European grayling and brown trout co-occurence & co-existence

Stephen D Gregory

Why did I volunteer?

  • Historically, European grayling Thymallus thymallus was considered a pest species and were “dispatched” 😧

  • Thought to impact game fish, incl. brown trout Salmo trutta, by competing for food & habitats, and even eating their eggs 😕

  • Hal Thirlaway (Pisc Soc Water Warden 1984) began monitoring grayling and trout populations in the Wylye to show they could co-exist 😍

  • I believe Hal was right!

Literature review

  • Searched WoS for: (TI=(Grayling)) AND TI=(Trout)
  • Read, thinned, & searched “Related records”


  • Final number: 30 papers 👏

A word cloud from paper titles

Findings (1)

  • Based on classic ecological theories and empirical studies, a review suggested likely competition among different salmonids species & life-stages [1] 🎓

  • Interactions are presumed to via competition for limiting foods [2–4], although some suggestions that grayling are behaviourally dominant to trout [5] 🍤

  • Food competition studies are few and reveal conflicting findings: strong competition [4] and weak competition [6,7] 😵

  • Competition highest among juveniles, but grayling might be more efficient feeders [3] and trout use more foods of terrestrial origin [2,8] 👀

Findings (2)

  • Might need long and detailed population surveys to investigate this question… [1,9] 😃
  • Grayling appear more sensitive to environmental change [e.g., 10] and could confound observations
  • Grayling show pronounced ontogenetic shifts in habitat use [e.g., 11,12,13] and could confound observations

A Wylye young of year (YoY) grayling

Interim conclusion

Mixed findings + Regular co-occurence => Co-existence?

Observations from the WGTS

  • Juvenile trout positively associated with grayling YoY counts [14]
  • Large trout positively related to subadult grayling survival [15]
    • Both suggest shared preferred environmental conditions? 😕

Grayling declining, particularly recently and among adults, but trout steady (perhaps increasing?)
  • Juvenile trout negatively affected YoY grayling growth, but no effect of larger trout on subadult or adult grayling growth [16] 😮

Might WGTS help resolve this conundrum?

  • Not in isolation (IMO)… 😶
  • Co-varying numbers are phenomenological; understanding co-existence demands mechanistic studies
    • Energetics and tolerances [e.g., 17]
    • Diet and habitat (niche) overlap [e.g., 18]
    • … 😬

Recent diet overlap paper by Jan Arge Jacobsen [19]

Words of caution

  • Huge quantity of competition / co-existence studies
  • Could be difficult to do on wild fish?
  • Individual specialisation => large sample size
  • Many plausible covariates, e.g., developmental stage, seasonality, …
  • … 😬

Planning

Careful experimental design and power analyses will be essential (IMO) 😰

stephen.gregory@cefas.gov.uk

https://www.graylingresearchtrust.org.uk/

References

1.
Grossman GD, Simon TN (2020) Density-dependent effects on salmonid populations: A review. ECOLOGY OF FRESHWATER FISH 29: 400–418.
2.
Frossard V, Vagnon C, Rossignon C, et al. (2021) Variability of isotopic partitioning between sympatric brown trout (<i>salmo trutta</i>) and european grayling (<i>thymallus thymallus</i>) in the loue river (france). ECOLOGY OF FRESHWATER FISH 30: 285–295.
3.
Watz J, Bergman E, Piccolo J, et al. (2014) Prey capture rates of two species of salmonids (<i>salmo trutta</i> and <i>thymallus thymallus</i>) in an artificial stream: Effects of temperature on their functional response. MARINE AND FRESHWATER BEHAVIOUR AND PHYSIOLOGY 47: 93–99.
4.
Degerman E, Näslund I, Sers B (2000) Stream habitat use and diet of juvenile (0+) brown trout and grayling in sympatry. ECOLOGY OF FRESHWATER FISH 9: 191–201.
5.
Hagelin A, Bergman E (2021) Competition among juvenile brown trout, grayling, and landlocked atlantic salmon in flumes - predicting effects of interspecific interactions on salmon reintroduction success. CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES 78: 332–338.
6.
Haugen T, Rygg T (1996) Food- and habitat-segregation in sympatric grayling and brown trout. JOURNAL OF FISH BIOLOGY 49: 301–318.
7.
Haugen T, Rygg T (1996) Intra- and interspecific life history differences in sympatric grayling and brown trout in a norwegian reservoir. JOURNAL OF FISH BIOLOGY 48: 964–978.
8.
Nevoux M, Finstad B, Davidsen JG, et al. (2019) Environmental influences of life history strategies in partial anadromous brown trout (<i>salmo trutta</i>, salmonidae). FISH AND FISHERIES 20: 1051–1082.
9.
Walton SE, Nunn AD, Probst WN, et al. (2017) Do fish go with the flow? The effects of periodic and episodic flow pulses on 0+fish biomass in a constrained lowland river. ECOHYDROLOGY 10.
10.
Kemp P, Sear D, Collins A, et al. (2011) The impacts of fine sediment on riverine fish. HYDROLOGICAL PROCESSES 25: 1800–1821.
11.
Riley WD, Pawson MG (2010) Habitat use by <i>thymallus thymallus</i> in a chalk stream and implications for habitat management. FISHERIES MANAGEMENT AND ECOLOGY 17: 544–553.
12.
Riley WD, Ives MJ, Pawson MG, et al. (2006) Seasonal variation in habitat use by salmon, <i>salmo salar</i>, trout, <i>salmo trutta</i> and grayling, <i>thymallus thymallus</i>, in a chalk stream. FISHERIES MANAGEMENT AND ECOLOGY 13: 221–236.
13.
Nykänen M, Huusko A, Mäki-Petäys A (2001) Seasonal changes in the habitat use and movements of adult european grayling in a large subarctic river. JOURNAL OF FISH BIOLOGY 58: 506–519.
14.
Basic T, Britton JR, Cove RJ, et al. (2018) Roles of discharge and temperature in recruitment of a cold-water fish, the european grayling <i>thymallus thymallus</i>, near its southern range limit. ECOLOGY OF FRESHWATER FISH 27: 940–951.
15.
Marsh JE, Cove RJ, Britton JR, et al. (2021) Medium-term environmental changes influence age-specific survival estimates in a salmonid population. FRESHWATER BIOLOGY 66: 1530–1545.
16.
Marsh JE, Cove RJ, Britton JR, et al. (2022) Density dependence and environmental variability have stage-specific influences on European Grayling growth. OECOLOGIA 199: 103–117.
17.
Valerie O, Daniels MD (2021) Brook trout (salvelinus fontinalis) and brown trout (salmo trutta) summer thermal habitat use in streams with sympatric populations. Journal of Thermal Biology 98: 102931.
18.
Gregory SD, Macdonald DW (2009) Prickly coexistence or blunt competition? Opuntia refugia in an invaded rodent community. Oecologia 159: 225–236.
19.
Aykanat T, Jacobsen JA, Hindar K (2024) Diet drives performance trade-offs along the ontogeny in the atlantic salmon. bioRxiv.