The Biology and Management of Rainbow trout in small BC lakes. Eric Parkinson BC Ministry of Environment

Transcription

1 The Biology and Management of Rainbow trout in small BC lakes Eric Parkinson BC Ministry of Environment

2 Small Lakes Fishery Hatchery and Wild Hundreds of Lakes A Diversity of Lakes

3 Canada Vancouver USA Lakes on British Columbia s Interior Plateau - ~5000 lakes - ~250,000 km2 (~ United Kingdom)

4 Outline The Biology of Rainbow Trout: Density dependent processes regulate population density and size structure The Dynamics of Angler Effort Anglers move to lakes with the best fishing Managing the Fishery: What does management consist of? Quantitative analysis of management options Application to a management problem

5 Adult Migrants 2-4 years Rainbow Trout Biology 0-2 years Juvenile Migrants

6 Variation in habitat characteristics results in large differences in trout density among lakes Surprise Hardcastle Grassy Fly Sock Little Bear Johnson Hunka Frank Fourpound Fish Donna Coffee Avola Slager Phyllis Patricia Montigny Misery Laurel Ejas Corsica Buck Arrowhead Stoney Snag Siam Renee Lorenzo James' Heidi Heather Elk Island Edney Dewey (Mom's) Christina Belcache Gillnet Catch Rate (fish/net-night)

7 umber of Lakes An example of variation in Habitat Quality: e.g. Dissolved nutrients in 1294 BC lakes Oligotrophic = Low capacity to support fish Mesotrophic Eutrophic = High Capacity to support fish >600 Total Dissolved Solids (ppm)

8 Research Objective: Predict the response of the population to variation in harvest rates and habitat quality Lots of life history info growth rates, maturity schedules, fecundity, migration size and timing, diet, physiology etc. Stream Processes are well understood Density dependent processes food, space, territories Density independent processes habitat quality (e.g. silt, LWD, temperature) Lake processes are poorly understood few experimental manipulations little survival information

9 Research Methods Whole lake experiments manipulated density and age structure Sampling populations by gillnets depletion estimate of population size growth rates activity and space use patterns Diet/food zooplankton, benthos Tethering predation risk in time and space Snorkel observations behavior, space use

10 CPH4 CPH3 CPH2 Crater Lake CPH1 4.1 ha 20m Alleyne Lake

11 Why does survival and growth change with density? Density Mortality - Predation - Cannibalism Competition Exploitation -lower food Interference -aggression Time in vulnerable size classes Growth Risk Behavior -activity level, foraging location Physiology -energy allocation Fecundity

12 Growth Rate (%/day) Growth rate varies with density R 2 = , ,000 Rainbow Trout Density (cm2/ha)

13 Mortality Rate (%/day) 1. Higher growth is associated with lower mortality 2. Small fish grow faster but have higher overall mortality 4% 3% 0.2 g 6 g 11 g 20 g 2% 1% Big Fish Small Fish 0% Growth rate(%/day)

14 Growth Rate (%/day) Mortality Rate (%/day) Density Density Dependent Processes Competition Exploitation -lower food Interference -aggression R 2 = , ,000 Rainbow Trout Density (cm2/ha) 4% 3% 2% Time in vulnerable size classes 1% 0% Growth 0.2 g 6 g 11 g 20 g Mortality - Predation - Cannibalism Risk Behavior -activity level, foraging location Physiology -energy allocation Fecundity Growth rate(%/day)

15 Weight at Age-2 (g) Growth rate variation produces an order of magnitude range in weight 200 small eggs 1500 big eggs R 2 = , ,000 Rainbow Trout Density (cm2/ha)

16 We now have lots of quantitative information on population regulation in rainbow trout Both growth and mortality are strongly related to density Competition reduces growth food resources are depleted at high density behavioral interference restricts the use of space by small fish Smaller fish experience higher mortality links growth conditions to mortality rates Mortality risk increases with density Females carry fewer eggs at high densities small changes in growth rate produce large changes in adult size and fecundity

17 Growth Rate (%/day) Mortality Rate (%/day) Catchability (proportion/ angler-hour) What are the management questions? - How many fish and what size fish to stock? - What are sustainable effort levels on wild stocks? - Which stocks are most at risk? How do we translate our scientific knowledge into answers? R 2 = % 3% Initial Size 0.2 g 6 g 11 g 20 g % , ,000 Rainbow Trout Density (cm2/ha) 1% 0% Growth rate(%/day) Length (cm)

18 Outline The Biology of Rainbow Trout: Density dependent processes regulate population density and size structure The Dynamics of Angler Effort Anglers move to lakes with the best fishing Managing the Fishery: What does management consist of? Quantitative analysis of management options Application to a management problem

19 The Economics and Biology of Harvest Simple decisions based on economics Harvesters try to achieve the greatest returns for their effort They prefer: Higher densities Easy access to the resource (low harvest cost) More valuable individuals (i.e. bigger) and species (e.g. salmon) Most animal predators are thought to behave in a similar manner (Ideal Free Distribution Theory) Under what circumstances does harvest result in population collapse

20 umber of Lakes Oligotrophic = Low capacity to support fish Mesotrophic Eutrophic = High Capacity Dissolved utrients >600 Total Dissolved Solids (ppm) atural densities and sizes of trout vary from lake to lake

21 Recruits In Stock Recruitment theory, both capacity and maximum reproductive rate can increase with habitat quality Eutrophic Mesotrophic Oligotrophic Increasing fish capacity e.g. higher dissolved utrients Spawners Higher Reproductive Rate e.g. better spawning habitat Better habitat results in higher densities and/or larger fish in unharvested populations

22 Recruits The response to harvest also varies with habitat quality Harvested Equilibriums UnHarvested Equilibriums Populations in Poor quality habitat can be driven to extinction Spawners

