NOAA Technical Memorandum NMFS-AFSC-184
 


Temporal Variability in the Food Habits 

of Arrowtooth Flounder (Atheresthes 

stomias) in the Western Gulf of Alaska 

by 

B. A. Knoth and R. J. Foy 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration
 


National Marine Fisheries Service
 


Alaska Fisheries Science Center
 


April 2008 
NOAA Technical Memorandum NMFS 

The National Marine Fisheries Service's Alaska Fisheries Science Center 

uses the NOAA Technical Memorandum series to issue informal scientific and 

technical publications when complete formal review and editorial processing 

are not appropriate or feasible. Documents within this series reflect sound 

professional work and may be referenced in the formal scientific and technical 

literature. 

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries 

Science Center continues the NMFS-F/NWC series established in 1970 by the 

Northwest Fisheries Center. The NMFS-NWFSC series is currently used by 

the Northwest Fisheries Science Center. 

This document should be cited as follows: 

Knoth, B. A., and R. J. Foy. 2008. Temporal variability in the food 

habits of arrowtooth flounder (Atheresthes stomias) in the Western Gulf 

of Alaska. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-184, 

30 p. 

Reference in this document to trade names does not imply endorsement by 

the National Marine Fisheries Service, NOAA. 
NOAA Technical Memorandum NMFS-AFSC-184
 

Temporal Variability in the Food Habits 

of Arrowtooth Flounder (Atheresthes 

stomias) in the Western Gulf of Alaska 

by 

B. A. Knoth and R. J. Foy 

Alaska Fisheries Science Center
 

Kodiak Laboratory
 

Kodiak Fisheries Research Center
 

301 Research Court
 

Kodiak, AK 99615
 

www.afsc.noaa.gov 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary 

National Oceanic and Atmospheric Administration 

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (ret.), Under Secretary and Administrator 

National Marine Fisheries Service 

James W. Balsiger, Acting Assistant Administrator for Fisheries 

April 2008 
This document is available to the public through: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

www.ntis.gov 
Notice to Users of this Document 

This document is being made available in .PDF format for the convenience of users; however, the 

accuracy and correctness of the document can only be certified as was presented in the original hard 

copy format. 

iii

ABSTRACT 

Within- and among-year variations in the diet and feeding activity of arrowtooth flounder 

(Atheresthes stomias) were examined in order to expand the existing knowledge of their food 

habits to include temporal variability in the western Gulf of Alaska. Stomach samples were 

collected during bottom trawl surveys conducted near Kodiak Island, Alaska, in May and August 

2002-2004. In 2002 and 2003, walleye pollock (Theragra chalcogramma) were the dominant 

prey for arrowtooth flounder (≥ 40 cm total length (TL)), whereas in 2004 the importance of 

walleye pollock declined significantly. In 2004, the importance of euphausiids and Pacific sand 

lance (Ammodytes hexapterus) in the arrowtooth flounder diet increased significantly. Several 

within-year dietary trends were noted during 2004. Most notably, the importance of euphausiids 

in the arrowtooth flounder diet decreased significantly from May to August, whereas the 

importance of capelin (Mallotus villosus) increased significantly. Ontogenetic dietary trends 

were found to vary both temporally and spatially and temporal changes in feeding activity were 

more pronounced in the smaller arrowtooth flounder (20-39 cm TL). The dietary trends generally 

reflected differences in prey availability or abundance and highlighted the adaptable feeding 

behavior of this key predator. 

v

CONTENTS 

INTRODUCTION .......................................................................................................................... 1 

MATERIALS AND METHODS.................................................................................................... 2 

Study Area and Sampling Procedure .......................................................................................... 2 

Laboratory Analysis.................................................................................................................... 2 

Data Analysis.............................................................................................................................. 3 

Diet Analysis............................................................................................................................... 3 

RESULTS ....................................................................................................................................... 4 

General Diet Description ............................................................................................................ 4 

Interannual Food Habit Variations.............................................................................................. 4 

Within-year Food Habit Variations ............................................................................................ 5 

2002.................................................................................................................................. 5 

2003.................................................................................................................................. 5 

2004.................................................................................................................................. 6 

Ontogenetic Food Habit Variations in 2004 ............................................................................... 6 

May .................................................................................................................................. 6 

August.............................................................................................................................. 7 

DISCUSSION................................................................................................................................. 7 

General Diet Composition .......................................................................................................... 7 

Temporal Variations ................................................................................................................... 8 

Ontogenetic Variations ............................................................................................................. 10 

Ecosystem Considerations ........................................................................................................ 11 

ACKNOWLEDGMENTS ............................................................................................................ 13 

CITATIONS ................................................................................................................................. 15 

TABLES......................................................................................................33 

FIGURES......................................................................................................37 

INTRODUCTION 

Arrowtooth flounder (Atheresthes stomias), a relatively large, predatory flatfish species in 

the family Pleuronectidae, are becoming increasingly important in the Gulf of Alaska food web 

because of their dramatic increase in abundance over the past 25 years. Since the early 1970s, the 

biomass of arrowtooth flounder in the Gulf of Alaska has increased nearly sevenfold and they are 

currently the most abundant groundfish species in the system with an estimated biomass of over 

2 million metric tons (t) (Turnock et al. 2005). Juvenile arrowtooth flounder are important prey 

for many groundfish species including Pacific cod (Gadus macrocephalus), sablefish 

(Anoplopoma fimbria), and Pacific halibut (Hippoglossus stenolepis) (Yang and Nelson 2000), 

as well as marine mammals such as Steller sea lions (Eumetopias jubatus) (Sinclair and Zeppelin 

2002). Conversely, adult arrowtooth flounder are top-level predators that feed on forage fish 

species such as juvenile walleye pollock (Theragra chalcogramma), capelin (Mallotus villosus), 

and eulachon (Thaleichthys pacificus) and their diet overlaps with other top-level fish and marine 

mammal predators in the Gulf of Alaska (Yang 1995, Yang and Nelson 2000, Sinclair and 

Zeppelin 2002). To date, temporal and spatial variations in these species interactions are not 

known in detail. In order to quantify the significance of such a dramatic population increase for 

this top-level predator a thorough understanding of these variations is needed. 

