked in the throat or gut) (64%). Butcher et al. (2008) reported that post-release survival of dusky flathead was high (>92%) with most mortalities caused by deep hooking.
The vast majority (93%) of anglers interviewed in Mallacoota Inlet during the 2000s thought the dusky flathead LML should be increased to at least 30 cm TL. However, modelling of the potential effects of increasing the dusky flathead LML indicated that raising the LML to 30 cm TL would have negligible impacts on retained catches, and that an increase of the LML to 40 cm TL would be needed to reduce the retained catch by 30% or more.
Growth data suggests that Mallacoota Inlet dusky flathead grow approximately 12 cm in the 2nd year of life and 8 cm in the third year. An increase in the LML of 10 cm would therefore be expected to protect fish from the effects of fishing for an extra year.
The effectiveness of management measures, such as legal minimum lengths and daily bag/ possession limits, can be improved by assessments that are based on recreational fishing data and are guided by sustainable harvest objectives.
Conclusions
The access point creel survey (December 2003 to October 2008) and attitudinal survey (September 2004 to May 2006) undertaken in Mallacoota Inlet provided valuable data to assess the impacts of new catch limit regulations on dusky flathead fishing in Mallacoota Inlet. It confirms that since a survey undertaken in the 1980s there has been increased targeting of dusky flathead and anglers are now commonly using lures such as soft plastics, instead of bait, to catch them.
The retained catch rates of dusky flathead were higher than for released fish and have increased in recent years compared with catch rates in the 1980s.
While growth of Mallacoota Inlet dusky flathead is similar for the first three years, females subsequently grow at a faster rate and reach a larger size than males. Dusky flathead are currently 1+ to 2+ when recruited to the fishery. Further research into sexual maturity and egg production of female dusky flathead in eastern Victorian estuaries is needed to better understand the potential effects of either existing or proposed alternative fishery management measures
During the 2000s relatively few Mallacoota Inlet anglers caught their daily bag limit of five dusky flathead. Reducing the daily bag limit to four fish is likely to reduce fishing mortality by only 6–8%. The majority of anglers agreed with the current dusky flathead daily bag limits.
Few dusky flathead ≥ 60 cm TL have been caught by anglers since 2004/05, and these were most likely to be females. Assuming a similar maturation size for female dusky flathead as that found in NSW (56 cm TL), it is likely that in Mallacoota Inlet most of the catch of female dusky flathead consists of immature fish. Further investigation is needed on the potential effects of this catch profile on reproductive capacity, and on the most effective ways to control fishing impacts to mitigate these effects if necessary.
The majority of anglers felt the then dusky flathead LML of 25 cm TL should be increased to at least 30 cm TL and a third wanted the LML increased to at least 35 cm TL. Increasing the LML to 30 cm TL is predicted to have little effect on reducing the retained catch (0–2%) while increasing the LML to 40 cm TL is likely to initially reduce the retained catch by 19–39%.
Most anglers (76–84%) were satisfied with the overall quality of fishing in Mallacoota Inlet. Of those not satisfied the main reason given was poor catches. Strategically applying catch limits or other management measures to this recreational fishery in the future has the potential to minimise the impacts of fishing on stock abundance and thus to maintain or improve the quality of fishing.
Acknowledgements
This project was funded by the Recreational Fishing Licence Trust Fund using Recreational Fishing Licence fees and Fisheries Victoria (Project numbers 11/03/04R, R/06/07/04, R/05/06/06).
We wish to express our thanks to the many recreational anglers who have, over the years, freely provided us with information needed for this study.
We would also like to thank John Minehan for his efforts in interviewing several thousand recreational anglers as part of the angler survey. We also like to acknowledge the efforts of David Bull, Frank Richards, Erin Webb, Mike Kirwin, Dave Fuller, Andrew Mason and Evan Dungey who assisted with the angler survey work.
Thankyou to Peter and Paul Spehr for providing otolith samples for ageing.
Thanks to Pam Oliveiro, Katrina Halse, Vicki Nicholas and Tina Whillock for data editing and entry.
Thanks to Karina Ryan for preparing onsite survey lengths and catch rate data and to Daniel Grixti, James Andrews and Jon Presser for their comments on this report.
References
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Claramunt, R.M., Kolb, T.L., Clapp, D.F., Hayes, D.B., Dexter Jr., J.L. and Warner, D.M. (2009). Effects of increasing Chinook salmon bag limits on alewife abundance: Implications for Lake Michigan management goals. North American Journal of Fisheries Management 29, 829–842.
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Appendix 1
Dusky flathead catch rates and size composition data from an access point survey undertaken in Mallacoota Inlet from 1981/82 to 1984/85, are presented here for comparison. Further results from this survey are presented in Hall et al. 1985.
Table 8. Number of interviews and fish caught (kept and released) during access point surveys undertaken in Mallacoota Inlet from 1981/82–1984/85.
|
Financial year |
n |
|||||
|---|---|---|---|---|---|---|
|
1981/82 |
1982/83 |
1983/84 |
1984/85 |
|||
|
No. interviews |
78 |
58 |
116 |
13 |
265 |
|
|
All fish |
No. caught |
189 |
92 |
253 |
49 |
583 |
|
No. kept |
129 |
49 |
199 |
43 |
420 |
|
|
No. released |
60 |
43 |
54 |
6 |
163 |
|
|
Dusky flathead |
No. caught |
73 |
8 |
58 |
13 |
152 |
|
No. kept |
66 |
5 |
58 |
13 |
142 |
|
|
No. released |
7 |
3 |
0 |
0 |
10 |
|
Figure 18. Estimated mean catch rates (± 95% confidence limits) of dusky flathead retained by anglers in Mallacoota Inlet from 1981/82–1984/85.
Figure 19. Estimated mean catch rates (± 95% confidence limits) of dusky flathead released by anglers in Mallacoota Inlet from 1981/82–1984/85.
Figure 20. Length (TL)-frequency distribution of dusky flathead retained by anglers fishing in Mallacoota Inlet from 1981/82 to 1984/85 (n=142).
Figure 21. Frequency of primary target species nominated by anglers interviewed in Mallacoota Inlet from 1981/82 to 1984/85 (n=265).
Figure 22. Frequency of bait used by anglers targeting dusky flathead in Mallacoota Inlet from 1981/82 to 1984/85 (n=78).