342 



Alaska — Our Livini^ Rt'soiirces 



,-\rctlc I.ISCO i(_'iirt\^iinu\ aitiiun- 



IUltl\\ Courtesy R West, USFWS 



Small Arctic cisco. 



Courtesy W,J Wilson, LGL Research Alaska, Inc 



Broad uhitefish iCoregomis 



naSIIS)- Courtesy n west, USFWS 



Least ci.sLO {Corf!>imus sanlinel- 



la)- Courtesy R West USFWS 



Dolly Varden char {Salvelinus 

 nialnia}. 



Courtesy WJ Wilson, LGL Research Alaska, Inc 



Fig. 2. Season-averaged catch 

 rates (catch-per-unit-effort. CPUE) 

 for (a) Arctic cisco (Coregonus 

 autunmalis) cohorts I-IV. (b) broad 

 whitefish (C. nasus) cohons I-IV. 

 (c) least cisco (C sardinella) 

 cohorts I and II. and (d) Dolly 

 Varden char {Salvelinus malma) 

 cohorts I and II. in the Prudhoe 

 Bay study area, 1985-93 (Endicott 

 Fish Monitoring Program. BP 

 Exploration [Alaska]. Inc.). 



Mackenzie River. Canada. Upitii emergence, 

 Noung fish are swept downstream and transport- 

 ed along the coast with prevailing nearshore cur- 

 tents. During years when easterly winds prevail. 

 cun-ents cany juveniles westward into Alaskan 

 waters. Their migration is passive and recruit- 

 ment varies annually. Juveniles in Alaska 

 become mature after 7-9 years. They then return 

 to spawn in the Mackenzie system. In Alaska, 

 fish winter in the Colville River, and to a lesser 

 extent, in the Sagavanirktok River deltas. Each 

 June, young t'lsh move to the coastal sea and are 

 common in Prudhoe Bay. The commercial gill- 

 net fishery is selective for 5- and 6-year-old fish. 



Trends in abundance for four age groups of 

 Arctic cisco captured in Prudhoe Bay since 1985 

 illustrate the cyclic nature of the species abun- 

 dance by cohort in northern Alaska (Fig. 2a). 

 The size and age structure observed in the popu- 

 lation before 1985, and after causeway construc- 

 tion, generally follow predicted patterns expect- 

 ed from historical wind records. 



The annual commercial catch of Arctic cisco 

 from the Colville River fishery has ranged from 

 9,000 fish in 1979 to 72,000 in 1973 (Fig. 3). 

 During the same period mean catch-per-unit 

 effort (CPUE) ranged from 12 fish/net/day in 

 1979 to 19.5 fish/net/day in 1986. Biologists 

 think that the availability of harvestable fish is 

 due to natural mortality and interannual varia- 

 tions in numbers of misrants from Canada. 



a) Arctic Cisco CPUE, by cohort, 

 Prudhoe Bay study area, 1985-93 

 - 60 - 



1 1 III I ill Qiv 



■^ 50 



40 - 



30 - 



20 |- 



LEO 



Qll - ,1 _ il ^ |_ 



85 86 87 88 



c) Least cisco CPUE, by cohort, 

 Prudhoe Bay study area, 1985-93 

 - 30 



90 91 92 93 



Year 



Broad Whitefish 



Broad whitefish are indigenous to the 

 Sagavanirktok and Colville rivers. Monitoring 

 concentrated on the Sagavanirktok's population 

 because of causeway construction in the river 

 delta. Cohort analysis shows low catch rates in 

 Pmdhoe Bay from 1985 to 1987, followed by 

 annual increases that peaked in 1990, and declin- 

 ing abundance thereafter (Fig. 2b). The existing 

 data suggest a cycle of strong year-class success 

 followed by several years of poor juvenile sur- 

 vival, which probably results from adult displace- 

 ment of juveniles from optimal winter habitats. 



A 10-year population cycle is suggested, 

 underscoring the critical, if not limiting, nature of 

 freshwater habitat for broad whitefish. Without 

 long-term monitoring, the reduced abundance of 

 juveniles in the late 1980's would have been 

 attributed to causeways and not competition 

 between fish at freshwater wintering sites. 



Least Cisco 



The center of distribution for least cisco in 

 the Alaskan Beaufort Sea is the Colville River. 

 Biologists have captured all cohorts of least 

 cisco in Prudhoe Bay. No trends in CPUEs are 

 apparent from cohort analysis (Fig. 2c), although 

 catch rates were high in 1990. possibly because 

 of prevailing west wind conditions that year. 



Least cisco are of secondary importance in the 



b) Broad whitefish CPUE. by cohort, ■ n ■ [a 



Prudhoe Bay study area. 1985-93 1 1 11 H I m i IV 



Year 



d) DollyVarden char CPUE, by cohort, 

 Prudhoe Bay study area. 1985-93 

 — 12 



85 86 87 



90 91 92 93 



85 86 87 



Year 



89 90 91 92 93 

 Year 



