The effect of depth of operation and soaking time on catch rates in the experimental tuna longline fisheries in Lakshadweep Sea, India
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Iranian Journal of Fisheries Sciences 15(1) 597-605 2016
The effect of depth of operation and soaking time on catch
rates in the experimental tuna longline fisheries in
Lakshadweep Sea, India
Aneesh Kumar K.V.1*; Pravin P.1;Paresh Khanolkar S.1;
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Baiju M.V.1; Meenakumari B.2
Received: July 2014 Accepted: June 2015
1-Centre for Marine Living Resources and Ecology (CMLRE), 6th Floor, C-Block, Kendriya
Bhavan, P.B. No. 5415, CSEZ P.O., Kochi - 682 037, India
2-Indian Council of Agricultural Research, Krishi Anusandhan Bhavan, New Delhi, India,
110 012
*
Corresponding author's Email: menoncift@gmail.com
Keywords: Longline, Tuna, Sharks, Depth, Soaking time, Lakshadweep
Introduction yield of oceanic tuna resources is 2.78
Most of the marine fish landings from lakh tonnes (Pillai and Jyothi, 2007).
the Indian waters are from the fishing Potential of total tuna resources in
operations in the coastal shelf area, Lakshadweep Islands is estimated at
especially from the shallower region about 50,000 tonnes (Pillai et al., 2006).
ranging from 5 to 100 m depth (Rao, A total tuna landing in India in 2010
2010). Heavy demand for seafood in was 60,512 tonnes along the mainland
domestic and international markets and 7,883 tonnes in Lakshadweep. The
underlines the need for increasing the landings trends of these high values
marine fish production. Catch trends fishes indicated a further scope for the
indicated that the production from the expansion of the fisheries. The oceanic
coastal fisheries is almost stagnant and tuna fishery of the Indian Ocean is
point towards the need for harvesting contributed mainly by four species
unexploited or under exploited oceanic viz.,yellowfin tuna, southern bluefin tuna,
fish resources. Present fleet size of the albacore tuna and bigeye tuna (Joseph,
distant water fishing vessels is very less 1972). Longline operations are in its
in spite of India’s vast EEZ of 2.02 infancy state in India. Surface longline
million sq km and two Islands groups, gears can operate at a range of depths,
viz., Andaman, Nicobar and and hooks placed at different depths can
Lakshadweep.The estimated potential have different fishing efficiencies,
598 Aneesh Kumar et al., The effect of depth of operation and soaking time on catch …
depending on the target species and its time on catch rates vary considerably
behaviour. With better knowledge of between species to species. Soak time
the relationship between hook depth during dusk showed higher overall
and foraging behaviour of the targeted catch rates (Ward et al.,
fish, catch rates could be improved by 2004).Experimental longline operations
placing the majority of hooks at the were initiated in the Lakshadweep Sea
depth range favoured by the target to tap the unexploited oceanic tuna
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species. Fishing efficiency of the fishes. This paper discusses the effect of
longline gears are influenced by minor depth of operation and soaking time on
changes in the gear configuration such the overall catching performance and
as type of terminal gear and depth of species selectivity in the longlines
hooking operations (Broadhurst and operated.
Hazin, 2000).Deep setting of the
longline gear found to be very effective Materials and methods
to reduce the sea turtle bycatch (Shiga Fishing operations were carried out
et al., 2000; Beverly et al., 2009). from three Pablo boats (7.6 to 8.5 m
Marine mega faunal bycatch is a serious LOA) modified for longlining in the
concern in longline fisheries which Lakshadweep Sea around Agatti Island
needs serious attention (Lewison et al., (10°38' - 11°07' N; 70°08' - 72°08' E)
(Fig. 1), during 2009-2011. Pablo boats
2004; Diaz, 2005; Garrison,
selected for the study were mechanized
2007).Major group of animals
wooden fishing boats of Lakshadweep
contributing to the marine mega faunal Islands ranging from 7.62 m to 8.5 m
bycatch are sharks and cetaceans LOA with engine capacity ranging from
(Gilman et al., 2008; Mandelman et al., 10 to 23.5 hp. Total length of the
2008; Milian et al., 2008; Mangel, mainline is 5 km. Mainline and branch
2010).The depth at which longline lines of the experimental gear were
fishes is mainly influenced by the gear made of polyamide monofilament of 3
configuration, primarily by the length mm and 1.8 mm, respectively and float
of mainline between floats (baskets), lines were made up of 4 mm dia
sagging rate and parameters such as polyester. Branch lines were 22.5 m
long and hooks were deployed in the
wind and currents (Suzuki et al., 1977;
depth range of 35-100 m by adjusting
Boggs, 1992). Tuna shows an
the length of float lines. Japanese tuna
aggregation nature near the floating hooks of 3.4 sun with 10° offset were
objects which can be effectively utilised used. The overall depth of the fishing
by vertical longline operations in the ground ranges from ~ 500 m to
floatsams or FADs (Naeem and ~ 2000m.
