Water body surveys

      Image:Water body survey.jpg

Turtles are often readily visible when basking, and water body surveys provide an effective means for detecting turtles. Several methods are available and should be chosen with study objectives in mind. Standard survey methods by the B.C. Ministry of Environment describe approaches for obtaining three types of information: 1. presence/not detected; 2. relative abundance; and 3. absolute abundance (i.e., population size or density)[1]. Methods for the presence/not detected level require the least effort, and this information is often all that is needed. Absence is notoriously difficult to ascertain; hence these surveys are referred to as presence/not detected surveys.

Obtaining estimates on population size requires capturing turtles and should be undertaken only when needed for a specific purpose and conducted with help from turtle biologists.These surveys are not discussed further in this section, and the methods below refer to surveys at presence/not detected and relative abundance levels.

The general method consists of searching a water body for basking turtles either from water or from vantage points on land. A boat is needed for a thorough survey of most water bodies  -  a canoe or kayak is ideal, but a boat equipped with a quiet electric motor may be used in larger lakes. While slowly circumventing the water body, the observers scan the shoreline and shallow water areas with binoculars for basking or swimming turtles. It is important to start scanning from a distance, as turtles can be wary and quick to dive into water before a positive identification can be made. It is also possible to locate turtles by snorkeling[2]. A telescope is useful when searching from vantage points on land.

Conduct surveys on sunny days from spring to fall. On Vancouver Island, April - June is the optimal period to detect turtles[3]; the weather is still relatively cool for turtles to spend considerable time basking, and aquatic and emergent vegetation are not yet obscuring vision, as they do later in the season. The optimal time of day depends on the season and weather. On cool days in early spring, turtles may be most easily seen during the warmest part of the day, whereas on warm days, they are most easily seen in the morning.

To obtain an index of survey effort, the time spent surveying and the number of observers should be recorded; from this information the survey time (number of person hours) can be calculated. Small water bodies can be searched in their entirety, whereas only a portion of larger lakes may be surveyed.

If information on relative abundance is needed, then the surveys need to be systematic, and the sampling done accordingly to a specific design, for example, using stratified random sampling. Pre-determined lengths of shoreline with different vegetation are surveyed. For presence/not detected level of surveys, such survey designs are not necessary, although it is desirable to survey all different types of habitats present in each water body.

 

For further information, see Inventory Methods for Pond-breeding Amphibians and Painted Turtle: http://www.llbc.leg.bc.ca/public/pubdocs/bcdocs/324504/assets_pond.pdf

 

  1. MELP. 1998. Inventory methods for pond-breeding amphibians and painted turtle. Standards for components of British Columbia’s Biodiverslty No. 37. Resource Inventory Branch, Ministry of Environment, Lands and Parks (available at http://www.ilmb.gov.bc.ca/risc/alphastand.htm). pp 94
  2. St. Clair, R. C. 1989. The natural history of a northern turtle, Chrysemys picta bellii (Gray).fckLRMasters thesis, University of Victoria, Victoria, B. C.
  3. Ovaska, K. and C. Engelstoft. 2010. Western Painted Turtle surveys and stewardship activities on Vancouver Island and the Gulf Islands in 2009. Report prepared for Habitat Acquisition Trust (contact Adam Taylor), Victoria BC. 60 pp.