Disturbance and Fish Daniel D. Magoulick USGS, Arkansas Cooperative Fish & Wildlife Research Unit, Department of Biological Sciences, University of Arkansas

Disturbance Two ways to define disturbance –Effects on organisms “any relatively discrete event that removes organisms and opens up space and other resources that can be used by individuals of the same or different species.” (Townsend and Hildrew 1994) Response to event is part of definition –Response must occur –Difficult to compare among systems –Physical nature of event Defined by the nature of their damaging properties, especially intensity, frequency, predictability, spatial extent and temporal duration Response to disturbance is examined separately

Types of Disturbance Pulse – short-term, sharply delineated –Floods –Non-persistent pollution Press – arise sharply, reach constant level –Sedimentation after fire –Dam building –Persistent pollution Ramp – steady increase in time, may level off –Drought

Perturbation Types Perturbation – combo of cause and effect related to disturbance

Response to Disturbance Resistance – ability of the community to avoid displacement by disturbance Resilience – ability of community to return to its former state after disturbance

Drought as Disturbance

Two types of Drought Seasonal – drying in a particular season(s) –Predictable –Periodic or regular Supra-seasonal – drying over multiple seasons –unpredictable

Perturbation Types During Drought Seasonal –press disturbance and response Supra-seasonal –Ramp disturbance and response

Factors Affected by Drought

Questions What factors are most important in determining fish and crayfish assemblage structure in drying streams? What habitats act as refugia and how does refuge use influence fish and crayfish assemblage structure in drying streams?

Questions What habitats act as refugia during stream drying? –Hyp: Pools act as refugia  Net migration into pools Does stream drying lead to a concentration effect? –Hyp: Reduced area and fish migration increase densities in pool habitats (refugia) –Hyp: Reduced area and fish migration lead to unchanged densities in riffle/run habitats 3km

YOY Central Stoneroller Pool Riffle July Sept

Conclusions Survival rates were low and species- dependent. Refuge habitats are species and size- dependent –Pools  Adult creek chubs and central stonerollers –Riffles  YOY central stonerollers and bigeye shiners Reduced habitat area and fish migration led to increased densities

Logitudinal Drying Patterns Dowstream drying Headwaters drying Mid-reach drying

Questions How do fish use intermittent streams? What factors affect fish movement between mainstem and intermittent tributary? Can intermittent streams act as spawning and nursery areas?

Methods

Results 59 marked bass Buffalo River 324 – 445 mm 480 – g Bear Creek 319 – 403 mm 452 – g

Buffalo River residents 24 Bear Creek residents 23 Using both streams 12 Stream-use categories

Smallmouth Bass Locations

Smallmouth Bass Movers

Kernel density estimate (km) CategoryN 95% 95% 90% 90% 50% 50% Buffalo resident 80.74A0.66A0.10A Bear resident 60.28A0.28A0.03A Using both A3.25A0.05A “Summer” Home Range

Kernel density estimate (km) CategoryN95%90% 50% 50% Buffalo resident AB11.17AB0.22A Bear resident 44.17A2.87A0.32A Using both B30.41B0.32A “Entire Study” Home Range

Conclusions Smallmouth bass use intermittent portions of Bear Creek. Summer drying events appear to limit bass movement. Immigration of fish into Bear Creek can be substantial –Spawning migrations Larval fish drift densities are very high in Bear Creek –Substantial in intermittent portion of stream

Otolith Microchemistry What are otoliths? Application of microchemistry Relationship with water Advantages and disadvantages

Elemental Discrimination

Determine temporal stability and spatial variability of elemental signatures in Bear Creek and Buffalo River Associate water chemistry from Bear Creek and the Buffalo River with otolith chemistry in resident fish Use otoliths to describe previous locations of fish within Bear Creek and the Buffalo River Objectives

Methods Collected water samples October 2003 – April 2005 Analyzed chemical concentrations of water Collected smallmouth bass August 2004 Extracted otoliths

Otolith Ablation

Data Integration

r = 0.77; P <

r = 0.87; P =

Element:Ca (mmol/mol) in otolith edges Sample site Ba:Ca Ba:CaMg:CaSr:Ca Buffalo River A0.030 A0.71 A Lower Bear A0.028 A1.03 B Middle Bear A0.044 A2.03 C Upper Bear B0.029 A1.64 C

Site fidelity across consecutive summers Trace element concentrations in Bear Creek Useful trace elements Classification of fish to collection sites Discussion

Survival Objective: examine and compare bass survival in Bear Creek and Buffalo River

Survival White and Burnham 1999 Kaplan-Meier known fate Kaplan-Meier known fate 5 month cutoff for unknowns5 month cutoff for unknowns Examined survival among stream-use categories and periods Examined survival among stream-use categories and periods AICc to select model AICc to select model Model averaging Model averaging

Ŝ annual = (Ŝ 5month ) 5 (Ŝ 7month ) 7 Delta method  var(Ŝ annual ) Williams et al Annual Survival

Modelk AICc wt. ΔAICc period + sex + intercept period group period + total length period + group period + sex period + length + sex period + length * sex Minimum AICc = Survival

Survival

Survival

DiscussionSurvival Angler mortality Compared to other estimates

Conclusions Consideration of tributary populations Mainstem quality reflects tributary quality Water development in tributaries Flow dynamics