Estuaries and Fish Ecology Tim Essington School of Aquatic and Fishery Sciences.
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Transcript of Estuaries and Fish Ecology Tim Essington School of Aquatic and Fishery Sciences.
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Estuaries and Fish Ecology
Tim EssingtonSchool of Aquatic and Fishery
Sciences
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Outline
• Fish diversity• What do fish use estuaries for, why?
– Dynamics of fish populations– Predation and Predation risk– Fish life histories and ontogenetic shifts
• Estuaries as nurseries
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What do fish use estuaries for?
• Estuarine residents• Saltwater spawners
– Active and passive processes move larvae into estuaries
– Weakfish migration up the Hudson River• Estuarine spawners • Anadromous / Catadromous species
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Boccacio Rockfish
Max. Size, 75-91 cm, Max weight = 6.8 kgLife Expectancy 50 – 100 yearsInternal live bearer (20,000 – 200,000 eggs)
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Pacific Halibut
Reach sizes up to 2.5 m, > 300 kgLive approximately 30 yearsFecundity: 100,000–2,800,000 per year
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Atlantic Silverside
Maximum size of 15 cm“Annual” species, mature at age 1, few survive to age 2Fecundity = 5,000 – 13,000 eggs
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Spiny Dogfish
Maximum age ~ 75 yearsMature at age 30OvoviviparousPups are 18 – 30 cm at birthFemales produce fewer than 10 pups over a 2 year period
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Why use estuaries?
• Productivity?• Refuge from predators?• Stability / predictability?
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The m / g rule and ontogenetic habitat shifts
Werner and Gilliam, 1984. Ann. Rev. Ecol. Syst. 15: 393-425.
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Predation Happens in Limited Time / Spatial “Arenas”
Implications: Habitat use of small fish is restricted
Promotes density dependent growth and survivorship
Decouples fish from their own food (local prey depletion)
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Johan Hjort and “Year- Class Strength
Used scales to assess cohort-strength of norwegian herring
Realized that population dynamics were driven by variable year-class strength
Hypothesized that year-class strength was likely determined by survivorship through a critical period
This critical period is likely to occur very early in a cohort’s life (egg / larvae)
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Simple model of bipartite life historyPrevailing Advection Field
Unsuitable habitat
Suitable Habitat
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Value of Estuaries to US Fisheries
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Nursery Role of Estuaries
Movement of larval stages into estuaries
Rearing in estuarine habitats
Movement to coastal ecosystem
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Beck et al: What is a “Nursery Habitat”
• Context: long history of considering estuaries as critical / essential nursery habitats– Deegan 1993: Fish migration can be a significant
route of nutrient and energy flux• What makes a habitat a “nursery habitat”
– Importance judged by per-area production to adult stages
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4 key processes:
Density (habitat selection)GrowthSurvivorshipMovement
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Gillanders et al:
• What is evidence of movement between nursery-> non nursery habitats?
• What methods are used?• What are the scales of movement?
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Web of Science Search “Otolith microchemistry”
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Eelgrass (Zostera marina) in Puget Sound
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Heck et al.: Density, survivorship and growth
• Meta-analysis of each demographic rate– Compares seagrass meadows to other habitats– Unstructured habitats routinely have lower:
• Density• Survivorship• Growth
– BUT: seagrass meadows were not especially “better” than other structured habitats
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Questions:
• Why are estuaries so commonly thought of as nursery habitats?
• Is the operational definition of ‘nursery habitats’ necessary, and if so in what contexts?
• How might these definitions account for the dynamic contribution of estuaries to coastal populations?
• Fisheries are one “ecosystem service” that estuaries provide. How might this be quantified?
• What anthropogenic changes are most likely to threaten fish and invertebrate populations, and why? What might be important interactive effects?
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Intensity of Seasonal Hypoxia and Springtime Conditions
Data from HCDOP Citizens Monitoring Program
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Hypoxia Impacts in Hood Canal
Seasonal hypoxia
unimpacted
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Hypothesized Effects
• Persistent effects: those present in Hoodsport even when DO is high– Demographic
• Immediate effects: those present in Hoodsport that are only manifest during hypoxia– Behavioral
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General Results
Hoodsport Hazel Point Possession Sound Useless Bay
Den
sity
(#
/ 100
m2 )
0
5
10
15
20
25
30
35Sessile invertebratesMobile invertebratesBenthic fishesDemersal fishes
Hoodsport Hazel Point Possession Sound Useless Bay
Den
sity
(#
/ 10
0 m
2 )
0
5
10
15
20
25
30
35
June September
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Hypoxia Impacts: Log response ratios to capture chronic vs. acute responses
Benthic Fish
Bentho-Pelagic Fish
Mobile Invertebrates