1. Analysis of heterogeneous fishing effort and catch Michael Robinson UCSB Geography

2. Question Do homogeneous and heterogeneous fishing fleets produce different catches? If so, what is the impact?

3. Goal Understand the role of fisherman effort and catch heterogeneity on total fleet catch, average catch, and stock size.

4. Relating catch to… Total Dives Total Hours Average Divers Average Hrs/Trip 1998 DFG Red Sea Urchin logbook data Each dot represents the yearly effort of one diver/boat

5. Frame Schaeffer model Focus on C = qEB –q = efficiency = biomass removed (L) ÷ stock biomass (B) –E = effort = % season fished = days fished ÷ days in season

6. Frame Schaeffer model Focus on C = qEB –q = efficiency = biomass removed (L) ÷ stock biomass (B) –E = effort = % season fished = days fished ÷ days in season

7. Frame Let N = fleet size (e.g. number of boats) and assume fleet composition does not change over time.

8. Frame Homogeneous fleet catch Heterogeneous fleet catch

9. Experiment Create fishing fleets with and without heterogeneity (effort and catch). Compare total fleet catch, average catch, and stock biomass.

10. Experiment Homogeneous case Heterogeneous case Heterogeneity may be an issue if

11. Experiment Homogeneous case Heterogeneous case Heterogeneity is an issue if

12. Experiment Define where Then FLEET AVERAGE EACH FISHERMAN’S ANOMALY 0 0

13. Results Year Fleet Size N Season Length Avg Catch L bar Average DivesNL bar E bar Σl' i e' i (LE) bar = ΣL i E i % increase 199812923929,79226.88432,293630,2731,062,56659.32 199911823944,89641.04909,752706,4631,616,21643.71 200011424027,82327.36361,583310,365671,94846.19 20019124026,20427.41271,177263,661534,83949.30 20028324141,49537.45535,127399,202934,32942.73 20038224057,84243.57861,126528,9021,390,02938.05 20048225675,30246.801,128,946683,6861,812,63337.72 20057925576,33742.411,002,853598,7831,601,63637.39 avg =9724447,46136.62687,857515,1671,203,02444.30 stdev =20720,3848.20325,523170,742471,5717.44

14. Results Year Fleet Size N Season Length Avg Catch L bar Average Dives% increase 199812923929,79226.88432,293630,2731,062,56659.32 199911823944,89641.04909,752706,4631,616,21643.71 200011424027,82327.36361,583310,365671,94846.19 20019124026,20427.41271,177263,661534,83949.30 20028324141,49537.45535,127399,202934,32942.73 20038224057,84243.57861,126528,9021,390,02938.05 20048225675,30246.801,128,946683,6861,812,63337.72 20057925576,33742.411,002,853598,7831,601,63637.39 avg =9724447,46136.62687,857515,1671,203,02444.30 stdev =20720,3848.20325,523170,742471,5717.44

15. Results Year Fleet Size N Season Length Avg Catch L bar Average Dives% increase 199812923929,79226.88432,293630,2731,062,56659.32 199911823944,89641.04909,752706,4631,616,21643.71 200011424027,82327.36361,583310,365671,94846.19 20019124026,20427.41271,177263,661534,83949.30 20028324141,49537.45535,127399,202934,32942.73 20038224057,84243.57861,126528,9021,390,02938.05 20048225675,30246.801,128,946683,6861,812,63337.72 20057925576,33742.411,002,853598,7831,601,63637.39 avg =9724447,46136.62687,857515,1671,203,02444.30 stdev =20720,3848.20325,523170,742471,5717.44

16. Anomalies 19982005

17. Discussion Strong correlation between yearly effort and yearly catch Those who fish significantly more than average tend to catch significantly more than average The “low liners” do not balance the “high liners” Stock harvest models that use average values for effort and catch favor the “low liners” and could underestimate fishing impacts by ~44%

18. Questions Are more experienced fishermen those who catch more than average? Does fleet composition change over time? Others?