Inter-annual variation in the spring ichthyoplankton assemblages in the Strait of Georgia, 2007 – 2010
Lu Guan1, John Dower1, Skip McKinnell2 and Pierre Pepin3
1Department of Biology, University of Victoria, BC, Canada 2North Pacific Marine Science Organization (PICES), BC, Canada 3Fisheries and Oceans Canada, St John’s, NL, Canada The Strait of Georgia (SoG) The Strait of Georgia (SoG)
¾Most productive area on Canada’s Johnstone Strait west coast Mainland
z Semi-enclosed coastal basin z Numerous islands, reefs & inlets z Strong tidal mixing along edges & straits z Local winds: week z Fraser River: primary forcing of Vancouver estuarine circulation Island
¾Long history of oceanographic study
Examples: Haro Strait z Estuarine circulation (Li et al., 1999) z Water mass (Masson, 2006) Juan de Fuca Strait z Deep water renewal (Masson, 2002) z Chlorophyll distribution (Masson and Pena, 2009) z Long-term temperature trend (Masson and Cummins, 2006) z Major species of Phytoplankton (Stockner et al, 1979) z Major species of Zooplankton (Parsons et al., 1970) The Strait of Georgia (SoG)
Johnstone Strait Mainland
Vancouver Island
Haro Strait
Juan de Fuca Strait SoG Ichthyoplankton Surveys As part of the Canadian Healthy Oceans Networks (CHONe)
Ichthyoplankton Quantify changes in ichthyoplankton community & Community Examine associated driving factors
Population Quantify patterns of spatiotemporal variability Connectivity & Explore dispersal pathways
2009 & 2010 Same time period: (~35 sites in central SoG) Apr, 24th –May, 1st (2007, 2009 & 2010)
Field procedure: 1m2 Tucker trawl Vancouver 1mm mesh size Nanoose Bay Station top 0-50m 15min @ 1m/s Nanaimo
Lab process: Sort, Identify, Measure How is the SoG environment changing?
100 Timing of Spring bloom
90 Without seeding With seeding
80
70
Day ofDay year 60
50
2003 2004 2005 2006 2007 2008 2009 2010 2011 40 Year
(courtesy of J. Gower)
Time series of Zooplankton Max Fraser River Discharge
12000 / s)
3 11000 2007
10000
9000
8000 2009
7000 2010 6000 Fraser River Max Discharge (m Discharge Max River Fraser 5000 155 160 165 170 175 180 Day of year (courtesy of D. Mackas) Changes in species diversity & richness ?
2.6 Margalef's index 2.4 Shannon diversity
2.2
2.0
1.8
1.6
1.4
1.2
1.0 2007 2008 2009 2010 Year Shannon-Wiener diversity index Same trend: 2007 = 2009 < 2010 Margalef’s index Abrupt increase from 2009 to 2010 Changes in community composition? ¾ Most abundant fish species and groups: Pacific herring, Pacific hake, Walleye pollock, 2007: 95.77% of total larval Northern smoothtongue, Slender sole, 2009: 90.21% abundance Rockfishes, Flatfishes 2010: 94.41%
¾ Composition (late Apr): very different among sampling years Changes in community composition?
¾ Method: 0.10 Year Canonical analysis of 07 principal coordinates on the 09 10 Station-based multivariate data 0.05 ¾ Species composition: 3 clusters
0
PERMANOVA: P = 0.0001 CAP2
-0.05
-0.10 -0.10 -0.05 0 0.05 0.10 CAP1 Changes in community composition?
¾ Method: 0.10 Year Canonical analysis of 07 principal coordinates on the 09 10 station based multivariate data Slipskin snailfish 0.05 Enlish sole ¾ Species composition: Flathead sole Poachers Dwarf wrymouthPacific sand lance 3 clusters Rock sole Walleye pollock Starry flounder R.F sp. Sculpin 0 Pacific herring Butter sole PERMANOVA: P = 0.0001 CAP2 Slender sole
Lumpsucker ¾ Dominant species (late-Apr) shift: Pacific hake -0.05 2007: Pacific hake Pelagics 2009: Pacific herring -0.10 Walleye pollock -0.10 -0.05 0 0.05 0.10 CAP1 2010: Rockfish sp. Flatfishes Demersals
How did larval abundance change?
Total larval abundance Pelagics / Demersals abundance ratio
300 3.0 ) 3
250 2.5
200 2.0
150
1.5 100
1.0 50 Pelagics / Demersals ratio Total larval abundance (# / 1000 (# / m 1000 abundance larval Total 0 0.5 2007 2008 2009 2010 2007 2008 2009 2010
Total larval abundance: 2009 < 2007 = 2010
Very low abundance in 2009
Pelagics / Demersals ratio: decreasing How did larval abundance change?
Dominant species Flatfishes 35 Pacific herring Rock sole 140 )
) Walleye pollock English sole 3 3 30 Rockfish sp. Flathead sole 120 Pacific hake Slender sole 25 100 20 80
15 60
40 10
5 Larval abundance (# / 1000m Larval abundance (#
Larval abundance (# / 1000m 20
0 0 2007 2008 2009 2010 2007 2008 2009 2010 Walleye pollock Rock sole Pacific hake 2009 < 2007 & 2010 English sole 2007 = 2009 < 2010 Rockfish sp. Flathead sole Pacific herring 2007 = 2009 = 2010 Slender sole 2009 < 2007 = 2010
2009: lowest in abundance 2009: lowest; 2010: highest
Poor year in 2009 for a lot species + Dramatic increase in 2010 Changes in mean standard length? 18 Walleye pollock Pacific hake 16 Slender sole Flathead sole 14 Rock sole English sole 12
10
8 Standard length (mm)
6
4 2007 2008 2009 2010 Consistent trend in standard length: Pacific hake Walleye pollock 2009 > 2010 > 2007, consistently Flatfishes 2007: Poor zoop year Low growth rate 2009: Low larval abundance, big in size Fish spawned early? Evidence of early spring in 2009 Larvae hatched early? Changes in Phenology? – Pacific hake
110 Examine the otolith Larvae Hatch DOY 105 Read the rings 100 Age the larvae Back-calculate hatch date 95
90
In 2009: of Year Day 85 Hatched early Cold environment, good food 80 Estimated by otolith Estimated by equation: Age = 6.68 * Length – 21.9 Late Apr: less abundant & larger 75 2007 2008 2009 2010
2007 2009 2010 Mean hatch DOY 105 88 98 Range of hatch DOY 101-108 81-98 97-99 Larval abundance Highest Lowest Intermediate Larval size Smallest Largest Intermediate Summary
2007 2009 2010 Temperature Warm phase Cold phase Intermediate Spring bloom time Feb 14 Feb 25 Mar 23 FR max discharge (m3/s) Jun 09 (10800) Jun 20 (7490) Jun 28 (5950) Zooplankton biomass Poor Good Good
Diversity & Richness 2007 = 2009 < 2010 Pelagic/Demersal dominance Pelagics Pelagics Demersals Larval fish abundance High Poor High Larval fish standard length Smallest Largest Intermediate Timing Probably spawning / hatch earlier in 2009
Large inter-annual variability between 2009 and 2010
Follow up question: specific driving mechanisms??