The analysis of the food habits of abundant top-level fish predators is critical in assessing 

ecosystem dynamics. Knowledge of diet composition and feeding patterns may afford insight 

into the interactions among key species, such as predator-prey relationships, and help clarify the 

roles of various species in marine ecosystems (Wootton 1990). A better understanding of the 

underlying dynamics of marine ecosystems, including species interactions, is essential to 

facilitate ecosystem-based fishery management practices (Larkin 1996). 

 The food preferences of arrowtooth flounder in Alaska waters have been previously 

described in some detail (Rose 1980, Yang and Livingston 1986, Yang 1995, Yang and Nelson 

2000). Large arrowtooth flounder (> 40 cm) are mostly piscivorous and typically consume 

commercially and ecologically important species such as walleye pollock, Pacific herring 

(Clupea pallasii), and capelin. In addition, invertebrate prey including shrimp and cephalopods 

are also relatively important diet components. Small arrowtooth flounder consume higher 

proportions of euphausiids, shrimp, and forage fish than larger cohorts. At this time, it is not 

clear if the ontogenetic trends are consistent on different spatial and temporal scales throughout 

their range. 

 Despite the considerable number of studies describing the diet of arrowtooth flounder in 

the Gulf of Alaska, relatively little is known about temporal variability in their diet. Reports 

describing temporal trends in the diet of arrowtooth flounder are mostly anecdotal and limited in 

scope (Rose 1980, Livingston et al. 1986). High-latitude fish species commonly exhibit temporal 

variability in food habits that are a reflection of seasonal changes in the marine environment and 

the resulting prey availability (MacKinnon 1972, Livingston et al. 1986, Yamamura et al. 2002). 

Arrowtooth flounder are opportunistic predators and as such, temporal changes in their prey 

consumption would likely reflect changes in prey abundance or availability. More detailed 

studies are required on appropriate scales to quantify the breadth of trophic interactions between 

arrowtooth flounder and their prey in the Gulf of Alaska. 

 We studied trends in the food habits of arrowtooth flounder during the summer feeding 

period of 2002-2004 near Kodiak Island, Alaska. These waters provided an excellent area to 
2

study the food habits of arrowtooth flounder because they are highly productive and support

some of the largest concentrations of arrowtooth flounder in the western Gulf of Alaska 

(Turnock et al. 2005). Our objectives were 1) to quantify the interannual variations in the diet 

composition and feeding activity of arrowtooth flounder from 2002 to 2004, 2) to quantify the 

within-year variations (between May and August) in the diet composition and feeding activity of 

separate arrowtooth flounder size classes in each year and 3) to quantify the ontogenetic 

variations in diet composition and feeding activity of arrowtooth flounder during each sampling 

period (May and August) in 2004. These objectives allow for a more detailed assessment of the 

trophic relationships of this key predator in the nearshore ecosystem of the western Gulf of 

Alaska. 

MATERIALS AND METHODS 

Study Area and Sampling Procedure 

 This study was based on the analysis of stomach contents from arrowtooth flounder 

collected in the nearshore waters of Kodiak Island in the western Gulf of Alaska (Fig. 1). The 

study area encompassed waters of Chiniak and Marmot Bays and sampling stations were located 

within a 20 nautical mile (nmi) radius around Long Island. Fixed sampling stations were 

distributed among a variety of locations and depths in the study area and they were sampled 

twice annually, in May and August, from 2002 to 2004. 

Bottom trawls were conducted onboard a commercial stern trawler using a DanTrawl 

Fiska Trawl II 380/55 model net with a 2.22 cm codend liner with 4.0 m2

 NETS (Nor’ Eastern 

Trawl Systems) Fishbuster doors at each station. The vessel maintained a speed of 3 knots 

(5.5 km/hr) for the duration of each 10 minute tow and covered an average distance of 0.90 km. 

All tows were conducted during daylight between 0600 and 2300 hours. The catches were sorted 

by species and counted upon retrieval. 

Up to 20 arrowtooth flounder specimens from each tow were set aside for analysis. Only 

arrowtooth flounder ≥ 40 cm total length (TL) were collected in 2002 and 2003; however, all 

size classes were collected in 2004 in order to investigate ontogenetic dietary shifts. Specimens 

that displayed evidence of regurgitation or net feeding activities were excluded from the samples. 

Each specimen’s total length (to the nearest 1.0 cm), wet weight (to the nearest 0.01 kg), sex, and 

macroscopic maturity status were recorded. Stomach samples were preserved in 10% formalin–

seawater solution and brought back to the laboratory for analysis. 

Laboratory Analysis 

 Stomachs were removed from cloth bags, blotted dry, and weighed (to the nearest 

0.001 g) in the laboratory. The stomach wall was rinsed, blotted dry, and re-weighed after the 

contents were removed. Total stomach content weight (to the nearest 0.001 g) was calculated by 

subtracting the stomach wall weight from the initial stomach weight. Stomach contents were 

placed on a 300 μm mesh sieve and gently rinsed with distilled water before analysis. Prey 

organisms were separated and identified to the most practical taxonomic level with an emphasis 
3

on the identification of fish, crab, and shrimp prey. Identification keys and reference collections 

of fish otoliths and diagnostic bones were used to identify digested fish prey. 

Intact prey organisms were counted, weighed (to the nearest 0.001 g), and measured (to 

the nearest 1.0 mm TL). The total count of paired structures such as invertebrate eyes and fish 

otoliths were divided by 2 in order to estimate the number of completely digested prey. The total 

length of digested (and partially digested) walleye pollock, capelin, and Pacific sand lance 

(Ammodytes hexapterus) was estimated using regressed relationships between fish total length 

(cm) and diagnostic bone length (mm) (including the cleithra, opercle, and dentary bones). Fresh 

samples of prey species collected during this study were used to derive the relationships between 

fish total length and bone length. 

