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Kahawai Final Advice Paper
Ministry
of Fisheries
29
June 2004
ANNEX
ONE
Other sources of information
MFish initial position
- Other sources of information were summarised in the IPP in
paragraph 102.
Submissions
- Mark Feldman submits that the current biomass is unknown and
MCY estimates pure conjecture. He and other recreational submitters
consider that far more weight should be given to the following
sources of information.
- Recreational fishing perception surveys. Recreational groups
surveyed have repeatedly expressed concern about the state of
the kahawai stocks. These are:
- Readership surveys. The IPP discussed at paragraph 102 readership/club
survey results, but Feldman submits it failed to mention the high
level of experience of respondents (more than half of the respondents
indicated that they had fished more than 20 years); and
- Responses from the option4 website.
- Summary of option4 email respondents is as follows with the
response rate in brackets.
- I support the option4/NZBGFC submission to restore the non-commercial
kahawai fishery:
- Do you think management objectives for kahawai should focus
on restoring non-commercial access to a healthy fishery?
- Should Commercial Fishing companies be targeting kahawai with
purse seiners and spotter planes and then exporting their catch
to low value markets (such as Australia for crayfish bait where
it sells for about $A1.20 per kg?)
- Should fishery managers discount the catch history of bulk fishing
practices before they make quota allocations to commercial fishers?
- What level would you like to see the kahawai fishery managed
at?
- there should be more kahawai available (1 165)
- its about right (73)
- there should be less kahawai available (209)
- Would you like to see commercial catches of kahawai
- increase (2)
- stay the same (85)
- decrease (1 389)
- Fishing competition catch records and Club reports:
- New Zealand Angling Limited Event Catch Records
NZ Angling Limited submits that they have held
saltwater fly-fishing events each year since beginning in 1994.
Since 2000 a Kahawai world championship event was organised as
part of the tournament for “all species”. NZ Angling
Limited submits that since 2000 the proportion of kahawai to “other
species” has declined and the average weight of kahawai
has also reduced. The submission states that declining kahawai
numbers has resulted in the cessation of the “Saltwater
Sundays” programme in the Hauraki Gulf. It submits that
the next most marked reductions in catch rates have been in Whangaroa
Harbour in the Far North and to a lesser extent at the Bay of
Islands.
- Club reports
The RFC reports that while there has been no
change to the state of the kahawai fishery in the past twelve
months, clubs fishing KAH 1 at Whakatane, Opotiki, TeKaha and
Waihau Bay all reported poor tournament results for kahawai. A
tournament at Mount Maunganui of 115 anglers caught 57 kahawai
and at Waihou Bay 92 anglers caught 9 kahawai.
The RFC report that until recently there appeared to be no significant
decline in the recreational CPUE in KAH 2. However, clubs fishing
KAH 2 such as Gisbourne, Napier, Waiarapa and Ngati have all noted
a decline in the school sizes of kahawai. The Eades Fishing Tournament
(Wanganui) had 800 anglers reporting the catch of one kahawai.
The RFC submission notes that locals in KAH 3 are reporting fewer
mature fish, with juvenile fish present within the Marlborough
Sounds but few schools elsewhere in the area.
Mark Roberts submits that members of the Pania
Surfcasting Club (Napier) were able to catch 10 kahawai per weekend
as a self-imposed club limit until 2000. Since members have been
unable to catch 5 kahawai during a weekend. He submits that this
change might be due to changes to currents or the availability
of prey species, but doubts that fishing kahawai down to BMSY
is likely to improve the situation.
- Tagging analysis. Mark Feldman considers that
important information was omitted from the IPP. He notes that
tagging studies were undertaken during 1983 and 1991 and that
a simple comparison of the tag return rates supports the conclusion
of kahawai changing from a predominantly recreational to a predominantly
commercial fishery during this time (the proportion had reduced
from 72% of the 1983 tags to 27% of the 1991 tags being returned
by recreational fishers).
- Length based studies. Mark Feldman considers
that mean lengths of purse seine caught kahawai in the Bay of
Plenty declined 5.7 cm between 1983 and 1992. Further, he submits
that recreational caught fish measured at various locations during
the same period show similar declines at every site examined.
- Recreational catch per unit effort (CPUE).
Mark Feldman notes that little data is available to quantify the
recreational catch during the 1980s prior to the development of
the purse seine fishery. He cites the availability of recreational
CPUE for the Motu River Mouth in 1982 that was repeated in 1992.
