vival. If several years of poor upwelling occur 

 in a row, there may be several years of poor 

 commercial catches, after some lag time. The 

 converse should be true as well, assuming food 

 is limiting. This paper will examine these pos- 

 sibilities by attempting to relate catches of 

 Dungeness crab from the coasts of Washington, 

 Oregon, and northern California to an upwelling 

 index. 



Certain aspects of the crab fisheiy make it 

 uniquely suited for direct comparison to coastal 

 upwelling. At the winter start of any crab fish- 

 ing season, a finite number of legal-sized male 

 crabs exist. The season essentially ends when 

 virtually all of these animals are harvested. 

 Tagging studies at Grays Harbor, Wash., in 

 1947 and 1948 found that minimally 79 and 

 87% , respectively of the available males were 

 harvested (Cleaver, 1949. In California, re- 

 search has indicated (Pacific Marine Fisheries 

 Commission, 1964) that between 90 and 100% 

 of the male crabs have been taken annually 

 since 1928 or 1929. I am assuming that the 

 intensity of the Oregon fishery has been similar. 

 The Pacific Marine Fisheries Commission 

 noted in 1964 that "... a few years ago, it took 

 probably seven months to remove 90-95% of 

 the available crabs. Now it takes hardly seven 

 weeks." Fishing effort data are not required, 

 since very few of the available animals escape 

 capture. Therefore, total pounds landed in a 

 given season is an excellent indicator of popu- 

 lation size and possibly grovrth rate. 



Reproduction is unaffected by the fishery, 

 since males have several opportunities to mate, 

 and females are not legally harvested. In Oregon 

 and Washington, reproduction can occur at 

 age 2. By age 3 probably most males have mated 

 at least once during the summer mating season 

 (Cleaver, 1949). These animals may reproduce 

 again the following summer before entering the 

 winter fishery at age 4V2 yr. In California, mat- 

 ing occurs earlier, during late winter and 

 spring. Males IV2 yr old have been observed 

 mating, but generally do not until 2^/2 yr of age. 

 At age 3V2 males enter the fishery (Poole and 

 Gotshall, 1965), 1 yr earlier than Washington 

 and Oregon crabs. All along the west coast, 

 females rarely, if ever, attain the legal size 

 for males of 6V4-inch carapace width, and thus 



they are not generally retained in crab pots. The 

 crab population may even be benefited by re- 

 moval of those 4-yr-old males who have fulfilled 

 their copulatory obligations, since this may re- 

 duce intraspecific competition for food required 

 by growing 2- and 3-yr-old males, and egg- 

 bearing females. 



Coastal Upwelling and Dungeness Crabs 



Ekman's theory (Bakun, in press) states that 

 the net mass transport of water set in motion 

 by sea surface winds will be 90° to the right 

 of the direction in which the wind is blowing, 

 in the northern hemisphere. The intensity of 

 this water transport (referred to as Ekman 

 transport) is a function of the intensity and 

 duration of the wind stress. 



Along the Oregon coast for example, winds 

 generally blow from the north and northwest 

 from April to September. The effect is a trans- 

 port of surface water away from the coastline. 

 This offshore near-surface transport is balanced 

 by an onshore deep transport of cool, nutrient- 

 rich water, coming to the surface. This phenom- 

 enon is called upwelling. 



Strong upwelling off Oregon occurs when 

 strong winds have a northerly component. The 

 opposite phenomenon, downwelling, can occur 

 if the winds have a southerly component. In 

 this case warm surface waters are carried on- 

 shore, and cooler deep water moves offshore. 

 Both phenomena occur in any given summer. 

 The result of continuous steady northerly 

 winds would be a summer of strong upwelling. 

 A relative increase in the frequency of weak 

 northerly and/or southerly winds would result 

 in a summer of weak upwelling. 



There is evidence that one of the biological 

 effects of upwelling (i.e., increased production 

 of copepods) is felt primarily along a rather 

 narrow band paralleling Oregon's coastline, 

 only a few miles wide, in close proximity to the 

 shore. Zooplankton samples collected with fine- 

 mesh nets off Newport, Oreg. (lat. 44°40'N), 

 during periods of upwelling show the greatest 

 abundances of phytoplankton and microcopepods 

 at stations 1, 3, and 5 nautical miles from the 

 beach. Microcopepod numbers drop rapidly 

 farther offshore. Dungeness crabs are found 



903 



