No abstract

Forty-three species of fishes and 16 species of larger crustaceans were caught by trawl and seine during a 4 yr study on a sandy beach on the west coast of Scotland. There were considerable differences in the species composition of the trawl and seine catches such that neither alone provided an adequate description of the sampled cornnlunity. Approximately monthly s a m p h g demonstrated a clear seasonal cycle in abundance and species composition. A few species were resident on the beach all year round; the majority were only present from spring to autumn. Increases in both numbers and species were caused mainly by the recruitment of young of the year individuals whose numbers subsequently declined rapidly probably due to a combination of predation and emigration. There were marked differences in both species composition and abundance between years. Annual cycles in species richness and abundance closely paralleled those of temperature and sahnity. It is suggested that the cycles result mainly from recruitment and mortality rather than from immigration and emigration in response to physical factors.

ABSTRACT. Fishes were sampled by seine and beam trawl over tidal and diel cycles on a sandy beach on the west coast of Scotland in J u n e and August Species composition of the catches of the 2 gear types differed. There was a signif~cant pos~tive relationsh~p between depth (0 to 5 m ) and species richness but a few specles were restricted to depths of < S m Although s~gnif~cantly more species and individuals were caught at night and at low tide there was no evidence for the existence of d~stinct 'day' and 'night' communities. D~fferences between catches at hlgh and low water were caused by the movement of a few species into the ~ntertidal zone on the rising tide. Diel differences In abundance were pnnc~pally d u e to an inshore migration of several species of gadoids at dusk and movement offshore at dawn. Longer term changes in abundance and distr~bution were attributed to predation and movement ~n t o deeper water

The ability ofjuvenile plaice (1 8-190 mm) to bury in sands varying in grain size from 0.062-2 m m was examined. For fish greater than approximately 30 mm in length the relationship between the proportion of the body covered with sand (0, total length (L, mm) and grain size (S, mm) can be estimated from the equation: logit C = 3.250+0.069L-6,771S. Based on their performance in coarser sediments, fish smaller than approximately 30 mm did not bury as well as expected in the finest sediments (0.062 and 0.125 mm).

Stratified depth sampling was used to investigate the distributional changes of newly settled plaice Pleuronectes platessa and dabs Limanda limanda, and resident populations of shrimp Crangon crangon on a sandy beach. During the settlement period, the smallest newly settled plaice are found in deeper water than the larger fish that settled earlier. After settlement, plaice concentrate in water <1 m deep and there is a positive relationship between length and depth. Later in the year the fish gradually migrate into deeper water as they grow. Dabs settle later and in deeper water than plaice. Shrimp are concentrated in deeper water early in the year but migrate onshore in the summer. The movements of plaice are considered to be related to the predation risk caused by the shrimp and other predators in deeper water and to the higher temperatures in shallow water that promote faster growth. Once a size refuge from predators has been reached, the plaice move into deeper water. Intertidal pools probably serve as refuges for the smallest sizes of plaice because predators are less numerous in pools than in the sea. The use of shallow water by plaice represents the occupation of a niche which not only reduces predation and maximises growth, but may also greatly reduce competition for food in the earliest stages when densities are highest and competition with dabs is likely to be greatest.