Diet Preference and Prey of Olive Ridley Turtles (Lepidocheyls ...

OPEN JOURNAL OF OCEAN AND COASTAL SCIENCES Volume 1, Number 1, October 2014

OPEN JOURNAL OF OCEAN AND COASTAL SCIENCES

Diet Preference and Prey of Olive Ridley Turtles (Lepidocheyls olivacea) along East Coast of India, Odisha Subrata K. Behera1 *, K. Sivakumar2 , B. C. Choudhury3 , Sajan John3 1

Integrated Coastal Zone Management Project Unit, Berhampur Forest Division (T),Odisha, India Wildlife Institute of India, Dehradun, Chandrabani, PO Box 18, Dehradun, 248001, India *Corresponding author: [email protected] 2,3

Abstract: This study was made on gut content of 182 dead wash ashore olive ridley turtles, (56 sub-adults, and 126 adult) of which 77, 100 and 5 guts were from Gahirmatha, Devi and Rushikulaya respectively. Autopsy was done during the breeding seasons of February 2008 to April 2010 at Odisha coast on three arribada beaches of the world. To identify the food preference of Olive ridley volumetric and frequency of occurrence percent was calculated. Gut content of turtles was segregated into four size class based on curve carapace length (CCL) (< 49cm, 50-59 cm, 60-79 cm, and > 80cm) and classified into two groups sub-adult and adult. In total 88.15% was of animal prey 6.65% of volume was plant. Although there was no significant difference within two size class of the sub-groups, sub adult and adult. But the diet differs significantly in adult and sub adult group. On analyzing the diet through Percent similarity index among the size class of turtles the most preferred phyla of prey items taken was Mollusca which add 30% of volume in food to all size class of turtles with highest diversity of 12 families and Muricidae family gave more prey item in invertebrate. Keywords: Adult; Curved Carapace Length; Lepidocheyls olivacea; Sub Adult; Volumetric; Percent Similarity Index

1. INTRODUCTION Olive ridley sea turtles arrives in the coastal water of Odisha by early November and remains in this coastal water for six months for the breeding and nesting. Although many studies have been done along the east coast of India on this species, few study were made in Indian Ocean that revels these turtles feed on algae which is major component of diet [1]. In Bay of Bengal an attempt was made and algae were found to be major component of diet but it was not a systematic study [2]. There is very diminutive information about the feeding habit of this population. In another study at Gahirmatha, Aganasi Island turtles were found with 66.92% of volume as animal prey and 26.37% was of vegetation [3, 4]. This study was conducted on five ridleys and was scant in information according to size class and sex. 73


By understanding diet of sea turtles which is the fundamental to their conservation and knowledge of food resources this study can identify important benthic food resources, which can guide to make decision regarding management of endangered population [5, 6]. Thus study could be an important component for olive ridley recovery effort which permits this population to manage appropriately. The diet of these turtles is poorly known along the east coast of India during their breeding period. Mostly it is known to be omnivorous [7]. The diet of juvenile olive ridley is not yet known, but some effort had being made on the diet pattern of sub adult olive ridley [8]. Adult olive ridleys utilize a wide range of foraging habitats. Turtles use to feed even in deep water [9] and are pelagic [10, 11]. Olive ridley sea turtles feed in shallow benthic water near estuarine [8]. The largest study on the diet was conducted on 139 mature turtles at Mexico [12]. Few study had being conducted in case of the olive ridley sea turtle around the world and most of the studies are restricted to Pacific Ocean only, two studies had being conducted at Indian Ocean till now.

2. METHOD 2.1 Measurements Measurements were taken prior to autopsy of turtle. We measured straight carapace length (SCL) (SCL ± 0.1 cm) from the nuchal notch to the posterior most portion of rear marginal using calipers (Forestry Suppliers, Jackson, MS). Similarly the straight carapace width was measured at the widest part of the carapace [6]. We have also measured the curve carapace length (CCL) and curve carapace width (CCW) of the washed ashore turtle. Sex of all the washed ashore turtles was identified.

