Auxis thazard; major contributor in Sri Lankan Neritic tuna fishery

Full text

IOTC–2015–WPNT05–18 Rev_1
Auxis thazard; major contributor in Sri Lankan Neritic tuna fishery
Bandaranayake, K.H.K., Maldeniya, R, and Perera, H.A.C.C.
National Aquatic Resources Research and Development Agency (NARA), Crow Island, Colombo
15, Sri Lanka
Abstract
Of the three key neritic tuna species; Auxis thazard (frigate tuna) is currently the highest contributor
in the neritic tuna production and there is a great demand for this species among local consumers.
Their catches are mainly confined to the shelf, shelf slope and outer fringes of offshore waters.
Fishing gear employed in exploitation of the species is mainly medium mesh gillnet, ring net and
lesser amount of trolline. However, over the time, relative contribution of the fishing method
showed noticeable variations where in the recent coastal ring nets dominated the catch. A
considerable increase in the frigate tuna production can be observed after 2010. The increase in the
production could be mainly attributed to the higher fishing effort exerted by ring nets after
loosening of government restrictions on ring net operations. In 2013, Auxis thazard represented
around 42% of the total neritic tuna production and 5% of the total tuna production. A remarkable
variation of frigate tuna catch was also noted among the different vessels. The vessels mostly
operated in continental slope and bordering areas of offshore reported higher catches than the
vessels operated in shallow waters and high seas. The size range of frigate tuna Fork Length (FL)
recorded during 2010-2013 ranged between 19 cm to 72 cm. The relationships obtained for
different L-L measurements of frigate tuna were SL = 0.853TL, SL = 0.928FL and FL = 0.918TL:
SL-standard length, FL- fork length and TL- total length.

IOTC–2015–WPNT05–18 Rev_1
Introduction
There are three main neritic tuna species frequently found in Sri Lankan waters, namely, Auxis
thazard (frigate tuna), Auxis rochei (bullet tuna) and Euthynnis affinis (kawakawa). Scomberomorus
commerson (narrow-barred spanish mackerel) is dominated the catch of other species associated
with neritic tuna. Among them, Auxis thazard plays an important role with its great demand among
the local consumers. Auxis thazard is a small tuna belonging to the family of Scombridae and is
abundantly found in tropical waters. In Sri Lanka, they are mainly confined to the shelf, shelf slope
and outer fringes of offshore waters. The contribution of Auxis thazard in the past has shown that it
is prominent among other neritic tuna species (Sivasubramanium, 1973; Bandaranayake and
Maldeniya, 2012). This paper discusses some aspects related to this species including present status
of the fishery and morphometric relationships.
Objective
To analyze frigate tuna landings in Sri Lanka and to estimate morphometric relationships
Methodology
PELAGOS database of the National Aquatic Resources Research and Development Agency
(NARA) of Sri Lanka was mainly used for this analysis. Catch and effort data of frigate tuna by
gear and craft were analyzed for the period of 2010-2013. A total of fifty individuals were taken
from the western coastal landings and analyzed to obtain the length-length relationships. Lengths of
the fish (Standard Length - SL, Fork Length -FL and Total Length -TL) were measured to the
nearest 1 mm using a measuring board.

IOTC–2015–WPNT05–18 Rev_1
Results and Discussion
Production trend
Relative contribution of frigate tuna showed time to time variations in the past decades. From early
1980s to mid 2000s the frigate was the dominant species among the neritic tunas followed by
Kawakawa and Bullet tuna respectively. However a considerable change was noted in the
production for the period of 2005-2009 where Kawakawa became dominant resulted by multiple
reasons: expansion of the fishing zone and new fishing practices etc (Bandaranayake and
Maldeniya, 2012). After 2010, again frigate tuna became the major contributor with a remarkable
increase in the production (Figure 1). The increase in the production could be mainly attributed to
the higher fishing effort exerted by ring nets after loosening of government restrictions on ring net
operations. In 2013, Auxis thazard represented around 42% of the total neritic tuna production and
5% of the total tuna production (Figure 2).
Figure 1. Frigate tuna annual production in Sri Lanka: 2005- 2013 (IOTC, 2014)
0
2,000
4,000
6,000
8,000
10,000
12,000
2005 2006 2007 2008 2009 2010 2011 2012 2013
Production in Mt
year

IOTC–2015–WPNT05–18 Rev_1
Figure 2.Neritic tuna production by species in 2013 (Source: PELAGOS, 2014)
Neritic tuna
production
12%
Oceanic tuna
prodution
88%
KAW
18%
FRI
42%
BLT
40%
0
1
2
3
4
5
6
Frigate tuna Bullet tuna Kawakawa
Contribution of neritic tuna species %
Neritic tuna species

