Farm salmon escape event: levels of farm/wild hybridisation
Results of a genetic survey to examine levels of farm/wild hybrid salmon in rivers local to a large-scale farm escape in in south west Scotland and north east England. This occurred in 2020 when MOWI’s Carradale North fish farm shifted position after its seabed anchors became dislodged during Storm Ellen.
Family structure
The majority of families in both years (88.8% and 86.8% in 2020 and 2021, respectively) consisted of single fish (i.e. there were no full siblings) or family groups of two full sib members (8.6% and 9.2% in 2020 and 2021, respectively) (Table 2, Figure 2). In 4% of cases, in both years, full-sib family sizes ranged from 4 up to a maximum of 24 individuals. Overall, in most cases, family groups were small, suggesting the sampling had captured the diversity present at a site. As such all data were retained for analysis.
| Family size | Year | |
|---|---|---|
| 2020 | 2021 | |
| 1 | 88.8 | 86.8 |
| 2 | 8.6 | 9.2 |
| 3 | 1.4 | 1.5 |
| 4 | 0.3 | 0.8 |
| 5 | 0.3 | 0.3 |
| 6 | 0.1 | 0.3 |
| 7 | 0.3 | 0.3 |
| 8 | 0.1 | 0.1 |
| 9 | 0.0 | 0.3 |
| 10 | 0.0 | 0.2 |
| 11 | 0.1 | 0.1 |
| 12 | 0.1 | 0.1 |
| 13 | 0.1 | 0.1 |
| 24 | 0.0 | 0.1 |
There was no significant difference in family composition between the two years of sample collection (Paired t-test df = 13, p-value = 0.215).
Contact
Email: David.Morris@gov.scot
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