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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