Sea Trout Scale Reading Report

About Sussex Ouse Sea Trout

Sussex Ouse Sea Trout Studies

Part 1 - Scale reading report

Part 2 - Smolt age

Part 3 - Effects of dry & wet years on survival

Sea Trout Glossary

adult sea trout : a sea trout that is returning to the river after a period of at least one year since migrating from the river as smolt.

alevin : young sea trout that have hatched from the egg but remain attached to the yolk sac which serves as food. When they have used up the contents of the yolk sac, they emerge from the redd site as a swim-up fry.

circuli : the rings that appear on a magnified fish scale.

kelt : an adult sea trout that has recently spawned and is the process of returning to the sea. This is a transient phase which ends when the fish returns to the marine environment. A proportion of kelts die after spawning – particularly older fish.

kype : the enlarged, beak-like shape of the jaws of an adult cock sea trout that forms as the spawning season approaches. It appears to be designed as a weapon to enable the cock fish to defend ‘his' hen fish from the unwanted attention of other cock fish.

maiden : an adult sea trout that has not spawned previously. Around 55% of sea trout in river Ouse are in this category. Most are fish that have spent just over one year in the sea, some have spent just over two years in the sea without returning to spawn, while a very few have spent three such years.

mature : these are sea trout which are returning for a second or subsequent occasion after having spawned on a previous occasion(s). Around 45% of anglers' catches in river Ouse are in this category.

parr : a parr is a young sea trout in its early freshwater life. This stage is reached after a few weeks from hatch and lasts until migration to sea after 1–4 years in freshwater. Parr are difficult to distinguish from similar sized brown trout that do not migrate to sea.

redd : a formation of gravel on the river bed in which a pair of sea trout have deposited fertilised eggs during the act of spawning. The redd is shaped by the actions of the hen fish, using movements of its body and tail to shift the gravel. The ideal gravel size 3 is around 2–5 cm for fish of the size that inhabit river Ouse.

smolt : is a young sea trout that has come to the end of its early freshwater life and is either actively moving down to the sea or is about to do so. The trout adopts a silvery colouring then migrates to sea. Smolt ‘runs' usually begin early in the year and tail off in early summer.

smolt age : the age at which sea trout parr becomes smolts, generally from just over 1 year (1+) up to 4 years.

spawning : the act, carried out by a pair of sea trout, of digging a redd in the gravel, depositing and fertilising eggs in it and covering the eggs with gravel.

spawning mark : a distortion on the scales of fish that have spawned during the previous winter(s) caused by erosion of parts of some of the outer circuli, followed by fresh growth as the fish returns to the sea.

swim-up fry : are young sea trout that are newly emerged from the redd site to become free swimming fish. This stage lasts for only a few weeks before the fish becomes a parr.

whitling : small sea trout (size range 30–40 cm) returning to the river after spending from 3–12 months in the sea after smolt migration. Runs of whitling are usually later than adults, but in some years whitling have been seen and caught in river Ouse as early as the second week in July; the normal period for whitling returns is September–January. Whitling usually remain in the lower reaches but have been observed upstream in lower spawning tributaries, and main river Ouse as far upstream as Goldbridge.

Copyright © (2008) Clive L. Fetter. Reproduced by kind permission of the author.