ICES Journal of Marine Science (2011), 68(8), 1679–1688. doi:10.1093/icesjms/fsr101
Using fishery-dependent data to inform the development and
operation of a co-management initiative to reduce cod mortality
and cut discards
S. J. Holmes 1 *, N. Bailey 1, N. Campbell 1, R. Catarino 1, K. Barratt 2, A. Gibb 2, and P. G. Fernandes 1
1
Marine Scotland Science, Marine Laboratory, PO Box 101, 375 Victoria Road, Aberdeen AB11 9DB, UK
Marine Scotland Science, Pentland House, 47 Robb’s Loan, Edinburgh EH14 1TY, Scotland, UK
2
*Corresponding Author: tel: +44 1224 295507; fax: +44 1224 295511; e-mail: [email protected]
Holmes, S. J., Bailey, N., Campbell, N., Catarino, R., Barratt, K., and Gibb, A., and Fernandes, P. G. 2011. Using fishery-dependent data to inform
the development and operation of a co-management initiative to reduce cod mortality and cut discards. – ICES Journal of Marine Science, 68:
1679 –1688.
Received 14 October 2010; accepted 18 April 2011; advance access publication 8 July 2011.
The Scottish conservation credits scheme is a voluntary programme introduced in 2008, designed to reduce mortality and discarding of cod in line with EU Common Fisheries Policy management objectives. The scheme was expanded in 2009, building on the
initial elements of real-time closures (RTCs) and gear requirements. Various measures were agreed in a co-management framework
involving fishers, non-governmental organizations, government officials, and scientists. The main objective was to encourage cod
avoidance and the reduction of cod discards using spatial tools such as RTCs and seasonal closures, along with gear options
that reduce cod capture. The scheme was incentivized by rewarding participation with additional days at sea. Real-time monitoring
was carried out with extensive use of fishery-dependent information, allowing management to be adapted as required and to
address emerging problems. The use of vessel monitoring system data, logbook records, fishers’ knowledge, and observer data is
described in terms of implementing and assessing the scheme. Compliance with the closure elements of the scheme was
judged to have been good, and estimated catch rates by the Scottish fleet met target criteria, but the assessed catch savings
of cod from RTCs were less than predicted. Modifications to the scheme were introduced for 2010, reflecting improved knowledge
and experience.
Keywords: cod, conservation credits, discards, real-time closures, VMS data.
Introduction
The Scottish conservation credits (SCC) scheme is a voluntary
programme introduced in 2008, designed to reduce mortality
and discarding of cod, in line with the management objectives
of the Common Fisheries Policy of the European Union (EU).
It was based on gear requirements and real-time closures
(RTCs), conceived to discourage vessels from operating in
areas of high cod abundance. RTCs applied to areas closed for
21 d when catch rates of cod, detected by the marinemonitoring and enforcement agency (Marine Scotland
Compliance), exceeded a trigger level. The scheme was incentivized by rewarding participating skippers with additional days
at sea.
A new long-term management plan for cod was introduced for
2009 (CEC, 2008), in which the means of controlling fishing effort
changed considerably (CEC, 2009). Fishing gears are categorized
into effort groups according to gear design, and are allocated,
mesh size. Based on historical records for national fleets, annual
effort quotas in terms of vessel kW-days are allocated to EU
Member States. Depending on the assessed state of the cod
stocks relative to reference biomass levels, the management plan
specifies the reduction in fishing mortality to be achieved in the
# Crown
copyright [2011]
following year through adjusted total allowable catches (TACs)
and, for effort groups most significant in catching cod, corresponding effort adjustments.
If effort reductions are imposed, the cod long-term plan
permits the fishing effort in a group to be increased up to the
level allocated the previous year, if the fleet participates in a
cod-avoidance or discard-reduction plan expected to deliver at
least as great a reduction in mortality as anticipated from the
effort cut. The 2009 target of the management plan was a 25%
reduction in fishing mortality (F ) compared with 2008. The
SCC scheme aimed to achieve the reduction in cod mortality
through the measures described below.
Compulsory RTCs for Scottish vessels
Analysis of 2008 data from a vessel monitoring system (VMS)
identified vessels that had been fishing in RTC areas immediately
before closure. Comparing the landed cod weights before and
during closures provided estimates of “saved landings” per RTC
and, after applying a discard rate estimated from observed trips,
“saved catch” per RTC. The target number of RTCs was increased
to the level considered capable of delivering an 11% reduction in
cod fishing mortality.