IOTC–2015–WPNT05–18 Rev_1
Fishing crafts and catch rate
The fishing fleet involved in different fisheries in Sri Lanka consists of different types of fishing
crafts. A range of fishing crafts which includes both single day and multiday fishing crafts catch
frigate tuna while they target oceanic tuna. However, few single day boats seasonally engage in
tuna fishery targets frigate tuna. A classification of single day and multiday vessels which may
catch frigate tuna is shown in Table 1. UN1 and UN2A are single day boats whereas others are
multiday boats. UN2A boats are mainly operated in shallow waters while UN3A within Exclusive
Economic Zone (EEZ). UN3B category can be operated within EEZ or beyond the EEZ. A
considerable variation in the frigate tuna catch was noted among the different vessels. The vessels
mostly operated in continental slope and bordering areas of offshore (UN 2B and UN 3A) reported
higher catches than the vessels operated in shallow waters and high seas (Table 2). The highest
catch rate by UN3A boats can mainly because of the ring nets they utilized for obtaining bait.
Table 1 Classification of single day and multiday fishing vessels in Sri Lanka
Boat
category
Boat Description
UN1
5.5 - 7.2 M (17' - 21') FRP dinghy Outboard engine - 8-40 HP (usually 15 - 25 HP)
Single day boats - assumed to be fishing in coastal waters
UN2A
8.8 - 9.8 mm (28' - 34') displacement hull. FRP or wooden.
Inboard engine (single) - 40 HP
No ice box or insulated fish hold, no gear hauler, navigational
or acoustic equipments. Single day boats - assumed to be fishing in coastal waters
UN2B
8.8 - 9.8 m (28' - 34').
FRP or wooden, Inboard engine (single) - 40 HP
Insulated fish hold - no gear hauler, may have GSP/sounder/fish finder
UN3A
9.8 - 12.2 m (34' - 40'). FRP or wooden. Inboard engine (single) - 60 HP
Insulated fish hold and may have gear- hauler/ GSP/sounder/fish finder
UN3B
12.2 m – 15.2 m (40' - 50').
FRP or wooden. Inboard engine (single) - 60 + HP. Insulated fish hold and may have
freezer facilities. Gear Hauler/GSP/sounder/fish finder

IOTC–2015–WPNT05–18 Rev_1
UN4
15.2 - 18.3 m (50' - 60')
Inboard engine, fish storage facility, may have RSW or CSW or freezing facility, gear
hauler, GPS, echo-sounder/fish finder, radio communication
Table 2 Frigate catch rates (catch in kg per trip) by different craft types
Boat category Average of Weight (kg)
UN1
28
UN2A
125
UN2B
164
UN3A 277
UN3B 65
Fishing gear and catch composition
Due to the multispecies nature of large pelagic fishery in the country, various types of gears
including traditional fishing methods such as trolling, pole and line are being utilized to catch
neritic tuna. Earlier gillnet, pole & line and trolline for some extent were effective for catching of
frigate tuna (Maldeniya et al., 1988). However, Pole and line fishery declined partly due to
problems associated with the supply of live bait while trolline declined due to fuel crisis (Joseph
and Moyiadeen, 1985). Motorization of crafts together with introduction of synthetic nets resulted
gillnet to become key fishing gear in the tuna fishery and thereby gillnet has firmly been established
as the dominant gear for tuna including frigate (Joseph and Moyiadeen, 1985 and Joseph and
Moyiadeen, 1986).
Relative importance of fishing gear has changed time to time. Trolline fishery is employed
traditionally and is confined to specific sites. The contribution of the fishery is comparatively low.
Popularity of ring nets immerged as a seasonal activity since 1990s in certain localized areas. Ring
nets appear as a more efficient and year round than the rest of gear. Ring nets are mostly operated in
coastal waters during the day time targeting small, localized free mixed schools of carangids and

IOTC–2015–WPNT05–18 Rev_1
small tuna varieties mainly frigate. Until 2010, the ring net operations were discouraged by the Sri
Lankan Government due to the social unrest (Bandaranayake and Maldeniya, 2012). However,
government restrictions on ring nets were loosen after. As a result, contribution of ring nets
accounted more than 60% in 2012 and 2013 (Perera et al, 2014 and Figure 3).
Figure 3. Percentage landings of frigate by major gear, 2013 (PSRN-Ringnet, LL- Longline,
LLGI- Longline/Gillnet combination, GN- Gillnet, HL-Handline, TL- trolline) ( PELAGOS,
2014)
Note: There is no any consistency in the catches made annually by pole and line fishery. The
fishery is highly depended on bait availability, thus successful fishing operations depend on spatial
and temporal conditions. It results sporadic nature in the pole and line landings.
A considerable variation in the catch rate could be observed as per the gear employed for catching
frigate tuna (Table 3). The highest catch rate was 322.0 Kg per trip for vessels operated with ring
net whereas the lowest catch rate of 30.8 Kg reported for vessels operated with handline. Among
the catches recorded by long line/ gill net combination, it was noted that total amount was harvested
by gillnets.
GN
29%
LLGI
1%
HL
2%
PSRN
67%
TL
1%

