Ecological interactions between parasites and wildlife

Transcription

1 Ecological interactions between parasites and wildlife Case study: salmon farms, wild salmon, and sea lice Sean Godwin November 21, 2018 Guest lecture #3 Introduction to Ecology

2 Outline 1. Pathogens and parasites in wildlife populations 2. Sub-lethal effects 3. Salmon farming 4. My research on sea lice and wild salmon 5. Summary

3 White nose syndrome in North American bats Bovine tuberculosis in mammals Pathogens and parasites can be major threats to wildlife Varroa mites in honey bees Chytridiomycosis in amphibians

4 E.g., White nose syndrome in North American bats Frick et al. 2010

5 Abundance Pathogens and parasites shouldn t drive their hosts to extinction As host abundance goes down, so too must pathogen or parasite abundance Time With only one host, if pathogens or parasites drive their host to extinction, they drive themselves to extinction as well

6 Abundance But if there are other hosts to act as reservoirs for the parasite Reservoir host (host #2) Time then pathogen or parasite abundance can be maintained in the environment even at low population densities of host #1

7 Example of this phenomenon: Domestic dogs African wild dogs Canine distemper virus shared between the two extinction of wild dogs in Serengeti

8 Population growth rate (dx/dt) Per capita growth rate 1/x dx/dt Population size (x) Extinction may occur via Allee effects (a) Population growth rate Logistic growth Strong Allee effect Weak Allee effect (b) Per capita growth rate (c) Population trajectory Population size (x) Population size (x) Time dashed lines X 0 = 21 solid lines: X 0 =19

9 Outline 1. Pathogens and parasites in wildlife populations 2. Sub-lethal effects 3. Salmon farming 4. My research on sea lice and wild salmon 5. Summary

10 Macleans Direct mortality from pathogens and parasites often obvious, clear effects e.g., sea star wasting syndrome

11 Indirect mortality from pathogens and parasites called sub-lethal effects far less obvious than direct mortality, but can have an even bigger influence on survival e.g., effects on host reproduction, growth, behaviour, etc.

12 Example #1: Sub-lethal effects Bumblebees infested with protozoan parasite Crithidia bombi Infested bumblebees have weakened abilities to recognize rewarding flowers based on their colour - are therefore worse foragers This sub-lethal effect has obvious implications for survival Wildlife & Wetlands Trust

13 Example #2: Sub-lethal effects Bewick s swans are often infected with avian influenza A This virus doesn t cause direct mortality, so wasn t thought to be much of an issue But infected swans: - delay their migration - can t fly for as long - don t feed as successfully Wildlife & Wetlands Trust

14 Outline 1. Pathogens and parasites in wildlife populations 2. Sub-lethal effects 3. Salmon farming 4. My research on sea lice and wild salmon 5. Summary

15 Domesticated animals often act as reservoir hosts for pathogens and parasites of concern to wildlife Aquaculture the farming of aquatic organisms

16 Why do we need aquaculture? aquaculture capture fisheries FAO 2018

17 Top 10 Cultured Fish Species Species Environment Tonnage (millions) Grass carp freshwater 5.23 Silver carp freshwater 4.59 Common carp freshwater 3.76 Nile tilapia freshwater 3.26 Bighead carp freshwater 2.90 Catla (Indian carp) freshwater 2.76 Crucian carp freshwater 2.45 Atlantic salmon marine 2.07 Roho labeo freshwater 1.57 Milkfish freshwater 0.94 FAO 2013

18 Salmon farms open-net pens in the ocean hold hundreds of thousands of fish almost always Atlantic salmon high densities of farmed fish lead to outbreaks of pathogens and parasites can then spread to wild salmon Simon Ager

19 Farmed Atlantic salmon as reservoir hosts in BC Wild salmon Farmed salmon

20 Sea lice native ectoparasites to BC feed on surface tissue and mucus of fish salmon farms act as year-round reservoirs for lice in absence of salmon farms, wild juvenile salmon are not usually infested by lice, only wild adults cost the global industry >$400 million per year Alexandra Morton

21 Salmon life cycle marine out-migration is a period of extremely high mortality, but we don t know much about it Cohen Commission 2012

22 Juvenile salmon have many stressors to contend with during their early marine migration salinity predators migration competition rising temperatures pathogens

23 BC is the only place in the world that produces a large portion of both the worlds wild and farmed salmon BC s wild salmon are of huge ecological, economic, and cultural importance Tavish Campbell Royal DSM

24 Map of Salmon Farms in BC (wild salmon are everywhere)

25 Outline 1. Pathogens and parasites in wildlife populations 2. Sub-lethal effects 3. Salmon farming 4. My research on sea lice and wild salmon 5. Summary

26 Part of my PhD: Assessing the potential sub-lethal effects of sea lice on wild salmon

27 How we collect wild juvenile salmon migrating up the coast (for interest; video not in PDF)

28 Sub-lethal effect study #1 Are wild juvenile salmon with more sea lice worse at competing for food?

29 Transported fish to a floating research station to perform a competitive feeding experiment Amy McConnell Amy McConnell Emma Atkinson

30 We held fish in net pens (ironic) and fed them a known, limited amount of food (for interest; video not in PDF)

31 Lepeophtheirus salmonis >99% infested (!), so unable to have Caligus clemensi uninfected categories of fish in experiments

32 Competitive ability experiment Each trial had two groups of fish: 1) highly infested 2) lightly infested After feeding finished, we weighed the stomach contents to figure out how much each fish ate

33 We predicted that lightly infested fish would eat more during our experiment than highly infested fish We also predicted that bigger fish would eat more (better eyesight, faster swimmers, etc)

34 Yes, lightly infested fish ate more than highly infested fish, on average. Competitive foraging ability also increased with body size, as expected.

35 Relative stomach fullness = stomach content weight body weight Even after accounting for body size, licier fish were worse at competing for food

36 Sub-lethal effect study #2 Are wild juvenile salmon with more sea lice less successful at feeding in the wild?

37 Even though licier fish are worse at competing for food, maybe they can still successfully feed! Maybe there s actually lots of prey to eat (so competition is low)

38 We collected wild juvenile salmon during their coastal migration and immediately weighed their stomach contents to see how much they ve been eating

39 Again, lightly infested fish were more successful at feeding than highly infested fish, on average Foraging success also increased with body size again

40 Relative stomach fullness = stomach content weight body weight Even after accounting for body size, licier fish were worse foragers

41 Salmon need to grow quickly To feed more effectively To feed on larger prey To escape predation

42 Sub-lethal effect study #3 Do wild juvenile salmon with more sea lice grow more slowly?

43 Fish otoliths (earstones) otoliths have annual growth rings (like trees) they also have daily growth rings distance between rings proportional to body growth daily growth rings! (400x magnification)

44 On average, highly infested salmon grew 8% more slowly than uninfested fish

45 The effect of sea lice on salmon growth decreases with fish body size Also, bigger fish grow faster

46 Putting it all together: Potential for a snowball effect / vicious cycle Competitive ability + + Sea lice Foraging success + Growth rate + Body size + + So sea lice may have long-term, lasting consequences for their hosts

47 Outline 1. Pathogens and parasites in wildlife populations 2. Sub-lethal effects 3. Salmon farming 4. My research on sea lice and wild salmon 5. Summary

48 Summary Reservoir hosts can decouple the abundances of hosts and their pathogens/parasites - In extreme circumstances, this can lead to Allee effects and extinction of the host Sub-lethal effects of pathogens and parasites can be critically important for host survival Sea lice are native parasites to salmon, but salmon farms are a new reservoir host Sea lice likely have sub-lethal effects on wild salmon

49 Questions?