Decline
of the Kahawai Fishery
Report
by Mark Feldman
late
1990's
The following report was prepared for one of the Ministry meetings
that occurred in the late 1990’s. It is a collection of the
scientific data available at that time that highlighted the declining
catches and smaller size of kahawai available to the recreational
sector.
Much of this data had not been integrated properly into the knowledge
base and still isn’t. This information, when viewed as a whole,
shows how much the kahawai fishery has declined.
The Status of the Kahawai Stocks from the
Point of View of the Recreational Sector
Introduction
The Big Game Fishing Council, the Recreational Fishing Council and
the vast majority of 400,000 marine recreational fishers believe
the kahawai resource available to them has declined significantly
over the past decade. We believe this decline in our resource is
the direct result of excessive purse-seine fishing and an expanding
commercial set net fishery.
Part II, Section 10a, of the new Fisheries Act declares, “
Decisions should be based on the best available information.”
We believe the information we are presenting here is the best available
for kahawai and is far more reliable than the simple model developed
at the last Working Group meeting.
Instead of focusing on a speculative model it is important for the
Working Group to keep in mind that we don’t know the MSY for
kahawai, but we do know that the access of recreational fishers
to the resource is poor, and that commercial fishing operations
have taken a huge toll on the resource; about 45 million kahawai
caught in the past decade.
There are two main aspects of the last Working Group report that
we believe need to be changed. One is the assumption that recreational
catches were lower in the 1980’s than they are now. We don’t
believe that is correct. It’s much more likely that recreational
and customary catches were two or more times today’s levels.
We also believe that the emphasis of the Working Group needs to
shift away from our focus on our simple model towards the available
evidence that indicates a serious loss of access to kahawai for
the recreational and customary fishers.
When evaluating the following arguments it is important to consider
them all as a group. It is easy to nit-pick most
of the individual arguments to death by demands for more accuracy,
but when you consider all the arguments together
it is simple to understand why we believe the recreational sector
has been disenfranchised over the past decade.
The following arguments are divided into two aspects
- The present recreational kahawai catch is very poor.
- The recreational CPUE was much better a decade ago.
The Present Recreational
Catch
Over the past few years a variety of boat ramp and diary studies
have been completed. These studies have concluded that the average
fisher catches 0.4 kahawai per person per fishing trip. We don’t
believe any reasonable person would disagree that this is a very
poor catch rate.
For those of you who are not recreational fishers it might be helpful
to point out that the CPUE for snapper in the North Region is three
times higher than the kahawai CPUE and it’s well established
the snapper fishery is below the Bmsy in the North.
A Comparison of Recreational CPUE in the 1980’s and
1990’s.
The following five arguments, when considered as a group,
strongly suggest that the recreational CPUE has declined dramatically
between 1983 and the present. It is our belief that the average
recreational CPUE in the early 1980’s was 1-2 kahawai per
person per fishing trip. This is 2-5 times today’s CPUE.
Listed below are summaries of our five main points. Details on each
of the five arguments can be found on the pages indicated at the
end of each summary.
- Changing pattern of tag returns in the Bay of Plenty between
1983 and 1991.
A comparison of the tag returns from the kahawai tagging programs
in 1983 and 1991 was made. The comparison was based on the tag
returns from purse-seine operations and recreational rod and line
fishermen; it was limited to the Bay of Plenty.
In 1983 the rod and line fishers returned 72% of the tags. By
1991 that proportion had dropped to 27%. During the same period
the proportion of kahawai tags returned by the purse-seine operators
rose from 28% to 73%.
We believe this reflects the decline in kahawai available to the
recreational sector because of excessive commercial fishing activities.
A more detailed explanation follows on page 4.
- Fishing magazines surveys of recreational kahawai fishers.
In 1997 both major fishing magazines cooperated to distribute
a kahawai survey to their members. A total of 2002 replies were
received. Of those 2002 replies 47% felt that kahawai stocks had
declined significantly over the previous five years, 32% felt
the stocks had declined a little, 11% felt they were the same,
8% felt they had increased a little and 2% felt they had increased
significantly. Most of these fishermen had over 20 years experience.
