Date:
2018/06/13
Time:
14:45
Room:
K305 Alvar
An assessment of juvenile Atlantic cod Gadus morhua distribution and growth using diver operated stereo-video surveys
(Oral)
Sophie A. M. Elliott
, Pauliina A. Ahti
, Michael R. Heath
, Bill Turrell
, David M. Bailey
SEE PEER REVIEW
While the relatively infamous Atlantic cod (Gadus morhua) fisheries have recovered in some areas, the cod fishery in the Firth of Clyde on the west coast of Scotland remains depleted. The role of juvenile fish survival in determining the future cohort sizes is important, yet the key habitats for juvenile marine fishes in the U.K. have received little attention. Many juvenile fish inhabit shallow coastal areas, where the monitoring of fish is not possible using fisheries dependent methods. Here, we conducted 31 stereo-video scuba transects during daylight hours from June to September 2013 within a proposed marine protected area (MPA) in the Firth of Clyde. More juvenile Atlantic cod Gadus morhua of fork length (LF) range 6–11 cm were observed in substrata containing mixed gravel, including maerl, than in boulder-cobble substrata with high algal cover, or sand with low density seagrass. Community composition was significantly different between substratum types. A decrease in G. morhua abundance was observed over the period of data collection. Over time, mean and variance in G. morhua LF increased, indicating multiple recruitment events. Protecting mixed gravel substrata could be a beneficial management measure to support the survival and recruitment of juvenile G. morhua; other substrata might be important at night given their diel migratory behaviour. Stereo-video cameras provide a useful non-destructive fisheries-independent method to monitor species abundance and length measurements.
INTRO: The problem of the study was explicitly presented.
MERITS: The findings in this study are indeed significant and it shows how in-situ monitoring of populations in their respective habitat can be done void of fisheries dependent methods.
CRITIQUE: I think the range/average total length (TL) should be mentioned aside from the fork length (FL). What about the approximate length of the transect?
DISCUSSION: Data from night surveys may help considering their diel behaviour and many species exhibit nocturnal behaviour/active in the night. Additional data from fish visual census (FVC) may also help since behaviour and preferences of some fishes can be influence by other species in the area. This can be helpful to enrich the discussion part.
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INTRO: This study deterimes the habitat types where juvenile cods are most abundant during day time across the summer season with measurements of the sizes of the cod with non intrusive stereo-videoed scuba transects.
MERITS: If the method is replicable at larger scale it may be useful for the population estimates of the fish. Proper sample size.
CRITIQUE: The inference that juveniles may be in other habitats when not vidoed (night time) is not really supported by the data.
DISCUSSION: Perhaps a worthwhile study.