# Presentation: 544023

## The influence of nearshore circulation on primary productivity and sustainability of populations in MPAs.

- Louis W. Botsford
- Department of Wildlife, Fish and Conservation Biology
- University of California
- Davis, CA 95616

## Coastal

- Circulation

- 1. Spatial management via Marine Protected Areas

- 2. Primary productivity from Upwelling winds

## Sustainability of populations in Marine Protected Areas (MPAs)

- Sustainability - single populations
- Sustainability - spatial
- Examples from Marine Life Protection Act

- Dependence on larval dispersal, therefore circulation, therefore environmental change

## Single Population Sustainability

- Total egg production per year

- Number of recruits produced

- 1/(Lifetime Egg  Production, LEP)

- Equilibrium Population level

- Recruit = fish entering population at young age

## Sustainability of Populations: how hard can we fish?

- fecundity

- age

- abundance

- Egg Production

- Recruitment

- Slope=1/LEP

- Lifetime
- Egg
- Production
- (LEP)

- Note:  Population collapses when1/LEP>slope-at -the-origin of egg/recruit relationship.
- Highly uncertain.  Why?

## SUSTAINABLE POPULATIONS

- REPLACEMENT

- In humans, a couple replaces themselves with 2 babies

- How many eggs does it take to
- replace one fish?

- Sustainability requires that individuals in a population replace themselves in their lifetime.

- What is the required Lifetime Egg Production (LEP)?

**Notes:**
Sustainable populations are ones that replace themselves.  Easy to figure out for humans - how do you figure that out for fish?

## How much LEP is enough?

- a.k.a. Spawning Potential Ratio

- Here I call it the Critical Replacement Fraction

- From examples where we have data:
**35%** (Clark 1991)
**30%** (Mace and Sissenwine 1993)
**40%** (Clark 1993, Mace 1994)
**55-60%** (Dorn 2002, for rockfishes)

## What determines sustainability of spatially distributed populations linked by larval dispersal?

- Replacement through all possible paths
- Botsford, et al. (2001) Ecology Letters
- Hastings and Botsford (2006) Proceedings Nat. Acad. Sci.

## Sustainability and Lifetime Egg Production with reserves

- Reserve

- Fished

- Reserve

- Fished

- Reserve

- COAST

- Same minimum replacement=35-60% Fraction Natural Settlement at sustainable point

**Notes:**
How does replacement work when reserves are involved? A replacement condition still has to be satisfied, but in this case in addition to LEP at each location, we have to include how likely a larva is to make it to a good location.  
Because there needs to be adequate replacement at each point, return flow of the offspring of each larvae is important.
The minimum required value of this spatial LEP for a species to be sustainable at a location is still 35-60%.

## To calculate replacement through all possible paths we need:

- Dispersal patterns
- FLEP at each location

## s

- w

- R

- F

- R

- F

- R

- F

- Dispersal
- 	fraction dispersing x->y =(a/2)e-a|x-y|
- 	1. Symmetric
- 	2. Mean dispersal distance 1/a
- 	3.  Fixed amount

## Results

## Not habitat

- (a)

- (b)

- 0-30m		    30-100m

## Example of habitat/reserve distribution

- (Pt. Conception)

- North
- (Monterey)

- 0-30 m Hard Habitat

- Reserves (red)
- Habitat (green)

- Distance Along Coast (km)

## Example of resulting distribution of FLEP

- 0-30 m Habitat

- Critical level
- (0.35)

- FLEP in MPA
- habitat
- areas is 1.0

- FLEP in
- non-MPA
- habitat areas
- is fishery
- dependent
- (0.2 here)

- FLEP in non-
- habitat areas 0.0

## Equilibrium Settlement

## Two General Tendencies

- Short distance dispersers - sustained in reserve of any size
- Long distance dispersers - sustained only where there is a high enough density of reserves

- Problem:  Dispersal distances poorly known

## 0-30m

- (a)

- (b)

- 30-100m

## Short dispersers

- FLEP=0.2

- FLEP=0.3

- 0-30 m

- 30-100 m

- (a)

- (b)

- (c)

- (d)

## Short dispersers

- FLEP=0.2

- FLEP=0.3

- 0-30 m

- 30-100 m

- (a)

- (b)

- (c)

- (d)

- Long dispersers

## Conclusions:

- 1.  For long distance dispersers, sustainability is much less “predictable.”

