AbStraCt.-Ichthyoplankton were 

 sampled weekly in Auke Bay, south- 

 eastern Alaska, from March or early 

 April through June, 1986-89. The 

 spring primary production bloom oc- 

 curred in April, and was followed in 

 May by the annual maximum in 

 herbivorous copepods. Each year, 

 the five most-abundant fish larvae 

 were osmerids. Pacific sandlance 

 Ammodytes hexapterus, walleye 

 pollock Theragra chalcogramma, 

 fiathead sole Hippoglossoid.es elasso- 

 don, and rock sole Pleuronectes 

 bilineatus. Each species tended to 

 occur at the same time every year, 

 and could be categorized either as 

 synchronous species that were 

 present at the time copepod abun- 

 dance was maximized, or early spe- 

 cies that were most abundant be- 

 fore the spring phytoplankton bloom. 

 Pacific sandlance and rock sole lar- 

 vae always reached maximum abun- 

 dance prior to the spring bloom, 

 whereas larvae of walleye pollock, 

 fiathead sole, and osmerids were 

 most abundant at the time of the 

 copepod maximum. Physical and bi- 

 otic conditions experienced by early 

 and synchronous larvae differ mark- 

 edly, suggesting that survival 

 through early life history is deter- 

 mined by different processes in the 

 two groups. 



Abundance patterns of marine 

 fish larvae during spring in a 

 southeastern Alaskan bay 



Lewis Haldorson 

 Marc Pritchett 

 David Sterritt 

 John Watts 



School of Fisheries and Ocean Sciences, University of Alaska 

 1 1 1 20 Glacier Highway. Juneau, Alaska 99801 



Manuscript accepted 20 August 1992. 

 Fishery Bulletin. U.S. 91:36-44 ( 1993 1. 



Fluctuation in recruitment to ex- 

 ploited fish populations remains a 

 central problem in marine fish man- 

 agement. There are indications that 

 much of the variation in year-class 

 abundance in marine fish populations 

 results from processes and events in 

 planktonic early-life-history stages 

 (Houde 1987, Pepin & Myers 1991). 

 Interannual variation in survival 

 through egg and larval life stages 

 is undoubtedly determined by mul- 

 tiple and interacting mechanisms; 

 however, timing of reproduction has 

 often been implicated as a factor 

 contributing to the success or fail- 

 ure of year-classes. For example, 

 Hjort's (1914) critical-period hypoth- 

 esis and Cushing's (1975) match- 

 mismatch hypothesis describe the 

 importance of synchrony between 

 production of larval fishes and their 

 planktonic prey. 



In subarctic regions, nearshore 

 marine ecosystems display marked 

 seasonal changes in physical and bi- 

 otic conditions (Smetacek et al. 

 1984). In such systems, timing of 

 reproduction may be extremely im- 

 portant, as conditions that result in 

 high survival through planktonic 

 life-history stages may be transi- 

 tory. A dominant feature in the an- 

 nual subarctic nearshore production 

 cycle is the spring phytoplankton 

 bloom, an event that contributes 

 much of the annual production 

 (Smetacek et al. 1984). The phyto- 



plankton bloom is followed by the 

 herbivorous copepod maximum 

 (Smetecek et al. 1984), a period of 

 1-2 months that produces an an- 

 nual optimum in foraging conditions 

 for those larval fishes that feed on 

 copepod nauplii. Water temperature 

 and predator density may also de- 

 termine survival of fish eggs and 

 larvae (Houde 1987) and could con- 

 stitute important constraints on 

 timing of reproduction. 



In this paper we report the re- 

 sults of a 4-year investigation of lar- 

 val fishes in a coastal subarctic ma- 

 rine ecosystem. Our observations 

 describe when larvae of some north- 

 east Pacific Ocean fish species oc- 

 cur relative to the spring produc- 

 tion cycle. The study was part of 

 an interdisciplinary project (AP- 

 PRISE, Association of Primary Pro- 

 duction and Recruitment in a Sub- 

 arctic Ecosystem) that provided a 

 detailed description of the physical 

 and biotic environment present dur- 

 ing the period from late winter 

 through early summer. 



Study area 



The study was conducted in Auke 

 Bay (lat. 58 22' N, long. 134 40' W), 

 southeast Alaska. (Fig. 1). The 16knr 

 Bay varies in depth from 40 to 60 m. 

 Physical conditions in Auke Bay are 

 typical of nearshore subarctic marine 



36 



