Game & Wildlife Conservation Trust Fisheries Research in Review
In light of the publication of the Game & Wildlife Conservation Trust’s ‘Review of 2020’, we’re delighted to be able to summarise the fantastic work of the GWCT Fisheries Team last year, and the integral part they have played in the key activities of the Missing Salmon Alliance.
The River Frome
River Frome Atlantic salmon population
Monitoring salmon smolts is hard work. Starting in March each year, the GWCT fisheries team spend six weeks checking their rotary smolt screw trap day and night. The 2020 smolt run came just as the nation found itself in lockdown. Despite the restrictions they managed to operate, but only thanks to the support of partners.
The fieldwork was divided across research staff and a PhD student, each joined by their partners who volunteered to help during night shifts to reduce potential risk. This fantastic teamwork and lots of help enabled the fisheries team to continue their data collection in a challenging 2020.
The 2020 salmon smolt estimate was 40% higher than the 10-year average and the mean size of the 2020 smolts was large, boding well for their return rate. The juvenile life stage was the only one with disappointing results in 2020. Poor recruitment, particularly in the upper part of the River Frome catchment from last winter’s spawning, resulted in fewer juvenile salmon than normal available for tagging. A good number of spawners was recorded in 2020, which is promising for the recruitment of juvenile salmon in 2021.
SAMARCH overview and progress
The SAlmonid MAnagement Round the CHannel project 2017-2023 (SAMARCH) is led by the GWCT and includes 10 partners from France and England who are a blend of research and regulatory organisations, and key stakeholders.
The English Channel is one of the busiest parts of the ocean for shipping, commercial fishing, especially with gill nets, and marine developments. This poses several challenges for the salmon and sea trout that spawn in the 80 or so rivers in the south of England and northern France which flow directly into the Channel.
The project presented a number of key findings over the last year:
Thirty-eight percent of sea trout mortality at sea is due to predation.
Sea trout migration behaviour seems to differ between populations.
Sea trout swim to a depth up to 80 metres.
Twenty-three percent of the data storage tags deployed in adult sea trout have been recovered.
River Frome juvenile salmon grow best overwinter when it is warm and wet. River Frome smolts are migrating to sea earlier and following warmer winters.
River Sélune adult salmon sea ages appear related to sex-specific post-smolt growth in their first-sea winter. The GWCT’s research has shown that smolts that grew well in the river and their first summer at sea were more likely to return to spawn after only one year at sea. For further information please go to www.samarch.org.
Timing of migration by juvenile Atlantic salmon
Every spring juvenile Atlantic salmon in the River Frome undergo physical and behavioural changes: they become sleeker, more silver in colour and start to abandon a previously solitary life in favour of joining their conspecifics in small shoals.
The annual smolt run, where the young salmon get the urge to leave the river that they have resided in since hatching, head down the River Frome, pass rapidly through Poole Harbour and travel towards their oceanic feeding grounds, where they will feed and mature into adult Atlantic salmon. This migration is crucial for Atlantic salmon, as they can access far greater feeding resources at sea than in fresh water, enabling them to grow into mighty adults. Salmon smolts face environmental conditions novel to them as they enter the estuary for the first time, including saline waters and different temperature regimes. They also face new predators, such as large piscivorous fish and seabirds.
Increases in water temperature and discharge encourage smolts to migrate past our facility at East Stoke. Large smolts migrate earlier than small smolts, usually in isolation and not in a school. The GWCT’s observations suggest that schooling behaviour changed during the smolt run.
Low summer discharge and salmonid ecosystems
Increased abstraction and climate change will likely reduce summer flow in southern chalk streams in the future. The resultant change in discharge is considered one of the biggest future threats to chalk stream and salmonid ecosystems.
A 30-day experimental discharge reduction in three streams within the River Itchen catchment significantly impacted depth, velocity and wetted width of the streams. Despite changing the physical characteristics of the streams, the fisheries team observed limited impact on detritus and algae, macroinvertebrates and the fish community composition. Fish behaviour was impacted by discharge reduction with site loyalty reduced for many groups and evidence for older trout leaving the affected streams during discharge reduction.
The full Fisheries Report will be published soon, keep an eye on the GWCT website for more information about any of these projects. The GWCT is one of the founding member organisations that make up the Missing Salmon Alliance, all with the shared goal to help the wild Atlantic salmon survive and thrive in our rivers and seas. Working closely with Dylan Roberts, Head of Fisheries, The Game and Wildlife Conservation Trust, this key research feeds into the MSA’s research, activities and communications.
As an Alliance of five organisations, we will build on the existing work of our partners and maximise our impact by taking a coordinated approach and vital action in order to halt and reverse the decline of wild Atlantic salmon.
The goal of the Missing Salmon Alliance is to build an evidence-base to influence national and international decision-makers to regulate activities that adversely impact wild Atlantic salmon.
The Missing Salmon Alliance
The MSA is comprised of the following members:
Game & Wildlife Conservation Trust, Atlantic Salmon Trust, the Angling Trust with Fish Legal, The Rivers Trust and Fisheries Management Scotland.
https://www.missingsalmonalliance.org