Data Analysis 

A qualitative analysis of stomach contents did not detect substantial dietary differences 

related to sex therefore the diet composition data for the two sexes were pooled. Arrowtooth 

flounder dietary differences related to depth of capture have been previously reported (Yang 

1995); therefore, the stomach content samples were qualitatively examined for depth-related 

differences. As expected, depth-related differences were observed and thus the samples were 

categorized into < 100 m, 100–200 m, and > 200 m depth intervals for all further analyses. 

Samples from waters deeper than 200 m were excluded from all subsequent analyses because of 

small sample sizes (Table 1). Additionally, the stomach content samples were categorized into 

two size categories (20-39 and ≥ 40 cm TL) for all analyses because previous studies have 

indicated arrowtooth flounder change their feeding behavior and become more piscivorous 

around 40 cm (Yang 1995, Yang and Nelson 2000). 

Individual prey items were grouped into categories to analyze temporal and ontogenetic 

variations. Fish species that did not occur in at least 5% of the specimens were pooled into an 

“other fish” category. Walleye pollock, capelin, and Pacific sand lance each exceeded these 

requirements and they were not pooled into the other fish category. Individual shrimp and 

euphausiid species were pooled into “shrimp” and “euphausiid” categories, respectively, because 

no individual species occurred in at least 5% of the specimens. Similarly, all other invertebrate 

prey items were pooled into an “other prey” category because no individual species occurred in 

at least 5% of the specimens. Lastly, unidentified digested prey material was excluded from all 

dietary analyses because it may have contained more than one prey taxon and, therefore, could 

have biased the results (Schafer et al. 2002). 

Diet Analysis 

 The general diet composition of the arrowtooth flounder samples was described by the 

percent frequency of occurrence (%FO) and percent weight (%W) for each prey category. These 

indices provide independent information into the feeding habits of the predator (Hyslop 1980). 

Frequency of occurrence data gives insight into population-wide feeding habits (Cailliet 1977) 

and weight data reveals the prey item’s nutritional value (Macdonald and Green 1983). Temporal 

variations in the diet and feeding activity of arrowtooth flounder were assessed among the study 

years (2002-2004) and within each year (between the May and August). Specifically, the 
4

analyses of interannual variations in the diet and feeding activity included only adult arrowtooth 

flounder (> 40 cm TL) and were restricted to specimens collected in the 100-200 m depth 

interval due to small sample sizes at other depths. Within-year variations were assessed using 

only stomach samples of adult arrowtooth flounder (≥ 40 cm TL) captured in the 100-200 m 

depth interval in 2002 and 2003. The within-year dietary variations in 2004 were analyzed 

separately for each size class (20-39 and ≥ 40 cm TL) and depth interval (< 100 and 100-200 m). 

Finally, ontogenetic variations in arrowtooth flounder diet and feeding activity were quantified 

for each sampling period and depth interval in 2004. 

The diet composition and feeding activity data failed normality tests, therefore nonparametric methods were chosen for all statistical comparisons. Kruskal-Wallis and MannWhitney U-tests (Zar 1984) were employed to test for significant variations in the percent weight 

contribution of the main prey categories. A prey item’s percent weight contribution was used as 

the principal index in the statistical comparisons because it is an appropriate measure of the 

energetic value of the prey. Feeding activity was assessed by analyzing both stomach fullness 

(stomach content mass as a percentage of body mass) and the percentage of empty stomachs. 

These two indices combined provide a more accurate description of feeding activity than using a 

stomach fullness index alone (Cortés 1997). Temporal and ontogenetic variations in these indices 

were also analyzed using non-parametric tests (Kruskal-Wallis test, Mann-Whitney U-test or X2

 -

test of independence). 

RESULTS 

General Diet Description 

A total of 742 arrowtooth flounder stomachs were examined and 465 (63.0%) contained 

some food. Over 2,800 prey items consisting of 41 different taxa were identified (Table 2). The 

predominance of pelagic prey in the stomachs, including forage fish, pelagic shrimp, and 

euphausiids, reveals arrowtooth flounder feed mainly in the water column. Fish were clearly the 

most important prey category and included at least 11 species. Walleye pollock, Pacific sand 

lance, and capelin were the most important fish prey on both a weight and occurrence basis. 

Other fish prey included unidentified eelpouts, flathead sole (Hippoglossoides elassodon), and 

juvenile arrowtooth flounder. Euphausiids, mainly Thysanoessa spp., occurred in 30% of the 

stomachs and comprised 17.7% by weight of the total stomach contents. Shrimp were also 

relatively important and occurred in 12.0% of the arrowtooth flounder stomachs. Pandalid 

shrimp, including Pandalus borealis, were the most important shrimp in the diets. Other prey 

items including miscellaneous mysids, copepods, and bivalves were largely incidental and 

contributed relatively little (by weight) to the total stomach contents. 

Interannual Food Habit Variations 

 Arrowtooth flounder (≥ 40 cm TL) displayed substantial differences in diet composition 

among the years in each of the sampling periods (Table 3, Fig. 2). In the May sampling period, 

walleye pollock were the main prey item in arrowtooth flounder diets in 2002 and 2003 but were 
5

significantly less important (Hs = 6.68, 2 df, P = 0.036) in 2004. Other fish prey also decreased in 

importance in the arrowtooth flounder diet during 2004. Conversely, euphausiids were 

significantly more important (Hs = 12.11, 2 df, P = 0.002) in the diets of these fish during 2004. 

A similar trend was observed during the August sampling period in that walleye pollock were 

significantly less important (Hs = 6.25, 2 df, P = 0.044) in the arrowtooth flounder diet in 2004 

compared to previous years. However, a similar trend in the importance of euphuasiids among 

the years was not observed during this sampling period. It is also worth noting that Pacific sand 

lance were not found in arrowtooth flounder stomachs in either sampling period during 2002 or 

2003 but they occurred frequently in each sampling period in 2004. 

