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International Journal of Marine Science 2014, Vol.4, No.46, 1-12
http://ijms.biopublisher.ca
9
bathymetry (Wagle, 1993) and habitats (Rodrigues et
al., 1998). The coastal waters receive perennial
nutrient-rich freshwater influx from the adjoining
estuaries, particularly the Mandovi-Zuari estuarine
complex (15°25’N-15°31’N and 73°45’E-73°59’E;
Qasim and Sen Gupta, 1981).
The present study area (Figure 7) comprised (i)
inshore fishing grounds (sand-silt substratum), lower
regions of Mandovi-Zuari estuaries (clayey substratum),
Aguada and Mormugao bays (mixed substratum
interspersed with submerged rocky patches) situated
between 15°28’N-15°32’N and 73°45’E-73°57’E, and
(ii) fishing grounds off the mouth of Sal estuary
(15°00’N-15°16’N and 73°00’N-74°41’E) comprising
two different habitats i.e. silty substratum towards the
north of the mouth and submerged rock outcrops
towards the south. In addition, occurrence of tropical
reef fishes in the inshore trawl catches during the
present study suggested the presence of coral reef
patches towards the south of the estuary (Padate et al.,
2010).
Figure 7 Map of the study area indicating sampling sites
3.2 Sample collection
Sample collection involved participation in fishing
trips onboard commercial fishing trawlers to collect
fishes (both elasmobranchs and teleosts). Samples
collected from 158 bottom trawls (total fishing effort of
220 h) during 2006-2010 formed the study material.
Seasons were defined as monsoon (June–September),
post-monsoon (October–January) and pre-monsoon
(February–May). Sampling was not carried during the
monsoon due to a fishing ban (Goa Marine Fishing
Regulation Act, 1981). Geographical position of each
sampling station was recorded with 12-Channel
Geographical Positioning System (GPS) and sampling
depth was obtained from Naval Hydrographic Chart
No. 2022. Trawl net with 20 m head and foot rope
lengths, and mesh sizes of 25, 15 and 9 mm at mouth
end, middle and cod end, respectively was towed at an
estimated speed of 2–3 knots.
Initially, the trawl catch was examined for species
composition. In the case of trawl hauls, five
sub-samples, each weighing approximately 1 kg were
randomly picked. Out of the 158 trawl hauls, 128
yielded catch in excess of 30 kg, hence only these
were subjected to sub-sampling.
3.3 Auxiliary data
Sea surface temperature (SST) data was obtained from
Group for High Resolution Sea Surface Temperature
(GHRSST) Level 4 (AVHRR) Advanced Very High
Resolution Radiometer, Path Finder, available at
POET.PODAAC website.
3.4 Species identification and size
Taxonomic identification involved meristic counts and
morphometric measurements up to the nearest 0.01 cm
using vernier callipers. Life stage of specimens was
determined by comparing the present morphometric
data with published data on length at first maturity (L
m
)
(Froese and Pauly, 2011; Palomares and Pauly, 2011).
For this comparison, two morphometric parameters
namely Total Length (for sharks and skates) and Disc
Width (for rays) were used for comparison.
3.5 Diet analysis
A total of 165 guts belonging only to three species
Scoliodon laticaudus, Chiloscyllium griseum
(Müller
and Henle, 1838)
and
Himantura walga
(Müller and
Henle, 1841) were analyzed for their feeding habits,
due to insufficient number of specimens of the other