Burkett 



Chapter 22 



Food Habits and Prey Ecology 



They grow to about 20 centimeters in length (Miller and 

 Lea 1972). There has been much confusion over the 

 taxonomy of the sand lances throughout the world since 

 they are similar in external appearance (Hardy 1965: 209- 

 210; McGurk and Warburton 1992). Of this confusion 

 Hardy (1965: 210) wrote, "It all goes to show how 

 elusive. ..these sand-eels are. They are all very much alike; 

 little silvery eel-like fish which occur in large shoals in 

 sandy parts of the sea and escape from their predators by 

 diving like a flash into the sand and becoming completely 

 covered." They are most abundant in the shallow regions 

 around the coast, but may also be found on sand banks far 

 out on the continental shelf (Hardy 1965: 211). 



The most interesting characteristic of the sand lances is 

 their ability to burrow into sand or gravel and remain there 

 for long periods. Both burrowing and emergence are extremely 

 rapid, the fish entering and leaving the surface almost vertically 

 at swimming speed. Coastal sand lance may bury themselves 

 above low-water mark and remain buried as the tide recedes 

 and until it covers the area again. This habit demands a 

 loose, porous substrate in which respiratory water maintains 

 sufficient oxygen to support life (Scott 1973). 



Food habits of 486 specimens (15-31 cm) of northern 

 sand lance (A. dubius) taken at various localities and seasons 

 from Nova Scotia Banks revealed copepods as the most 

 frequent food item, followed by crustacean larvae, invertebrate 

 eggs, and polychaete larvae. Volumetric analysis showed 

 copepods to comprise the bulk of the food (65 percent), 

 followed by polychaete larvae ( 1 5 percent) and euphausiids 

 (14 percent). The latter two food items were selected for in 

 greater volume when compared to availability, since 

 euphausiids made up less than 4 percent of the volume of 

 simultaneous plankton tows (Scott 1973). 



McGurk and Warburton (1992) conducted an intensive 

 study of environmental conditions and the effects on sand 

 lance larvae in the Port Moller estuary in Alaska. They 

 found that three waves of spawning sand lance entered the 

 estuary from mid- January to late May. Peak spawning occurred 

 in January, March, and April. Eggs incubated for a period of 

 45 to 94 days. Slow growth was directly responsible for the 

 reduced number of cohorts and the long time periods between 

 peak hatch dates compared to other demersally-spawning 

 fish such as herring or capelin, because first-feeding sand 

 lance larvae took longer to vacate their feeding niches. The 

 larvae fed primarily during the day on a diet of copepod eggs 

 and nauplii, copepodites, and small adult copepods. This 

 type of prey and its average length and width were similar to 

 that of herring larvae, indicating that the larvae of these two 

 species shared the same food resource. 



McGurk and Warburton (1992) concluded that the stock 

 of sand lance that spawns in Port Moller belongs to a class of 

 stocks that have an entirely estuarine or coastal early life 

 history, in contrast to some stocks of sand lance whose 

 larvae disperse offshore from inshore spawning sites. This 

 life history strategy may have evolved in response to the 

 unique physical conditions of the Port Moller estuary a 



shallow, well-mixed site with sandy substrate that is suitable 

 for incubation of demersal eggs next to a deep, stable fjord 

 with a rich zooplankton community that is suitable for rearing 

 of larval and juvenile sand lance. 



Variation in physical factors, particularly, storm events, 

 local wind-forced surface currents, baroclinic surface currents, 

 and regional downwelling events at the boundary of the 

 estuary cause annual variation in recruitment. Additionally, 

 density-dependent factors such as competition for food between 

 sand lance, between sand lance and other planktivorous fish 

 larvae such as herring, and between sand lance and invertebrate 

 planktivores such as chaetognaths may play as important a 

 role as density-independent physical factors (McGurk and 

 Warburton 1992). McGurk and Warburton noted that the 

 small scale of dispersal in the Port Moller stock also leaves it 

 more vulnerable to industrial development such as dredging 

 or release of toxic chemicals. 



Sherman and others (1981) summarized research in the 

 North Sea which documented an increase in sand eel 

 (Ammodytes sp.) as a result of depleted herring and mackerel 

 (Scomber sp.) stocks. In the absence of a sand lance fishery 

 on the east coast of North America from which to estimate 

 population trends, researchers in this area used ichthyoplankton 

 surveys. As in the North Sea, population explosions of small, 

 fast-growing sand eel coincided with depletions of larger 

 tertiary predators, including herring and mackerel. From 

 1974 to 1979 the percentage of sand eel increased from less 

 than 50 percent of the total mid-winter ichthyoplankton 

 community to more than 85 percent (Sherman and others 

 1981). This change followed significant fishing stress of the 

 northwest Atlantic ecosystem, where fish biomass in the 

 region was reduced by 50 percent from 1968 to 1975 (Clark 

 and Brown in Sherman and others 1981). 



Clark and Brown concluded that reductions in herring 

 and mackerel on both sides of the Atlantic in response to 

 heavy fishing mortality, followed by increases in sand eel 

 and other small, fast-growing fish, made unlikely the 

 hypothesis that the changes were due to environmental factors. 

 They concluded that, when a large biomass of mid-size 

 predators is removed, it can be replaced by smaller, faster- 

 growing, opportunistic species (Sherman and others 1981). 



This relationship was further evaluated by Fogarty and 

 others (1991) with a mathematical model. A significant 

 negative interaction between sand lance recruitment and an 

 integrated measure of herring and mackerel biomass was 

 indicated. However, since both herring and mackerel feed 

 on sand lance, it was impossible to distinguish the relative 

 roles of the two predators. The authors concluded that 

 direct evidence of predation by mackerel and herring was 

 available to support the inference of interactions between 

 sand lance and pelagic predators, though alternative 

 hypotheses could be formulated. 



Recent changes in the population of sand eels (Ammodytes 

 marinus) at Shetland were studied in relation to estimates of 

 seabird predation (Bailey and others 1991). Since 1974 there 

 has been a sand eel fishery in inshore waters around Shetland, 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



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