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S. J. Holmes et al.
The governing principles of the RTC element of the scheme were:
(i) A maximum of 12 closures in place at any one time. Each
closure area was equivalent in size to a square 7.5 × 7.5 nautical miles, or 1/16th of an ICES statistical rectangle at
North Sea latitudes. Closure shapes, however, were only
restricted to having six or fewer vertices.
(ii) Closures applied for 21 d and then were automatically
reopened.
(iii) The seas around Scotland were divided into four zones by
lines of latitude (588N in the west; 58830′ N in the east)
and longitude (48W; Figure 1). The purpose of the zones
was to prevent the impact of closures affecting vessels operating from any one port disproportionately.
(iv) In general, there would always be at least one closure in each
zone.
(v) Within any “commercial impact zone” (CIZ, up to 25 nautical miles around a closure), no more than three closures
could be adopted at any one time.
(vi) Closures within 12 miles of the coast could be smaller and of
different shape, taking account of geography, community
needs, and fleet structure. They were always based on
at-sea physical inspections.
(vii) Closure triggers were:
(a) Physical inspections of catches revealing more than 40
cod per hour of fishing. This preset trigger level was
expected to cause ten closures over a year, based on a frequency distribution of observed catch rates from the previous year.
(b) Analysis of landings and VMS data identifying, for each
RTC zone, 25 areas of RTC size with the highest landings
per unit effort (lpue) in that zone. Each VMS analysis
would be assessed by Marine Scotland Compliance,
who could recommend up to ten closures at a time in
total, bearing in mind principles (i) –(vi). The limit of
ten closures was to allow for those triggered through
at-sea inspections.
Seasonal closures and amber areas
Seasonal closures were non-permanent but intended to be in place
longer than RTCs. They were identified through a combination of
fishers’ knowledge and analysis of VMS data.
Amber areas were zones with high cod abundance but below
the level that would trigger an RTC. Their definitions were
updated quarterly based on data from the same period the previous year. Vessel avoidance of these areas was voluntary but
incentivized by awarding additional days at sea.
Technical gear measures
Fishers could adopt various gear options designed to reduce the
catchability of cod. They were voluntary and incentivized by
additional days at sea.
The design, appraisal, and modification of the SCC scheme
were undertaken by the Conservation Credits Steering Group
(CCSG), which met monthly during 2009. It comprised fishery
managers, fishery scientists, officers from Marine Scotland
Compliance, fisher representatives, and non-governmental organizations. Vessels choosing not to adopt voluntary measures were
allocated less effort to ensure that the overall 25% reduction in
cod mortality could be achieved. There were various administrative penalties to ensure compliance, including a deduction of 5 d
from the effort allocation for fishing within an RTC, and loss of
any extra award days if found fishing within an amber area. The
compulsory elements of the scheme were only legally binding on
vessels registered in Scotland, but administrations from other
countries were informed of all closures and asked to encourage
their vessels to avoid those areas.
This paper describes the use of fishery-dependent data to define
and evaluate the success of seasonal, amber, and RTCs, and the
overall SCC scheme in reducing cod mortality, particularly
through reduction of discards.
Use of fishery data in the SCC scheme
Defining RTCs using VMS and logbook data
To help maintain 12 active RTCs at any one time, a combined
VMS and logbook analysis was conducted as closures became
due for reopening. Data were taken from a 14-d period leading
up to the time of analysis. To allow consideration by Marine
Scotland Compliance, there was usually a 1- or 2-d gap between
the 14-d period used for lpue analysis and the implementation
of new RTCs.
Data availability and filtering
Figure 1. Map showing the determination of amber areas
(polygons) for management period 2 (May – July) in 2009.
Highlighted squares are the top 15% in terms of cod lpue values for
the same months in 2008. Also shown is the permanent closure
known as the windsock (hatched area). Dashed lines indicate the
borders of the four zones over which lpue results were calculated.
VMS data were available from the Scottish Government’s Fisheries
Information Network (FIN) database for all UK vessels fishing in
Scottish waters and all voyages landing into Scotland. Logbook
data were taken for all voyages using whitefish or Nephrops
trawls from a separate FIN table. Linked VMS/logbook data
(cross-referenced using the vessel RSS number) were limited to
Scottish vessels and boats 15 m or longer landing into Scotland.