Interannual trends in stomach fullness and percentage of empty stomachs suggest that 

arrowtooth flounder feeding activity decreased in 2004 (Table 4). Arrowtooth flounder stomach 

fullness differed significantly among the years in each sampling period (May- Hs = 6.58, 2 df, 

P = 0.040) (August- Hs = 12.29, 2 df, P = 0.002) and the stomachs were the least full (P < 0.05) 

in 2004. Additionally, the proportion of empty stomachs varied significantly among the years 

(May- X2 = 13.87, P < 0.05) (August- X2 = 18.80, P < 0.05) and the highest percentages of empty 

stomachs were found in 2004 (May 48.9%, August 46.4%). The size of walleye pollock 

consumed by arrowtooth flounder varied considerably among the years. The mean size (range) of 

walleye pollock in 2002 and 2003 was 325 (229-519) and 378 (290-489) mm (TL), respectively, 

while in 2004 it was 118 (50-455) mm (TL). The smaller mean walleye pollock size in 2004 

resulted from the high abundance of age-0 fish (< 100 mm TL) in the diets. Age-0 walleye 

pollock were not found in arrowtooth flounder stomachs in 2002 or 2003. It appears that 

arrowtooth flounder consumed only adult capelin (> 85 mm TL), whereas they consumed both 

juvenile and adult Pacific sand lance (55-115 mm TL) during the study years. 

Within-year Food Habit Variations 

2002 

In 2002, the diet of arrowtooth flounder (≥ 40cm TL) was noticeably similar between the 

May and August sampling periods (Table 3, Fig. 3). Walleye pollock and other fish were the 

dominant prey and together they comprised ≥ 70% (by weight) of the total stomach contents in 

each of the sampling periods. Shrimp were also relatively important in each of the sampling 

periods. There was no noticeable difference in the feeding activity of these fish between May and 

August as indicated by a lack of significant difference in either stomach fullness (Us = 118, P = 

0.940) or percentage of empty stomachs (X2 = 0.25, P > 0.05) (Table 4). 

2003 

 There were no discernible trends in the diet composition of the arrowtooth flounder 

(≥ 40 cm TL) collected in 2003 (Table 3, Fig. 3). Similar to 2002, walleye pollock and other fish 

were the dominant prey in each of the sampling periods. At this time, these prey comprised 

nearly 80% (by weight) of the total stomach contents in each of the sampling periods. We did not 

detect any noticeable change in arrowtooth flounder feeding activity between May and August in 

2003 (Table 4). 
6

2004 

 Each size class of arrowtooth flounder displayed substantial within-year diet differences 

during 2004 in depths 100-200 m (Table 3, Fig. 4). For the smaller arrowtooth flounder 

(20-39 cm TL), euphausiids, shrimp, and other prey were the dominant prey during May. The 

importance of euphausiids in the diets of these fish decreased significantly (Us = 252.50, 

P = 0.007) from May to August, whereas the importance of capelin significantly increased 

(Us = 241.50, P = 0.001). Other fish were also an important prey for these during August. The 

smaller arrowtooth flounder appeared to increase their feeding activity between May and August 

as evidenced by a significant increase (Us = 227, P = 0.008) in stomach fullness and the slight 

decrease (38.0% to 32.0%) in the percent of empty stomachs (Table 4). For the larger arrowtooth 

flounder (≥ 40 cm TL), euphausiids were clearly the dominant prey during May (Table 3, Fig. 4). 

Pacific sand lance, shrimp, and walleye pollock were relatively important at this time as well. 

The importance of euphausiids in the diets of these fish significantly decreased (Us = 304, 

P < 0.001) from May to August, whereas the importance of capelin significantly increased (Us = 

462.50, P = 0.037). This trend is similar to the one observed for the smaller arrowtooth flounder. 

Other fish and walleye pollock replaced euphausiids as the dominant prey in August. There was 

no noticeable change in the feeding activity of these large arrowtooth flounder, as indicated by a 

lack of significant difference in both the stomach fullness (Us = 493, P = 0.477) and percentage 

of empty stomachs (X2 = 0.21, P > 0.05) between May and August (Table 4). 

 We also observed substantial within year diet differences for each arrowtooth size class 

in the shallow depths (< 100 m) in 2004 (Table 3, Fig. 5). The smaller arrowtooth flounder (20-

39 cm TL) fed almost exclusively on euphausiids in May and the importance of euphausiids in 

the diets of these fish significantly decreased (Us = 66, P < 0.001) in August. Conversely, the 

importance of capelin in the diets significantly increased (Us = 182, P < 0.001) in August for 

these fish. In addition, Pacific sand lance and other prey were significantly more important in the 

diet of these smaller fish (Pacific sand lance- Us = 263, P = 0.046 and other prey- Us = 262, 

P = 0.042) during August. Further, the smaller arrowtooth flounder had significantly fuller (Us = 

139, P < 0.001) stomachs during August, although the proportion of empty stomachs did not 

differ significantly (X2 = 0.47, P > 0.05) (Table 4). Pacific sand lance and euphausiids were the 

dominant prey items, in terms of occurrence and weight, in the diet of larger arrowtooth flounder 

(≥ 40 cm TL) in both sampling periods at these depths (Table 3, Fig. 5). The importance of both 

walleye pollock (Us = 553.50, P = 0.040) and capelin (Us = 533, P = 0.017) increased 

significantly during August even though each item contributed little to the overall diet at this 

time. The feeding activity of the larger arrowtooth flounder did not differ between May and 

August, as indicated by a lack of significant difference in both the stomach fullness (Us = 561, 

P = 0.530) and percent of empty stomachs (X2

 = 0.76, P > 0.05), at these depths (Table 4). 

