Loo Botsford, CPB seminar

“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