biol570 spr'15 leopard shark demographics
Post on 13-Aug-2015
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Leopard Shark, Triakis semifasciata
• Elasmobranch, Carchariniformes, Triakidae• Common in bays and estuaries• Average length is 120cm –
150cm • Feeds on clams, crabs, bony
fish, shrimp etc.• Aplacental viviparous
HypothesisH0 : There is no difference in leopard shark
demographics compared to previous beach seines
Ha : There is a difference in leopard shark demographics compared to previous beach seines
Method• A beach seine was
conducted at Half Moon Bay on February 16th
• A boat was rowed out to deploy a seine net before dragging it to shore
• The sharks were quickly measured and released to minimize stress
PredictionsMore females than males
Birth occurs between March and JuneMore juveniles than adults
Bays and estuaries are a favored nursery spot
ResultsA total of 36 leopard sharks caught
19 males, 17 females30 juveniles and 6 adults
All females were juvenilesFemales mature at 10-15 years, 100cm total
lengthMales mature at 7-13 years, 105cm total length
Sizing it up Smallest male: 43cm
Largest male: 129cm
Smallest female: 53cm
Largest female: 103cm
Standard length (cm)
40-49 50-59 60-69 70-79 80-89 90-99100-109
110-119
120-129
Male 1 2 4 1 3 2 2 0 4
Female 0 6 2 4 4 0 1 0 0
Seine in 2012-2013
September October December February March April May June July August September October0
5
10
15
20
25
Leopard Sharks
MalesFemalesUnknown
Month
Am
ount
Caught
Results Graph
40-49 50-59 60-69 70-79 80-89 90-99 100-109 110-119 120-1290
1
2
3
4
5
6
Leopard Shark Gender and Standard Length
Male Female
Standard Length (cm)
Num
ber
ConclusionThere were more males than females
Females may be aggregating elsewhere Juveniles far outnumber adults
Bays and estuaries are good shelters and nurseries for juveniles
Ha is accepted
Thanks to:Professor Crow, TA Brooke and all my BIOL 570
classmates for helping out with the beach seine!Didn’t get any leopard sharks on the second
beach seine, but good work still!
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