“Effects of Fishing on the Sensitivity of Fisheries to Climate Variability”
Truncation of age structure.
juvenation (younger population), maternal effects (first-year breeders are poor), genetic selection, ability to track environment (vs smoothing – averaging over longer times).
Outline:
Empirical evidence for increased variability, model explanations
Story begins with Hsieh, et al 2006. Long time series, increasing fluctuations. (Hsieh et. al. 2006)
Anderson et al no age structure model (Anderson et. al. 2008). Imagine waht age structure would do. Mortality rate as noise (funny, since it’s not so variable). Assumed increase r leads to instability.
Shelton and Mangel (2011) Shelton & Mangel, 2011. some age structure, same dome-shaped Ricker for recruitment. Conclude noise necessary for variability – it’s not in intrinsic oscillations (large r/chaotic).
Cohort resonance
Starts with (BJORNSTAD et. al. 2004).
Leslie matrix (i.e. linear), except with Beverton-Holt in recruitment. Intersection of 1/LEP with stock-recruitment curve is the equilibrium.
Lou’s work (Worden et. al. 2010) finds: Resonance increases with fishing. Random growth rate drives resonance more strongly than survival.
Mechanisms governing increasing sensitivity with fishing
Drive this system with white noise, introduces variability on a low-frequency trend. Easily mistake these long-term trends for climate change effects?
Different signals in different measurements:
Implications for science, management
Scientific conclusions
It’s not Environment -> Catch.
It’s Environment -> Growth & Survival -> Recruitment. Egg Production. Catch
Use not just variance, but the spectrum.
Management
Current Magnuson Act calls for explicit estimates in uncertainty and precaution scaling with uncertainty.
stage structured lumping loses many of the fluctuations.
References
Hsieh C, Reiss C, Hunter J, Beddington J, May R and Sugihara G (2006). “Fishing Elevates Variability in The Abundance of Exploited Species.” Nature, 443. ISSN 0028-0836, https://dx.doi.org/10.1038/nature05232.
Anderson C, Hsieh C, Sandin S, Hewitt R, Hollowed A, Beddington J, May R and Sugihara G (2008). “Why Fishing Magnifies Fluctuations in Fish Abundance.” Nature, 452. ISSN 0028-0836, https://dx.doi.org/10.1038/nature06851.
BJORNSTAD O, NISBET R and FROMENTIN J (2004). “Trends And Cohort Resonant Effects in Age-Structured Populations.” Journal of Animal Ecology, 73. ISSN 0021-8790, https://dx.doi.org/10.1111/j.0021-8790.2004.00888.x.
Worden L, Botsford L, Hastings A and Holland M (2010). “Frequency Responses of Age-Structured Populations: Pacific Salmon as an Example.” Theoretical Population Biology, 78. ISSN 00405809, https://dx.doi.org/10.1016/j.tpb.2010.07.004.
Fluctuations of Fish Populations And The Magnifying Effects of Fishing, A. O. Shelton, M. Mangel, (2011) Proceedings of The National Academy of Sciences, 108 10.1073/pnas.1100334108