Latheefa, 1994).A successful fishing
and catch rates greatly depends on the
soaking time. The effect of soakingIranian Journal of Fisheries Sciences 15(1) 2016 599
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Figure 1: Map showing the fishing area in Lakshadweep waters, Arabian Sea, India (10° 38’ - 11°
07’ N lat. and 72° 01’ - 73°18’ E long.) from 16 Nov 2009 to 23 April 2011. The fishing
locations are marked as black dots. The depth of the fishing ground ranges from ~ 500 m
to ~ 2000m.
The fishes caught during the fishing recorded. The hooking rate was
operations were grouped into four calculated based on the number of fish
categories as tuna, sharks, sailfish and caught per 1000 hooks.
miscellaneous fishes for the analysis. The statistical tests were performed
The miscellaneous fishes were using SPSS (IBM SPSS Statistics,
contributed by lagoon fishes, which Version 20). The data collected were
include Lutjanus gibbus, Aprion compiled and analysed using 2 for test
virescens, and Epinephelus polylepis. of goodness of fit and two factor
The study compared the effect of hook ANOVA.
depth on the overall catching
performance of the longliners. The Results and discussion
depth of operation was grouped into Effect of hook depth on catch rates
four categories viz., 35, 60, and 100 m. The study compared the effect of hook
The starting and finishing times of both depth on the overall hooking rate and
shooting and hauling were recorded to the species composition. The overall
calculate the soaking time of each hooking rate observed at 35, 60 and 100
operation. Soaking time is the duration m depth were 8.78, 12.96 and 6.89 per
between completion of setting and the 1000 hooks respectively (Fig. 2). No
initiation of hauling of the longline. The significant association was observed
soaking time has been categorized into between the overall hooking rate and
three groups for the analysis i.e. Group depth of operation (2 = 2.030, p>0.05,
A (1 to 3 h), Group B (3.1 to 5 h) and df =2).
Group C (>5.1h). During hauling, the The study compared the effect of
parameters such as type of species, size, hook depth on the species selectivity in
number, condition (live or dead) were the longline fishing operations (Fig. 3).600 Aneesh Kumar et al., The effect of depth of operation and soaking time on catch …
At 35 m depth, shark hooking rate was Sailfish hooking rate was found to be
found to be higher (5.56 per 1000 high (1.05 per 1000 hooks) when the
hooks) compared to other group of soaking time was 3.1-5 h and no sailfish
fishes. Hooking rate of miscellaneous was caught when soaking time was
fishes observed at 35 m depth is 1.27 higher than 5.1 h. Miscellaneous group
per 1000 hooks followed by tunas and of fishes was found to be high (1.09 per
sailfish (0.98 and 0.88 per 1000 hooks). 1000 hooks) when the soaking time was
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Shark catch was dominated at 60 m 1-3 h compared to soaking time of 3.1
depth by contributing 9.4 per 1000 and >5.1 h (0.93 and 0 per 1000 hooks,
hooks followed by tunas, sailfish and respectively). Sailfish hooking and
miscellaneous fishes (2.67, 0.51 and miscellaneous fishes hooking rate was
0.38 per 1000 hooks, respectively). found to be zero when the soaking time
Sharks were the dominant group of was higher than 5.1 h. Soaking time
fishes caught at 100 m depth (4.51 per failed to show any significant effect on
1000 hooks), followed by tunas, overall hooking rate (2=1.335, p>0.05,
miscellaneous fishes and sailfish (1.9, df=2). Soaking time does not show any
0.47 and 0.24 per 1000 hooks, significant difference on hooking rate of
respectively). Sharks dominated at all species (p>0.05).
