Salmonid Field Protocols Handbook: Techniques for Assessing Status and Trends in Salmon and Trout

Snorkel Surveys

Jennifer S. O’Neal

doi: https://doi.org/10.47886/9781888569926.ch15

Snorkeling is the underwater observation and study of fish in flowing waters. Snorkeling gear is worn by biologists who, individually or in small teams, survey fish abundance, distribution, size, and habitat use while slowly working in (generally) an upstream direction. This technique is most commonly used to survey juvenile salmonid populations but can also be used to assess other species groups. This document discusses the critical elements necessary for the design and implementation of a snorkel survey program to encourage a standardized procedure for the use of underwater techniques to survey fish species in streams. Much of the information in this paper was adapted from Thurow (1994), who provided vital information for use in standardized snorkel surveys.

Snorkel surveys are widely used to monitor fish populations in streams and to estimate both relative and total abundance (Slaney and Martin 1987). Snorkeling can also be used to assess fish distribution, presence/absence surveys, species assemblages (i.e., diversity), some stock characteristics (e.g., length estimation), and habitat use. Each objective will affect how the survey should be conducted. Specific directions for implementing snorkeling to address various objectives are presented in this chapter.

A variety of fish species can be assessed using snorkel surveys; however, salmonids, due to their territorial nature in freshwater and propensity for using habitats with high water clarity, are the group for which snorkel surveys are most frequently conducted. Snorkel surveys have recently been used to assess sculpin diversity (C. Jordan, NOAA Fisheries, personal communication). Snorkel surveys are often selected as the best method for surveying salmonids because they result in relatively little disturbance to the target species, reasonable accuracy, and less cost outlay. Cost optimization methods are discussed at the end of this protocol and explained in detail in Dolloff et al. (1993).