There are many examples of how standardization of procedures in production and data collection have led to remarkable advances in industry and science, but standardization is lacking regarding protocols for sampling fish populations in inland, freshwater systems. Reasons given why biologists often resist standardized sampling protocols include perceptions that differences in regions invalidate standard techniques; use of standard sampling is costly and reduces innovation by regional biologists; the variation already present in nature masks any gains introduced by standardization; and historical trend data is lost. We examine these reasons and provide procedures that may serve as a template by describing how development and implementation of standardized sampling protocols were achieved by the Washington Department of Fish and Wildlife. These procedures included obtaining support from high-level management within the agency and input from a wide variety of sources; emphasizing benefits to manageme...

Standard Sampling of Inland Fish: Benefits, Challenges, and a Call for Action

The diel variation in boat electrofishing catches was investigated on the lower Murray River (south-eastern Australia), downstream of three low-level weirs. Fish assemblage composition did not differ among three sites, but differed substantially between day and night. Significantly more small-bodied species (e.g. Australian smelt Retropinna semoni, flyspecked hardyhead Craterocephalus stercusmuscarum, bony herring Nematalosa erebi and Murray rainbowfish Melanotaenia fluviatilis) and some large-bodied predators (e.g. golden perch Macquaria ambigua) were caught during daytime samples. Significantly more flatheaded gudgeon Phylipnodon grandiceps, carp gudgeon Hypseleotris spp. and perch Perca fluviatilis were collected at night. The size composition of the fish assemblage also changed over the diel cycle. Significantly smaller goldfish Carassius auratus, flyspecked hardyhead, bony herring and Australian smelt were sampled during the day, while generally smaller individuals of golden perch and the common carp Cyprinus carpio were caught at night. These findings suggest that sampling during both day and night is required to adequately characterize riverine fish assemblages in the context of fish migration studies.

Determining diel variation in fish assemblages downstream of three weirs in a regulated lowland river

The establishment, spread, and impact of the invasive bivalve Corbicula fluminea (C. fluminea), in Lake Tahoe threatens native species distribution in the lake and, potentially, has long-term implications for water clarity. In 2009, UBC-Gavia, an Autonomous Underwater Vehicle (AUV), was used as a platform to collect georeferenced imagery of the benthic regions of Lake Tahoe to determine the lake-wide distribution of C. fluminea. Images were collected in water depths less than 10 m at an approximately constant height above the bottom of 2 m. Images were processed using a semi-automated procedure to determine the ratio of the lakebed covered by exposed C. fluminea shells. A visual review was conducted on a subset of the images to determine presence of filamentous algae that has been observed in association with C. fluminea. Nearly 100km of shoreline was covered over a 7-d period, and C. fluminea presence was reconfirmed in 4 regions and additional 10 regions identified. In regions where the presence of C. fluminea was confirmed, C. fluminea depth distribution was validated by comparing image detection counts and results from a benthic sediment grab sample survey. Three regions around the lake were identified to have filamentous green algae or charophyte species. It was impossible to identify species of the known filamentous algal taxa (Cladophora glomerata, Spirogyra spp., and Zygnema spp.). The collected imagery provides a synoptic view on species distribution within the lake that can be used for efficient monitoring of invasive species in freshwater and saltwater bodies. © 2012, by the American Society of Limnology and Oceanography, Inc.

Quantitative assessment of invasive species in lacustrine environments through benthic imagery analysis

I examined the use of scuba diving as a nondestructive, cost-effective alternative to sampling black bass with an electrofishing boat, which can injure or kill fish, is not effective in clear water or water of extreme (low or high) conductivity, can be labor intensive, and can be difficult along developed shorelines as well as intrusive to residents. I compared the relative efficiency of nighttime electrofishing and daytime scuba diving for estimating the density and size structure of black bass in three western Washington lakes. Catch per unit effort (number of stock-length fish/400 m shoreline) of electrofishing and scuba diving did not differ significantly for largemouth bass Micropterus salmoides or smallmouth bass M. dolomieu. The length-frequency distributions of sub-stock-length and longer black bass sampled while electrofishing and scuba diving were not significantly different in two of the three lakes surveyed. In some cases, scuba diving may be preferable to electrofishing because of it...

A Comparison of Electrofishing and Scuba Diving to Sample Black Bass in Western Washington Lakes

I developed a way to rapidly evaluate the size structure of fish populations designed to be readily understood by a wide audience. Relative length frequency compares the length frequency of fish from a particular water body with an average developed for a region. This technique is analogous to relative weight, relative condition, or relative growth, which are used to compare the condition or growth of fish in a particular water body with rangewide or regional standards. Relative length frequency can be used in conjunction with relative weight or relative growth to rapidly identify factors potentially limiting fish production. I demonstrate this method with data on largemouth bass Micropterus salmoides from Washington State and roundtail chub Gila robusta from Arizona that were collected during standardized electrofishing surveys.

Relative Length Frequency: A Simple, Visual Technique to Evaluate Size Structure in Fish Populations

Three lakes were repeatedly sampled at night using boat electric fishing, experimental gill netting, and fyke netting from May to November 1993 to evaluate the feasibility of using proportional stock density (PSD) to monitor warm-water fish populations in Washington State, USA. Additionally, average night-time boat electric fishing catch-per-effort of largemouth bass, Micropterus salmoides (Lacepede), from 30 Washington lakes was also analysed to determine the amount of effort required to obtain adequate samples for precise PSD estimates. Temporal variations in PSD were not large enough to affect the management of warm-water fish populations in the small Washington lakes studied. However, the considerable effort required to obtain precise PSD estimates may limit its usefulness for warm-water fisheries surveys in the Pacific Northwest. On average, from three to 13 nights of electric fishing effort are needed to capture enough stock-length largemouth bass for PSD estimates, depending on the precision desired (80–95%) and the location of the lake (eastern or western Washington). Catch of stock-length fish can be maximized by using electric fishing for centrarchids and gill netting for yellow perch, Perca flavescens (Mitchill), in June or September. Adequate samples for precise PSD estimates can be difficult to obtain from Pacific Northwestern lakes, even when using recommended gear at optimum sampling times. Inability to capture an adequate sample size for precise PSD estimates may be responsible for some of the fluctuation in PSDs in some studies of warm-water fish populations in northern areas. Managers in other northern climates may find that low sample size may account for large variations in PSDs reported.

E. Anderson

Papers

Monitoring warm‐water fish populations in north temperate regions: sampling considerations when using proportional stock density