Data were filtered to include only cod. For each trip, daily totals
of recorded cod landings and VMS pings were determined. Pings
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were discarded when the vessel was stationary in port, or apparently emanated from faulty equipment (defined by .10% of
VMS pings being separated by .3 h; this situation applied to
fewer than 4% of all pings). The data were further filtered to
include only fishing pings, defined as those where the vessel
speed was between 0 and 5 knots.
Landings per unit effort
Each VMS ping was assigned to a rectangle defined by dividing
standard ICES rectangles into 16 equal parts. The ping interval
was generally 2 h but did vary; in Norwegian waters, it was 1 h.
Fishing pings were weighted by the time since the last ping, with
the first one of a voyage having a default weight of 2 h. To avoid
distortions arising from very large or small weights, those over
2 h 9 min were allocated the same weight as the nearest accepted
ping, and the minimum weight was set to 1 h.
The physical weight of cod recorded in the logbook for each day
of a trip was allocated to each VMS ping for that date according to
the statistical weight of each fishing ping. Therefore, the cod landings, Lt,s, of a particular trip t, from square s, were calculated from
Lt,s =
lt,d Pt,d,s
Pt,d
,
(1)
where lt,d is the landings recorded in the voyage logbook for day d
of trip t, Pt,d the total weights of the fishing pings for that voyage
on that day, and Pt,d,s the corresponding total for those pings in
square s. Over the 14-d evaluation period, cod weights and ping
weights were aggregated over all voyages within each square. A
measure of the lpue for each square was then calculated as
Lt,s
lpues = t
,
P
t t,s
(2)
where Pt,s = d Pt,d,s .
Within each of the four RTC zones, the squares were ranked
according to lpue, and the top 25 in each zone were notified to
Marine Scotland Compliance to make final proposals for closures.
Squares with only one ping were excluded to avoid distortion
effects. The final areas chosen were not necessarily the same
shape as the squares. For example, oil pipelines have been identified as locations where cod congregate, and a closed area could
be defined to reflect this.
Amber areas
Amber areas were updated quarterly using VMS-derived lpue
values obtained from the same months in the previous year.
Within each zone, squares were ranked by lpue, with the top
15% highlighted as potential amber areas (Figure 1). Defined
amber area polygons were chosen according to the following
criteria:
(i) encompassed the highest lpue values;
(ii) minimized the complexity of the polygon, with a minimal set
of latitudes and longitudes, so areas could therefore include
white space (low lpue) once the vertices were joined;
(iii) combined contiguous squares to produce fewer, large areas in
preference to many small ones; each area consisted of more
than four squares.
In common with many fishery-management measures updated
yearly, the SCC scheme runs from 1 February to 31 January.
Therefore, the management periods of the amber areas did not
match calendar quarters, but were rather displaced by 1 month.
Seasonal closures
Seasonal closures were introduced to make use of fisher knowledge
and to provide protection to known aggregations of cod. Initially,
the industry proposed the location, size, shape, and duration of
such closures, but they were finally decided upon after analysis
of VMS fishing pings around the proposed closure dates in the
previous year, and dialogue between scientists and fishers.
Initially, a single closure in the area known as the Long Hole
was applied from 1 December 2008 (Figure 2). Information
from industry suggested that closure of the Long Hole fishing
grounds could reduce bycatches of cod while still allowing relatively unrestricted access to surrounding Nephrops stocks; observer
data collected by Marine Scotland Science (MSS) supported this.
The closure was initially set until 31 March 2009, although reopening depended on a test haul conducted by a commercial vessel and
observed by MSS scientists. If a catch per unit effort (cpue)
threshold of 200 cod per hour was exceeded, the closure would
be extended by a month and the sampling haul repeated. A
further three seasonal closures were identified to protect predictable but temporary aggregations of cod. Unlike the Long Hole,
those areas were automatically reopened.
Use of fishery data to assess the efficacy of the
scheme
Assessment of the SCC closures can be considered in terms of
vessels avoiding RTCs, seasonal closures, and amber areas (avoidance), and their effect on the fishing mortality of cod (effectiveness). The avoidance of RTCs was assessed by comparing VMS
fishing pings, and the number of associated vessels, before,
during, and after each closure. Analysis of 14-d periods before
and after a closure was chosen to match the number of days
used by the VMS –lpue method to define areas for possible
closure. Seasonal closures were considered in a similar manner.