Ontogenetic Food Habit Variations in 2004 

May 

 We found substantial ontogenetic diet differences for arrowtooth flounder collected from 

shallow depths (< 100 m) during May 2004 (Table 3, Fig. 6). Euphausiids were clearly the 

dominant prey, in terms of weight and occurrence, in the diets of the smaller arrowtooth flounder 
7

(20-39 cm TL). The smaller arrowtooth flounder also frequently consumed other fish, shrimp, 

and other prey, although these prey contributed very little (< 10% of total stomach content 

weight) to the overall diet at this time. Euphausiids were significantly more important (Us = 159, 

P < 0.001) in the diets of smaller arrowtooth flounder, whereas Pacific sand lance were 

significantly more important (Us = 683.5, P < 0.001) in the diets of larger arrowtooth flounder 

(≥ 40 cm TL) in May. We detected no substantial changes in either stomach fullness or 

percentage of empty stomachs among the two size classes of arrowtooth flounder in the 

shallower depths during May 2004 (Table 4). The ontogenetic dietary differences were less 

noticeable in the deeper depths (100-200 m) during this sampling period (Table 3, Fig. 6). 

Euphausiids were the dominant prey, in terms of weight and occurrence, for both size classes at 

these depths. Other prey and shrimp were somewhat more important in the diets of smaller 

arrowtooth flounder (20-39 cm TL), whereas walleye pollock and other fish were relatively more 

important to the larger arrowtooth flounder (≥ 40 cm TL). The two size classes of arrowtooth 

flounder displayed similar levels of feeding activity in these waters (Table 4). 

August 

 The diet composition of the two size classes of arrowtooth flounder differed considerably 

in the shallower depths (< 100 m) during August 2004 (Table 3, Fig. 7). Capelin and other prey 

were significantly more important in the diets of the smaller arrowtooth flounder (capelinUs = 228, P = 0.036 and other prey- Us = 279, P = 0.031) at these depths. Conversely, Pacific 

sand lance were noticeably more important in the diets of large arrowtooth flounder. 

Interestingly, euphausiids were relatively important, in terms of both weight and occurrence, for 

both of the size classes in these waters. The smaller arrowtooth flounder had significantly fuller 

(Us = 145, P < 0.001) stomachs compared to the large arrowtooth flounder, although the 

proportion of empty stomachs did not differ significantly (X2 = 0.09, P < 0.001) in the shallow 

waters at this time (Table 4). We also found substantial ontogenetic diet differences in the deeper 

waters (100-200 m) during this sampling period (Table 3, Fig. 7). Capelin comprised a 

significantly larger portion (Us = 634, P = 0.026) of the diets of small arrowtooth flounder and 

walleye pollock comprised a greater portion (Us = 647.50, P = 0.013) of the diets of large 

arrowtooth flounder in these depths. The remaining prey groups were relatively similar for each 

size class of arrowtooth flounder at these depths. Similar to the trend observed in specimens 

collected in the shallow waters, the smaller arrowtooth flounder had significantly fuller 

(Us = 419, P < 0.001) stomachs and a smaller percentage of empty stomachs, compared to the 

large arrowtooth flounder, at this time (Table 4). 

DISCUSSION 

General Diet Composition 

The diet composition results indicate the arrowtooth flounder near Kodiak Island 

consumed mainly fish, euphausiids, and shrimp, which are consistent with previous findings. For 

example, Rose (1980) found that fish, decapods, and euphausiids were the main prey, 

respectively, in arrowtooth flounder diets in the northeast Gulf of Alaska. Similarly, fish were 
8

the top prey (by weight) in arrowtooth flounder stomachs sampled during Gulf-wide trawl 

surveys in 1993, 1996, and 1999 (Yang and Nelson 2000). Benthic invertebrate prey such as 

mollusks, annelids, and echinoderms were incidental items in the arrowtooth flounder diets, 

which is also consistent with previous findings. 

Despite these similarities, we found several key differences in arrowtooth flounder prey 

composition between this study and previous reports that appear to reflect changes in the Gulf of 

Alaska community during the past 30 years. Rose (1980) reported that osmerids were the most 

common fish prey in arrowtooth flounder diets and that walleye pollock occurred in less than 2% 

of the samples during his 1975-76 study. Conversely, walleye pollock were the most common 

fish encountered in the arrowtooth flounder diets in this study (Table 2). Furthermore, shrimp 

were seen twice as frequently in arrowtooth flounder diets in the 1975-76 study compared with 

the present study. The Gulf of Alaska was dominated by forage fish and shrimp species in 1975-

76 and in the late 1970s the ecosystem underwent a large-scale shift to a community dominated 

by piscivorous flatfish and gadid species (Anderson et al. 1997, Anderson and Piatt 1999). 

Hence, changes in the diet reflect the differences in prey availability during these two periods. 

Additionally, Pacific sand lance was a far more important prey item in this study 

compared to earlier studies (Rose 1980, Yang 1995, Yang and Nelson 2000). Pacific sand lance 

tend to be patchily distributed in nearshore waters because they prefer shallow depths and sandy 

substrates (Ostrand et al. 2005). Therefore, the importance of such a site-specific species may 

have been obscured in previous studies, which sampled a far wider range of habitats, compared 

with this project. Consequently, Pacific sand lance appear to be a locally important prey of 

arrowtooth flounder in the shallow waters of Marmot and Chiniak Bays. 

Temporal Variations 

 Interannual diet comparisons revealed several key shifts in the diets of adult arrowtooth 

flounder among the study years that appear to reflect temporal changes in prey availability. For 

example, the consumption of Pacific sand lance varied significantly among years and was 

highest in 2004. In fact, only 2 of 121 arrowtooth flounder stomachs examined in 2002 and 2003 

contained this prey species. Little is known about the population dynamics of Pacific sand lance 

within the study area, however, changes in their abundance or availability may be reflected in the 

diets of other top level predators. For instance, there was an increase in the importance of Pacific 

sand lance in the diets of tufted puffins Fratercula cirrhata in Chiniak Bay from 2002 to 2004 

(Cory Williams, University of Alaska Fairbanks, Fairbanks, Alaska, pers. commun.). Taken 

together, these findings suggest that Pacific sand lance were more available as a prey source in 

2004. Furthermore, it would benefit arrowtooth flounder energetically to consume Pacific sand 

lance when available because they are one of the most energy-rich fish in the area (Payne et al. 

