Evaluating assessment programs for humpback 

chub in the Grand Canyon

Background 

- Glenn Canyon dam completed in 1964.

- Humpback chub were listed on the federal list of endangered species in 1967.

- Monitoring program based on mark-recapture methods.

- Complicated life-history ontogeny & movement between CR and LCR.

1

Tuesday, November 2, 2010
Age-Structured Mark-Recapture analysis (ASMR, Coggins et al. 2006)

• A combination of VPA and SCA methods to jointly estimate abundance and agespecific capture probabilities.

• VPA to reconstruct untagged population

• SCA to predicted fate of tagged individuals

• Assumptions include:

 - M is known

 - no aging error

• Historical estimates of abundance are extremely precise; so what is the 

problem?

Method used to assess chub abundance

2

Tuesday, November 2, 2010
Expensive monitoring programs for HBC, or glorified rafting trips for 

biologists?

Tuesday, November 2, 2010
Overarching project objective

• Examine how estimates of uncertainty in HBC abundance would change if 

monitoring efforts were reduced such that capture probabilities were reduced 

by as much as 50% over the current levels.

• Two steps to achieve this objective:

1. Use historical sampling data to establish appropriate spatial and temporal 

sampling coverage that is consistent with the current program.

2. Develop an IBM model to simulate mark-recapture data from reduced 

sampling efforts to quantify changes in estimates of uncertainty. 

4

Tuesday, November 2, 2010
Scenarios

• Scenario 1 represents the base line scenario where all available records between 1989 and 2009 

are used to construct the ASMR input file.

• Scenario 2 all September and October USFWS records have been removed (i.e., no fall sampling).

• Scenario 3 all September USFWS records have been removed.

• Scenario 4 all October USFWS records have been removed.

• Scenario 5 all lower 1200 records have been removed.

• Scenario 6 all April or first sampling trips of the spring have been removed, second trip or May 

trips have not been excluded.

• Scenario 7 all USFWS lower 5 km samples have been removed from the spring sampling periods 

(lower 1200 spring trips have not been excluded).

5

Tuesday, November 2, 2010
Estimates of adult abundance

6

1

1

1

1

1 1

1

1

1

1 1 1 1 1 1

1 1

1

1

1 1

1990 1995 2000 2005

4

6

8 10

Year

Adults (1000s age 4+)

2

2

2

2

2 2

2

2

2

2

2 2 2 2 2 2 2 2

2

2 2

3

3

3

3

3 3

3

3

3

3 3 3 3 3 3

3 3

3

3

3 3

4

4

4

4

4 4

4

4

4

4 4 4 4 4 4

4 4

4

4

4 4

5

5

5

5

5 5

5

5

5

5 5 5 5 5 5

5 5

5

5

5 5

6

6

6

6

6 6

6

6

6

6 6 6 6 6 6

6 6

6

6

6 6

7

7

7

7

7 7

7

7

7

7

7

7 7

7 7 7 7 7 7 7 7

Tuesday, November 2, 2010
Estimates of age-2 recruits

7

1 1 1

1 1

1

1

1 1

1

1 1

1

1

1

1

1

1

1

1990 1995 2000 2005

1

2

3

4

Year

Age-2 recruits (1000s)

2 2 2

2 2

2

2

2 2

2

2 2 2

2 2

2 2

2

2

3 3 3

3 3

3

3

3 3

3

3 3 3

3

3

3

3

3

3

4 4 4

4 4

4

4

4 4

4

4 4

4

4

4

4

4

4

4

5 5

5

5 5

5

5

5 5 5

5 5

5

5

5

5

5

5

5

6 6 6

6 6

6

6

6 6

6

6 6

6

6

6

6

6

6

6

7 7 7 7 7

7

7

7 7 7

7 7 7 7 7

7

7

7 7

Tuesday, November 2, 2010
Summary

8

• Historical data suggests non-random sampling is occurring:

• Status quo: current population is at 78% of its 1989 abundance.

• Temporal patterns: omit fall sampling, 57% depletion level.

• Spatial patterns: omit lower 5km, 32% depletion level.

• Future changes (spatial or temporal) in sampling effort are likely to result in biased 

estimates of abundance.

• Reduced sampling frequency (e.g., every other year) may provide unbiased but less 

precise estimates of abundance.

Tuesday, November 2, 2010