Estimating Fish Abundance In the Cape Fear River. Chip Collier NC Division of Marine Fisheries

Transcription

1 Estimating Fish Abundance In the Cape Fear River Chip Collier NC Division of Marine Fisheries April 10, 2013

2 Presentation Outline Methods to Estimate Population Size Historical Data Experiment in Estimating Number of Fish

3 Counting Fish Similar to Counting Trees Except: Fish Move and We Can t See Them Rely on Relative Index of Abundance. Estimated using statistical techniques Determines sustainability

4 Sustainability Abundance Overfishing Overfished Time

5 Fish Accounting Recruits Births Natural Mortality Deaths THE STOCK Growth Gaining Weight Death by Misadventure Fishing Mortality

6 Fish Accounting Recruits Births Natural Mortality Deaths THE STOCK Fishing Growth Gaining Weight Death by Misadventure Mortality

7 Fish Accounting Births Recruits Natural Mortality Deaths THE STOCK Growth Gaining Weight Death by Misadventure Fishing Mortality

8 Data Needed Landings Fishing Effort Fish Age Maturity Schedule Growth Rate Migration Patterns Natural Mortality 1,200,000 1,000, , , , ,000 0 Commercial Recreational

9 Anadromous Fish Stocks Status of Anadromous Stocks Coastwide Cape Fear River Commercial Landings Overfished Overfishing Except Striped Bass No current stock assessment for Cape Fear River Stocks

10 Factors Influencing Stocks Blockages to historic spawning grounds Water Quality Historic Overfishing

11 Atlantic Sturgeon Survey Data Listed as Endangered by NMFS in 2012 Size Structure Max 170 Age Structure Max 60 years Unknown trend in abundance

12 American Shad Survey Data The Founding Fish Mostly Semelparous Age Structure Max 8 Low but steady trend in abundance NY Dept of Conservation

13 Striped Bass Survey Data Rockfish Size Structure Max 50 Age Structure Cape Fear River Mean CPUE Max 17 Trends in abundance Low abundance CPUE (striped bass per hour) Year

14 Acoustic Telemetry Tagging Methods Used to track fish migrations Fish can be tracked along the Cape Fear River and beyond Expensive and only a limited number of fish can be tagged Conventional Tagging Used to estimate population abundance and fishing mortality Fish tagged with external and internal tags

15 28 Listening Stations Three Species Tagged by NC DMF American Shad The Nature Conservancy shad Atlantic and Shortnose Sturgeon NMFS Section 6 Grant sturgeon Striped Bass Cape Fear River Watch Striper Foundation bass Sonic Tagging

16 Striped Bass Conventional Tagging Results Many fish were juveniles Significant catches of hatchery raised fish Recapture rate of 6% Tag Status Total Tag Recap

17 Calculating Population Size Tag Status Total Tag Recap Number of Fish Marked = Total Number Marked in Population Total Number of Fish Sample Total Number of Fish in Population = 38?? Answer = 1,145 Striped Bass

18 Tagging Experiment Estimate How Many Goldfish are in Each Bag Take 1 scoop with sampling device each round Mark each fish and return to bag and shake After the first two marking events, start to estimate the number of goldfish in the pond on the sheet provided.

19 Goldfish Estimates Pond 1 Pond 2 Pond 3 Pond 4 Pond Pond 6 Pond 7 Pond 8 Pond 9 Pond ,025 1, Now that we have an estimate. What does it mean?

20 Shifting Baselines

21 Shifting Baselines

22 Shifting Baselines Last 20 Years Last 10 Years

23 Cape Fear Anadromous Fish Stocks Species Population Potential Current Estimate Atlantic Sturgeon 8,700 (based on historic landings, Earll 1887) <300 (ASSRT 2007) Shortnose sturgeon 31,000 (based on Kynard) <100 (Moser and Ross 1995) American shad 447,000 (based on historic habitat, St. Pierre 1979) NA Striped bass 100,000 (based on historic landings from Chestnut and Davis and personal communication with J. Hightower, NCSU/USGS 10,000 (based on tagging estimates) *Table from Cape Fear River Partnership Draft Plan

24 Conclusions Estimating fish populations is complex. Anadromous fish populations are at low levels. Restoration efforts are helping rebuild stocks. Rebuilding stocks takes time.

25 Questions Funding and Assistance Acknowledgements NC DMF NC WRC Cape Fear River Watch Striped Bass Foundation The Nature Conservancy NMFS Section 6 Endangered Species Grant

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27 American Shad Striped Bass Sturgeon Migration Maps