Marine
Where do fish live?
October 23, 2017 by Marine Directorate Communications No Comments | Category Fisheries, Marine Directorate Science, Research Vessel Surveys
Last week, our scientists were involved in a programme aimed at providing fine-scale data on the habitat associations of cod, haddock and whiting at a key period in their life history – following the transition from pelagic to demersal habitat.
The programme also provided them with an opportunity to add to the fish trap and fixed-position baited underwater video data obtained earlier in the year, which is used to further inform 0-group distribution models and samples for otolith-based growth and survivorship analysis.
During the programme, which was conducted on board the MRV Lady Nicola, scientists deployed fish traps over various habitat types within and around the Small Isles MPA and also synchronously deployed baited remote underwater video camera frames fitted with twin cameras calibrated for post-survey photogrammetric analysis.
Fish traps were deployed at the start of each working day, in fleets of 3, 2 and 2 traps, to be picked up again following a minimum soak time of 6 hours. The deployment location (GPS latitude and longitude), soak time, and bait type and quantity were recorded and captured fish released from the trap, with measurements of total length (to 1 cm) and weight (to 0.01 g). Otoliths from gadoid species (cod, haddock, and whiting) were also extracted to establish age, with tissue from a subsample of the catch and stored in ethanol for genetic analysis. Time was set aside during each day to collect fresh bait.
Both underwater video camera frames were deployed at distances sufficient to avoid any interaction with the fleet ground gear (recommended minimum 500 m between deployments). Two cameras oriented ±6° perpendicular to the frame base were synchronously recording high definition video for a nominal period of 1.5 hours. Footage was then downloaded to external media at the end of each working day. Species type, relative species densities (MaxN) and substrate type (assessed visually) were classified post-survey.
Table 1: Latitude, longitude & habitat variables of potential survey stations.
| Station | Substrate | Longitude | Latitude (dd) | Longitude | Latitude | Depth (m) |
| 1 | Rock & Other Hard Substrata | -6.47643 | 57.05647 | 006° 28.58596′ W | 057° 33.87997′ N | 48.4 |
| 12 | Mixed | -6.4066 | 57.05017 | 006° 24.39607′ W | 057° 30.10482′ N | 62.8 |
| 20 | Sandy Mud – Muddy Sand | -6.5747 | 56.92952 | 006° 34.48182′ W | 056° 55.77110′ N | 88.7 |
| 24 | Sand | -6.20849 | 57.01463 | 006° 12.50945′ W | 057° 08.77659′ N | 50.8 |
| 7 | Coarse/Mixed Sediments | -6.39688 | 56.95936 | 006° 23.81250′ W | 056° 57.56159′ N | 49.2 |
| 8 | Mud | -6.56517 | 57.0306 | 006° 33.91008′ W | 057° 18.35910′ N | 69.7 |
| SI_01 | Rock/Biogenic Reef | -6.60639 | 57.0602 | 006° 36.38324′ W | 057° 36.11881′ N | 16.1 |
| SI_02 | Rock/Biogenic Reef | -6.57409 | 57.06484 | 006° 34.44535′ W | 057° 38.90486′ N | 13 |
| SI_03 | Rock/Biogenic Reef | -6.53778 | 57.07331 | 006° 32.26683′ W | 057° 43.98393′ N | 24.4 |
| SI_04 | Rock/Biogenic Reef | -6.49853 | 57.07099 | 006° 29.91172′ W | 057° 42.59426′ N | 22.5 |
| SI_05 | -6.58524 | 57.04178 | 006° 35.11412′ W | 057° 25.06538′ N | 9.9 | |
| SI_06 | -6.55298 | 57.04953 | 006° 33.17855′ W | 057° 29.72089′ N | 5.2 | |
| SI_07 | -6.52064 | 57.05089 | 006° 31.23856′ W | 057° 30.53686′ N | 2.9 | |
| SI_08 | -6.49293 | 57.04335 | 006° 29.57559′ W | 057° 26.00770′ N | 13.1 | |
| SI_09 | Coarse/Mixed Sediments | -6.37188 | 57.05886 | 006° 22.31260′ W | 057° 35.31412′ N | 31.1 |
| SI_10 | Rock/Biogenic Reef | -6.40763 | 57.03812 | 006° 24.45761′ W | 057° 22.86995′ N | 20.9 |
| SI_11 | Rock/Biogenic Reef | -6.43775 | 57.02183 | 006° 26.26522′ W | 057° 13.09882′ N | 16.7 |
| SI_12 | Rock/Biogenic Reef | -6.46154 | 57.01092 | 006° 27.69257′ W | 057° 06.55039′ N | 32.4 |
| SI_13 | -6.43177 | 56.99241 | 006° 25.90618′ W | 056° 59.54469′ N | 6 | |
| SI_14 | Rock/Biogenic Reef | -6.41057 | 56.98095 | 006° 24.63396′ W | 056° 58.85701′ N | 15.9 |
| SI_15 | -6.35911 | 56.94771 | 006° 21.54636′ W | 056° 56.86235′ N | 19.5 | |
| SI_16 | Sand | -6.29011 | 57.04751 | 006° 17.40676′ W | 057° 28.50321′ N | 12.1 |
| SI_17 | Sand | -6.2573 | 57.03721 | 006° 15.43800′ W | 057° 22.32887′ N | 24.8 |
| SI_18 | Sand | -6.24367 | 57.02166 | 006° 14.62042′ W | 057° 12.99781′ N | 22.6 |
| SI_19 | Sand | -6.23116 | 57.00311 | 006° 13.86964′ W | 057° 18.64878′ N | 43.2 |
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Tags: fish traps, underwater video
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