Download Estuaries and Fish Ecology

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
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 kg
Life Expectancy 50 – 100 years
Internal live bearer (20,000 – 200,000 eggs)
Pacific Halibut
Reach sizes up to 2.5 m, > 300 kg
Live approximately 30 years
Fecundity: 100,000–2,800,000 per year
Atlantic Silverside
Maximum size of 15 cm
“Annual” species, mature at age 1, few survive to age 2
Fecundity = 5,000 – 13,000 eggs
Spiny Dogfish
Maximum age ~ 75 years
Mature at age 30
Ovoviviparous
Pups are 18 – 30 cm at birth
Females 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 yearclass 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 history
Prevailing 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)
Growth
Survivorship
Movement
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”
50
45
Citaions / Year
40
35
30
25
20
15
10
5
0
1985
1990
1995
2000
2005
2010
2015
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
unimpacted
Seasonal hypoxia
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
35
35
25
20
15
10
5
30
2
2
Density (# / 100 m )
30
Density (# / 100 m )
Sessile invertebrates
Mobile invertebrates
Benthic fishes
Demersal fishes
25
20
15
10
5
0
0
Hoodsport
Hazel Point Possession Sound Useless Bay
June
Hoodsport
Hazel Point Possession Sound Useless Bay
September
Hypoxia Impacts: Log response ratios
to capture chronic vs. acute responses
Benthic Fish
Mobile
Invertebrates
Bentho-Pelagic Fish