Experience, age and home location did not influence the answers
to questions about the status of the kahawai stocks. Similar results
were obtained during surveys in 1989, 1990 and 1992.
A more detailed explanation follows on page
7.
- The fork length of kahawai has declined in the Bay of Plenty.
We believe there has been a decline of 5.7cm in the fork length
of purse-seine caught kahawai in the Bay of Plenty between 1983
and 1992. This issue has been debated at the Pelagic Working Group
before. However, there were two significant errors made at the
Working Group and two items of new information, including a wide
ranging evaluation of kahawai fork length between 1983 and 1991.
All the data presented indicates that the fork length of kahawai
available to the recreational sector has declined over the past
decade.These are described in detail on page 9.
- The recreational CPUE had declined dramatically in the Bay of
Plenty.
From January – April 1982 a recreational survey at the Motu
River mouth in the Bay of Plenty revealed a CPUE of 2.55 kahawai
per hour for visitors to the area and 4.17 fish per hour for the
local residents.
From March – April 1991 a MAF survey of the area from Opotiki
to Te Kaha (includes the Motu) showed a CPUE of 0.1 kahawai per
hour. This comparison is not ideal because the survey area in
1991 included areas outside the Motu and a different time period.
However, the surveyor in 1991 has stated that catch rates at the
river mouth were approximately the same as other areas along the
beach, and peak catches in the area generally occur in March (a
month included in both surveys).
This issue has been discussed at the Working Group before but
there is new evidence made available from a more detailed breakdown
of the 1991 MAF survey and an interview with the surveyor in 1991.
- Declining purse-seine catch in KAH3
For years now the purse-seine vessels have been unable to catch
their limit in KAH3. With two boats operating in KAH3 the purse-seiners
were able to catch up to 5000 tonnes per year in the late 1980’s.
From 1991-92, 92-93, 93-94 and 94-95 these same two boats were
unable to catch their limit at any time. This suggests their CPUE
is 1/2 to 1/3 of what it used to be in the late 1980’s.
If the purse-seiners, guided by airplanes, cannot land kahawai
in KAH3, it’s easy to understand why recreational fishers
feel they can no longer catch kahawai either. Given that it is
much easier to catch kahawai with an airplane, its reasonable
to assume the recreational CPUE in KAH3 is less than 1/3 of what
it used to be in the 1980’s.
Conclusion
It is widely accepted by stock assessment scientists that decreasing
fork length, declining CPUE for commercial vessels and poor recreational
catch rates are the early signs of a declining fishery. We believe
that all these factors now apply to kahawai.
The new Fisheries Act has made it clear that our priority is to
be “cautious when information is uncertain, unreliable or
inadequate”. We believe that the last report from the Working
Group failed to do this.
The emphasis of the Working Group needs to shift from relying on
a poorly developed model, towards focussing on the well established
fact that there are no longer enough kahawai to supply the needs
of recreational and customary fishers in NZ.
To achieve this goal the report of the Working Group needs to be
changed as follows:
- Under ‘Recreational Fisheries’ emphasis needs to
be placed on the poor recreational CPUE in the key area of KAH1.
We also need to point out there has been a decline in the size
of kahawai available to the recreational fisher as well as the
number.
- Under ‘Biology’ lower values of “M”
need to be considered and perhaps other changes made as well.
Clearly there’s a problem with our model since it does not
correspond to the experience of fishers on the water.
- Under ‘Stock Assessment’ the assumptions about past
recreational catches need to be increased to accommodate the information
we’ve presented here. We suggest the probable recreational
catch in the 1980’s was probably 4000-5000 tonnes.
In addition, the emphasis of the entire section needs to shift
away from our poorly developed model towards the evidence we’ve
presented here because this evidence represents the “best
available information” required under the new Fisheries
Act.
- Under ‘Status of the Stocks’ the basic message needs
to change from a positive one to an acknowledgement that recreational
and customary fishers have inadequate access to the kahawai stocks
because of excessive commercial fishing over the past decade.
