A10. Snorkeling

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1. Objectives

Many snorkelling surveys exist, which allow for:

  • Quantitative density (White et al., 2012), relative abundance (O’Neal, 2007), distribution (Allison, 2016) and population size and structure (i.e. ratio of males to females, juveniles to adults) estimation (Pinter et al., 2019).
  • Coupling with a mark-recapture protocol.
  • Qualitative information on habitat use by juveniles and adult fish species (Thurow, 1994).
  • Surveying sedentary fish that won’t be assessed by survey methods for migrating fish (e.g. resistivity counters).
  • Surveying long river sections.
  • Surveying river sections where environmental conditions are not suitable for electrofishing due to depth, salinity, bank accessibility or safety reasons.
  • Counting protected fish without handling.
  • Studying fish behaviour (spawning and feeding movements) (O’Neal, 2007), quantify the daily movements of fish and their patterns of recolonisation following disturbance (Lonzarich et al., 2004).
  • Measurement of stream characteristics (depth, water velocity, temperature).

2. Method summary

Snorkel surveying is valuable in assessing fish populations and has been positively compared to electrofishing (Joyce and Hubert, 2003; Lonzarich et al., 2004; Pinter et al., 2019). It consists of surveying part of a stream by one or several aligned people, who slowly swim up or downstream along transects. A designated stream portion has to be chosen beforehand and a habitat assessment performed. River characteristics and targeted species may strongly influence the survey choice and number of snorkellers involved. Fish are identified, counted and their size estimated according to habitat or river portion.

3. Advantages

  • Cost effective technique for estimating fish abundance compared to depletion or mark-recapture surveys (Chamberland et al., 2014).
  • Little equipment required.
  • Can assess remote locations which are unsuitable for netting (hoop nets, fyke net, or electrofishing gear).
  • Not harmful to fish and minimal disturbance to fish and environment (substrate not disturbed and no dispersal of mud or sediment into the water column) (O’Neal, 2007).
  • Snorkelling surveys may result in higher density and biomass estimates of different size classes of many salmonid and cyprinid species (Chamberland et al., 2014).
  • Provides an indication of the fish populations and species spatial distribution in the stream (Plichard et al., 2016).

4. Limitations

  • Less accurate than electrofishing for estimating smaller size classes (Joyce and Hubert, 2003), but provides the same results for larger class sizes (Macnaughton et al., 2015).
  • Electrofishing can provide accuracy in community identification and abundance but data are often correlated (Mullner et al., 2000).
  • There is potential for bias, which has several consequences (Stein et al., 2014); for example, bias exists between snorkellers in estimating fish size, identifying species and estimating fish schools.
  • Bias can come from detectability of some species due to their colour, benthic ecology, nocturnal activity, cryptic behaviour, or from the environment, (stream size, water clarity, temperature, and cover) (Thurow, 1994; Pinter et al., 2019).
  • Small fish are more difficult to see and identify than larger fish.
  • Fish activity and detectability are influenced by the time of the day.
  • Shade over the stream, instream cover of macrophytes, and encumbered habitats or pools reduces accuracy (Apperson et al., 2015).

5. Recommendation for method application

  • Safety is the priority during snorkelling surveys. Snorkellers should be accompanied by a partner, who is them self a proficient swimmer, has all the necessary safety equipment (first aid kit and emergency numbers) and are able to perform CPR. During survey the partner keeps an eye on the snorkeller from the bank.
  • Snorkeller may need a qualification in recognising and treating hypothermia.
  • Black or dark suits should be worn to avoid scaring fish with bright colours.
  • It is recommended that the use of ropes or survey tapes on snorkeller’s equipment is avoid since it poses a risk of entanglement.
  • Carefully characterise the site and identify strong currents and turbulence, underlying waterflows, cliffs, logs and water release features. Seek local knowledge of safety conditions before snorkelling. Select appropriate sampling unit.
  • Adapt your survey to the targeted species and its habitat use, relating to its stage.
  • Summer is often more convenient because of lower water levels and turbidity. Depth and temperature are important, for peoples’ safety and fish behaviour.
  • Do intercalibration exercises for fish counting, identification, and size-estimation between snorkellers.
  • Record all habitat observations and environmental variables.
  • Record snorkeller’s name with their own data as it may prevent strong bias when analysing data.