Avoidance of amber areas was voluntary. Vessels opting to
avoid them may, of course, not normally fish there. The likely
impact of amber areas can be judged by comparing the proportion
of cod landings associated with vessels inside and outside the
scheme. VMS data when available were used to compare the
fishing activity in 2009 and 2008 for Scottish vessels inside
the scheme.
The appropriateness of each amber area was considered by
overlaying onto the amber areas the top 15% of lpue rectangles
identified from 2009 data. The temporal stability of high-lpue
squares was considered by comparing (i) adjacent management
periods (intra-annual stability), and (ii) the same months in adjacent years (interannual stability). In addition, the average
VMS-derived lpue of cod from inside all amber areas was compared with the average lpue from outside the areas.
A simple measure of the RTC contribution to cod avoidance is
given by comparing the landings from vessels operating in areas
which subsequently became RTCs with those once the RTC was
in place and the vessels had moved away. Assuming a constant
lpue if they had continued fishing in the RTC, and a consistent
ratio between landings and discards, then savings accrue if the
vessel moves to areas where the catch rate is lower. The greater
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S. J. Holmes et al.
Figure 2. Map showing seasonal closures (filled black areas) and amber areas implemented in 2009. The colour of amber area borders indicate
the management period (Q1– Q4): red, Q1; yellow, Q2; blue, Q3; green, Q4. Coincident boundaries have been slightly displaced for visual
clarity. The straight grey lines show zonal boundaries of the RTC scheme.
Figure 3. Map showing RTCs implemented in 2009 as shaded boxes indicating the method that triggered the closure: black, VMS and logbook
lpue analysis; white, positive sample from at-sea inspection (.40 cod per hour of fishing); hatched, combination of lpue analysis and positive
sample. The straight grey lines show zonal boundaries of the RTC scheme.
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Reducing cod mortality
the differential between the catch rate in the RTC and the new
location, the greater the saving.
Whether through RTCs, seasonal closures, amber areas, or
technical measures, the SCC scheme was required to ensure that
the cod catch of the Scottish fleet matched the recommendations
in the ICES annual stock assessments, as modified by the national
quota share, i.e. to deliver the anticipated partial F for the fleet.
The catch trajectory of Scottish vessels compared with the
annual target was considered as an overall test of the SCC
scheme. This was limited to the North Sea, because of uncertainties in the west of Scotland (ICES Division VIa) cod assessment
and the sparse observer coverage in the west of Scotland.
Landings totals for the gear categories TR1 (bottom trawls and
seines of mesh ≥100 mm) and TR2 (bottom trawls and seines
of mesh ≥70 and ,100 mm), as defined in CEC (2008), were
compiled monthly for 2008 and 2009. Observer data were used
to produce a quarterly discard rate for each category.
Results from 2009
Location of RTCs and amber areas
In all, 144 RTCs were implemented in 2009; Figure 3 shows the
cumulative total of RTCs. The locations of seasonal closures and
amber areas are shown in Figure 2. No closures were deemed
appropriate in the SW zone because of the very low lpue values
there. The concurrent closure limit (12) was reached briefly on
two occasions; the greatest number was in the NE zone. Details
of all closures to date, maps of current RTCs and their associated
CIZs, amber areas, and a link to the results from at-sea observer
sampling of cod have been made available on the Internet at
http:/www.scotland.gov.uk/Topics/Fisheries/Sea-Fisheries/
COMPLIANCE/closures/.
Compliance with RTCs, and take-up of amber area
avoidance
In all, the VMS dataset contained nearly 720 000 fishing pings
from 625 vessels. From the 144 RTCs in 2009, the number of closures with zero pings appears small (38% of closures), but
instances of only one or two pings during a closure were recorded
for another 21 areas. Vessels were generally given a short period of
grace once a new RTC was established. Thereafter, they could be
asked informally when found in an RTC to encourage compliance,
although penalties were enforced if such incursions persisted.
Figure 4 presents histograms of the effort changes associated
with RTCs. There was less fishing activity during almost all closures compared with the 14-d periods immediately before and
Figure 4. Histograms showing changes in fishing effort associated with RTCs. Number of fishing pings (top panels) and vessels (bottom
panels) within RTCs when comparing the periods before and during closure (left panels), and during and after closure (right panels).