2.2 Autopsy of Carcasses This study was done for the freshly washed ashore turtles, out of which 77, 100 and 5 guts where from Gahirmatha, Devi and Rushikulaya respectively, were analysed during two year of study period, Of 182 olive ridleys guts examined, 139 guts had food. 43 number of dead turtles found in Gahirmatha were without food in their gut. For all sample autopsy was done and the gut was carefully taken out, all the food material in the gut was extracted [13, 14]. Only the esophagus to stomach content was used for analysis for the misinterpretation of the soft body part in the lower alimentary canal of the gut [15–17]. All dietary samples were rinsed thoroughly in clean seawater and sieved in 0.5 mm fine mesh sieve which was finally fixed in a 4% formalin solution. We sorted prey groups by species (i.e., one species equals one prey group). Food items were identified to the lowest taxonomic level possible with a binocular dissecting scope [13, 18]. Entire sample volume and relative volume of each prey group were calculated through water displacement in a graduated cylinder to the nearest 10 ml. [19, 20]. We determined mean sample volume (% vol) and frequency of occurrence (% F) of each prey group as follows:

74

Diet Preference and Prey of Olive Ridley Turtles (Lepidocheyls olivacea) along East Coast of India, Odisha

%vol =

(Total volume o f diet item in all samples × 100) (Total volume o f all samples)

%vol =

(Number o f samples containing diet item × 100) (Total number o f samples)

Any item with a relative volume > 5% in at least one sample was considered a major diet constituent [20].

3. RESULT We analyzed esophageal lavage samples from 139 fresh washed ashore Olive ridley turtles grouped into two (33 sub-adult, 106 adult) out of which 34 were the male and 105 females. As the male turtles were low in compare to females no analysis was done within the sex. Mean curved carapace length (CCL) of washed ashore Olive ridley turtles was 65.8 cm (S.E = 0.8, range = 45.4 - 75.6 cm, N = 139) All diet data were collected between February and April of during study season (Figure 1). The average gut content was 529.6 ml (S.E = 30.3, ranged between 120 to 1032 ml) in volume. The volume of food in each size class was 357-689 ml (Figure 1). In general animal prey content in diet of olive ridley was 88.15% of the total volume, algae 6.65% and fishing gears and substrate material, and mangrove leave was 4.96%, 7.35% and 0.25% respectively (Table 1). Diet Composition was significant within two size classes of two groups, sub adult and adult. There was no difference within the diet composition of two size classes of same sub group. Sub adult (F = 3.18 df= 6, 8 P < 0.05) and (F = 0.39, df = 6, 10 P < 0.03) in adults. But the prey item of Sub adult and adult turtles varied significantly in the percent volume (F = 1.58, df = 10, P < 0.25) and the percentage frequency (F = 3.77, df = 10, P < 0.02) of seven prey items. The most noteworthy differences were that sub adults turtles consumed greater amounts of fish and adult turtles ate greater amounts of molluscs, fish, and other materials (Table 1, Table 2). Diet composition: Through analysis of volume percent and frequency occurrence (Figure 2(a), Figure 2(b)) two groups reveal that fish prey ( 49.84 %) was most volumetrically during the breeding season in sub adult groups, 23.64% was mollusca, 17.43% arthropods and 0.94% algae, in frequency of occurrence sub adult differs as Arthropods (32.30%) prey items were mostly preferred followed by Mollusca 23.32%, and fish 20.83 %. In the group of adult turtles, Mollusca (46.46%) was important prey item followed by algae was 12.36%, arthropods 12.14 %, fish was 5.75% annelids 2.55% respectively of the volume. In frequency of occurrence Mollusca (58.31%) remained in the most preferred item followed by Annelida 14.28%, Arthropoda 14.34%. Animal items: The prey items represented four Phyla and 16 Family of invertebrates. Coelentrata, Annelida, Arthropoda and Mollusca were phyla present in food prey items. Arthropoda make up 14.79 % of all prey items by volume. Within three arthropod families (Pandalidae, Portunidae, Palinuridae), Fam. Pandalidae adds volume to food (Table 1). The most abundant phyla Mollusca in prey comprise of 12 Family making up 30.40% which were identified up to family and 10.58% remained unidentified volume of all prey items (Table 2). Among two groups of turtle prey items the most dominant invertebrate’s diet was Molluscan (Table 2) species of which (fam. Muricidae) was dominated in frequency of occurrence and in volume of percent (Table 1). Besides invertebrates, fish was the most abundant prey items which make up 27.79% of all prey items. But it remained unidentified. 75


Figure 1. Histogram showing the average volume of the food content in 139 olive ridleys washes ashore along Odisha coast in different months of breeding and nesting period.