1999, Anthony et al. 2000). 

There were also noticeable changes in the importance of euphausiids in arrowtooth 

flounder diets among years, especially during the May sampling period. Zooplankton abundance 

and species composition are mainly influenced by changes in the salinity and temperature of the 

water column in Gulf of Alaska shelf waters (Coyle and Pinchuk 2003). The temperature and 

salinity of the surface waters of Chiniak and Marmot Bays fluctuated among the study years and 

within these waters the production of the local zooplankton community varied accordingly (Xian 

Wang, University of Alaska Fairbanks, Fairbanks, Alaska, pers. commun.). It is possible that 
9

fluctuating oceanographic conditions affected euphausiid abundance, which in turn influenced 

their relative rates of consumption by arrowtooth flounder, during the study years. 

It appears that arrowtooth flounder shifted from consuming mostly age-1 and -2 walleye 

pollock in 2002 and 2003 to age-0 walleye pollock in 2004. In 2004, age-0 walleye pollock were 

highly abundant in the bottom trawls conducted in the study area unlike previous years when 

they were not as prevalent (Robert Foy, University of Alaska Fairbanks, Kodiak, Alaska, unpubl. 

data). The increase in the consumption of juvenile walleye pollock as their availability increased 

in 2004 reflects the trophic adaptability of arrowtooth flounder. 

The increase in the number of samples collected and analyzed in 2004, compared to the 

previous years, may have resulted in an increase in prey diversity in the diets. However, the 

principal prey items were consistent throughout the study years, with the exception of Pacific 

sand lance. The importance of Pacific sand lance may have been overstated in 2004 (or 

understated in previous years) due to discrepancy of sample sizes among the years. Although the 

frequent occurrence of Pacific sand lance in the diets during 2004 regardless of size class, depth 

interval, or sampling period, indicates they were more highly available at this time. 

Seasonal variations in temperature and day length in high latitude regions impose strong 

seasonal effects on the composition and production of nearshore fish communities (Nash 1988, 

Robards et al. 1999). As a result, top-level predators experience considerable variability in the 

abundance and quality of prey throughout the year. Seasonal dietary differences have been 

observed for many predatory flatfish species (Libey and Cole 1979, Livingston et al. 1986, 

Tokranov 1990). Arrowtooth flounder are believed to feed opportunistically on the most 

abundant prey in the environment (Rose 1980, Yang and Livingston 1986) and consequently 

within-year dietary shifts most likely reflect seasonal changes in prey abundance and/or 

availability. 

The importance of euphausiids and capelin in the arrowtooth flounder diets varied most 

strongly between May and August in this study. Euphausiids tended to be more important in the 

diets during May, which is consistent with previous findings for arrowtooth flounder in the 

northeast Gulf of Alaska (Rose 1980). In the northern Gulf of Alaska shelf waters, the annual 

biomass peak for zooplankton occurs during May (Coyle and Pinchuk 2003). Furthermore, in 

high latitude regions many fish species begin moving onshore in May as water temperatures 

increase and do not peak in relative abundance until mid-summer (Robards et al. 1999). 

Therefore, the importance of euphausiids in arrowtooth flounder diets during May possibly 

reflects a combination of the high zooplankton production and relatively low availability of fish 

prey at this time. 

Unlike euphausiids, capelin were mostly non-existent in the arrowtooth flounder diets in 

May but rose in importance in August. Capelin spawn on intertidal beaches in the North Pacific 

during a protracted spawning period from late spring through early summer (Pahlke 1985) and 

spawning activity near Kodiak Island, Alaska, generally peaks around June or July (Doyle et al. 

2002). Only adult capelin (90 to 120 mm TL) were consumed by arrowtooth flounder in this 

study and ripe females were noted frequently in stomach samples. This finding indicates that 

arrowtooth flounder were possibly targeting adult capelin congregating nearshore to spawn 

during August. This behavior would benefit arrowtooth flounder because capelin may be more 

vulnerable to predation during spawning and they are a particularly energy-rich food source, 

especially the ripe females (Payne et al. 1999, Anthony et al. 2000). The ability to take advantage 

of this energetically valuable late summer food source demonstrates their adaptable feeding 

behavior. 
10

Temperate fish species commonly exhibit seasonal cycles of feeding activity that are 

driven by changes in abiotic and biotic factors such as water temperature, food supply, and 

reproduction (MacKinnon 1972, Dawson and Grimm 1980, Dygert 1990). In this study, we 

found that the smaller arrowtooth flounder displayed higher feeding activity levels during August 

when bottom temperatures were on average 1.48°C higher than in May (Knoth 2006). The higher 

feeding levels in August may be a mechanism to cope with greater energetic costs, associated 

with the higher temperatures, during this time. These differences may also reflect a more diverse 

and abundant food supply available to these fish during August. Larger arrowtooth flounder may 

utilize different strategies to counter changes in their thermal environment, such as migrating to 

deeper, cooler waters and benefiting from the associated lower metabolic costs. 

Ontogenetic Variations 

We found that the ontogenetic diet variations varied spatially. For instance, Pacific sand 

lance were noticeably more important in the diets of the larger arrowtooth flounder, compared to 

smaller cohorts, in the shallow depths only. This is likely a combination of factors including prey 

availability and physical limitations. Pacific sand lance have a preference for sand and gravel 

substrates in shallow waters, which limits their availability to predators (O’Connell and Fives 

1995). It has been noted previously that arrowtooth flounder display an increasing trend towards 

piscivory as they grow (Rose 1980, Yang and Livingston 1986, Yang and Nelson 2000), thus 

prey consumption for each size group may be dictated by a physical limitation such as gape size. 