TOP
A
Comparison of the Rates of Recovery by Purse-seiners and Rod and
Line Fishers of Tagged Kahawai from the 1983 and 1991 Tagging Studies
in the Bay of Plenty
Summary
A comparison of the tag returns from the kahawai tagging programs
in 1983 and 1991 was made. The comparison was based on the tag returns
from purse-seine operations and recreational rod and line fishermen;
it was limited to the Bay of Plenty.
In 1983 the rod and line fishers returned 72% of the tags. By 1991
that proportion had dropped to 27%. During the same period the proportion
of kahawai tags returned by the purse-seiner operators rose from
28% to 73%.
We believe this indicates the recreational kahawai catch was much
higher in the 1980’s than it is now, and the number of kahawai
available to the recreational sector has declined significantly.
A change needs to be made to the Working Group document to reflect
the probability that the recreational catch and CPUE were higher
in the 1980’s than they are now.
Background
The boat ramp and diary studies done by the Ministry during the
1990’s have revealed an average catch of one half of a kahawai
per person per trip in the North Region; a poor catch by any measure.
Unfortunately there is very little data available to quantify the
recreational catch in the mid 1980’s, before the sharp increase
in purse-seine catches that were associated with the introduction
of the QMS. Up until now only one study was available; a CPUE study
at the Motu River mouth done in 1982. This study was never repeated
in exactly the same manner, but a comparable study of the Bay of
Plenty in 1991 suggested a severe decline.
In 1997, the results of the 1991 kahawai tagging study became available.
For a number of reasons outlined by Elizabeth Bradford in her 1997
paper called, “Estimation of Kahawai Recreational Catch from
Tagging Returns ….” It was not possible to use either
the 1983 or the 1991 tagging studies to calculate a kahawai biomass
or quantify the recreational catch. In both of these studies all
the tags recovered were not returned, the amateur and commercial
effort distributions were not the same and the tagged kahawai were
probably not evenly distributed in the population.
Since both the 1983 and 1991 tagging studies suffer from the same
flaws in the same way it is reasonable to assume the effects smooth
out when the studies are compared. For instance, its well known
that tags from individually handled fish are more likely to be returned
than tags from purse-seine caught fish. That is not a problem if
you only want to compare the studies, because tags recovered by
purse-seiners had the same chance of being returned in both 1983
and 1991. Likewise, tags recovered by hook and line fishers had
the same change of being returned in 1983 and 1991.
In a similar fashion, the differences between the amateur and commercial
effort distributions were likely to be the same in 1983 and 1991,
and the irregularities of the mix of tagged kahawai with the general
population were probably equivalent too.
In 1983 most of the kahawai tagging operations were performed from
June to September. In 1991 the tagging was completed in July. During
the 1980’s- 1990’s the total recreational fishing effort
was probably stable with population increases offset by a lower
percentage of people fishing. Weather conditions, which influence
the total recreational catch, were actually better after the 1991
tagging effort than after the 1983 effort, so weather was not the
cause of the decline in the proportion of kahawai caught by the
recreational sector. The total purse-seine catches in KAH1 during
the periods 1983-87 and 1991-95 were almost identical so that is
also not a factor in the relationship. The percentage of tag returns
in the 1983 study was 9.7% (138/1427) and the percentage for 1991
was 11.9% (551/4622); certainly comparable return rates.
Results
During both the 1983 and 1991 tagging studies large numbers of kahawai
were tagged in the Bay of Plenty. Records of tag returns were kept
over the following years. These tag returns were divided between
the purse-seine fishery and the recreational rod and line fishery.
By using these tag return figures it is possible to calculate a
relationship between the proportion of tag returns by the purse-seiners
versus rod and line fishers in 1983 and 1991.
In 1983 72% of all tags returned in the Bay of Plenty were from
rod and line fishers. In 1991 that proportion declined to 27% of
all tag returns. The reverse was true for the purse-seine fishery;
in 1983 28% of tag returns were from the purse-seiners. By 1991
that proportion had increased to 73% of returns.