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S. J. Holmes et al.
after them. Most closures reduced the fishing pings by around 10
or 20 (equivalent to 10 –40 h trawling), but for some the reduction
was well over 100. The converse occurred when areas reopened.
Vessel reductions during closures compared with pre-closure
were mostly between 1 and 6. Usually, the number of vessels
active in an area increased again upon reopening, suggesting
that there would have been more fishing had the RTC not been
in place.
Of the seasonal closures, only the Coral Edge implementation resulted in significantly reduced activity (Table 1). Of
the 104 fishing pings recorded during the Papa Bank closure
(0.01% of total pings), 100 were from a vessel not required
to adhere to the closure, being registered outside Scotland. As
a result of the test hauls conducted, the Long Hole remained
closed all year.
In 2009, a total of 65 vessels notified intention to avoid amber
areas. At any one time, between 55 and 60 vessels were participating in the scheme, roughly 10% of those eligible. The proportion of cod landings attributable to VMS-equipped vessels
participating or not participating in the scheme changed little
between 2008 and 2009 (Figure 5a). Little evidence of altered
fishing patterns by participating vessels was seen in VMS maps
(not shown).
Table 1. Summary of seasonal closures, with a comparison of
fishing activity before, during, and after the closures.
Number of fishing pings (vessels)
Closure
area
Long Hole
Papa Bank
Stanhope
Ground
Coral Edge
Duration of
closure (d)
365
60
69
Pre-closure
n/a
15 (4)
21 (3)
During
closure
100 (17)
104 (2)
13 (4)
45
127 (8)
12 (3)
Post-closure
n/a
18 (1)
2 (1)
2 (1)
Durations of the pre- and post-closure periods are 14 d, and n/a indicates
not relevant because the closure was in place for the whole of 2009.
Cod landings
Estimated catch savings attributable to vessels moving away from
RTC areas are greatest in the North Sea where most closures
were called (Table 2). Overall, the savings were 430 t of cod landings which, when raised by the discard rate, amount to 707 t of
catch.
Location of amber areas
Given the low uptake of amber area avoidance, the VMS and lpue
data from 2009 provide a qualitative test of the appropriateness of
amber area locations. Management period 2 (May –July) highlights a common problem. Some squares with high lpue using
data for May–July 2009 (yellow boxes) fell within the amber
Table 2. Landings and catch savings (t) arising from Scottish
vessels shown by VMS data to move away from RTCs in 2009.
Landings
Area and
pre-RTC
quarter
(t)
North Sea
Q1
492
Q2
502
Q3
631
Q4
170
Annual
1 795
West of Scotland
Q1
34
Q2
141
Q3
135
Q4
23
Annual
333
Both areas
Q1
526
Q2
643
Q3
766
Q4
193
Annual
2 128
Landings
during RTC
(t)
Landings
difference
(t)
“Catch”
difference
(t)
359
496
384
177
1 416
133
6
247
27
379
218
10
405
212
622
54
64
147
17
282
220
77
212
6
51
232
126
219
11
86
413
560
531
194
1 698
113
83
235
21
430
186
135
386
21
707
Figure 5. Scottish vessels equipped with VMS. (a) Proportion of cod landings attributable to vessels participating in the amber area scheme
(filled squares) and not participating (open triangles); solid lines, 2009; dashed lines, 2008. (b) lpue values in 2009 from inside (filled squares)
and outside (open triangles) amber areas derived from vessels regardless of participation. The average lpue over all trips is shown by filled
diamonds. MP, management period.
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Reducing cod mortality
area polygons (defined using data from the same months in 2008),
but most did not (Figure 6a). The 2009 data result in high-lpue
squares that are completely removed from the amber areas
defined for that period, e.g. to north and northwest of Shetland.
Figure 6b shows 2009 data from February to April, again overlaid on the amber areas implemented in management period
2. Comparing the two panels, the locations of high-lpue squares
show little consistency between these adjacent management
periods, so defining amber areas for May–July 2009 using data
from February to April of the same year (instead of May–July
the previous year) would not appear to improve their appropriateness. These results show that the highest lpue values can occur in
areas with relatively few fishing pings. Figure 5b, however, demonstrates consistently higher lpue from within amber areas (combined) than elsewhere.
