demographic or ecosystem management?
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Demographic or ecosystem management?. 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? - PowerPoint PPT PresentationTRANSCRIPT
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Demographic or ecosystem management?
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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?
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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?
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Methods of Harvesting: Purse Seine
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Long-line fishing
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Halibut on long line
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Sport fishing – 900 lb tuna
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Ling cod
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Otter Trawl
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Why do nekton populations change?
• Natural cycles• Trophic interactions (food, predators,
disease)• Direct harvest• Habitat disruption• Climate change
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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
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Cyclic environmental fluctuations
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Fluctuations in fish populations with ENSO
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Fish species react differently to ENSO
• Anchovy & sardine cycle out of phase• Differences in habitat (sardines more
offshore, deeper)• This impacts natural food webs
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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.
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Trends in phytoplankton and cod success
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How do we predict a “sustainable harvest”?
• And what about effects on non-target species = “bycatch”?
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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.