the three depths. High tuna hooking rate Studies were carried out to
was observed at 60 m depth. Highest understand the effect of fishing depth
hooking rate for sailfish and on the overall catching performance and
miscellaneous group of fishes recorded species selectivity in the longline
at 35 m depth. fishing operations in the Lakshadweep
Sea. There was no significant relation
Effect of soaking time on catch rates between the depth of operation and
The overall hooking rate was found to overall hooking rate. The study
be high when the soaking time was 1-3 analyses the species selectivity at three
h (13.23 per 1000 hooks), followed by different depths of operations. The
3.1-5 and >5.1 h (9.68 and 8.1 per 1000 results indicated that the depth of
hooks, respectively) (Fig. 4). Further operation has effect on the species
studies were carried out to understand selectivity. Further studies are needed
the effect of soaking time on the species to understand the effect of depth of
selectivity. Shark catch was observed to operation on the species selectivity
be high (8.86 per 1000 hooks) when the beyond 100 m depth. Previous research
soaking time was 1-3 h and low (4.86 indicated that the species selectivity of
per 1000 hooks) when soaking time was tuna is more evident at deeper depths
>5.1 h (Fig. 5). Tuna catch was found to (Bigelow et al., 2006).
be high (3.24 per 1000 hooks) when the
soaking time was >5.1 h and low (1.17
per 1000 hooks) when it was 3.1 -5 h.Iranian Journal of Fisheries Sciences 15(1) 2016 601
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Figure 2: Hooking rate at three different depth levels during the longline fishing operations
in Lakshadweep waters from 16 Nov 2009 to 23 April 2011 (the values expressed as
number/1000 hooks).
Figure 3: Species wise hooking rate at three different depth levels during the longline fishing
operations in Lakshadweep waters from 16 Nov 2009 to 23 April 2011 (the values
expressed as number/1000 hooks).
Figure 4: The overall hooking rate reported at three different soaking durations (the values
expressed as number/1000 hooks.
Figure 5: The species wise hooking rate reported at three different soaking durations (the values
expressed as number/1000 hooks.602 Aneesh Kumar et al., The effect of depth of operation and soaking time on catch …
Bigeye tuna was the major group of statistically not significant to establish
species caught when the fishing carried effect of the soaking time on the species
out beyond 200 m depth in the wise hooking rate. Morgan and Carlson
Hawaiian longline fishing (Boggs, (2010) confirmed the correlation of
1992). Bigelow et al. (2006) confirmed soaking time with the mortality of the
the superiority of deeper hooks to catch sharks caught in bottom longline fishing
tunas. The fishing depth for targeting operations. Previous studies indicated
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bigeye and yellowfin tunas usually that soaking time can enhance the
ranged from 100 to 300 m (An et al., mortality of the sharks caught in the
2008). Honamoto (1976) and Beverly et longline gear (Carlson et al., 2004;
al. (2009)opined that the CPUE of Morgan and Burgess, 2007). Further
bigeye tuna and Bluefin tuna can be studies at deeper depths from 100 to
improved by deep deployment of the 300 m have to be carried out to
hooks. The deep deployment of the understand the effect of depth of
hooks helps to reduce the hooking of operations on the species selectivity in
the incidentally caught species such as longline operations in Lakshadweep
marine turtles, seabirds, sharks and Sea. The shark catch was found to be
dolphins (Shiga et al., 2000; Francis et decreasing with an increase in soaking
al., 2001; Gilman et al., 2008). High time and these results are substantiated
billfish hooking rate was noticed in the with further experiments.
shallower hooks in the longline fishing
operation targeting large tunas Acknowledgement
(Bigelow et al., 2006). The yellowfin The authors are deeply grateful for the
tunas are found to be occupying the encouragement given by the Director,
surface mixed layer above the CIFT, Kochi. The authors wish to
thermocline and are restricted to the express their gratitude to Dr. M. R.
water temperature no more than 8°C Boopendranath for the evaluation of
colder than the surface layers (Dagorn manuscript. The financial assistance
et al., 2006). received from NAIP, ICAR,Govt. of
Vega and Licandeo (2009) opined India is thankfully acknowledged.
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