Discard rates and cod-catch trajectory
Figure 6. Maps showing VMS fishing pings (black dots), and the top
15% of squares ranked by lpue (yellow boxes) for (a) May – July 2009,
and (b) February– April 2009, overlaid on amber areas (polygons
outlined in red) implemented in May–July 2009. The hatched area is
a permanent closure, known as the windsock.
Using data from observer trips, discard estimates as a percentage of
catch for the TR2 gear type vary (Table 3). This may reflect less
sampling coverage of vessels not targeting finfish. Better observer
coverage of, and more consistent discarding behaviour within,
the TR1 fleet resulted in more-reliable estimates from that fleet
(which took the bulk of the cod landings). In 2008, the TR1
discard rate was consistent over the first two quarters, then rose,
possibly because of quota restrictions towards year end; this
pattern continued in 2009. However, the point estimates for
2009 were lower than any from 2008.
In Figure 7, trajectories of North Sea cod landings by Scottish
vessels in 2008 and 2009 (solid black lines) are compared with a
Scottish “landings quota”, i.e. the sum of allocations to Scottish
Producer Organizations (POs). The latter rises during each year
because the POs benefit from quota exchanges between countries
as each season progresses. Applying discard rates from Table 3 to
their respective fleet landings, the resulting cumulative catch
(upper boundary of the hatched area) can be contrasted with a
hypothetical cumulative catch (upper boundary of pale grey
area) based on the 2008 and 2009 discard rates calculated for the
international fleet by the ICES assessment working group (ICES,
2009) and a Scottish “catch quota” derived using the same ICES
discard rates (44% in 2008, 37% in 2009).
In 2008, the empirical discard rate for the Scottish fleet was
greater than the estimated international rate. Consequently, the
total catch is estimated to have considerably exceeded the 2008
Scottish catch quota although landings were consistent with the
landings quota (Figure 7a). In 2009, the empirical discard rate
was lower than the international one until the third quarter;
although by year end, the estimated cod catch was marginally
higher than the Scottish catch quota (Figure 7b).
A final comparison is between the realized Scottish catch and a
Scottish quota share predicted by ICES to match the EU codmanagement plans (Figure 7, dot –dashed line). These plans
called for year-on-year F reductions of 10% and 25% in 2008
and 2009, respectively (ICES, 2008, 2009). The total catch in
2008 did approximately match the required F reduction, although
the total weight of cod discarded was greater than that landed. The
cod catch in 2009 was well below that consistent with a 25%
reduction in mean F compared with 2008.
Table 3. Estimates of cod discards as a percentage of catch from observer trips on Scottish vessels in the North Sea.
2008
2009
Gear
type
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4
TR1
53.8 (22.2 –73.4) 53.8 (41.1–58.6) 65.5 (47.2–76.6) 80.1 (57.8 –94.0) 25.5 (6.4–49.6) 12.1 (5.3 –22.6) 39.6 (25.4 –62.4) 50.0 (46.5–61.7)
TR2 100.0 (100 –100) 36.8 (18.6–100) 64.0 (26.1–100) 72.0 (44.4 –100) 36.0 (19.3–74.8) 70.0 (32.5–91.9) 81.6 (73.7 –93.7) 91.1 (78.6–97.8)
TR1, bottom trawls and seines of mesh ≥100 mm; TR2, bottom trawls and seines of mesh ≥70 and ,100 mm. Numbers in parenthesis give 95% confidence
intervals after bootstrapping (1000 repetitions).
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S. J. Holmes et al.
Figure 7. Cumulative Scottish landings and discards of North Sea cod in (a) 2008 and (b) 2009. Discard estimates are raised from Scottish
observer data for all sizes of fish. Solid black line, cumulative landings, the top of the hatched area representing the cumulative catch (using
raised discard estimates); overlaid grey area, cumulative catch assuming annual international discard rates estimated by ICES (2009). Broken
lines represent annual limits for (moving from lowest to highest): landings quota, landings assigned to Scottish POs, i.e. the quota share of
international TAC (dashed); catch quota, landings quota plus discards calculated by applying the annual discard rate for the international fleet
(ICES, 2009; dotted); F ¼ 0.9 × F07 quota and F ¼ 0.75 × F08 quota, Scottish quota share of the cod removals in 2008 and 2009, respectively,
predicted by ICES to deliver a 10 and 25% reduction in F compared with the previous year (dot– dashed line). The value of all three quotas can
change during the year as a consequence of landings quota exchanges between countries.
