Abstract
Stereo‐video scuba transects were conducted during daylight hours from June to September 2013 within a proposed marine protected area (MPA) in the Firth of Clyde, west of Scotland. More juvenile Atlantic cod Gadus morhua of fork length (L F) 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 L F 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.
Highlights
With increasing concern over the state of the marine environment, much attention has been paid to the development of marine protected areas (MPAs) as an ecosystem-based approach to protect vulnerable substrata and restore species and their habitats (Roberts et al, 2005; Seitz et al, 2014)
The MPA contains within its boundaries the Lamlash Bay no take zone (NTZ), designated in 2008 and prohibiting all fishing within its boundaries under the Inshore Fishing (Scotland) Act of 1984 (Axelsson et al, 2009)
Data collected have enabled fine-scale abundance and distribution information to be gathered for the first time on G. morhua during daylight hours within the Firth of Clyde
Summary
With increasing concern over the state of the marine environment, much attention has been paid to the development of marine protected areas (MPAs) as an ecosystem-based approach to protect vulnerable substrata and restore species and their habitats (Roberts et al, 2005; Seitz et al, 2014). Factors affecting the survival of temperate marine fishes are not well understood (Langton et al, 1996) This is of particular relevance within European waters where measures to restore fish stocks have focused primarily on reducing fishing effort, fishing gear adaptations to reduce by-catch and fisheries closures (Fernandes & Cook, 2013; Hilborn, 2011). Since the first phase of the G. morhua recovery plan was introduced (early 2000s) (Anon, 2001; Kraak et al, 2013), measures have been implemented to try and restore stocks, including the prohibition of targeted fishing and a seasonal spawning area closure implemented in the outer Firth of Clyde (Anon, 2001, 2002; Clarke et al, 2015). In the U.K., little attention has been paid to key habitat requirements for juveniles in comparison to Canada, the U.S.A. and Scandinavian countries (Bailey et al, 2011)
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