Abstract
Fish communities in the shallow waters (9–20 m depth) of outer Malangen (69o N), Northern Norway was studied to investigate effects of season, bottom substrate associations and population dynamic parameters on the fish assemblages. In four fieldtrips during one year at four locations, fish were sampled by trammel nets and bottom substrate composition was monitored by underwater video. A total of 16 species of fish were caught, including four species from Pleuronectidae and six from the Gadidae family. Cod (Gadus morhua Linnaeus, 1758) was the most numerous species followed by plaice (Pleuronectes platessa Linnaeus, 1758), lemon sole (Microstomus kitt Walbaum, 1792) and halibut (Hippoglossus hippoglossus Linnaeus, 1758). Cod dominated the catches in all months except March, in which plaice and other flatfishes were most dominant. On a community scale, fish species richness was highest in October and lowest in March. Furthermore, the species richness and diversity were generally higher at locations with greater bottom substrate evenness. Cod showed a positive association with large macroalgae coverage and were less numerous at locations dominated by sand and pebble. Plaice and common dab (Limanda limanda Linnaeus, 1758) showed positive associations with sand and pebble coverage, while lemon sole was more associated with maerl beds, cobble and low algae coverage. Only halibut younger than 8 years of age were observed, and the sampling areas are suggested to be nursery area for this species. Von Bertalanffy growth functions were estimated for cod, plaice and lemon sole, and the growth coefficient K of cod and plaice were higher than for populations from adjacent fjords or the North Sea populations. Total mortality rates of cod and plaice were lower than for areas further south, and this may contribute to high and relative stable biomasses in the shallow Malangen area.
Highlights
Fish assemblages in shallow waters are affected by many biogenic factors, such as macroalgae coverage, predation and competition (Aus ter, 1988; Fahrig, 2003; Fraser et al, 1996; Gratwicke and Speight, 2005; Sissenwine, 1984)
The bottom substrate is a result of biogenic factors as well as physical factors, especially current and exposure levels (Buhl-Mortensen et al, 2012; Rinde et al, 2014; Sivertsen, 1997) and many of the mentioned physical factors have high seasonal variation in subarctic areas
Fish community compositions in outer Malangen were mainly affected by bottom substrate variability
Summary
Fish assemblages in shallow waters are affected by many biogenic factors, such as macroalgae coverage, predation and competition (Aus ter, 1988; Fahrig, 2003; Fraser et al, 1996; Gratwicke and Speight, 2005; Sissenwine, 1984). Macroalgae habitats can function as shelter for juvenile fish species (Demartini and Roberts, 1990), thereby influencing the predator-prey dynamics (Sivertsen, 2006) Physical factors such as bathymetry, currents, wave exposure, temperature, salinity, light, turbidity and bottom substrate affect fish communities (Buhl-Mor tensen et al, 2012; Claireaux and Dutil, 1992; Ruppert et al, 2009), and it is more likely that several rather than a single factor decide how a species use a habitat (Gili and Petraitis, 2009). There are few studies of fish communities in these areas and knowledge of population and community dynamics for species in these shallow areas are important for proper coastal resource and ecosystem man agement. It is impossible to survey these shallow waters with conventional survey bottom trawls due
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