IOTC–2015–WPNT05–18 Rev_1
Table 3 Average catch rates of frigate tuna by gear (2010-2013)
Gear
Average catch rate (catch in kg per trip)
Ring net
322.0
Trolline
138.2
Gill net
129.5
Longline and gillnet
combination
104.5
Handline
30.8
Statistical zone wise production
The coastline around Sri Lanka has been divided into seven statistical zones for large pelagic
fisheries data collection: West, Southwest, South, Southeast, East and Northeast. South east zone
contributed more than 60% of the total frigate tuna production followed by South region (22%)
(Figure 4). In the regions of southeast, south and southwest ring net is being used for catching
considerable amount of frigate tuna (Figure 5).
Figure 4 Fisheries statistical zone wise contribution to frigate tuna production, Sri Lanka: 2010-
2013 (Source: PELAGOS, 2013)
East
0.02%
Northeast
1%
Northwest
0.05%
South
22%
Southeast
62%
Southwest
8% West
7%

IOTC–2015–WPNT05–18 Rev_1
Figure 5 Relative contributions to the frigate tuna production by gear and area (2010-2013)

IOTC–2015–WPNT05–18 Rev_1
Length -Length relationships
Officials from different institutions are being taking different types of length measurements (total
length (TL), Fork length (FL) and Standard length (SL)) for their research purposes and production
estimations. It reveals the necessity of formulating relationships among different length
measurements.
Length-Length relationships obtained for frigate tuna were as follows.
SL = 0.853TL (R2 =0.955)
FL = 0.918TL (R2 =0.974)
SL = 0.928FL (R2 =0.972)
All Length - Length relationships were significant at 0.01.
Size composition
Length frequency analysis in recent past reveals that the fork length of frigate tuna ranged between
19 cm to 72 cm. The estimated annual mean length of frigate tuna from 2010 to 2013 was 34.07
±5.16, 34.41±4.06, 34.15±4.06 and 34.01±3.76 respectively (Table 4). It is clear that there is a
consistency in obtaining two size groups in each year. However major representation was in the
second size group where most of the catches were over 35cm (Figure 6).
Fork length (cm)
Frequency
160
120
80
40
0
5550454035302520
200
150
100
50
0
5550454035302520
200
150
100
50
0
160
120
80
40
0
2010 2011
2012 2013
Figure 6. Length frequency distribution of frigate tuna 2010-2013

IOTC–2015–WPNT05–18 Rev_1
Table 4 Summary of length frequency data (length in cm): 2010-2013
Year Average length Minimum Maximum
2010 34.07 ±5.16 20 51
2011 34.41 ±4.06 22 72
2012 34.15 ±4.06 19 44
2013 34.01 ±3.76 20 47
Acknowledgement
The support given by Staff members of the Marine Biological Resources Division, NARA is highly
appreciated. We acknowledge to Dr. Sisira Haputhantri of NARA for his valuable comments for the
manuscript. Special thank is due to Mr. Malith Anupama and Ms. Madura Weerasekera for his
support in providing necessary data.
References
Bandaranayake, K.H.K and Maldeniya, R. 2012 A review on Neritic tuna species in Sri Lanka,
Second Working Party on Neritic Tunas, Penang, Malaysia, 19–21 November 2012
Indian Ocean Tuna Commission, 2014. Nominal Catch Database. [Last updated on 01-10-2014]
Available from: (http://www.iotc.org/data/datasets)
Joseph, L. and Moyiadeen N.M. 1985. Recent trends in the tuna fisheries in Sri Lanka, Paper
presented at the 2nd Working Group Meeting on the tunas around the Republic of Maldives and Sri
Lanka, Colombo

IOTC–2015–WPNT05–18 Rev_1
Joseph, L. and Moyiadeen N.M, 1986. Tuna Fishery – An update for Sri Lanka. Paper presented at
the 3rd Working Group Meeting on the tunas around the Republic of Maldives and Sri Lanka,
Colombo, Sept. 1986
Maldeniya, R., Moyiadeen, N.M. and Amarasiri, C. 1988. Present status of the fishery for small
tuna species, billfish and seer fish in Sri Lanka, Report of workshop on small tuna, seer fish and bill
fish in the Indian Ocean, 24-37
Perera, H.A.C.C., Maldeniya, R. and Bandaranayake, K.H.K. 2014 Importance of Neritic tuna in
large pelagic fisheries in Sri Lanka. Fourth Working Party on Neritic Tunas, Phuket, Thailand, 29-
30 June 2014
Sivasubramanium, K. 1973. Co-occurrence and the relative abundance of narrow and broad
corseletted frigate mackerels Auxis thazard and A. rochei around Ceylon, Poceed. Symp. on living
resources of the seas around India.