1. Sharks in the Sound How An Apex Predator Chooses Habitat Prepared by Charles Bangley, Coastal Resources Management Program, East Carolina University Scott Taylor

2. 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 ReserveEmily Woodward

3. What are the Abiotic and Biotic Factors in this Image?

4. 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

5. 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 OcaCecilia Krahforst

6. 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

7. The Sharks Cecilia Krahforst Blacknose shark (Carcharhinus acronotus) Cecilia Krahforst Blacktip shark (Carcharhinus limbatus) Steven Licthi Atlantic sharpnose shark (Rhizoprionodon terraenovae) Meganne Rose Bonnethead shark (Sphyrna tiburo)

8. 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

9. 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. Mean: =AVERAGE(Top cell:Bottom cell) Formulas Standard Deviation: =STDEV(Top cell:Bottom cell) Minimum: =MIN(Top cell:Bottom cell) Maximum: =MAX(Top cell:Bottom cell)

10. 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