On September 7^th we met with Mobrand Biometrics to receive a report on their initial application of Ecosystem Diagnosis and Treatment (EDT) to Puget Sound chinook stocks[1]. We are meeting again on October 4^th to review these results and determine if this method will be useful to us in developing interim recovery goals. In the meantime, we are to look over the EDT results to see if they make sense in terms of what we know from other sources.

Here I present a comparison of the values presented for productivity and capacity for the North Fork Stillaguamish summer chinook stock to see how close they came to other information available for this system. I think that this sort of information assembled for a few different stocks ahead of time will facilitate a productive discussion on the 4^th.

Previously I developed estimates of adult equivalent exploitation rates and adult equivalent recruitment of North Fork Stillaguamish chinook for eight brood years, 1986-1993. These were based on escapement surveys conducted by the Stillaguamish Tribe and WDFW and recoveries of coded-wire tags from the Stillaguamish Tribe’s indicator stock program.[2] The relevant results are in the following table:

North Fork Stillaguamish chinook
	Original	Subsequent	Expl.	AEQ	Recruits/
Br. Yr.	Escapement	Escapement	Rate	Recrut.	Spawner
1986	980	505	0.6647	1,506	1.54
1987	1,065	695	0.4562	1,278	1.20
1988	516	654	0.6429	1,831	3.55
1989	510	458	0.8199	2,543	4.99
1990	575	488	0.6651	1,457	2.53
1991	1,331	486	0.5330	1,041	0.78
1992	466	596	0.3789	960	2.06
1993	563	585	0.4978	1,165	2.07

In the above, the “original escapement” includes all chinook spawning naturally in the North Fork Stillaguamish, while the “subsequent escapement” includes the naturally-produced fish from the give brood year returning to spawn in the North Fork Stillaguamish. The estimate of AEQ recruits is this “subsequent escapement” value divided by (1 – the exploitation rate). Thus, this short data set allows us to look at the relationship between natural spawning escapement and subsequent recruits produced by those spawners.

The EDT analysis resulted in estimates of parameters of spawner-recruit relationships. In particular, estimates of recruits per spawner at low density (productivity) and adult capacity were provided. I used these to derive parameters of Beverton-Holt and Ricker spawner-recruit functions, where:

R = S / (aS + b) [Beverton-Holt]

R = dS e^-^gS [Ricker]

In the above, S is original spawners, R is subsequent recruits, and a, b, d, and e are parameters derived from the EDT analysis. For each of the EDT runs, estimates of maximum adult capacity (C) and low-density productivity (P) were provided. These can be used to compute the parameters of the spawner-recruit models as follows[3]:

a = 1/C

b = 1/P

d = P

g = P / (Ce)

There were several analyses presented in the EDT results. The validation analysis looked at current habitat conditions and assumed a constant exploitation rate of 0.35 and a loss of genetic fitness based on current conditions. The current conditions analysis used current habitat conditions. The PFC analysis used a set of habitat conditions in freshwater that conform to the “properly functioning conditions” defined by NMFS. The historic potential analysis used an assumption of undisturbed historic habitat conditions.

The following table shows the productivity and capacity estimates from EDT, along with the corresponding estimates of the parameters of the spawner-recruit models.

EDT Run

Parameter

Validation

Current

PFC

Historic

C

900

1,600

20,100

28,200

The following are computed from the above.

0.0011111

0.000625

0.00004975

0.0000355

0.1666667

0.1

0.05882353

0.043478

0.002453

0.002299

0.000311

0.0003

The following figure shows the two spawner-recruit curves from the validation run compared with the observed values for spawning escapement (of natural origin fish).

In the above, the diamonds represent the observed values for the 8 brood years looked at, while the curves represents the Beverton-Holt and Ricker relationships as parameterized according to the validation analysis.

The following figure compares the observed relationship of recruits to spawners with the two spawner-recruit functions based on the parameters from the current conditions analysis.

Again, the diamonds represent values computed for the 8 brood years examined, only, in this case the y-axis represents total adult equivalent recruitment rather than escapement of natural origin spawners.

Finally, in order to be able to visualize the difference between “current conditions”, “PFC”, and “historic” conditions, I graphed the spawner-recruit curves implied by each of these EDT runs.

The following graph compares the Beverton-Holt curves implied by the three runs (along with the 8 observed values).

The following graph compares the Ricker curves implied by the three runs (again, with the 8 observed values included).

Clearly the PFC and Historic EDT runs indicate much higher potential production of chinook from this system than we have observed in recent years. There is little data available to help answer the important question of whether these much higher production levels have ever been observed or are even theoretically possible. However, information provided in the technical background document for a Stillaguamish chinook recovery plan[4] suggests that historic terminal area harvest levels for Stillaguamish chinook may have been in the range of 10,000 – 20,000.

Rather than discussion any of my own conclusions at this time, I will leave you with all of the above information from which you can draw your own conclusions. Actually, I hope that, before October 4^th, we will have a number of comparisons like this to look at and that we can draw more general conclusions about the applicability of EDT to the development of chinook recovery goals by the comanagers,

[1] Preliminary Assessment of Recovery Objectives based on Properly Fiunctioning Habitat Conditions. Submitted to WDFW and NWIFC by Mobrand Biometrics, September 2000.

[2] See Stillaguamish Summer Chinook:Productivity Estimates from Coded-Wire Tag Recoveries and A Simple Model for Setting Interim Exploitation Rate Objectives, Kit Rawson, May 17, 2000, for more details.

[3] See Ricker, W E. 1975. Computation and interpretation of biological statistics of fish populations. Appendix III.