Have Invasive diluviana Altered the Carrying Capacity of Osoyoos L, for Sockeye Salmon ?.

Kim Hyatt1, Don McQueen2, Athena Ogden1 1.Science Branch, Fisheries and Oceans Canada, Nanaimo, B. C. 2. Professor Emeritus, Queens University, Ontario

Washington-BC Amercian Fisheries Society Meeting, March 2018, Kelowna, BC.

Fisheries and Oceans Pêches et Océans Canada Canada Canada Osoyoos L. Study Site

• Shallow (mean 40 m) & warm (surface temps > 250C)

• Mesotrophic (7-15 ug.l-1 P)

• Deeper waters often hypoxic (< 4 ppm O2.l-1) in late summer.

• Historically known to produce relatively large Sockeye smolts (6-40g at age-1). Fisheries and Oceans Pêches et Océans Canada Canada Canada Mean growing season biomass of phytoplankton (ug.l-1) 2005-2013

3000 Chlorophyta Osoyoos phytoplankton

biomass 2005-13 2500 Haptophyta

Chrysophyta 2000 3 - m

3 Cryptophyta 1500 mm Dinophyta 1000

Phytoplankton Phytoplankton biomass Bacillariophyta 500 Cyanophyta

0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Blue-greens dominate biomass, followed by diatoms with remainder a mix of greens, golden browns and dinophytes

Fisheries and Oceans Pêches et Océans Canada Canada Canada Seasonal mean biomass of (ug.l-1 dry wt) 2005-2013

350

Osoyoos zooplankton Diaphanosoma 300 biomass 2005-13 Daphnia

250 Bosmina dw

Epischura 1

- 200 Diacyclops

µg L 150 Leptodiaptomus 100 Nauplii Zooplankton biomass Rotifer 50

0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

• Zooplankton numbers and biomass both dominated by copepods such as Leptodiaptomus, Diacyclops and large, but rare, Epischura.

• Cladocerans contribute smaller numbers, less biomass than copepods with 2-3 species of Daphnia plus much smaller-bodied Bosmina.

• Note the trend for higher biomass of zooplankton from 2005-2010 relative to 2011-2013.

Fisheries and Oceans Pêches et Océans Canada Canada Canada 1800 180

1600 160

1400 140 dw

- 1 ww

- 1

1200 120 µgL

1000 100 Physical Drivers of Biota

• Phytoplankton and 800 80 zooplankton biomass in Osoyoos L. controlled by phytobiomass

600 60 Okanagan R. discharge.

Zooplankton biomass µg µg biomass Zooplankton L • Discharge drives high contrast 400 40 0.0 0.2 0.4 0.6 0.8 (roughly 3-fold changes) in potential “bottom-up” forcing May-October cumulative of lower trophic level food 3 discharge km abundance for fish & mysids !

Fisheries and Oceans Pêches et Océans Canada Canada Canada Seasonal mean biomass of Mysis diluviana (ug.l-1 dry wt) 2005-2013

40

gravid female 35 Osoyoos Mysis biomass 2005-13 adult female - released eggs 30 dry weight dry

1 adult female - 25

20 adult male

15 immature female Biomass µg L 10 immature male

5 juvenile 0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

• Mysis diluviana is an invasive macrozooplankter that appeared in Osoyoos Lake sometime between the late 1980s (Shepherd, unpublished observations and late 1990s (Hyatt and Rankin) .

• Mysis exhibits a one-year life-cycle in Osoyoos L. (unlike Okanagan L) and despite large annual fluctuations in phytoplankton and zooplankton food sources maintains stable numbers and biomass in all years but 2011.

Fisheries and Oceans Pêches et Océans Canada Canada Canada Juvenile Sockeye Abundance (no.ha-1) in Osoyoos Lake 2005-2013

1 -

10000

8000

6000

4000 Average fish density ha

2000

0 2005 2006 2007 2008 2009 2010 2011 2012 2013

High contrast in pelagic fish abundance during 2005-2013 from as few as 1200 fry.ha-1 to as many as 8300 fry. ha-1 has potential to establish strong top-down forcing by fish on zooplankton prey (i.e. roughly 8 fold change in abundance among years ! )

Fisheries and Oceans Pêches et Océans Canada Canada Canada Seasonal Growth Performance of Sockeye Fry in Osoyoos Lake

7

2005 2006 6

2007 2008 5

4 2009 2010

3 2011 2012

2 2013 Mean weight (g) at (g) at Mean age weight

1

0 Mar May Jul Sep Nov Jan Mar

• Lowest abundance years (2008, 2010) have highest growth performance.

• Highest abundance year (2009) has relatively poor growth performance.

• Suggests exactly what one might expect from a top-down density dependent growth model.

Fisheries and Oceans Pêches et Océans Canada Canada Canada “Top-down” Food-web Correlations

Top-down correlations p-unt p-trans

10 Age-0 fry density Von Bertalanffy 0.04 W∞ Sig. 11 Age-0 fry density Von Bertalanffy K 0.16 ns 12 Age-0 fry density Age-0 fall fry weight (Nov) 0.07 ns 13 Age-0 fry biomass Age-0 fall-fry weight (Nov) 0.16 ns 14 All fish biomass Age-0 fall-fry weight (Nov) 0.19 ns 15 Age-0 fry density Age-0 nerkid survival 0.10 ns 16 Age-0 fry biomass Age-0 nerkid survival 0.16 ns 17 All fish biomass Age-0 nerkid survival 0.19 ns 18 Age-0 frydensity Total Zpl biomass 0.42 0.14 ns 19 Age-0 frybiomass Total Zpl biomass 0.41 0.15 ns 20 All fish biomass Total Zpl biomass 0.39 0.21 ns 21 Age-0 fry density Mysis biomass 0.37 ns 22 Age-0 fry biomass Mysis biomass 0.44 ns 23 All fish biomass Mysis biomass 0.50 ns Only 1 of 14 top-down correlations exhibited a significant association between Van-B. W∞’ and Sockeye fry density !

