Biological limits to submerging salmon

Transcription

1 Biological limits to submerging salmon Tim Dempster - Jon-Erik Juell - Institute of Marine Research 1

2 Why submerge salmon?! Surface-based cages function well most of the time however 2

3 Why submerge salmon?! Storms and ice! Sea lice! Unsuitable temperatures, low oxygen levels, algal or jellyfish blooms Submergence may enable these problems to be avoided 3

4 Salmon swim bladders! Physostomous connected to the stomach! Salmon gulp air from the surface to regulate buoyancy! Contrasting results from previous submergence trials of salmon 4

5 Aim! Determine effect of submergence on behaviour and growth of salmon 5

6 Methods! Cage Environment Laboratory! 4 x 1200 m 3 cages (10 x 10 x 15m)! 500 salmon of 1.7 kg per cage 6

7 Experimental Design Continuous submergence 17 days Sub cage 1 surface sub surface Repeated short-term submergences 2, 3 and 4 days Sub cage 2 surface sub surface sub surface sub surface Controls n = 2 Control surface cages surface

8 Poor surface conditions Continuous submergence 17 days Sub cage 1 surface sub surface

9 Storm Repeated short-term submergences 2, 3 and 4 days Sub cage 2 surface sub surface sub surface sub surface

10 Variables! Growth 10

11 Variables! Growth! Initial, after 23 days, after 3.5 months 100 PIT tagged fish per cage 11

12 Variables! Growth! Behaviour! Individuals! Group structure 12

13 Variables! Growth! Behaviour! Individuals! Group structure Underwater cameras Echo-sounders below each cage 13

14 Variables! Growth! Behaviour! Individuals! Group structure! Environmental variables! e.g. salinity, temperature, oxygen, light 14

15 Variables! Growth! Behaviour! Individuals! Group structure! Environmental variables! e.g. salinity, temperature, oxygen, light Profiling CTD 15

16 Results group distribution Depth fish 3 fish fish 6 9 Before submergence 2-days submerged 10-days submerged Time of day Time of day Time of day signal from cage bottom! Fish remained at the surface in control cages! Fish held at 5 m in submerged cages! After 10 days of submergence, fish also used deeper areas of the cage 16

17 Results behavioural differences! Fish swim faster when submerged 17

18 Results behavioural differences! Fish swim faster when submerged Body lengths s Swimmingspeeds Control 1 Control 2 Submerged 1 Submerged Day 18

19 Results behavioural differences! Fish swim faster when submerged Swimmingspeeds Control Sub 1 submerged Control 2 Submerged 1 Body lengths s Submerged 2 Sub 1 re-surfaced Day 19

20 Results behavioural differences! Fish swim faster when submerged Swimmingspeeds Control 1-1 Body lengths s Sub 2 submerged Sub 2 re-surfaced Sub 2 submerged Sub 2 re-surfaced Sub 2 submerged Control 2 Submerged 1 Submerged 2 Sub 2 re-surfaced Day 20

21 Results - growth! No difference between control and submerged cages After 3.5 months 21 % growth (length) After 23 days Control 1 Control 2 Sub 1 Sub 2 % growth (length) % growth (weight) % relative growth( Length) % relative growth( (weight ) % growth (weight) Control 1 Control 2 Sub 1 Sub

22 Conclusions! Salmon can tolerate days to weeks submerged! Under the environmental regime and salmon density we used in this experiment! The real question is: Under what conditions would it be of benefit to submerge salmon? Compare submergence to unfavorable surface conditions 22

23 Thank you 23