Data and Sources
A Comparison of Total Tag Returns Between the 1983 and 1991 Kahawai
Tagging Studies in the Bay of Plenty
Year
Tags Were
Returned |
1983 Tagging
Study
(1434 kahawai tagged) [1] |
1991 Tagging
Study
(4622 kahawai tagged) [2] |
Year 0 - 1 |
76 tags or 5.2% |
366 or 7.9% |
Year 1 - 2 |
49 tags or 3.4% |
216 or 4.7% |
Year 2 - 3 |
13 tags or 1.0% |
91 or 2% |
TOTALS |
138 or 9.6% |
673 or 14.6% |
A Comparison of the Tag Recoveries by the Purse-seine versus
the Rod and Line Fisheries (only) from the 1983 and 1991 Kahawai
Tagging Studies in the Bay of Plenty
Source of Tags |
1983 Tagging Study
(1434 kahawai tagged) [1] |
1991 Tagging Study
(4622 kahawai tagged) [2] |
Purse-seine |
18 or 28% |
424 or 73% |
Rod and Line |
47 or 72% |
158 or 27% |
Conclusion
From this data, it is reasonable to assume that the recreational
kahawai catch was much higher in the 1980’s than it
is now. Although it is impossible to be certain, a figure
of 4000-5000 tonnes per year would be most likely.
Since the number of recreational fishers has probably been
stable over the decade a catch of 4000-5000 tonnes in the
1980’s implies a dramatic decrease in the recreational
CPUE over the past decade.
[1] Wood, B.A. Bradstock, M.A. and James, G.D. 1990: Tagging
of Kahawai in NZ, 1981-1984. NZ Technical Report No. 19
[2] Bradford, E. 1995: Growth and Biomass results from the
1991 kahawai Tagging Experiment.
TOP
1997 Kahawai Recreational Fishing
Survey Results
Summary
In 1997 both major fishing magazines cooperated to distribute a
kahawai survey to their members. A total of 2002 replies were received.
Of those 2002 replies 47% felt that kahawai stocks had declined
significantly over the previous five years, 32% felt the stocks
had declined a little, 11% felt they were the same, 8% felt they
had increased a little and 2% felt they had increased significantly.
Most of these fishermen had over 20 years experience. Experience,
age and home location did not influence the answers to questions
about the status of the kahawai stocks.
Background
Recreational fishing surveys have been performed in 1989, 1990 and
1992. The surveys had between 400-1000 replies each. All of the
surveys showed that over 80% of recreational fishermen believed
the kahawai resource was in decline. The average respondent was
over 35 years of age with 15 years of fishing experience; so these
survey results reflect a considerable amount of expertise over time.
Survey Results: Key survey results are as follows:
How many years have you been fishing?
More than 20 years |
53% |
11 - 20 years |
20% |
5 - 10 years |
19% |
Less than 5 years |
8% |
How many days a year do you go fishing?
More than 50 days per year |
25% |
21 – 50 days per year |
51% |
10 – 20 days per year |
18% |
Less than 10 days per year |
6% |
On what percentage of your trips do you target kahawai at least
some of the time?
Target kahawai at least 76 –
100% of the time |
11% |
Target kahawai 26 - 75% of the time |
27% |
Target kahawai 10 – 25% of the time |
30% |
Target kahawai less than 10% of the time |
32% |
Think back five years. In the intervening time do you think the
kahawai stocks have…
Declined significantly |
47% |
Declined a little |
32% |
Remained the same |
11% |
Increased a little |
8% |
Increased a lot |
2% |
A copy of the survey
follows.
TOP
1997 Kahawai Survey
Preliminary results: 1709 replies
Question Five
Think back five years. In the intervening time do you think the
kahawai stocks have…
Declined significantly |
47% |
Declined a little |
32% |
Remained the same |
11% |
Increased a little |
8% |
Increased a lot |
2% |
Question Two:
How many years have you been fishing?
More than 20 years |
53% |
11 - 20 years |
20% |
5 - 10 years |
19% |
Less than 5 years |
8% |
TOP
The Decline of Fork Length of Kahawai in
the Bay of Plenty Purse-seine Fishery from 1983 to 1992
Summary
We believe there has been a decline of 5.7cm in the fork length
of purse-seine caught kahawai in the Bay of Plenty between 1983
and 1992. This issue has been debated at the Pelagic Working Group
before. However, there were two significant errors made at the Working
Group:
- We were misinformed about the nature of the 1983 catch samples.
