Jennifer L. Boldt, Thomas W. Therriault, Douglas E. Hay, Jacob Schweigert, & Matthew Thompson Fisheries and Oceans Canada, Science Branch, Pacific Biological Station,

Nanaimo, BC, Canada

Nearshore fish community dynamics in the Strait of Georgia: information from juvenile herring surveys

B.C. Seafood Landed Value

British Columbia Pacific Herring

DFO 2010

(HG)

(PRD)

(CC)

(WCVI)

(SOG)

5 major & 2 minor fishing stocks

Map courtesy of Kristen Daniel, DFO

• SOG herring are migratory

• Migrate between SOG and WCVI

• Spawning occurs in late Feb-early March

• Juveniles are found nearshore for about the first 1.5 years of life

• Mature and recruit at age-3

Background

• Recruitment in Pacific herring is highly variable

• Juvenile herring surveys were designed to forecast recruitment based on the density of juvenile herring in the SOG during their first year of life

• Thus, the forecast would be made 2½ years prior to the fishery and provide advanced “information” for fisheries management

Survey Justification

89

4

35

1

2

6

10

11Strait of Georgia

89

4

35

1

2

6

10

11

89

4

35

1

2

6

10

11

89

4

35

1

2

6

10

11Strait of Georgia

• 10 “Core” Transects

•Both open water and channel type habitats

• Annual sampling between 1992 and 2011(except 1995)

•September-October

“Core” SOG Transects

Stations at Transects

5 stations per transect

Transects perpendicular to shore

Gabriola I.

Galiano I.

Valdes I.

Strait of Georgia

Fisheries Pêches and Oceans et Océans

1

2

“Open Water”

“Channel”

Generally one transect sampled per night 8

94

3 5 12

1011

6

Sampling

• “Blind” purse seine sets made after dusk• Fish sorted, identified and enumerated

Fisheries Pêches and Oceans et Océans

• Determine age classes of herring by length frequencies

• Include all successful purse seine sets (even zero catches)

• Transformed catch weights, ln(wt+1)

• Estimate annual average catch weight for age-0 herring

• Mean across samples

• Bootstrapped mean and variance (1000 times)

• Correlate survey catch with age-3 recruits (3 years later)

Herring Recruit Methods

Mean catch wt Bootstrap mean catch wt

Survey catch age-0 correlated with age 3 recruits

R2 = 0.74

0

2

4

6

8

10

0 2 4 6 8 10

ln(btstrp mean catch wt Age 0)

ln(A

ge 3

recr

uits

)

R2 = 0.76

0

2

4

6

8

10

0 2 4 6 8 10

ln(mean survey catch wt Age 0)

ln(A

ge 3

recr

uits

)

Recruit Predictions

Recruit year Predicted age 3 recruits *106 Recruit category .(non-bootstrap method)

2012 753 (698) Good (Average)

2013 679 (670) Average (Average)

Recruit categorybased on 33% & 66% of ranked recruitment time series (1952-2011):

Poor/Average cutoff = 414

Average/Good cutoff = 714

Additional Benefits?• Given the amount and type of data collected

and the cost of these surveys, are there any other benefits to be derived from this survey data?

• For example, can we detect community-level change?

Are there differences over time, between open water and channel sites, across depths?

Fisheries Pêches and Oceans et Océans

• Removed rare species not sampled well by gear (<10 occurrences in the 19 year time series). Chub Mackerel, Eelpout, Goby, Greenling, Invertebrate (non-squid), Kelp Perch, Lingcod, P. Cod, P. Lamprey, P. Sardine, P. Tomcod, Pile Perch, Poacher, Ratfish, Rockfish, Skate, Snailfish, Surfperch

• Species included = fish and squidP. Herring, N. Anchovy, Chinook Salmon, Chum Salmon, Coho Salmon, Sockeye Salmon, Pink Salmon, Dogfish, Flatfish, Gunnel, Midshipman, Pipefish, Sandlance, Sculpin, Shiner Perch, Smelt, Stickleback, P. Hake, W. Pollock, Snake Prickleback, Squid

• Include all successful purse seine sets (even zero catches)