While noting differences in approach by the two studies, he considers
the comparison provides evidence of severely reducing recreational
CPUE over this period (4.7 fish per hour for residents and 2.6
for visitors in 1982 as compared to 0.1 fish per hour in 1992).
Further, Mark Feldman doe not agree with the conclusion reported
in the IPP “that kahawai catch rates estimated at boat ramps
during 1991 and 1994 might be artificially low”. This is
because he believes:
- Catch data for the Motu River Mouth has also declined;
- Any reasonable person would conclude that a catch of 0.4 kahawai
per angler per trip to be a very poor catch rate; and
- The CPUE of snapper is three times greater than kahawai and
it is well known that the snapper fishery is below BMSY in the
north.
- The RFC submits that purse seining has been responsible for
an overall decline in the stock status of kahawai. It submits
that intensive purse seining in the Bay of Plenty and the top
of the South Island has resulted in an overall decline of kahawai
around the entire coast of New Zealand. This is explained by a
“sink” hypothesis whereupon concentrated purse seining
in hotspots creates a void into which kahawai from other areas
ultimately sink. The RFC submits much of the same evidence to
support their views as provided by Mark Feldman, apart from an
additional point about Kaharoa trawl survey data.
- Kaharoa trawl survey data. The RFC cites a report summarising
trawl survey results between 1982-93 (biennial trawl surveys were
undertaken by the Ministry of Agriculture and Fisheries research
vessel Kaharoa during this period). These research data suggested
declining mean lengths of kahawai taken in trawl surveys on the
west coast North Island and the Bay of Plenty during this period.
The RFC submits that there may be two explanations for this reported
decline:
- A major increase in recruitment; and
- A major increase in the removal of adults (overfishing).
The RFC submit that recruitment indices for the Hauraki Gulf suggested
poor recruitment during 1981, 1984, 1996 and for each year between
1987-91. Accordingly, the RFC concludes that decreases in mean
lengths cannot be due to recruitment of small fish and so are
most likely due to overfishing of the larger fish by purse seining.
- Non-Commercial Fishers submit that there was
considerable concern from recreational fishers about the disappearance
of kahawai 15 years ago. The Minister shared that concern in the
early 1990s because purse seine catch limits were introduced.
- However, Non-Commercial Fishers submit that there is no evidence
of a rebuild of fishstocks as reflected by non-commercial catch
rates since. Catch rates of kahawai from the 1996 national boat
ramp surveys show that fishers who report targeting kahawai catch
just 0.79 kahawai per hour - in other words five hours fishing
for four fish. Fishers who say they were targeting snapper on
their trip (most trips in the north) caught just 0.11 kahawai
per hour – in other words nine hours fishing for one kahawai.
- Sanford notes that recreational fishing organisations
have suggested that kahawai catch rates have declined substantially
in all areas, and that this indicates a substantial decline in
kahawai abundance due to high levels of commercial catch. Sanford
submits there is a lack of data to support this assertion.
- Sanford say that it is axiomatic that harvesting a fish stock
will lead to a reduction in biomass, but submits that other factors
(such as increased recreational fishing pressure and land use
changes) will also affect kahawai availability in near shore waters.
If kahawai stocks were under pressure, one would expect to see
other signs of this, such as a reduction in the proportion of
older fish, or reductions in catches by non-target fishing methods.
In support of these statements Sanford submits:
- That the 1996 stock assessment does not support any hypothesis
for over exploitation of the kahawai resource (discussed in next
section);
- The most recent age frequency data from the late 1990s shows
a broad spread of ages and a strong proportion of older fish,
consistent with a relatively low exploitation rate [11];
- Sanford provides an analysis of commercial aerial sightings
data and submits that these data do not show any clear trends.
Sanford considers this analysis highlights the large variations
in schooling kahawai from year to year, presumably as a result
of environmental and other factors, which will affect availability
of surface schooling fish to both recreational and commercial
operators; and
- Kahawai bycatch rates in non-target fisheries are not declining
in proportion to any hypothesized declines in overall abundance.
It submits that total bycatch has been relatively stable, or has
increased, in spite of the reduction in trawl effort in some areas
due to TACC reductions of the target species.
[11]
Taylor, P,D Ayers, B.Hartill and D.Fisher, 2004. Characterisation
of the amateur fishery for kahawai (Arripus trutta) in New Zealand.
NIWA Client Report WLG2004-012.