The ontogenetic diet differences also varied temporally and appeared more pronounced 

during the August sampling period. At this time, capelin were more important in the diets of 

smaller arrowtooth flounder compared to larger cohorts in each depth interval. The larger 

arrowtooth flounder favored larger fish prey such as walleye pollock or Pacific sand lance during 

the August sampling period. The larger arrowtooth flounder would be able to consume a wider 

size range and diversity of fish prey compared to smaller cohorts because of their larger gaping 

mouths (Yang and Livingston 1986). This type of ontogenetic diet shift may reduce the 

competition for food between large and small individuals of the same species (Grossman 1980) 

and is consistent with the optimum foraging theory (Gerking 1994). It is important to note that 

there may be ontogenetic differences based on sexual maturity that were overlooked. Sexual 

maturity was not examined and changes in feeding habits may be driven by changes in energetic 

needs due to reproduction. Arrowtooth flounder exhibit sexual dimorphism with respect to size at 

maturity, with females maturing at a larger size (females 50% maturity at 47 cm, males at 42 cm 

(Zimmermann 1997)). These lengths correspond roughly with the size cutoff (40 cm) that we 

used to designate the two size classes in our study. Arrowtooth flounder are group synchronous 

batch spawners with a fall to winter spawning period (Rickey 1995). In the Gulf of Alaska, the 

spawning season for arrowtooth flounder is unclear, but it is believed to begin after September 

(Zimmermann 1997). Taken as a whole, the August sampling period would represent a critical 

feeding period for large, sexually mature arrowtooth flounder seeking to acquire the necessary 

energy levels for reproduction. Thus, these factors may have contributed to the temporal 

variability associated with the ontogenetic diet differences. 
11

Ecosystem Considerations 

The ability to adapt to changing feeding conditions is a necessary trait for a species to be 

successful, particularly in a fluctuating environment like the Gulf of Alaska. The Gulf of Alaska 

ecosystem alternates between anomalous warm and cool states or “regimes” characterized by 

distinct atmospheric, oceanic, and biological conditions (Mantua et al. 1997, Hare and Mantua 

2000). Following the shift to a warm regime in the late 1970s, there was a marked improvement 

in the recruitment of groundfish species, including arrowtooth flounder, and a concurrent 

decrease in shrimp and forage fish species in the Gulf of Alaska (Hollowed and Wooster 1992). 

The ability of arrowtooth flounder to adapt to large-scale changes in prey resources likely 

contributed to their success during this period of transition. Furthermore, there have been at least 

two other documented climate shifts in the North Pacific since the late 1970s, but the biological 

response to these shifts have yet to be fully realized (Hare and Mantua 2000, Benson and Trites 

2002, Peterson and Schwing 2003). It is unlikely that a major decline in any single prey source 

would negatively affect the arrowtooth flounder population in the Gulf of Alaska because of their 

adaptable feeding behavior. 

Results of this study support previous findings that arrowtooth flounder mainly feed on 

pelagic and semi-pelagic forage fish and invertebrates (Rose 1980, Yang and Livingston 1986, 

Yang 1995, Yang and Nelson 2000). These prey species are critical links between primary 

producers (phytoplankton) and higher trophic level predators in the nearshore Kodiak Island 

ecosystem and throughout the western Gulf of Alaska. Additionally, other top-level fish, marine 

mammal, and seabird predators rely on these forage prey to varying degrees (Perez 1990, Hayes 

and Kuletz 1997, Witteveen et al. 2006, Yang and Nelson 2000, Yang et al. 2005). 

Consequently, the large arrowtooth flounder population in the Gulf of Alaska may affect 

multiple trophic levels in the system through predation and competition. 

Our findings may have important management implications because ecosystem-based 

management models rely extensively on detailed diet information in order to describe complex 

species interactions. We found significant temporal variations in the diet of arrowtooth flounder 

even though the time span of our study was limited in its scope. Many other marine fish display 

temporal, spatial, and ontogenetic variations in their diets as well (Libey and Cole 1979, 

Grossman 1980, Tokranov 1990, Gerking 1994) and these types of dietary variations are difficult 

to incorporate into ecosystem-based models (Pauly et al. 2000). Nevertheless, a lack of 

understanding of such diet variability may misrepresent the importance of key prey species 

across temporal and spatial scales. Therefore, the diet information included in ecosystem-based 

models needs to cover significant temporal variations in predator diets (Hanson and Chouinard 

2002, Pauly et al. 1998). 

Arrowtooth flounder display a highly adaptable feeding behavior that is evident in the 

degree of temporal variability in their food habits in an area of high abundance in the western 

Gulf of Alaska. We found that arrowtooth flounder diet and feeding activity, based on size class 

and depth distribution, vary both within and among years near Kodiak Island, Alaska. 

Arrowtooth flounder diets may reflect changes in prey availability and abundance or differences 

in feeding behavior associated with prey selection. To address this, future studies that assess the 

breadth of interactions between arrowtooth flounder and its prey need to concurrently measure 

prey abundance and distribution. Documenting arrowtooth flounder feeding behavior, in 

response to changing levels of prey abundance and composition, will allow for a better 
12

understanding of the trophic interactions of this key predator in the nearshore ecosystem of 

Kodiak Island and throughout the western Gulf of Alaska. 
13

ACKNOWLEDGMENTS 

 The project was a part of BAK’s M.S. thesis research at the University of Alaska 

Fairbanks (UAF). The project was supported financially from two sources: a NOAA grant 

(NOAA Grant NA16FX1270) to RJF while on the faculty at UAF to support the Gulf Apex 

Predator-Prey Project; and a Rasmuson Fisheries Research Center grant to BAK and RJF. The 

authors thank N. Hillgruber, G. Haas, A. Abookire, M-S. Yang, M. Wilkins, and D. Somerton for 

providing helpful comments on the manuscript. P. Livingston and M-S. Yang also provided 

useful reference materials for the stomach content analyses. We thank the captain and crew of 

the F/V Laura for their efforts during the survey cruises. Fish collections were made under the 

following permits: Alaska Department of Fish and Game (CF-02-072, CF-03-024, and CF-04-

31) and National Marine Fisheries Service (LOA#2002-07, LOA#2003-01, and LOA#2004-06). 

