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Sharks in the Sound
How An Apex Predator Chooses Habitat
Scott Taylor
Prepared by Charles Bangley,
Coastal Resources Management Program, East Carolina University
Habitat Selection
Organisms choose habitat based on abiotic and biotic factors
Abiotic Factors – local environmental conditions affecting habitat choice
Depth, salinity, temperature, dissolved oxygen
Biotic Factors – biological processes that influence habitat choice
Prey availability, predator presence, reef-building organisms
Abiotic and biotic factors can influence each other
Examples – prey migrations triggered by temperature, low oxygen from
eutrophication
NC Coastal Reserve
Emily Woodward
What are the Abiotic and Biotic Factors in this Image?
Resource Partitioning
What happens if two species have the same habitat preferences?
Competition is strongest between species with similar habitat use behavior
Resource Partitioning – species use the same habitat differently to avoid competition
Two types:
Temporal – species use the habitat area at different times
Spatial – species use different areas of the habitat
Alexander Safonov
ECU Inshore Shark Survey
Research Goals – Identify habitat preferences of coastal sharks in NC estuaries,
determine if resource partitioning is occurring
Methods – Capture, identify, measure sharks using gillnet, longline, and drumline
gear, take environmental measurements
Data – Shark catch and environmental data from Back Sound, North Carolina
Maria de Oca
Cecilia Krahforst
The Data
Species – species of shark caught at the environmental values in that row
Abiotic factors – depth (m), temperature (°C), salinity (ppt), dissolved oxygen (mg/L),
distance from the nearest inlet (km)
Biotic factors – distance from the nearest seagrass habitat (m)
Charles Bangley
The Sharks
Cecilia Krahforst
Blacktip shark (Carcharhinus limbatus)
Cecilia Krahforst
Blacknose shark (Carcharhinus acronotus)
Steven Licthi
Meganne Rose
Atlantic sharpnose shark
(Rhizoprionodon terraenovae)
Bonnethead shark (Sphyrna tiburo)
Identifying Habitat Preferences
Habitat preferences identified by finding mean environmental values for each species
Mean – the average environmental value for that species
Many samples won’t fall exactly on the mean, we need to account for that
Standard Deviation – usual range of difference from the mean within your samples
Usually reported as Mean ± Standard Deviation
Mean of 5 ± 2 = average value is 5, but values from 3 to 7 are within the usual
amount of variation in your samples
Also useful to know the minimum (lowest) and maximum (highest) values for each
species
Charles Bangley
Basic Stats in Excel
Microsoft Excel will calculate some statistics using formulas
Step 1 – Sort the data by Species.
Step 2 – Type the formula into a blank cell.
Step 3 – highlight cells in the column containing the factor you’re analyzing.
Make sure to only highlight those next to the species name you’re working on.
Step 4 – Press Enter or Return to run the formula.
Formulas
Mean: =AVERAGE(Top cell:Bottom cell)
Standard Deviation: =STDEV(Top cell:Bottom cell)
Minimum: =MIN(Top cell:Bottom cell)
Maximum: =MAX(Top cell:Bottom cell)
Analysis Questions
1. What do the statistical values tell you about the habitat preferences and
behavior of each species?
2. What environmental variables differ between species?
3. How might habitat use differences allow these sharks to coexist in the same
estuary?
4. Based on habitat preferences, which of these sharks might be most affected by
habitat loss?
Steven Licthi