Fisheries and Oceans Pêches et Océans Canada Canada Canada “Bottom-up” Food-web Correlations

Potential bottom p-unt p-trans up correlations

1 Total Zpl biomass Age-0 nerkid November weight 0.23 0.21 ns

2 Total Zpl biomass Age-0 nerkid Von Bertalanffy W∞ 0.46 0.10 ns

3 Total Zpl biomass Age-0 nerkid Von Bertalanffy K 0.39 0.27 ns

4 Total Zpl biomass Age-0 nerkid survival 0.01 Sig.

5 Daphnia biomass Age-0 nerkid survival 0.01 Sig. 6 Epischura biomass Age-0 nerkid survival 0.01 Sig.

7 Mysis biomass Age-0 nerkid Von Bertalanffy W∞ 0.32 ns 8 Mysis biomass Age-0 nerkid Von Bertalanffy K 0.39 ns 9 Mysis biomass Age-0 nerkid survival 0.22 ns Several bottom-up correlations were significant (red highlights) for zooplankton biomass measures and Sockeye fry survival. Fisheries and Oceans Pêches et Océans Canada Canada Canada Bioenergetics-based Consumption of Zpl by Fisn & Mysids

1.2

1 - Dipteran 1.0 L. ashlandi Epischura 0.8 D. thomasi

1 - Leptodora d 0.6 Daphnia 0.4 Chironomid Mysis 0.2 Consumption fish by µg L

0.0 2005 2006 2007 2008 2009 2010 2011 2012 2013 1.2

1 - Diaphanosoma 1.0

µg L Rotifer 0.8 D. thomasi Mysis

1 L. ashlandi -

0.6d Daphnia 0.4 Bosmina

0.2 Consumption by

0.0 2005 2006 2007 2008 2009 2010 2011 2012 2013

Moderate overlap in diets of fish & mysids. Both consume Daphnia, Diacyclops & Leptodiaptomus. Only fish eat Epischura & mysids; Only Mysis eats Bosmina.

Fisheries and Oceans Pêches et Océans Canada Canada Canada Relative Consumption by Fish and Mysids of All Zooplankton and Zooplankton by Taxa

1.6

Wild age-0 nerkids 1.4 Mysids eat 45% to 75% Stocked age-0 1.2 sockeye of the total Zpl consumed 1.0 Nerkids age-1 by fish and mysids dry weight dry 0.8 Age 2+3 kokanee together. - 1 d 0.6 - 1 Other fish > 33cm 0.4 Bioenergetics analysis 0.2 indicates that at the 0.0 2006 2007 2008 2009 2010 2011 2012 2013 highest fish density levels 1.6 -1 and fish µg L Leptodiaptomu observed (>8000.ha ) 1.4 s Bosmina and lowest Zpl production 1.2 Mysis Mysis Diaphanosoma levels observed, Zpl 1.0 Diacyclops consumption by fish and 0.8 Daphnia mysids together may 0.6 Leptodora exert top-down control on 0.4 Epischura

0.2 Diptera cladoceran prey (e.g. Consumption by by Consumption 0.0 Daphnia and Bosmina). 2006 2007 2008 2009 2010 2011 2012 2013

Fisheries and Oceans Pêches et Océans Canada Canada Canada What Would Happen if Mysids Were Absent from Osoyoos L ?

• Mysid introductions /invasions are often associated with altered food-webs (losses of Zpl taxa e.g. Daphnia pulex) and population collapses by pelagic fish.

• In Osoyoos Lake, pelagic fish and mysids appear to coexist “happily”.

• Mysids, Sockeye fry & zooplankton in Osoyoos L. form a “trophic triangle” in which mysids and Sockeye eat common prey (e.g. Daphnia, Diacyclops) but Sockeye also eat mysids (i.e. the latter are a “source” and a “sink” for Sockeye fry from a food-web and energetics perspective).

• Evidence of “bottom-up” control exerted by Daphnia on Sockeye fry survival suggests Sockeye fry survival could be higher in the absence of mysids.

• The dominance of “bottom-up” control and virtual absence of strong “top-down” control precludes direct detection of an effect of mysids on Sockeye fry growth.

• BUT If one assumes that all the Daphnia mysids eat could be eaten by Sockeye, subtracts from this the quantity of Mysis that Sockeye eat and expresses the net result as proportion of current Sockeye diet, it would represent a 44% increase in Sockeye fry daily ration over the growing season i.e. Sockeye smolts would likley be significantly larger than at present.

Fisheries and Oceans Pêches et Océans Canada Canada Canada Conclusions

• Mysis diluviana alterations of food webs, Sockeye fry survival & growth have likely altered the carrying capacity of Osoyoos Lake for Sockeye production.

BUT

• Mysis occupation of Osoyoos Lake has not precluded restoration of Sockeye smolts or adults to levels at or above historic abundance

Fisheries and Oceans Pêches et Océans Canada Canada Canada