MFish
response
Recreational fishing perceptions
- option4 respondents identified areas they fished and were able
to choose any number of QMAs. Responses as a percentage of the
totals are: QMA 1 (58%); QMA 2 (12.5%); QMA 3 (0.5%); QMA 8 (24%);
QMA 4 and 10 attracted few responses. In comparison to the 2000-01
recreational diary results these proportions suggest that fewer
QMA 2 and QMA 3 anglers, and a higher proportion of QMA 8 anglers,
responded to the option4 website than might be expected.
- Over 90% of option4 respondents indicate that they have 11 or
more years of fishing experience with over 70% having fished for
21 or more days a year, although it is unknown what species they
might have been fishing for.
- Almost 82% of respondents indicate that kahawai has “decreased”
in size although 17% considered size has “remained the same”.
- 63% of respondents consider that the numbers of feeding schools
are “much less frequent” in terms of their experience
and 34% “less frequent”. MFish notes that 70% of respondents
report their level of experience exceeding 20 years (before the
introduction of purse seine catch limits). Nevertheless, only
2.6% of respondents report “about the same number”
of schools in their experience and less than 1% reports any improvement.
- 88% of respondents indicate that they perceive stocks of kahawai
have “declined a lot” and 10% that stocks have “declined
a little”. This compares with a 1997 readership survey recording
47% of its respondents indicating that stocks had “declined
significantly” and 32% that stocks had “declined a
little”. This suggests that not only has the total percentage
of respondents perceiving stocks to have declined increased by
10% but that a greater percentage of respondents believe that
this decline is more substantial than respondents did in 1997.
- MFish notes that the questions differ subtly in their wording
and therefore a direct comparison is not possible. The 1997 survey
(2 002) attracted a slightly greater number of respondents in
comparison to the option4 emails (1 790).
TOP
Fishing competition
Catch Records
- MFish has analysed data provided in submission showing the
proportion of kahawai caught in comparison to other species (provided
in the NZ Anglers submission of their tournament catch records)
and provide the results below.
- The proportion of kahawai caught in proportion to other species
varied between 1994 and 2000. The proportion of kahawai to other
species peaks in 2000 probably as a result of anglers’ more
actively targeting kahawai in comparison to other species as a
result of the new dedicated tournament for kahawai. Since 2000
the ratio has declined.
- Further interpretation is confounded by not knowing whether
fishing patterns were maintained over this period. MFish notes
that the number of kahawai caught per angler has reduced only
slightly between 1994 (4.6 kahawai per angler) and 2003 (4.4 kahawai
per angler). This suggests that the declining proportions of kahawai
could be attributed to increased catches of other species.
Tagging analysis
- MFish notes that the objective of tagging studies in the 1990s
was to study the movements of kahawai and not to measure the proportion
of catches by the fishing sectors. Any detailed analysis of tagging
returns relies on tagged fish becoming well mixed within the wider
population. However, the 1990s tagging studies were largely inconclusive
because of the effect of tagging on kahawai physiology and behaviour.
In addition, all tags recovered were not returned and the fishing
effort distribution of the sectors was not the same. Accordingly,
MFish does not consider the lack of any discussion of the tagging
data to be a major omission from the advice. Neither does MFish
consider that these data are useful for determining the relative
proportion of catches by sector groups as suggested by submissions.
Length based studies
- Discussion at the 1994 Plenary highlighted the ability of purse
seine vessels to selectively target kahawai by size. The Plenary
concluded that historical comparison of purse seine catch did
not provide reliable information on length frequency trends in
the population.
- MFish notes that a subsequent report has further highlighted
that the schooling behaviour and short and long term movements
makes sampling of kahawai lengths randomly and representively
very difficult. Nevertheless, the report considered samples from
the recreational fishery were better from a statistical point
of view and recommended that the recreational fishery be used
to monitor kahawai . Results of the first three years of the recreational
monitoring have detected no changes in annual length frequencies
between 2001-2003. As noted in the Sanford submission these results
show a broad spread of ages and a strong proportion of older fish,
which is consistent with a relatively low exploitation rate.
- MFish notes the R.V. Kaharoa trawl survey data but considers
that these small data sets are probably biased and unrepresentative
of the kahawai population. Trawl surveys are not considered a
good sampling method for kahawai because of their pelagic habit
(trawl surveys sample fish mainly found on the seabed most effectively).
The small number of samples obtained and the nature of the method
suggest no helpful conclusions may be drawn from these data.