• Estimate counts for species samples where weight, but not numbers were recorded (using avg. indiv. wt)

Multispecies Methods

Species Composition

0.0

0.2

0.4

0.6

0.8

1.0

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

Abu

ndan

ceW.PollockSticklebackSockeyeSalmonSnakePricklebackShinerperchSculpinSandlancePipefishPinkSalmonN.AnchovyMidshipmanGunnelFlatfishDogfishSmeltCohoSalmonChumSalmonChinookSalmonP.HakeSquidP.Herring

1992: due to 1 sample with a large catch of juvenile smelt1994: due to 2 samples with large catches of squid2002: due to 1 sample with a large catch of juvenile smelt

ANOSIMR=0.142p<0.1

Species Composition By Transect Type

0.0

0.2

0.4

0.6

0.8

1.0

Channel Open

Transect type

Abu

ndan

ce

W.PollockSticklebackSockeyeSalmonSnakePricklebackShinerperchSculpinSandlancePipefishPinkSalmonN.AnchovyMidshipmanGunnelFlatfishDogfishSmeltCohoSalmonChumSalmonChinookSalmonP.HakeSquidP.Herring

ANOSIMR=0.053p=<0.1

0.0

0.2

0.4

0.6

0.8

1.0

5 10 20 30 50 100 200 300 400

Depth interval (m)

Abu

ndan

ce

W.PollockSticklebackSockeyeSalmonSnakePricklebackShinerperchSculpinSandlancePipefishPinkSalmonN.AnchovyMidshipmanGunnelFlatfishDogfishSmeltCohoSalmonChumSalmonChinookSalmonP.HakeSquidP.Herring

Species Composition By Depth

ANOSIMR=0.102p<0.1

R2 = 0.33p = 0.01

0

1

2

3

4

5

6

7

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

Year

Ric

hnes

s

R2 = 0.45p = 0.002

0.0

0.2

0.4

0.6

0.8

1.019

92

1994

1996

1998

2000

2002

2004

2006

2008

2010

Sha

nnon

-Wie

ner i

nde x

Species Richness and Diversity

Decreased since 1997

0

1

2

3

4

5

6

O C O C O C C O C O

1 2 3 4 5 6 8 9 10 11

Transect

Ric

hnes

s

0.0

0.2

0.4

0.6

0.8

1.0

O C O C O C C O C O

1 2 3 4 5 6 8 9 10 11

Transect

Sha

nnon

-Wie

ner I

ndex

0123456

Channel OpenTransect Type

Ric

hnes

s

0.00.20.40.60.81.0

Channel OpenTransect

Sha

nnon

-Wie

ner I

ndex

Species Richness and Diversity By Transect

0

1

2

3

4

5

6

7

5 10 20 30 50 100 200 300 400

Depth interval (m)

Ric

hnes

s

0.0

0.2

0.4

0.6

0.8

1.0

5 10 20 30 50 100 200 300 400

Depth interval (m)

Sha

nnon

-Wie

ner I

ndex

Species Richness and Diversity By Depth

0123

4567

13 14 15 16

Sea surface temperature (deg.C)

Ric

hnes

s

0.0

0.2

0.4

0.6

0.8

1.0

13 14 15 16

Sea surface temperature (deg.C)

Sha

nnon

-Wie

ner i

ndex

No Relationship with SST (Sept-Oct)

Richness Diversity

HerringEntrance Is. lighthouse

0123456789

13 14 15 16

Sea surface temperature (deg. C)

ln(m

ean

surv

ey c

atch

wt A

ge0

• Catch weight of age-0 herring is a good predictor of age-3 recruits• Species composition varies a little over time, location, and depth• Decreased richness & diversity over time• Higher diversity & richness in open areas than in channel areas• Higher diversity and richness at 10-20 m depth• Diversity, richness, age-0 herring abundance not related to SST

Summary

• Examine other indicators of this data set – e.g., mean trophic level of the community?, etc.

• Relate community indicators & herring abundance to– biological drivers (e.g., zooplankton prey, predators)– environmental drivers (e.g., more site-specific SST)

Next Steps