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Popula'on dynamics of Arc'c cod in the US Chukchi Sea Jennifer M. Marsh, Franz J. Mueter and Terrance J. Quinn II University of Alaska Fairbanks, Juneau Center, School of Fisheries and Ocean Sciences, Juneau, AK 99801, jmmarsh@alaska.edu
Age-­‐0 w Na,t = number of females of age a at the start of year t Sa = survival fracCon at age a fa = net fecundity at age a Simulated abundance at age, assuming Lorenzen Mw 2.  Catch Curve Analysis (Quinn & Deriso 1999) = 1.28 10 y = -­‐1.28x + 8.90 8 R² = 0.98 6 4 2 0 0 1 2 3 4 5 6 Age 3.  Weight varying mortality Mw for marine fishes (Lorenzen 1996) Ages Mw log10(No. nmi-­‐2 + 1) Size & Age Composi'on Age ComposiCon (1+) 1 2 3 4 5 6+ 68% 26% 4% 1% 1% 1% Age composiCon was esCmated using age_slicing funcCon in the R package ALKr (Kell & Kell 2011) , the adjusted length frequency data, & von Bertalanffy growth parameters (Helser). 1 2 3 4 5 6+ 2.1 1.6 1.4 1.3 1.2 1.1 •  Slight decline in each age-­‐class over the 10 year period. Values for Arc'c cod in the Barents Sea based on Nahrgang et al. (2014) 40000 1 0.8 0.6 0.4 0.2 0 30000 20000 10000 0 2 3 4 5 6 Age (years) 7 •  = esCmated S0 (0.00033) •  = equilibrium S0 (0.00038) Summary and Conclusions • 
• 
Model Parameters: Fecundity 1 Sensi'vity of popula'on growth rate to variable S0 • 
W = wet weight (g); L = total length(mm) 0 PopulaCon growth rate 108% 30% -­‐6.5% Age-­‐class 8 Frac'on Mature Alaska
9 2012 2013 8 7 6
5 4 3 2 1 0 80 Billion 276.7 Billion (Alex de RoberCs) Observed length frequency distribuCon from the Eastern boMom trawl and the adjusted values based on net selecCvity. f3 Mortality assumpCon Hoenig M Catch Curve M Lorenzen Mw Natural mortality rate (Ma) es'mates: 1.  Longevity dependent (Hoenig 1983) = 0.47 (max age = 9) # of Eggs/Fish 3.3 Billion (area swept) f2 Age-­‐3+ Arc'c cod 72°0'0"N
70°0'0"N
68°0'0"N
66°0'0"N
75001 - 150000
Age-­‐2 S3+ Acous'c Survey: Age-­‐0 Es'mates 10001 - 75000
S2 Model Parameters: Survival Es'mates New Data from 2012 & 2013 Surveys: Abundance Es'mates 5001 - 10000
S1 *Age-­‐classes 1 – 6+ were used for ArcCc cod models. 1.  Construct a simple Leslie Matrix model with updated life history parameters and recent survey data, in order to beMer understand the populaCon dynamics of ArcCc cod in the US Chukchi Sea. 2.  Assess model sensiCvity to natural mortality and early life survival. 170°0'0"W 165°0'0"W 160°0'0"W
Age-­‐1 f1 Objec'ves Bo^om Trawl (2012 only): Age-­‐1+ S0 Simulated popula'on trajectories under different mortality assump'ons Ln(Catch-­‐at-­‐age) Currently, commercial fishing is prohibited in the US ArcCc due to insufficient data to assess the sustainability of potenCal fisheries. In the 2009 ArcCc Fisheries Management Plan (FMP) by the North Pacific Fishery Management Council, ArcCc cod (Boreogadus saida) was idenCfied as one of three potenCal target species. A preliminary assessment of ArcCc cod was completed for the ArcCc FMP based on boMom trawl surveys that occurred in 1990 and 1991 in the northeastern Chukchi Sea. CPUE (#/km^2)
E 0
1 - 1000
1001 - 5000
Preliminary Model Results Leslie Matrix Popula'on Model Introduc'on Net Fecundity Gross Fecundity Maturity 9 • 
• 
Given assumpCons about fecundity, maturity and age composiCon, Hoenig's M produced unrealisCc dynamics, whereas Lorenzen's Mw produced esCmates most consistent with a stable populaCon. Model esCmates are broadly consistent with observed numbers of age-­‐0 fish, possibly suggesCng a self-­‐sustaining populaCon in the Chukchi Sea. The relaCvely high values of mortality esCmated from Catch Curve analysis and weight are plausible given ArcCc cod’s ecological role as main prey for many seabirds and marine mammals. Overall, the Leslie Matrix model was a convenient tool for synthesizing informaCon on this data poor stock. Future work will incorporate adjustments for acousCc surveys. Acknowledgements Many thanks to the scienCfic teams, crews and captains of the F/V Alaskan Knight and the F/V Bristol Explorer. BoMom trawl informaCon was provided by Robert Lauth, growth parameters by Tom Helser, acousCc survey age-­‐0 esCmates by Alex de RoberCs. This work is funded through the Bureau of Ocean Energy Management and the Coastal Impact Assistance Program. Also, thanks to Alaska Sea Grant for travel funds Model Parameters: Survival at Age-­‐0 References: S0 = survival fracCon at age-­‐0 N1’ = abundance esCmate of age-­‐1 cod from the boMom trawl survey fa = net fecundity at age a Hoenig JM (1983) Empirical use of longevity data to esCmate mortality rates. Fishery BulleCn 82:898–903 Kell L., Kell, A (2011). A comparison of age slicing and staCsCcal age esCmaCon for mediterranean swordfish (Xiphias gladius). Collect. Vol. Sci. Pap. ICCAT. 66/4, 1522-­‐1534 Lorenzen K (1996) The relaConship between body weight and natural mortality in juvenile and adult fish: a comparison of natural ecosystems and aquaculture. :1–21 Nahrgang J, Varpe Ø, Korshunova E, Murzina S, Hallanger IG, Vieweg I, Berge J (2014) Gender Specific ReproducCve Strategies of an ArcCc Key Species (Boreogadus saida) and ImplicaCons of Climate Change. PLoSONE 9:e98452 Quinn TJ II, Deriso RB (1999) QuanCtaCve Fish Dynamics. Oxford University Press. New York, NY. pp 542.