Discussion
The SCC scheme is ambitious, particularly the RTC element. The
pattern of closure instigation and reopening depends on at-sea
inspections as well as each round of VMS analysis. It is therefore
more dynamic than if 12 closures had been set in place every 21
d. Speedy and reliable dissemination of information to fishers is
crucial for compliance. The analysis presented here shows evidence
that, among UK vessels landing into Scotland at least, RTCs are
being avoided. Although a low percentage of RTCs had zero
fishing pings, some recorded only one or two over the 21-d
closure. A better summary of compliance would be to consider
the number of areas where fishing activity dropped during a
closure period, and the extent of the decrease in activity. A
review by STECF considered that “the level of implementation
of the scheme has been quite high” (STECF, 2010). Of the seasonal
closures, only the Coral Edge implementation resulted in significantly reduced activity, but it can be argued that if the timing
and duration of these closures were chosen correctly, concentrations of cod (and the desire to fish them) should not be
present before or after the closures.
Aspects of the SCC scheme, e.g. the duration of RTC closures,
RTC zones, and use of CIZs, were decided as a compromise
between what was considered most effective for conservation
and what was most equitable for the fleet components within
Scotland. Also, initially, the knowledge needed to inform the
design of the scheme was limited.
Amber areas have now been dropped from the SCC scheme.
Analysis of fishery data showed mixed results in terms of the suitability of their locations, but the likely impact on cod mortality
was minor. This was because of the very limited voluntary participation by eligible vessels. Further, the fishing patterns of participating vessels did not change significantly, suggesting that their
previous activities had little impact on cod, so the amber area
avoidance was ineffective. Feedback to the CCSG suggested that
fishers catching significant quantities of cod regarded the
days-at-sea incentives as insufficient. There was a gap between
what managers could offer as incentives and what fishers considered as necessary to outweigh the loss of operational flexibility
and catch opportunities that participation might involve. As the
SCC scheme continues, such socio-economic issues are becoming
better understood.
The analysis of catch savings provides some evidence of cod
avoidance. However, the estimated catch savings from RTCs
were less than predicted. Going forwards, further reductions in
fishing mortality were sought for 2010. Analysis of cod-tagging
data has provided estimates of the proportion of cod expected to
Reducing cod mortality
remain within a given distance of a starting point after a given time
(P. Wright, pers. comm.). Combining this knowledge with the new
target for cod-catch reduction in 2010, and a desire to maintain
the 21-d closure duration, led to the RTCs being increased fourfold
in size (to 15 × 15 nautical miles) for the NE and SE zones. The
target for the 2010 management year was set at 107 closures.
The nature of some management measures being considered,
e.g. excluding vessels from an area at short notice, made it difficult
to assess their effect. The catch savings calculation could not estimate any catch changes resulting from fishers revising plans for
new trips because of closures known to be in place. The
dynamic nature of fish stocks and the fleets that exploit them
may mean that it is impossible to be sure how the vessel behaviour,
landings, and discards would have been different had any given
closed area not been implemented. The results presented here
are, however, useful information for fishery managers and the
CCSG. This in turn helped facilitate a key aspect of the SCC,
namely regular review and adjustment of measures as necessary.
Changes in addition to the larger RTCs introduced for 2010
included having only three RTC zones, by combining the two
western zones, in response to the consistently very low lpue
values recorded from the SW zone. There is now a requirement
for at least one closure at all times west of Scotland and no
minimum number of closures in the NE and SE zones, and the
number of high-lpue squares used to define new RTCs within
each zone has been increased from 25 to 50 in each zone.
New metrics for the effectiveness of management measures are
also evolving. An example is work comparing the activity of individual vessels (using VMS data) with a map of cod densities
derived from landings-independent data. Movements of individual vessels to areas of lesser (or greater) relative abundance of
cod are aggregated to form a histogram, the mean of which indicates the overall movement in terms of its significance for cod
(Needle and Catarino, 2011).
The efficacy of the method for locating closures depends on the
accuracy of logbook records and the reliability and interpretation
of VMS data. To prevent a highly smoothed and potentially uninformative lpue history resulting from whole-trip landings being
assigned evenly across all VMS fishing pings, the lpue values are
assigned to pings for each day within a voyage. For trips covering
large distances, it must be emphasized that logbook records give
the correct day when landed cod were caught. Errors may lead
to closures being sited where cod abundance is low, while areas
producing the greatest lpue are overlooked. In future, this aspect
of data reliability could be tested through cross-checks between
logbook information, observer records, and VMS data.
