{"id":4483,"date":"2015-12-14T10:02:57","date_gmt":"2015-12-14T10:02:57","guid":{"rendered":"http:\/\/blogs.scotland.gov.uk\/coastal-monitoring\/?p=4483"},"modified":"2018-04-11T10:57:34","modified_gmt":"2018-04-11T09:57:34","slug":"biologists-update-from-shieldaig-december-2015","status":"publish","type":"post","link":"https:\/\/blogs.gov.scot\/marine-scotland\/2015\/12\/14\/biologists-update-from-shieldaig-december-2015\/","title":{"rendered":"Biologist\u2019s update from Shieldaig: December 2015"},"content":{"rendered":"
\"Four<\/a>

Four different ages of trout from a single section of the Shieldaig River<\/p><\/div>\n

Late summer and autumn are busy periods at the Shieldaig field station. The two main tasks are running the river trap for sea trout (ascending) and silver eels (descending) and carrying out electrofishing surveys of the catchment. After a wet spring and summer, September was reasonably dry, allowing the electrofishing to be conducted without hindrance. This annual survey is designed to assess fish populations in the river and monitor the performance of stocked fish.<\/p>\n

The first photo shows a selection of trout captured at one of our sites. The large fish is a mature male which was expressing milt and ready to mate. Below this is a younger fish, in its third year (or, in the terminology of fish scale age analysis, a 2+ fish, indicating that the fish has grown through two summers and is part way through the growth of the third). Below this is a 1+ fish and at the very bottom is one of this year\u2019s fry.<\/p>\n

The second picture shows a finnock captured at the trap this September. Finnock<\/em> is a word of Gaelic origin emphasising the pale colour of the fish, and is used now to designate a young sea trout returning to the river after only a short spell at sea. Some insight into marine survival rates can be gained by comparing the proportions of descending and ascending trout to calculate return rates. Each descending smolt is tagged with a unique code, so that marine residence times and growth rates of the returning finnock can be calculated on an individual basis, allowing an assessment of the performance of each year\u2019s cohort. This finnock, for example, was tagged as a smolt on 11th<\/sup> May 2015 at 165mm in length. On return, after a maximum time at sea of 136 days, it was 233mm.<\/div>\n
\"A<\/a>

A Finnock<\/p><\/div>\n

Many years of electrofishing the same sites in the same river yield, eventually, an important long term data set on the performance of fish in fresh water, providing essential context in which current trends in populations can be assessed. An additional benefit of the repeated electrofishing surveys is a growing familiarity with the minutiae of river and bank habitats, making the process more efficient. Navigation begins to proceed by familiar rocks, structures and trees. In fact, during routine communication, the sampling sites lose their formal designations and become known by their individual features, for example \u2018the cleft rock\u2019 or \u2018the holly tree\u2019. This summer, while working around a site known formally as Shieldaig 36, but informally as \u2018the culvert\u2019, there was some unexpected company: a large adder some 50 cm long sunning itself on the remains of an old road bridge. A second, smaller, adder was heading for cover, while nearby half a dozen slow worms, legless lizards rather than snakes, were curled around each other in twos or threes.<\/p>\n

\"An<\/a>

An nathair, a nadder<\/p><\/div>\n

Snakes are rarely seen in Glen Shieldaig, so spotting these adders at close range was an unexpected pleasure. \u2018The culvert\u2019 was revisited several times over the summer and autumn and the snakes were present most days, sunning themselves on a south-facing bank. Adders incubate their eggs internally and give birth to live young, usually in late summer or autumn.<\/p>\n

The adder is the only snake found in the Highlands. Its Gaelic name is \u2018an nathair\u2019, which is of the same origin as the old English name for serpent, \u2018nadder\u2019; over time \u2018a nadder\u2019 became \u2018an adder\u2019. Will there be young nadders on visits to this site next year? If so \u2018the culvert\u2019 will be in danger of losing its former nickname for a more serpentine moniker.<\/p>\n

More Information<\/strong><\/p>\n