We were told the 1983 fish selected for measurement were the larger
fish available. This is not correct. They were selected at random.
- We were not presented with the results of a boot-strap analysis
that concluded there was a 95% chance the 1991-92 catches did,
indeed, have a smaller fork length than in 1983.
In addition, some new evidence has come to light about the fork
length of line caught fish in 1983 which shows a general decline
in the fork length of line caught fish throughout the North Island
when compared to 1991 data.
Available Information
As part of a 1983 tagging study of kahawai the fork length of 332
kahawai were measured in the Bay of Plenty. Of these 332 fish, 32
were line caught. Their median length was 49.8cm (see
page 12 for details).
The other 300 fish were purse-seine caught; three landings were
sampled with 100 fish sampled in each landing. The first two landings
measured represented a single school each. The last landing may
have involved more than one school (Gavin James provided this information).
The median length of the three landings of purse-seine caught fish
were 52.7, 49.3 and 51.8cm. These fish were selected at random.
The average of these means is 51.3cm.
In 1991-92 a shed study was done on kahawai. In 1991 five landings
were sampled with 6778 fish measured. These landings also represented
purse-seine targeted schools. The mean size was 46.1cm.
In 1992 seven landings were sampled. These landings also represented
purse-seine targeted schools. A total of 12,431 fish were measured.
The mean size in 1992 was 45.25cm.
The average of the 1991-92 means was 45.6cm.
Just recently an analysis was done comparing line caught kahawai
in 1983 to line caught fish in 1991 in various locations around
the North Island. In every location there was a decline in the fork
length of the fish. This data is available on page
15.
The majority of line caught fish in 1983 were caught trolling. Most
fish in 1991 were caught on bait. We were concerned about a possible
difference in size of fish caught, based on whether a lure or bait
was used. An analysis of available 1991 data indicates bait fishing
usually catches the biggest kahawai so that cannot be a factor in
the decrease in fork length we found. That data is available on
page 16.
TOP
Mean Fork Lengths of Kahawai
(target purse-seine only); 1983 vs. 1991-92
1983 |
1991-92 |
|
33.4 |
|
37.4 |
|
43.4 |
|
43.6 |
|
45.4 |
|
45.5 |
|
46.0 |
|
46.0 |
|
46.3 |
49.3 |
46.5 |
|
49.8 |
51.8 |
51.3 |
52.7 |
|
Discussion
Several points need to be made about the available data.
- It would be difficult to imagine how the combined commercial
and recreational fisheries in the Bay of Plenty could remove around
40,000 tonnes of kahawai (about 25 million fish) in a decade without
a decline in fork length.
- One of the arguments against accepting the 1983 data as representative
is that kahawai school by size; therefore just sampling three
or four schools is not adequate. It is true that kahawai school
by size; never-the-less, those sizes vary widely. Even a casual
glance at the graphs presented on pages 12 and
13 shows a 20cm range in the size of fish in each school.
That’s a big difference; it increases the chances our 1983
sample is truly representative of purse-seine caught fish at the
time because the concept of kahawai schooling “by size”
is really not so accurate.
- In 1994 Brian Jones did a bootstrap simulation of the data presented
in Table 2 from his 1994 stock assessment
paper (page 11 of this report). He selected any three of the 1991-92
means at random 600 times. The results were that 95% of the time
the 1991-92 catches had a smaller fork length than in 1983.
- The 32 line caught kahawai in the 1983 study had a mean size
of 49.8cm, a figure close to the size of the purse-seine caught
fish in 1983 and much larger than the sizes from the boat ramp
surveys (42.1cm in 1991 and 44.1cm in 1994) this decade. This
data is available on page 12.
-
The data presented on page 15
compares the fork length of line caught kahawai between 1983
and 1991. At all the locations with comparable data available
the fork length of kahawai have declined. This further supports
our argument that the fork length of kahawai available to recreational
fishers has declined over the past decade.
Table 2: Purse seine landings of kahawai sampled
in the Bay of Plenty in 1983, 1991 and 1992 (n = number in sample,
Mean = mean fork length, s.d = standard deviation).