6. Cost

The use of a dry suit or wetsuit depends on water temperature. Also requires a mask, footwear, and gloves, as well as knee and elbow pads. Around £250. Underwater writing equipment: £40. At least two people are needed: one snorkeller and one surveillance partner.

7. Data analysis

  • Fish abundance/ habitat per stream length or water surface.
  • Recruitment of salmonids.
  • Number of spawning fish.
  • Mark-recapture analysis.

Integrate upstream cover and water visibility to calculate detection efficiency and provide accurate models (Mullner et al., 2000).

8. Surveys

For survey selection and standardisation see: Thurow (1994) and Apperson et al. (2015)

  • Direct enumeration.
  • Expansion estimate.
  • Habitat use estimates.
  • Mark-recapture estimates.
  • SPA: Snorkelling Point Abundance. For characterising fish assemblages over long distances, using series of sampling points, and analysing spatial structure over long distances.

9. References

  1. Allison, M. N. (2016) A rapid assessment method to estimate the distribution of juvenile Chinook salmon (Oncorhynchus tshawytscha) in an interior Alaska river basin.
  2. Apperson, K. A. et al. (2015) ‘Field protocols for stream snorkel surveys and efficiency evaluations for anadromous parr monitoring’, (May). doi: 10.13140/RG.2.1.1717.3846.
  3. Chamberland, J. M. et al. 2014) ‘Comparison between electrofishing and snorkeling surveys to describe fish assemblages in Laurentian streams’, Environmental Monitoring and Assessment, 186(3), pp. 1837–1846. doi: 10.1007/s10661-013-3497-4.
  4. Joyce, M. P. and Hubert, W. A. (2003) ‘Snorkeling as an alternative to depletion electrofishing for assessing cutthroat trout and brown trout in stream pools’, Journal of Freshwater Ecology, 18(2), pp. 215–222. doi: 10.1080/02705060.2003.9664487.
  5. Lonzarich, D. G. et al. (2004) ‘Using Snorkeling To Quantify Fish Assemblage Structure in Arkansas Streams’, Methods, pp. 253–256.
  6. Macnaughton, C. J. et al. (2015) ‘A comparison of electrofishing and visual surveying methods for estimating fish community structure in temperate rivers’, River Research and Applications, 31(June), pp. 1040–1051. doi: 10.1002/rra.
  7. Mullner, S. A. et al. (2000) ‘Snorkeling as an Alternative to Depletion Electrofishing for Estimating Abundance and Length-Class Frequencies of Trout in Small Streams: Response to Comment’, North American Journal of Fisheries Management, 20(3), pp. 839–840. doi: 10.1577/1548-8675(2000)020<0838:saaatd>2.3.co;2.
  8. O’Neal, J. S. (2007) ‘Snorkel Surveys Background and Objectives’, Salmonid field protocols handbook: techniques for assessing status and trends in salmon and trout populations., American F(2), p. Pages 325–340.
  9. Pinter, K. et al. (2019) ‘Snorkeling-Based Fish Stock Assessment by Anglers—A Valuable Method for Managing Recreational Fisheries’, North American Journal of Fisheries Management, 39(1), pp. 82–90. doi: 10.1002/nafm.10246.
  10. Plichard, L. et al. (2016) ‘Comparing electrofishing and snorkelling for characterizing fish assemblages over time and space’, Canadian Journal of Fisheries and Aquatic Sciences, 74(1), pp. 75–86.
  11. Stein, J. A. et al. (2014). Comment: Not all Biases are Created Equal—A Comment on the Snorkel Survey Bias Observed by Hessenauer et al.(2014). North American Journal of Fisheries Management, 34(6), 1204-1206.
  12. Thurow, R. F. (1994) ‘Underwater methods for study of salmonids in the Intermountain West’, General Technical Report - US Department of Agriculture, Forest Service, (INT-GTR-307). doi: 10.5962/bhl.title.100074.
  13. White, S. M. et al. (2012) ‘Protocol for Snorkel Surveys of Fish Densities v1 . 0 COLUMBIA RIVER INTER-TRIBAL FISH COMMISSION Protocol for Snorkel Surveys of Fish Densities A component of Monitoring Recovery Trends in Key Spring Chinook Habitat Variables and Validation of Population’, (November 2016). doi: 10.13140/RG.2.2.26046.89920.