(a)

(b)

Figure 2. Percentage of Frequency and volume of prey items found in gut of olive ridley turtles.

Plant items: In case of the plants the algae was dominated as it was found in the diet of all most all 76


turtles and it make up the 6.65 % of all the prey items in volume (Table 1, Table 2). The percent similarity index (PSI) was calculated by using the proportions of the prey items in the stomachs (values in Table 2 ) to show diet overlap between four different size class of olive ridley turtles I & II were considered as sub – adult and other two were adult turtles. The upper diagonal sections in Figure shows the percent similarity values between different size classes of the turtles. The lower diagonal section shows diet overlap between species by categorizing the percent similarities into low (< 30%), medium (30-50%), and high (> 50%) levels of dietary overlap. The overlap values among sub adult olive ridleys were high (> 50 %) (Figure 3), since they fed mainly on fish, arthropods and small amounts (< 30%) mollusca. Within the adults (larger-sized) group, overlap values was medium as this may be due to less samples in IV (N = 11) group in comparison to group III (N =72) however the adult turtles feed on mollusca, arthropod, annelids. The overlap value between sub adult and adult turtles was medium because sub adults fed much more fish (75%) than adults. On the other hand adult feed on the mollusca (41.51%), annelids (27.5%) and most turtles preferred prey items of Mollusca which add as volume in food with highest diversity of 12 families and Muricidae family gave more prey item in invertebrate. This similarity results in the medium value overlapping among the adult and sub adult.

4. DISCUSSION Many studies on the biology of sea turtles had being made in recent years, but their feeding and prey is still unknown. Only the green turtle (Chelonia mydas) feeding ecology have being studied most frequently and it is mainly herbivorous [21–24] make a quantitative analysis of stomach contents of 243 green turtles taken from the east coast of Nicaragua found that the main food source of these marine organisms are herbs such as Thalassia testudinum [25] study at Uruguay the major component of the diet in stomach content was Ulva sp. [26, 27] found the tunicate was the major diet followed by algae in east pacific green turtles. Sea turtle of other species such as leatherback (Dermochelys coriacea), kimps ridley (Lepidochelys kempi), loggerhead (Caretta caretta) and hawksbill (Eretmochelys imbricata) are known to be primarily carnivores [28, 29]. Leatherbacks (D. Coriacea) Food habits are known primarily from the stomach samples of slaughtered animals [30–32] that it feed on pelagic medusae (jellyfish), siphonophores. Lepidochelys kempi Digestive tract contents were examined from 101 dead found stranded on south Texas beaches from 1983-1989. It consume items discarded from shrimp trawls and smaller trawls fishing for bait and diet is mainly carnivorous, based crustaceans, fish , Shellfish and jellyfish [33]. In the largest study of the diet of olive ridley (115 females and 24 males) at Mexico suggest that Slaps and the fish composed the largest percentage of the volume of stomach content (45 and 42 % respectively). However the most frequent food, items identified were the molluscs (66%), crustaceans (51%) and algae material (51%) [12]. In another study at Mexico suggest Jelly fish and crabs were the major component of the diet this study was done for only 20 turtles [34, 35]. In Indian Ocean from Srilanka the major part of the diet was algae [1, 2]. General diet: In our study olive ridley sea turtles in the east coast of Odisha, 88.15% of volume were animal prey 6.09% is of vegetation. It mainly feeds on the Mollusca as it is the major proportion of animal diet 30.40% in the volume as well as in the frequency of occurrence 31.32% which is different to the study of Montenegro as the fishes occurred as the major part of the food items, as our study shows it occurs in most of the turtles in our study area. In invertebrates the phyla mollusca had the highest diversity with 12 77


Table 1. Gut content of olive ridley turtles of Odisha (Four group were classified according to curve carapace length of turtle). sl.no

