Browsing All Posts filed under »fishing«

Freshwater fish surveys: direct observation works well

March 26, 2018

Comments Off on Freshwater fish surveys: direct observation works well

Although surveys of freshwater fish populations often rely on electrofishing, it’s difficult to use this technique in some habitats. An alternative sampling method is direct observation by snorkelling, an approach often applied in marine environments.  While comparisons of the sampling efficiency of electrofishing and snorkelling have been carried out, most of them have been based […]

How fishing changes catchability

March 27, 2017

Comments Off on How fishing changes catchability

The bolder members of a fish population – often defined as those most willing to continue to forage under the threat of predation – tend to be relatively exploratory, aggressive, territorial, and enjoy higher rates of food intake and specific growth than more timid individuals. However, their larger size makes bold fish more vulnerable to […]

Sustaining turtles

March 23, 2016

Comments Off on Sustaining turtles

Freshwater turtle populations are very vulnerable to increases in adult mortality, such as those caused by the incidental capture of turtles in commercial fishing nets. Modelling of data from Canada’s Lake Opinicon (780 ha) indicates that the loss of just two additional adult female map or painted turtles per year will lead to population extinction […]

A method for sampling biodiversity

July 20, 2015


Which field sampling methods give the most accurate picture of aquatic biodiversity? Working out an effective sampling design for biodiversity can be a lot more complicated than deciding how to target single species. This is because the usefulness of a given style of net, trap or other sampling device depends on the behaviour and body […]

Are there more large zooplankton out there?

July 20, 2015

Comments Off on Are there more large zooplankton out there?

Species of animal plankton often have very patchy distributions and this makes it difficult to assess their abundance accurately using traditional net-based sampling techniques. Recent advances in echosounding technology, in particular the use of multiple frequencies to separate the acoustic reflections of invertebrates and fish, offer the opportunity to scan sizeable volumes of water for […]

Assessing abundance when animals are hard to find

October 1, 2014

Comments Off on Assessing abundance when animals are hard to find

Aquatic animals are typically sampled by nets, by electrofishing or by snorkeling. Monitoring the status of rare, secretive and threatened species can be problematic because of the relatively high costs of intensive field surveys, and because there may be prohibitions on trapping or handling. A new and promising alternative approach relies on the fact that […]

Underwater video analysis

December 28, 2013

Comments Off on Underwater video analysis

Although electrofishing is probably the most commonly used method of surveying stream fishes, it can lead to serious short and long-term damage to the animals concerned. For example, in one study of rainbow trout, X-ray examination showed that the majority of electrofished individuals incurred spinal injuries. However, technical advances in the field of underwater video […]