Using CWT’s to assess survival, ocean distribution and maturation for Chinook stocks across the Pacific Northwest: Are there any predictive capabilities to assess year to year variation, and build them into our assessment tools Rishi Sharma, QERM Dr. Bob Francis & Dr.Nate Mantua School of Fisheries and Aquatic Sciences, University of Washington, Seattle, WA 98195
Primary Objectives • Does the ocean affect survival, distribution, and maturation rates of different stocks in the Northwest in a yearly and/or a longer time scale oscillation? • Do certain stocks in the Northwest cluster in terms of the above mentioned dynamics? • Are there any predictive capabilities to assess this year to year (or decadal) variation and can we use those to improve our preseason management capabilities ? • Do implicit assumptions of fixed ocean distribution, and maturation based on CWT’s effect our management capability ?
Overview of the data and methods • History of the CWT Indicator stock program for Chinook management • Stocks represented • Methods used • Illustrate methods with the URBS, Lower Fraser or Harrison, and Salmon River Indicator tag codes. • General outline of hypotheses and possible ocean data selection. • Using CWT’s to estimate natural production: A statistical catch at age analysis for Chinook
History of the Indicator Tag Program • 36 indicator stocks are used by the Chinook Technical Committee (CTC) for ocean distribution. • For 14 of these stocks escapement data not good enough for use by the CTC in the Exploitation Rate Analysis (ERA) for ocean fisheries. • 22 stocks used by the CTC to assess ocean impacts, and estimate an index to survival, maturation, distribution and Adult Equivalence rates. • Some of these estimates are then used in the Cohort Model used by the Pacific Salmon Commission for setting catch quotas based on ocean abundance forecasts.
Parameters estimated with CWT’s • Age 2 cohort size and an index of survival • Maturation rates by age • ocean distribution • exploitation rates
Stocks that data was compiled for • Columbia Upriver Bright Fall stock • Chilliwack or the Lower Fraser Harrison River Fall stock • Oregon coastal Fall stocks
Ocean Distributions and Exploitation rates Salmon River, OR Lower Fraser (Harrison BC) Columbia Upriver Brights, WA
Methods used to estimate survival and maturation Where: O is the ocean cohort at age a, OC, TC and E are the ocean catch, terminal catch and escapement at age a, NM is natural mortality at age a MR is the maturity rate at age a, and S is an index of survival
assuming effort is constant (100,000 fish recovered), and you adjust the recovery for Survival (S), i.e. in years of low survival you would adjust the recovery to a higher amount and vice versa in a year of increased survival, and have no effect at
Frame hypothesis around these patterns • Ocean Conditions affect survival of Chinook in the North Pacific. • Ocean Conditions affect Maturation Rates on a year to year (or decadal) basis for Chinook salmon. • Ocean currents and conditions affect distributions of Chinook in the North Pacific.
Data for ocean indicators Figures A and B are the Pacific Decadal Oscillation (PDO) Figures C and D are the Artic Oscillation (AO) Figures E and F are the Aleutian Low Pressure Index (ALPI). Regime shifts occur in 1925, 1947, 1977, 1989 and 1998 (Minobe 1997, Mantua et. al (1998) and Mantua and Hare (2000)
Can we use CWT’s to estimate Natural production for a system Ocean Terminal Area Where: N(a,t) is the population age a in the ocean at time t, and N(a,t)T is the population in terminal areas M is natural mortality for age a PM(a,t) is the proportion mature at age a and time t, q(o) and q(T) is the catchability coefficient in the ocean and terminal areas respectively, V is the vulnerability and F is the fishing Mortality