An investigation of morphological characteristics of spot croaker (Leiostomus xanthurus)

and white mullet (Mugil curema) from Assateague Island National Seashore, Virginia

Lee PuttENVT450 Environmental Studies Capstone

23 April 2014

Introduction to Common Atlantic Coastal Fishes

• Spot croaker, also known as spot, and white mullet are some of the most common species – very abundant, heavily fished and staple prey item– Inhabit shallow coastal waters , bays, beaches, and estuaries with sandy or

muddy bottoms and submerged vegetation as well as open water habitat

Range of Spot and White Mullet

• Broad range – from New Brunswick to Mexico

• Habitat diverse and varies – from shallow grassy beds, to open water

Tom’s Cove Off the Coast of Assateague Island

Importance of Coastal Habitats to Fish Populations

• Many species of fish coastal regions as nursery grounds • Play an important role in wetland and terrestrial food chains • As fish grow larger, often graduate to deeper water until they

completely migrate out into the open ocean

• Spot utilize the inlets and coves for nursery grounds

Objectives • Objective 1: to contrast body shapes of spot and white mullet using

geometric morphometric analyses to demonstrate how effectively these techniques distinguish interspecific differences

• Objective 2: to investigate if intraspecific body shape differences could be detected and correlated with variations in habitat for spot

Materials and Methods• In total, 33 white mullet and 108 spot were collected• Fish collected and euthanized in the field as required by the collection permit

Queen’s Sound – Intermediate Habitat

Inlet of Tom’s Cove – Shallow

Water

Offshore of Assateague Island –

Open Water

Fish Collection in Tom’s Cove

Fish Collection in Queen’s

Sound

Fish Collection off the Coast of

Assateague Island

Materials and Methods To Measure Shape Differences Among Fish:• Geometric morphometrics utilizes the X

and Y coordinates on an axis to conduct multivariate analyses

• Each fish included a unique classification number and a scale bar

• Consensus configuration– Calculates an average shape of the fish

through marked locations

• Relative warp analyses– Provides a visually benefit which shows shape

differences across the sample of fish– Often shows bending

12

34

5

6

7

8 9

10

11

12

Results – Interspecific Differences • Very distinct differences in shapes were found for white mullet and spot -

very strong interspecific differences– Also shows distinct differences in the spot population – Due to these differences, intraspecific differences were then tested on spot

White Mullet

Spot

Results – Intraspecific Differences

1

2

3

4 5

67

8

9

10

11

12

1314

15

16

17

1819

20

21

22

23

24

2526 27

2829

30

31

32

33

3435

36

37

38

39

40

41

424344 45

464748

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

686970

7172

73

7475

76

77

7879

80

81

82

83

84

85

86

87

88

8990

9192

93 94

95

96

97

98

99

100

101

102

103104105

106

107

Tom’s Cove

Open Ocean

Queen’s Sound

Discussion• The analysis of only spot agrees with other observations that body shape

differs with varying types of habitats in fish. – One study by Ruehl, Shervette, and Dewitt 2011 have found that spot and drum

collected from sea grass beds in South Carolina exhibit semi-terminal mouths – This variation in shape from the three spot populations suggest that adaptations

exist for numerous foraging techniques

Importance of Spot and Mullet• Spot and mullet are a vital part of the marine food chain in the mid-

Atlantic region• Coastal habitat is continually being stressed by overdevelopment and

pollution - if not protected, this regional food chain can become highly constricted and stressed

• Many areas in the mid-Atlantic are not protected and can be at risk from these factors– Pollution– Overfishing– Habitat destruction– Overdevelopment– Recreation – Seal Level Rise

Final Remarks• Through this study of geometric morphometrics, there are clear

interspecific differences between spot and white mullet – has been a useful tool in distinguishing statistical differences in shape

• Also shows clear intraspecific differences in spot and suggests that body shape could possibly be correlated with variations in habitat types – could be an adaptation for different foraging techniques

• Conservation strategies needs to recognize the range in habitats utilized by near-shore fish when managing this fishery

Acknowledgements I would like to thank Dr. Seiler for his invaluable insight and help with the project, the Chincoteague Bay Field Station for use of

their collecting equipment and facilities, as well as Dr. Thompson for his teaching instruction in Marine Ichthyology