Date |
n |
Mean |
s.d. |
31/05/83 |
100 |
52.72 |
2.48 |
13/06/83 |
100 |
49.34 |
2.54 |
16/06/83 |
100 |
51.79 |
2.83 |
|
|
|
|
14/05/91 |
3158 |
43.56 |
2.29 |
15/05/91 |
2758 |
37.16 |
4.91 |
27/05/91 |
821 |
45.46 |
3.96 |
28/05/91 |
741 |
45.19 |
4.39 |
31/05/91 |
1157 |
51.59 |
2.48 |
24/07/91 |
1029 |
45.83 |
4.23 |
05/08/91 |
2069 |
44.27 |
2.75 |
07/12/91 |
1029 |
49.62 |
3.30 |
04/01/92 |
300 |
50.40 |
1.97 |
08/01/92 |
560 |
45.99 |
2.50 |
11/04/92 |
564 |
53.6 |
2.60 |
14/04/92 |
3152 |
50.29 |
2.22 |
15/04/92 |
1493 |
41.15 |
5.00 |
16/04/92 |
1287 |
32.17 |
1.21 |
27/05/92 |
2620 |
43.45 |
3.66 |
28/05/92 |
2174 |
44.49 |
3.57 |
29/05/92 |
769 |
44.75 |
3.84 |
06/08/92 |
418 |
32.35 |
1.22 |
06/08/92 |
422 |
42.42 |
2.91 |
30/09/92 |
610 |
50.77 |
2.78 |
30/09/92 |
801 |
51.23 |
2.54 |
04/10/92 |
1104 |
45.42 |
4.05 |
11/10/92 |
577 |
46.96 |
2.42 |
11/10/92 |
646 |
51.27 |
2.55 |
12/10/92 |
333 |
36.00 |
1.49 |
02/12/92 |
726 |
54.10 |
1.98 |
10/12/92 |
747 |
38.33 |
4.45 |
16/12/92 |
239 |
50.90 |
2.50 |
16/12/92 |
257 |
36.95 |
2.61 |
(From: Kahawai information presented at the 1994 Stock Assessment
by J.B. Jones)
TOP
Biological Sampling
Data on length frequencies, sex composition,
age frequencies (otolith readings), and stomach contents were collected
from commercial landings and during tagging studies from damaged
fish.
Age and length frequencies
Little information on kahawai spawning and nursery areas is available,
but it appears that most sheltered bays and estuaries in the North
Island are used as nurseries, especially those off the east coast,
north of the Bay of Plenty. Apart from the sheltered estuarine waters
in Tasman Bay and near Farewell Spit, juveniles have not been found
in substantial numbers in South Island waters (NZ Ministry of Agriculture
and Fisheries unpublished data).
Age and fork length measurements were taken from kahawai caught
in several areas (Table 7). Although the catching
methods varied, the lengths of the fish en each area did not vary
with the method used (Tables 8a-d). Fish caught
by purse seine were assumed to represent local fish because the
mesh size of the nets was small enough to retain juvenile, as well
as mature, kahawai. Relatively more small fish were caught by line
than by purse seine, but this was probably because lining was usually
used to catch fish in sheltered nearshore waters where smaller kahawai
are often found. Within each area fish size did not vary substantially
between schools, though fish in one of the two schools sampled from
east Tasman Bay on 21 April 1983 were reported as being larger than
usual for the area.
Although almost 20% of the sample taken by setnet from the Waitaki
River in 1984 comprised small fish of about 40cm, the sample taken
by line in 1983 from this area had no fish of this size. It is unlikely
that this absence of small fish resulted from the fishing method
used, because 40cm fish were caught by lining in other areas that
year; it is more probable that there were no small fish in the sampling
area in 1983. Excluding this sample, the length frequencies of fish
caught by the two methods were similar.
Whole otoliths were read by the method described by Eggleston (1975).
For otoliths which required burning to read, rings were clearer
when the otolith was sectioned and polished before burning (Paul
1976, James 1984). The age – length relationships were similar
to those reported by Eggleston (1975). An age – length frequency
plot for all samples combined is given in Table 9. Although mean
length and age increased with latitude on the east coast South Island,
this trend was not apparent in other areas (see Table 7). Movement
of tagged fish between the North and South Islands..