- For long distance dispersers, sustainability if
-  fraction in reserves > critical replacement 					fraction

- These results assume “diffusion” only, advection reduces sustainability

- Environment changes dispersal distance?

- Environment changes mortality? Age of maturity?

- Environment increases alongshore advection?

## Upwelling Production Accounting for Off-Shelf Losses 

- From Mixed Layer Conveyor model:
- 	Constant winds
- 	Time-varying winds
- 	Optimal wind patterns

## How does productivity depend on wind?

-  “... study of the key processes explaining the integrated functioning of highly productive planktonic systems on wind-driven eastern boundary shelves.”
- PRODUCTION, RETENTION, TROPHIC INTERACTION

- WIND

- PRODUCTIVITY

- Can one identify a functional form?

- Wind Events and Shelf Transport (WEST)

## Production on EBC shelves

- Fishery biologists - why catch and recruitment vary (Logerwell, et al. 2003)

- Biological oceanographers - patterns  (e.g., Carr and Kearns 2003, Thomas, et al. 2003)

- Intertidal ecologists - community structure (e.g., Sanford and Menge 2001)

- Physical Oceanographers - climate change (e.g.,Bakun 1991)

## Test by correlation:

- 	Upwelling Index   vs.   Biological time series
- 	(volume upwelled)

## Mixed Layer Conveyor model

**Mixed Layer Conveyor model**

- Shelf production, higher trophic levels

- NPZ

## Constant Wind Result

- New Production

- Regenerated

- New

- Regenerated

- (Botsford, et al. 2003)

## Time-varying winds - time scales

- Shelf Transit Time

- Zooplankton

- Phytoplankton

**Notes:**
How frequently will production be cut short?

## Response to time-varying winds

- Which is it?

- Bakun Index

- Upwelled volume

- Production

- Earlier dome-shaped from constant wind case

## Answer:

- Neither one, necessarily

- Depends on time scale

## Date

- transit          time

- velocity

- Production per parcel

- Index

- 2001 buoy winds

**Notes:**
Cross shelf velocity , shelf transit time
Question:  is the blue line correlated with the red or green line over (synoptic) and (annual time scales

## Synoptic time scale

- Production, 10-day Correlations
- With Upwelling Index

- Date

## Annual Time Scale

- Production, P or Z

- Upwelling velocity (shelf width/Tprod)

- 1.0

- Shelf width

- Wind speed

## Correlation Uwindex vs P,Z

- Coefficient of Variation

- Shelf width (km)

- Phytoplankton

- Phytoplankton

- Zooplankton

- Zooplankton

## Another approach (borrowed from real biological oceanographers)

- What is the optimal pattern of upwelling winds?

- (e.g., 2 days upwelling, 3 days relaxation)

## To maximize production on the shelf

- The cross-shelf velocity must be periodic with period equal to the optimal cross shelf transit time from the constant wind case.

-  The mean cross-shelf velocity must be equal to     the optimal value from the constant wind case.

- n.b. The daily program (e.g.,2 on, 3 off) is irrelevant as long as these are satisfied.

## Phytoplankton production vs. period and average cross-shelf velocity

## Zooplankton production vs. period and average cross-shelf velocity

## Phytoplankton production vs. period and mean wind stress

## Zooplankton production vs. period and mean wind stress

## Cross-shelf velocity

- Optimal patterns

- Production per parcel

- Vol upwelled Vol phytoplo Vol zoopl

## Empirical Evidence

## Bodega Bay Crab Settlement

**“****Zooplankton”**

## B. MacFarlane, et al.

- Comparison of growth of chinook salmon in the Gulf of the Farallones between low upwelling (1998) and high upwelling (1999).

- No difference.

## Conclusions:

- In locations with high wind speeds and narrow shelves, losses off shelf can produce dome-shaped upwelling response on annual time scales

- 2.  Biological responses on synoptic time scales are predicted by upwelling volume

- 3.  On annual time scales highest production will occur when period of wind variability is near development time of phytoplankton or zooplankton (Tp), and mean cross-shelf velocity is (shelf width)/ Tp

- Account for when testing upwelling effects on shelf species?

## General Conclusions?(both talks)

- Both involve details of circulation
- Increasing direct observations with HF radar

## Slide 48

## Slide 49

## Slide 50