Recreational catch
per unit effort (CPUE)
- MFish agrees with submissions that little data is available
to quantify recreational catch rates during the 1980s prior to
the development of the purse seine fishery. However, an examination
of landings rates from boat ramp surveys conducted in 1991, 1994,
1996, 1998, 2001, 2002 and 2003, showed that throughout the time
series, landings rates have been similar in East Northland, Northland,
and Hauraki Gulf, both in magnitude and in the pattern of fluctuations.
Generally they have been lower in recent years than experienced
in the mid 1990s, but similar to those observed in 1991. In the
Bay of Plenty, landing rates have been higher and more variable
than in the other areas [12].
- While reported catch rates are low a range of factors including
variations in the time spent targeting other species can explain
this. Targeting kahawai can involve great amounts of time searching
for the highly mobile schools of fish.
- Dr Feldman submits that recreational surveys at the Motu River
provide evidence of severely declining CPUE between 1982 and 1991.
Dr Feldman notes that there are differences in approach between
the surveys. MFish considers that these differences confound any
conclusive comparison. MFish notes that the surveys differ both
in area surveyed and the time surveyed. Probably of most importance
is the time surveyed. Runs of kahawai in the Motu River are highly
seasonal. A study found that most of the kahawai at the Motu River
are adults, many of which are not feeding, but are approaching
sexual maturity, and may be part of a spawning migration [13].
Alternatively, because of the influence of the moon on the timing
of runs of kahawai, their presence may be influenced by the availability
of foods in the estuary such as smelt and whitebait. By surveying
later in the year during 1991 it is possible that seasonal effects
were responsible for the much lower CPUE. Alternatively there
might have been changes to spawning migrations or changed river
usage during 1982-91 may have reduced the runs of smelt or whitebait
that are a food source for kahawai.
[12]
Bradford, E. 2000 feasibility of sampling the recreational fishery
to monitor the kahawai stock New Zealand Fisheries Assessment Report
2000/11.
[13]
Penlington B.P. 1988 The kahawai fishery at the Motu River mouth
New Zealand Freshwater Fisheries Report No 103.
Commercial aerial
sightings data
- There is very limited information with which to examine trends
in kahawai abundance. However, the aerial sightings database contains
the longest available time series of information as data has been
collected almost from the onset of purse seining. Aeroplanes are
used to assist purse seine vessels locate surface schools of fish.
The pilots of these planes record their flying effort, location
and school sightings, which is furnished to MFish that maintain
a database.
- There are limitations on the use of these data as an index of
relative abundance. Data collection is opportunistic, is not random
and it has a commercial motive of assisting purse seine vessels
locating schools of fish. Further, it is unknown what proportion
of the population is seen and how this varies with environmental
conditions. Therefore, at best, these data can be interpreted
as only a rough index of relative abundance over time.
- Nevertheless MFish notes that there have been studies to refine
the quality of information that can be derived from aerial sightings
data. The report prepared as part of the Sanford submission is
the first step in an approach that is being developed elsewhere,
in which the objective is to produce stock indices for schooling
species standardised for a variety of environmental and fishery
related variables. Data is presented for East Northland, Bay of
Plenty and Hawkes Bay only. The Sanford report on aerial sightings
is not standardised and has not been reviewed by the Pelagic Working
Group.
- Sanford submits that sighting of surface schools of kahawai
is highly variable from year to year and that there has been no
major decline in school size and abundance. MFish does not agree
that this interpretation can be made from the data presented.
Some of the indices appear to be suggesting strong declines. MFish
suggests that no conclusions can be drawn from these data as presented.
Analysis of aerial survey data is complex and is subject to an
ongoing research program.
Commercial Bycatch
- MFish does not agree with industry submissions that there is
evidence of a stable bycatch CPUE and hence a stable stock abundance.
There is a body of literature that has examined the assumption
that changes in CPUE will, to some extent, reflect changes in
stock abundance. However, the assumptions involved cannot always
be tested and bycatch CPUE is not often a useful indicator of
abundance in these types of fisheries. Where different target
fisheries and fishing methods are combined, as is the case for
kahawai, standardisation of the data will be required.
- Careful consideration and standardisation of the measure of
fishing effort and other factors are required for CPUE analysis
to be useful. Trends in catching ability need consideration, as
changes in fishing practice can contribute to changes in landings
over time (an effect that may not be able to be disentangled from
trends in abundance).
- The use of CPUE analysis is much more problematic for a bycatch
fishery. This is particularly so when, as is the case with kahawai,
bycatch numbers and weight are relatively small per unit of effort.
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