Browsing All Posts filed under »fishing«

How fishing changes catchability

March 27, 2017

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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

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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

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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

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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

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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

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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 […]

Catch trout and protect native species

September 23, 2013

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The introduction of salmon and trout to areas outside their natural range often puts pressure on native fish species, which suffer increased predation, habitat displacement and reduced growth.   In the Southern Hemisphere, introduced salmonids have been linked to contractions in the distribution of native fish such as galaxiids (jollytails), but many details of the ecological […]