Food items

GROUP I ( n = 19) F% V%

GROUP II (n = 37) F% V%

GROUP III (n = 72) F% V%

GROUP IV (n = 11) F% V%

16.66

5.7

16.7

7.0

14.3

3.7

14.3

1.4

16.66

29

5.00

5.80

5.00

6.15

7.14

7.50

8.3

1.5

3.2

4.2

ANNELIDA 1

Unidentified MOLLUSCA

1

Muricidae

2

Veneridae

3

Arcidae

8.33

1.8

2.0

1.2

14.3

26.3

4

Mactridae

8.33

0.7

4.1

1.9

14.3

27.8

5

Turridae

12.3

3.7

14.3

8.6

14.3

10.5

7.1

4.8

14.3

13.2

6

Nassariidae

2.0

0.7

7

Dentaliedae

4.1

0.3

8

Cardittidae

2.0

0.3

9

Cuculladiae

2.0

0.3

10

Naticidae

2.0

0.6

11

Anomiidae

2.0

0.5

12

Donacidae

2.0

1.4

ARTHROPODA 1

Pandalidae

25.0

12.9

10.2

3.1

2

Portunidae

25.00

13.6

8.3

6.2

5.1

3.9

3

Palinuridae

7.3

2.7

1.0

3.7

4

unidentified

1.0

5.0

22.4

11.5

UNIDENTIFIED FISH 1

16.66

46.6

25.0

53.1

8.36

1.7

1.4

6.8

UNIDENTIFIED MOLLUSCA 1

23.3

UNIDENTIFIED JELLY 1

1.0

1.0

2.0

3.2

1.0

19.9

ALGAE 1

1.0

2.0

1.9

FISHING GEARS 1

1.5 OTHERS

1 MANGROVE LEAF 1

1.0

1.0

families and family Muricidae from phyla mollusca make up the major portion of diet. The vegetation was 6.09% of the total diet this proportion was of algae. Algae occurred in few of the turtles and it does 78


not give the volume to the diet. Importance of food found in volume was mollusca (fam.Muricidae) > fish > arthropod (fam. Pandalidae) > annelides where as in percentage of occurrence it differs slightly, mollusca > arthropods > fish > annelids were important diet present in the olive ridley turtles.

Table 2. Gut contents of (139) olive ridley washed ashore turtles at Odisha. Food Groups

N = 139 F%

V%

Annelida

15.47

4.46

Mollusca

31.32

30.40

Arthropoda

24.83

14.79

Unidentified fish

16.02

27.79

Unidentified mollusca

6.01

10.58

Unidentified jelly

0.50

0.14

Algae

2.29

6.65

Fishing gears & others

2.57

4.96

Mangrove leaf

1.00

0.25

Figure 3. Percent Similarity Index (%) of dietary overlap of Olive ridley turtles in Odisha coast according to size class.

Diet Overlap: In this study, because of the small sample group sizes of olive ridley, diet overlap values were calculated for the preference of prey items by combining the data from all stomachs analyzed. The diet overlap values between different sizes classes of olive ridleys were generally low (except the values between the groups of sub adult olive ridley turtles). A number of factors, such as predator size, morphology of the digestive system, and the abundance of prey and predators, could have contributed to the differences in feeding habits between predator species. This study provides the food habits of olive ridley in the east coast of Odisha, India during the breeding season where the turtle spent most of the time in near shore coastal waters and this will improves the understanding of the predator-prey interrelationships. Adult olive ridleys are representatives of the benthic fauna during the breeding season; as they fed mainly on benthic prey such as mollusca, arthropods and annelids. However, in case of the sub adult turtles, we also found fish as the major prey item in the stomachs. This means that olive ridley also played an important role in the water column. The olive ridleys are known to be bottom feeder and during 79


breeding period, it may be possible that they will be consuming greater amount of mollusca species while they are in the in shallow coastal water of Odisha. This study points toward the constraint for calcium during breeding period for the development and formation of eggs in their breeding ground. The medium Percent similarity index (PSI) among the two groups adult and sub-adult it is unambiguous that the prey items of olive ridley is mostly Mollusca and the sub-adult prefers on fish due to the necessity of protein for the growth and development simultaneously as they are benthic feeders they feeds on mollusca which is ascertain.

ACKNOWLEDGMENTS The authors are thankful to Director, Wildlife Institute of India (WII) for encouragement and support and PCCF, Odisha Forest Department for permission. The funding for this study was made available through the Directorate General of Hydrocarbon (DGH), Government of India through WII. We thank Field staff of Gahirmatha, Puri, Berhampur Forest Division for their co-operation.

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