5.3.1 Larval Fish Distribution 



TINA WYLLIE ECHEVERRIA and C. PETER McROY 



Institute of Marine Science. University of Alaska at Fairbanks. Fairbanks. Alaska. USA 



Introduction 



Zooplankton samples are routinely taken during Shelf 

 Transfer and Recycling Project (ISHTAR) cruises. Larval fish 

 occurred incidentally in the samples. We decided to identify 

 the fish and investigate the abundance and distribution of 

 species. These results are part of the Third Joint US-USSR 

 Bering & Chukchi Seas Expedition aboard the RA' Akademik 

 Korolev from 27 July to 2 September 1988. 



Materials and Methods 



Ichthyoplankton were collected along with zooplankton in 

 a 1 -m circular net with 505 jam mesh. A vertical tow was made 

 through the water column at 40 m/min. All larval fish were 

 identified to family. Species were identified and standard 

 length (SL) measured using vernier calipers for the Gadidae 

 and the Pleuronectidae. teleost families containing commercially 

 utilized species. The depth the larval fish occupied cannot be 

 determined from this sampling technique. 



Coachman and Shigaev (Subchapter 2.1, this volume) 

 delineate three principal water masses in the northern Bering 

 and Chukchi Seas. For the purposes of this study we are 

 interestedin two of these water masses: /. water originating in 

 the deep southern Bering Sea that travels in the Bering Slope 

 Current into the Gulf of Anadyr then north through Bering 

 Strait, herein referred to as Anadyr stream water (ASW); and 

 2. water that resides on the eastern central shelf of the Bering 

 Sea characterized by lower salinity than ASW, herein referred 

 to as Bering Shelf water ( BS W ). We delineated these two water 

 masses further by the presence of certain zooplankton species. 

 Indicator species for BSW are Thysanoessa raschii, Calanus 

 marsluillae. and Calanus glacialis. Indicator species for AS W 

 are: Thysanoessa inermis. Neocalanus cristatus. Neocalanus 

 plumchrus. and Metridia spp. Water masses were defined in 

 order to e.xplore the possibility of passive transport of fish 

 larvae into or through the study area. 



Chlorophyll a concentrations, as measured by fluorescence 

 (Parsons et a!.. 1984), were detennined for each station (see 

 Robie et ai. Subchapter 5.1.2, this volume), integrating the 

 concentrations from discrete depths for surface to bottom or to 

 50 m when depths were >50 m. 



Results and Discussion 



Seven families: Scorpaenidae (rockfishes), Liparididae 

 (snailfishes), Ammodytidae (sandlance), Cottidae (sculpins), 

 Stichaeidae (pricklebacks), Gadidae (codfishes), and 

 Pleuronectidae (flatfishes) were present. Three species of 

 Gadidae — Theragra chalcograinnia (walleye pollock). 



Boreogadus saida (arctic cod), and Eleginus gracilis (saffron 

 cod) — were identified and two species of Pleuronectidae — 

 Hippoglossoides elassodon (tlathead sole) and Limanda sp. 

 (yellowfin sole) (Table 1 ) (Matarese et ai, 1989). 



TABLE 1 



Larval fishes sampled from the northern 

 Bering and Chukchi Seas, the number of 

 stations where each family or species was 

 collected, the total number of each family 

 or species in the samples, and the percent 



of each family and species of the total 

 number offish sampled during the cruise. 



Fish larvae were found in 58 of the 90 stations sampled 

 (Frontispiece). Abundance ranged from 1 to 29 fish per station 

 (Fig. 1). Fishoccurthroughoutthestudy area, primarily along 

 the eastern border to the Gulf of Anadyr, in waters characterized 

 as both ASW and BSW. Larval fish may be associated with a 

 particular water mass, but we cannot detemiine this because we 

 did not take discrete depth samples. The association of larval 

 fish relative to phytoplankton fields as measured by chlorophyll 

 a concentrations can only be discussed generally. Integrated 

 data for each station shows an association of larval fish with 

 chlorophyll values less than 100 mg/m'. Theragra 

 chalacogranuna was the most abundant and widespread of the 

 identified species (Fig. 2). They were concentrated where 

 BSW overlay AS W ( Fig. 4 ), with associated chlorophyll values 

 below 100 mg/m- (Fig. 3). Two size classes, newly hatched 

 larvae (4—7 mm SL) and larvae 20-25 mm SL dominated the 

 samples (Fig. 5). The larvae occurred northward of known 

 spawning grounds and north of where known adult 

 concentrations occur (NOAA, 1987). 



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