Table 7: Age and length data for kahawai from areas
sampled
Area |
n |
Mean |
Median |
s.d.* |
Age (y)
Min-Max + |
Northland |
38 |
8.7 |
8 |
3.95 |
3-23 |
Bay of Plenty |
300 |
8.2 |
8 |
2.57 |
4-16 |
Ariel Bank |
97 |
8.8 |
9 |
1.57 |
5-12 |
Waikato River (1983) |
22 |
5.6 |
6 |
1.68 |
3-11 |
Waikato River (1984) |
100 |
9.8 |
10 |
2.11 |
6-16 |
New Plymouth |
39 |
8.5 |
8 |
4.25 |
3-18 |
Wellington Harbour |
137 |
8.1 |
8 |
2.52 |
2-20 |
South Taranaki Bight |
398 |
8.4 |
8 |
2.22 |
4-21 |
Farewell Spit |
300 |
6.1 |
5 |
2.14 |
4-14 |
East Tasman Bay |
149 |
11.1 |
11 |
2.84 |
7-19 |
Inner Tasman Bay |
100 |
4.2 |
4 |
0.43 |
3-05 |
Clifford Bay |
198 |
10.4 |
10 |
3.52 |
5-22 |
Kaikoura (1981) |
287 |
12.6 |
12 |
3.27 |
6-24 |
Kaikoura (1982) |
569 |
12.5 |
12 |
2.87 |
7-23 |
Waitaki River |
150 |
15.7 |
17 |
5.31 |
5-23 |
* Standard deviation
+ Minimum to maximum age
Area |
n |
Mean |
Median |
s.d.* |
Length (cm)
Min-Max + |
Northland |
38 |
48.2 |
48 |
6.50 |
34-59 |
Bay of Plenty |
300 |
51.3 |
52 |
3.00 |
42-58 |
Ariel Bank |
97 |
48.3 |
49 |
2.71 |
39-54 |
Waikato River (1983) |
22 |
38.6 |
39 |
5.12 |
28-49 |
Waikato River (1984) |
100 |
48.5 |
49 |
2.76 |
41-57 |
New Plymouth |
40 |
45.0 |
48 |
9.43 |
21-59 |
Wellington Harbour |
137 |
47.0 |
49 |
6.15 |
21-56 |
South Taranaki Bight |
400 |
48.0 |
48 |
2.87 |
40-58 |
Farewell Spit |
300 |
46.0 |
47 |
4.13 |
37-56 |
East Tasman Bay |
150 |
52.2 |
52 |
2.77 |
44-59 |
Inner Tasman Bay |
100 |
36.6 |
37 |
2.16 |
28-44 |
Clifford Bay |
199 |
51.4 |
52 |
3.60 |
39-61 |
Kaikoura (1981) |
293 |
53.1 |
53 |
2.70 |
46-60 |
Kaikoura (1982) |
572 |
52.9 |
53 |
2.56 |
44-62 |
Waitaki River |
151 |
53.7 |
56 |
6.24 |
28-62 |
* Standard deviation
+ Minimum to maximum age
Table 8a: Length frequencies for Bay of Plenty
samples by date and method of capture
Length
(cm) |
Purse
seine
31
May
1983 |
Line
3-15
June
1983 |
Purse
seine
13
June 1983 |
Purse
seine
16
June
1983 |
38 |
- |
1 |
- |
- |
39 |
- |
- |
- |
- |
40 |
- |
1 |
- |
- |
41 |
- |
1 |
- |
- |
42 |
- |
1 |
- |
1 |
43 |
- |
1 |
- |
- |
44 |
- |
- |
1 |
- |
45 |
- |
- |
5 |
- |
46 |
- |
1 |
5 |
- |
47 |
- |
1 |
11 |
8 |
48 |
4 |
1 |
23 |
3 |
49 |
6 |
4 |
12 |
13 |
50 |
14 |
5 |
13 |
9 |
51 |
7 |
3 |
9 |
5 |
52 |
17 |
3 |
6 |
17 |
53 |
10 |
3 |
9 |
16 |
54 |
20 |
1 |
3 |
12 |
55 |
7 |
1 |
2 |
8 |
56 |
7 |
4 |
1 |
3 |
57 |
6 |
- |
- |
4 |
58 |
2 |
- |
- |
1 |
Total |
100 |
32 |
100 |
100 |
TOP
Appendix 1

Appendix 2

TOP
Comparison between
average kahawai length (fork length cm) caught during the 1983
kahawai tagging programme and the 1991 recreational fishing survey.