We determined fishing pings using a simple vessel-speed criterion. Subsequent research based on CCTV systems that record
vessel speed, heading, and fishing activity has confirmed that
our fishing-speed range is appropriate (N. Campbell, pers. obs.).
Linking VMS data to observer logbooks in the Irish trawl fishery
showed that most fishing and non-fishing activities were correctly
identified using a fishing-speed range of 0.5 to 4 knots;
attempts to apply more complex algorithms did not lead to any
significant improvement (Gerritsen and Lordan, 2011). Bastardie
et al. (2010) showed that such improvements would be more
likely if ping frequency were to be increased.
Some 3 and 14% of VMS ping intervals were rounded down
and rounded up, respectively. Work is ongoing on how best to
deal with short ping intervals. During 2009, it was noticed that
in some deep-water rectangles, the very low fishing effort
1687
coupled with modest cod landings could result in very high
values of lpue. Consequently, it was decided to restrict potential
RTCs to the region within the 400-m depth contour.
The VMS methodology is currently restricted to vessels ≥15 m
long. Cod landings by smaller vessels constituted ,1% of the
Scottish total. Also, VMS is to be extended to vessels ≥12 m
from the beginning of 2012. However, on-board sampling as an
additional means of identifying closures is still regarded as important, and it measures catch rates directly.
The final outcome sought from the SCC scheme is an annual
catch that achieves the mortality reductions required by the cod
long-term management plan. Using quarterly summaries of
discard rates obtained from observer programmes, we can
provide estimated catch trajectories relative to annual targets
throughout the year. This allows midyear adjustment of the
scheme if necessary. Observers only cover a small proportion of
the fleet, and aggregating results over quarters rather than annually
increases the risk of bias in the estimates. The catch trajectories for
the North Sea are considered robust, however, and indicate that
the mortality-reduction objective was achieved by the Scottish
fleet in 2009. The picture is not so clearcut west of Scotland.
The raising method has used cod landings as the auxiliary variable,
leading to problems because the observed cod-discard rate in the
TR2 fleet has been 100% in quarters for which non-observed
TR2 vessels have landed cod from the west of Scotland. MSS is currently investigating whether there is a better means of raising discards that is both robust and sufficiently precise for end-uses such
as annual stock assessment, DCF reporting, and general fisherymanagement purposes.
We attempted to infer a partial F for North Sea cod taken by the
Scottish fleet in 2009 (STECF, 2010). However, this was unsuccessful for two reasons: first, there were incomplete data on landings
and/or discards from other nations; second, in the assessment of
North Sea cod, if trends in stock biomass and mean F over reference age groups differed between including and excluding commercial data, the mean F was calculated using survey data only.
Therefore, partial F values could only be calculated from
fishery-independent data and assuming discard rates for other
nations based on Scottish data. Progress in this area requires
more complete sharing of fishery-dependent information across
nations.
In September 2009, the EU and Norway implemented a similar
RTC scheme in the North Sea and Skagerrak, with the aim of protecting juvenile cod, haddock, saithe, and whiting. Fish below the
minimum landing size (MLS), which is lower in the Skagerrak
than in the North Sea for all these species, are regarded as juveniles.
Closures are decided by the percentage by weight of the juvenile
catch. As no fish smaller than the MLS should be landed, lpue
analysis using VMS and landings data is not appropriate for any
species. Therefore the EU–Norway scheme relies entirely on
inspections at sea, unlike the Scottish SCC.
With a large RTC element and extensive use of fishery data,
the SCC is a pioneering scheme within the EU, and it has
required many practical issues to be resolved to allow it to
operate smoothly. Fresh thinking has also been required for
the analysis of data to provide measures describing how well
the scheme is working. As experience is gained, there will be
adjustments to the way it is configured, but the measures so
far identified to indicate the performance of the scheme in
delivering reductions in cod discards and the associated mortality are encouraging.
1688
Acknowledgements
We thank Ian Hepburn and Greig Chalmers from Marine Scotland
Compliance for providing information used in this paper, and two
anonymous referees whose comments and corrections greatly
improved the manuscript.
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