estuaries and fish ecology
DESCRIPTION
Estuaries and Fish Ecology. Tim Essington School of Aquatic and Fishery Sciences. 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. - PowerPoint PPT PresentationTRANSCRIPT
Estuaries and Fish Ecology
Tim EssingtonSchool of Aquatic and Fishery
Sciences
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
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
Boccacio Rockfish
Max. Size, 75-91 cm, Max weight = 6.8 kgLife Expectancy 50 – 100 yearsInternal live bearer (20,000 – 200,000 eggs)
Pacific HalibutReach sizes up to 2.5 m, > 300 kgLive approximately 30 yearsFecundity: 100,000–2,800,000 per year
Atlantic Silverside
Maximum size of 15 cm“Annual” species, mature at age 1, few survive to age 2Fecundity = 5,000 – 13,000 eggs
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
Why use estuaries?
• Productivity?• Refuge from predators?• Stability / predictability?
The m / g rule and ontogenetic habitat shifts
Werner and Gilliam, 1984. Ann. Rev. Ecol. Syst. 15: 393-425.
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)
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)
Simple model of bipartite life historyPrevailing Advection Field
Unsuitable habitat
Suitable Habitat
Value of Estuaries to US Fisheries
Nursery Role of Estuaries
Movement of larval stages into estuaries
Rearing in estuarine habitats
Movement to coastal ecosystem
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
4 key processes:
Density (habitat selection)GrowthSurvivorshipMovement
Gillanders et al:
• What is evidence of movement between nursery-> non nursery habitats?
• What methods are used?• What are the scales of movement?
Web of Science Search “Otolith microchemistry”
Eelgrass (Zostera marina) in Puget Sound
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
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?
Intensity of Seasonal Hypoxia and Springtime Conditions
Data from HCDOP Citizens Monitoring Program
Hypoxia Impacts in Hood Canal
Seasonal hypoxia
unimpacted
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
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
(# /
100
m2 )
0
5
10
15
20
25
30
35
June September
Hypoxia Impacts: Log response ratios to capture chronic vs. acute responses
Benthic Fish
Bentho-Pelagic Fish
Mobile Invertebrates