1 / 21

Understanding Nekton Populations in Ecosystem Management

Explore the dynamics of fish populations in ecosystems, from defining populations to factors influencing abundance, harvesting methods, and predicting sustainable harvests. Learn about natural fluctuations, trophic interactions, and climate change impacts.

harmon
Télécharger la présentation

Understanding Nekton Populations in Ecosystem Management

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Demographic or ecosystem management?

  2. What is a “population” of a fish species? • How do we define “population”? • spatial component • reproductive component • in fisheries, “stock” is a synonym • Why do we want to know the size & distribution of populations? • What criteria can be applied to delimit populations of oceanic nekton?

  3. What do we need to know? • What influences nekton abundance? • Bottom-up influences • Intrinsic (physiological) influences • Top-down influences • How important are community-level interactions?

  4. Methods of Harvesting: Purse Seine

  5. Long-line fishing

  6. Halibut on long line

  7. Sport fishing – 900 lb tuna

  8. Ling cod

  9. Otter Trawl

  10. Why do nekton populations change? • Natural cycles • Trophic interactions (food, predators, disease) • Direct harvest • Habitat disruption • Climate change

  11. I. Natural fluctuations • Populations are not necessarily constant in the absence of human influence • Examples of naturally occurring cycles of environmental conditions? • Different scales of geographic extent • Different scales over time • e.g., large scale cycle ENSO Deposition of scales

  12. Cyclic environmental fluctuations

  13. Fluctuations in fish populations with ENSO

  14. Fish species react differently to ENSO • Anchovy & sardine cycle out of phase • Differences in habitat (sardines more offshore, deeper) • This impacts natural food webs

  15. Plankton effect on cod recruitment: Beaugrand et al., 2003, Nature 427:661 Long-term monthly changes (1958–1999) in the plankton index and cod recruitment.

  16. Trends in phytoplankton and cod success

  17. How do we predict a “sustainable harvest”? • And what about effects on non-target species = “bycatch”?

  18. The estimated annual rate of change, in each area (  ± 95% CI) and in all areas combined (  ± 95% CI), for coastal shark species: (A) hammerhead, (B) white, (C) tiger, and (D) coastal shark species identified from 1992 onward; and oceanic shark species: (E) thresher, (F) blue, (G) mako, and (H) oceanic whitetip.

More Related