23 The Economics and Biology of Harvest Simple decisions based on economics Harvesters try to achieve the greatest returns for their effort They prefer: Higher densities Easy access to the resource (low harvest cost) More valuable individuals (i.e. bigger) and species (e.g. salmon) Most animal predators are thought to behave in a similar manner (Ideal Free Distribution Theory) Under what circumstances does harvest result in population collapse

24 ow think about angler behavior: Anglers will move to where they can get the most, biggest fish for the least cost

25 Density of anglers is higher on lakes that are closer to big cities S S S S S S S S S S S S S S S S S S S S S S SS S S S S S S S S S S S S S S S S S S SS S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S SS S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S SS S S S S SS S 0-5 ang days per ha >100

26 CPUE (fish/angler day) Patterns in angling Quality - Lakes within a region have similar angling quality - Lakes farther from Vancouver have better quality angling - How much better was pristine angling quality?? > 6 hr Unfished Lakes <6 hr Travel time to Remote lakes Vancouver ear Vancouver Possible equilibriums Angling quality data from 52 lakes Length in Creel (cm)

27 Optimal fish densities are a function of biological parameters But actual fish densities are driven by the micro economics of angler harvest Fish density is often depressed by excessive effort on easily accessible lakes This problem is most severe on: - Populations in good habitat - Large, long-lived species

28 The economics and biology of harvest Simple Economics Harvesters try to achieve the greatest returns for their effort They prefer: Higher densities Easy access to the resource (low harvest cost) More valuable individuals (i.e. bigger) and species (e.g. salmon) The biological determinants of density Better quality habitat results in higher densities Under what circumstances does harvest result in population collapse? Species and stocks that are: Closer to home Preferred by fishers In better quality habitat This is not what you might expect

29 Outline The Biology of Rainbow Trout: Density dependent processes regulate population density and size structure The Dynamics of Angler Effort Anglers move to lakes with the best fishing Managing the Fishery: What does management consist of? Quantitative analysis of management options Application to a management problem

30 The Management Process Key Issues Conserving wild populations Maintaining optimal populations for anglers The solutions Lots of options but will any of them work The Role of Research Quantitative Assessment of Options

31 Catch Rate Fish Density Fish Density declines with more effort Angler Effort Maximum Angler Effort

32 So what can we do about this? Policy Options include: a variety of regulations restricting angler access habitat enhancement and protection a range of stocking strategies

33 Angler Effort (days/ha) Mortality Rate (%/day) e.g. Ecological Data 4% 3% 2% 1% Initial Size 0.2 g 6 g 11 g 20 g A variety of data is available to make predictions 0% Growth rate(%/day) e.g. Map-based data Time to Vancouver < 6 hrs > 6 hrs 0 Road 4X4 Road Walk Air Access Type

34 Prediction The Traditional Approach Fish Biology Mix of Client Groups Angler Behavior Angler Preferences? ETC. Decide on the Best Policy

35 Angler Effort Angling Quality PREDICTIO :QUATITATIVE ASSESSMET Think of this as a complex bookkeeping exercise Research Data on Fish Biology Angler Response to Angling Quality Client Breakdown from questionnaires ETC. Computer Model Evaluation ote hand broken in bar fight Option 1 Option 2 Time Option 1 Option 2

36 On hatchery lakes, in order to produce lots of angling effort at a minimum cost you need to stock the right number and sizes of fish. Fish*ha -1 released Angling Effort/ha Size at release (cm) Stocking Cost/Angler day $5 $20 $100

37 Yield (kg/ha) % Return to Creel ang.days/ha OTHER USEFUL IDICATORS e.g. Return rate of stocked fish, Yield Stocking Rate ang.days/ha Stocking Rate

38 Inputs and Outcomes of the Management Cycle Assessment of Client (and Potential Client) Base - Patterns of market segmentation - Preferences of market segments Science-Based Resource Assessment Capability/Suitability/Habitat Supply Model Collect Assessment Data on: Fishery, Fish Populations, Habitat Socio-economic Goals & Performance Measures - License Sales, angler days Management Implementation Regulations, Stocking, Habitat protection and enhancement Conservation Goals & Performance Measures - Healthy Wild stocks, refugia for non-game species Client-focused Recreation -Angling Effort and Catch -Angling Quality -Angler Satisfaction Benefits on-consumptive Use Conservation/Refugia Interpretive Centers Wildlife Viewing

39 Using information to make better resource management decisions PUBLISHED LITERATURE DIRECTED RESEARCH LOCAL EXPERIECE MODEL (POLICY OPTIOS) LAKE SPECIFIC DATABASES LAKE SPECIFIC DATA COLLECTIO MAAGEMET POLICY DECISIO

40 Outline The Biology of Rainbow Trout: Density dependent processes regulate population density and size structure The Dynamics of Angler Effort Anglers move to lakes with the best fishing Managing the Fishery: What does management consist of? Quantitative analysis of management options Application to a management problem Should we stock more lakes?

41 Do the benefits of stocking fishless lakes outweigh the loss of biodiversity? Proposed stocking in Fishless lakes

42 The big lakes are > 600km from Vancouver These lakes would generate high quality but low effort fisheries with a high stocking cost/angler day Lakes close to Vancouver add a very small increment to current opportunities Size of Fishless lakes

43 Don t stock new lakes Big lakes in Homathko drainage stand out as being very unusual fishless lakes Optimize management on currently stocked lakes Currently stocked lakes

44 Currently: Where are we going? Managers require expert assistance to do comparisons of policy alternatives Simulation model works well for stocked lakes Multi-lake model gives reasonable estimates of effort density and angling quality Future Directions: Extend the biology : to include stream limitations dual species situations across a productivity gradient