Year |
Area |
Method |
Time period |
Av.
Length |
No.
of
fish |
1983/84 |
Whangaroa – Bay of Islands |
Trolling |
Dec – Feb |
48.2 |
334 |
1991 |
Bay of Islands |
Baitfishing mainly |
Xmas – April |
41.2 |
96 |
1983/84 |
Bream Head – Sail Rock |
Trolling |
Dec – Feb |
51.2 |
268 |
1991 |
Bream Head – Sail Rock |
Baitfishing mainly |
Xmas – June |
45.8 |
78 |
1983 |
Motu River |
Surfcasting |
March |
50.1 |
301 |
1991 |
Motu area (Torere-Omaio) |
Surfcasting |
March |
43.3 |
18 |
1983 |
Wanganui – New Plymouth |
Trolling |
Jan – May |
48.6 |
776 |
1991 |
Wanganui – New Plymouth |
Baitfishing mainly |
April – May |
46.3 |
88 |
1983 |
Ahipara |
Trolling near the surfline |
December |
45.6 |
78 |
1991 |
90 Mile Beach |
Surfcasting |
April – May |
41.8 |
30 |
1991 |
Hokianga entrance |
Surfcasting |
March – May |
39.8 |
53 |
Comparison between average kahawai length (fork length
cm) caught by trolling and baitfishing during the 1991 recreational
survey
Area |
Method |
Time period |
Av. Length |
No. of fish |
Northland |
Bait fishing |
Dec – June |
42.7 |
317 |
|
Trolling |
Dec – June |
37.7 |
129 |
Hauraki Gulf |
Bait fishing |
Dec – June |
36.1 |
585 |
|
Trolling |
Dec – June |
33.3 |
235 |
Bay of Plenty |
Bait fishing |
Dec – June |
43.2 |
2277 |
|
Trolling |
Dec – June |
40.1 |
1081 |
West Coast |
Bait fishing |
Dec – June |
41.8 |
2583 |
|
Trolling |
Dec – June |
46 |
40 |
TOP
Decline in Recreational CPUE Around the
Motu River Mouth From 1982 to 1991
Summary
From January – April 1982 a recreational survey at the Motu
River mouth in the Bay of Plenty revealed a CPUE of 2.55 kahawai
per hour for visitors to the area and 4.17 fish per hour for the
local residents.
From March – April 1991 a MAF survey of the area from Opotiki
to Te Kaha (includes the Motu) showed a CPUE of 0.1 kahawai per
hour. This comparison is not ideal because the survey area in
1991 included areas outside the Motu and a different time period.
However, the surveyor in 1991 has stated that catch rates at the
river mouth were approximately the same as other areas along the
beach, and peak catches in the area generally occur in March (a
month included in both surveys). We also provide a new set of
data that involves just the beach area from Torere to Omaio (clustered
right around the river mouth) that indicates a catch rate of 0.09
kahawai per hour during peak season in March 1992.
Available Data from 1982 and 1991
Data from the
1982 survey of recreational fishing
at the Motu River mouth only |
Time Period |
# Fishers |
CPUE (kah/hr) |
Jan-Apr |
506 |
2.55 |
For a more detailed graph see page
18.
Data from the
1991 Recreational Survey
From Torere to Omaio (includes Motu River mouth) |
Month |
# Fishers |
CPUE
(kah/hr) |
Standard
Error |
March |
56 |
0.09 |
0.010 |
April |
28 |
0.03 |
0.008 |
May |
11 |
0.05 |
0.040 |
June |
37 |
0.11 |
0.013 |
July |
34 |
0.01 |
0.003 |
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