(1,814 kg, or an estimated 60,400 specimens) 

 was at 9 m and occurred near Coos Bay. The 

 14-m dei)th was an area of transition between 

 living and dead sand dollars. Catches made at 

 18, 23. and 27 m were composed entirely of 

 dead animals. At these depths, the largest 

 catches along the coast occurred between Ten 

 Mile Creek and Siltcoos River. 



Mean widths of the five samples of live speci- 

 mens ranged from 76.4 to 85.9 mm; the overall 

 mean was 80.1 mm. The catches from which 

 these samples were taken are marked with a 

 footnote in Table 2. 



Discussion 



Merrill and Hobson (1970) reported that two 

 types of distribution patterns occur in sand dol- 

 lar populations along the protected outer coast. 

 In one type, the populations run parallel to 

 shore as dense bands and maintain a character- 

 istic pattern that is reformed when disrupted by 

 occasional heavy seas. The outer margin of these 

 populations is well-defined in 4-12 m of water 

 and here the largest individuals and greatest 

 densities occur. The other type of distribution is 

 similar, except that it extends into deeper water, 

 below about 10-15 m; individuals become prog- 

 ressively smaller with depth. 



These distribution patterns are apparently 

 similar off the exposed outer coasts of Oregon 

 and Washington. My findings off Oregon and 

 Washington indicate well-defined seaward lim- 

 its, as essentially no live D. excentricus were 

 taken by the dredge at depths below 15 m. 



McCauley and Carey (1967) collected D. 

 e.vceiitricKs off Oregon in depths of 8 to 56 m. 

 They found the mean widths of specimens to be 

 78.2 mm at 8 to 13m, 35.8 mm at 22 m, and less 

 than 10 mm at 50 m. They concluded that mean 

 widths show a decrease in size with depth, sug- 

 gesting that animals may move shoreward with 

 increase in size or that in some way depth may 

 influence growth. They apparently sampled 

 both the near-shore and deeper water types of 

 distribution patterns. 



Merrill and Hobson (1970) speculated that 

 available food for D. excentricus off the protected 

 outer coast is most abundant just seaward of the 

 breaker line, where the water is about 10 m deep, 



and that beyond this depth available food de- 

 creases with depth. Our dredge catches of the 

 species off Oregon and Washington support 

 the hypothesis that optimum conditions for 

 D. excottricHs exist inside the 15-m depth inter- 

 val. 



It is difficult to explain why large numbers 

 of dead sand dollars were found primarily in 

 the deeper depths sampled during our surveys 

 (18-27 m). Merrill and Hobson (1970) found 

 that at Zuma Beach, Calif, (a protected outer 

 coast area) much of the sand dollar population 

 in shallow water is swept or carried seaward 

 during heavy seas, but when the sea is calm 

 individuals in the seaward part of the colony 

 move shoreward. This seaward movement dur- 

 ing heavy seas may be even more extensive in 

 populations in exposed outer coast areas off 

 Oregon and Washington where storms are often 

 more frequent and severe. Empty tests would 

 be even more subject to wave action and currents 

 than live specimens. During heavy seas they 

 may be swept seaward where they accumulate. 



My findings support earlier observations that 

 D. excentricus is widely distributed and, in addi- 

 tion, is abundant in many sandy bottom areas 

 within a depth of 15 m off the coast of Oregon 

 and Washington. 



Literature Cited 



McCauley, J. A., and A. G. Carey, Jr. 



1967. Echinoidea of Oregon. J. Fish. Res. Board 

 Can. 24:1385-1401. 

 Merrill, R. J., and E. S. Hobson. 



1970. Field observations of Dendraster excentricus, 

 a sand dollar of western North America. Am. 

 Midland Nal. 83:595-624. 

 Raup.D. M. 



1956. Dendraster: A problem in echinoid ta.xonomy. 

 J. Paleontol. 30:685-694. 

 Ricketts, E. F., and J. Calvin. 



1952. Between Pacific tides. 3d ed. rev. by J. W. 

 Hedgpeth. Stanford Univ. Press, Stanford, Calif., 

 502 p. 



Norman B. Parks 



Northwest Fisheries Center 



National Marine Fisheries Service, NOAA 



2725 Montlake boulevard East 



Seattle, W A 981 12 



1109 



