1. Seasonal and Interannual Variability of Peruvian anchovy Population Dynamics --progress report-- Yi Xu and Fei Chai June 2007

2. Key Questions  What are the key environmental factors regulate Peruvian anchovy growth dynamics? How do these factors vary on seasonal, interannual, and decadal time scale?  How do physical and biological conditions affect Peruvian anchovy recruitment and natural mortality?  What is the role of ocean current in controlling Peruvian anchovy larvae distribution and their growth dynamics? How do El Nino events affect larvae and adult distribution?  What is the impact of Peruvian anchovy on plankton biomass and productivity?  How can we use the model to evaluate and compare natural and fishing mortality of Peruvian anchovy?

3. Methods The Circulation Model: Regional Ocean Model System (ROMS) The Biogeochemical Model: Carbon, Nitrogen Silicate Ecosystem (CoSINE) The Fish Model: Individual Based Model(IBM)

4. Anchovy Life History Chart MATURE-SENILE LIFE SPAN ~3 YEARS PREDATE BY SEA BIRDS, MARINE MAMMALS AND OTHER FISHES LENGTH: ~20CM WEIGHT: ~55 gm OPTIMUM TEMP: 18.6°C SPAWN ~20 TIMES/Y EGGS YOLK-SAC LARVAE JUVENILE AGE-1 YOY AGE-3&3+ LIFE CYCLE OF PERUVIAN ANCHOVY (Engraulis ringens) OVAL EGG LENGTH: 1.72-2.25MM DURATION: 24 HOURS TEMPERATURE SENSITIVE NO SWIMMING ABILITY MORTALITY RATE>99% LENGTH: 46-100MM SMALL JUVENILE PREFER ZOOPLANKTON WHEN >80MM PREFER PHYTOPLANKTON LENGTH: 2.5-4.0MM FEED BY YOLK NO EXTERNAL FEEDING DURATION: 24-28 HOURS TEMPERATURE SENSITIVE SMALL SWIMMING ABILITY BECOME SEXUAL MATRUE READY TO SPAWN LENGTH: >~10CM FEED BY PHYTOPLANKTON AND ZOOPLANKTON FEED 3 TIMES A DAY START FROM FIRST FEEDING (~4.5DAYS) LENGTH: 4--46MM (AVE.30, POST LARVAE 30-50MM) MORTALITY~50% AFTER 5 TH DAYS AND ~80% AT THE 8 TH DAY AFTER HATCHING 3-5MM LIKE FEEDING 5-12MM ~NO FEEDING >12MM FEEDING AGAIN DURATION: ~80 DAYS WHEN REACH 4.75CM, FISHERY RECRUITMENT STARTS COUNTING

5. IBM An Individual Based Model (IBM) is established for Peruvian Anchovy. Model the entire anchovy life history: spawning events, egg hatching, larva development, growth of juvenile and adults Based on conservation of energy (bioenergetics): growth=consumption-respiration-egestion-excretion Input: temperature and four plankton groups from ROMS-CoSiNE Output: anchovy growth (length and weight)

6. Major Results One Fish Anchovy growth curve Comparing with otolith data or ELEFAN I method etc, the bioenergetics model can provide a nice way the study the growth of the Peruvian anchovy.

7. mesozooplanktonRecruitment diatom Major Results One Fish There is a clear seasonal and interannual variability characterized by anchovy recruitment to 5cm. Strong El Nino Moderate El Nino Temperature diatom mesozooplankto n Recruitment

8. Major Results Multi Fish (Pauly, 1987) Start with different eggs distribution, anchovy recruitment shows a seasonality.

9. Recent Model Modification (past 12 months) Anchovy Life history (One Fish) Egg hatching and yolk-sac larva development Post larva, juvenile and adults bioenergetics equations Population dynamics (Multi Fish) Mortality & Survival 3-D Model Configuration Passive drift Swimming behavior randomness

10. 3-D Model Configuration Multi-Time Steps: Eggs & Yolk-sac Larva: hourly Post larva, juveniles and adults: daily Spatial Resolution: 12.5km horizontally Standard depth vertically

11. 3-D model results Passive drift Using 12.5km ROMS-CoSiNE monthly output

12. 3-D model results Swimming Assumptions 1.Fish is able to search a given round area, the radius is determined by swimming speed. 1 3 2

13. 3-D model results Swimming Assumptions 2.The new location is determined by the highest potential growth rate within the search area. 3. If there are more than one preferred place, then randomly choose one. 1 3 2

14. 3-D model results Swimming Results 0m Regular swimmer Fast swimmer

15. 3-D model results at depth of 50m Swim No Swim

16. Concluding Remarks One Fish bioenergetic model is tested to be a convincing method to study the Peruvian anchovy growth. The days to recruit shows an clear seasonal and interannual variability. Multi Fish Model studied the population dynamics of Peruvian anchovy. The model simulated results show that not only the growth pattern but also the numbers of survival anchovies has a clear seasonal and interannual variation. Sensitivity studies suggest both temperature and food supply play important roles to Peruvian anchovy growth and population dynamics. The combination of both changes may magnify the anchovy oscillation.

17. Concluding Remarks (continue) 3-D Model is on its way. Criteria for three major effects are established in the model: passive drift, swimming behavior, and randomness. Preliminary results show that the surface drift is very strong to vanish anchovies offshore. At depth, the offshore current is much weaker and anchovy has stronger retention to stay along the coast. Swimming behavior and random walk allow anchovy to search larger area and potentially find better places to grow and survive.

18. Future Study Seasonal and interannual 3-D El Nino & La Nina Finer resolution of dataset Fishing behavior & activity Online vs Offline Close life cycle Comparison Studies more …