Fish treatment followed a protocol approved by the University of Alaska Fairbanks Institutional 

Animal Care and Use Committee (IACUC Nos. 04-21 and 01-11). 

15

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Table 1. -- Arrowtooth flounder (Atheresthes stomias) stomach samples* collected for each size, 

depth interval, sampling period and year near Kodiak Island, Alaska. 

Depth interval (m) 

Year Size (cm TL) Sampling period < 100 100-200 > 200 

2002 ≥ 40 May 5 20 3 

August 13 44 0 

2003 ≥ 40 May 0 18 0 

August 26 37 10 

2004 ≥ 40 May 71 87 37 

August 45 105 0 

20-39 May 40 70 8 

August 38 65 0 

* All stomachs collected including empty stomachs 
21

Table 2. -- Percent weight (%Wt) and percent frequency of occurrence (%FO) of arrowtooth 

flounder (Atheresthes stomias) diets sampled near Kodiak Island, Alaska, from 2002 

to 2004. Categories including fish, shrimp, euphausiid, and other prey show the sum 

of the components within that category. Asterisks indicate value was less than 0.1%. 

Prey categories % Wt % FO 

Fish 43.5 51.0 

Ammodytes hexapterus (Pacific sand lance) 9.6 12.9 

Atheresthes stomias (arrowtooth flounder) 1.1 1.3 

Cottidae (sculpin) * 0.2 

Fishery offal 0.2 0.2 

Gadidae (gadid fish) 1.4 2.2 

Hippoglossoides elassodon (flathead sole) 1.4 1.5 

Lumpenus sagitta (snake prickleback) 0.2 0.2 

Mallotus villosus (capelin) 8.5 9.7 

Pleuronectidae (unidentified flatfish) 0.5 0.6 

Sebastes sp. (rockfish) * 0.2 

Teleostei (unidentified fish) 5.0 8.0 

Thaleichthys pacificus (eulachon) 0.2 0.4 

Theragra chalcogramma (walleye pollock) 13.3 14.0 

Trichodon trichodon (Pacific sandfish) 0.2 0.2 

Zoarcidae (unidentified eelpout) 1.7 1.9 

Euphausiid 17.7 29.7 

Euphausia pacifica 0.2 0.2 

Euphausiacea (unidentified) 8.1 17.0 

Thysanoessa inermis 2.6 3.0 

Thysanoessa raschii 0.7 0.9 

Thysanoessa sp. 4.3 5.6 

Thysanoessa spinifera 1.9 2.8 

Shrimp 8.2 12.0 

Crangon communis * 0.2 

Crangon dalli * 0.2 

Crangonidae (unidentified) 0.0 0.2 

Eualus gaimardii 0.3 0.4 

Eualus sp. * 0.2 

Pandalopsis dispar 0.2 0.2 

Pandalopsis sp. 0.5 0.6 

Pandalus borealis 2.4 3.7 

Pandalus sp. 1.4 1.9 

unidentified shrimp 3.2 4.7 

Other prey 3.2 9.2 

Bivalvia (clam) 0.2 0.9 

Calanoida (copepod) * 0.6 

Chionoecetes bairdi (Tanner crab) 0.2 0.2 

Crustacea (unidentified) 1.0 3.7 

Decapoda (unidentified crab) * 0.4 

Echiuridae (marine worm) 0.2 0.4 

Gammaridea (unidentified amphipod) * 0.2 

Mysidae (unidentified mysid) 0.9 1.3 

Psolus sp. (sea cucumber) 0.3 0.4 

Snail eggs (unidentified) * 0.2 

Unidentified digested material 27.3 32.7 
22

Table 3. -- Interannual, within-year and ontogenetic variations in the percent frequency of 

occurrence (% FO) of the major prey categories in the arrowtooth flounder 

(Atheresthes stomias) diets collected in two depth intervals (< 100 m and 100-200 m) 

near Kodiak Island, Alaska. 

 

Year 

2002 2003 2004 

100-200 m 100-200 m < 100 m 100-200 m 

≥ 40 cm ≥ 40 cm 20-39 cm ≥ 40 cm 20-39 cm ≥ 40 cm 

 Prey 

categories May August May August May August May August May August May August

Capelin 0 8 5.9 0 0 41.7 0 12.5 0 36.8 0 15.6 

W. pollock 40 44 47.1 44.4 0 8.3 0 9.4 0 5.3 10.3 24.4 

P.sand lance 0 0 0 0 3.2 20.8 47.8 40.6 8.7 13.2 20.7 6.7 

Other fish 40 32 35.3 29.6 41.9 8.3 13 15.6 4.4 23.7 13.8 33.3 

Shrimp 20 24 11.8 7.4 38.7 12.5 8.7 6.3 21.7 23.7 13.8 15.6 

Euphausiids 10 16 11.8 14.8 83.9 45.8 43.5 43.8 43.5 21.1 51.7 22.2 

Other prey 0 8 17.7 14.8 48.4 37.5 39.1 18.8 39.1 10.5 20.7 22.2 

Sample 

size (n) 10 24 17 23 28 23 41 30 21 37 25 44 
23

Table 4. – Kruskal-Wallis (Hs), Mann-Whitney (Us), and Chi-square (X2

)test results 

investigating variations in arrowtooth flounder (Atheresthes stomias) stomach fullness 

and percentage of empty stomachs in specimens collected near Kodiak Island, 

Alaska. Interannual (2002 vs. 2003 vs. 2004), within-year (May vs. August), and 

ontogenetic (20-39 cm TL vs. ≥ 40 cm TL) comparisons were made. Significant Pvalues of the respective test statistic are denoted by: * P < 0.05, ** P < 0.01, and *** 

P < 0.001. 

Comparisons Stomach fullness Empty stomachs 

Interannual Hs P-value X2 P-value 

May 6.58 0.040* 13.87 < 0.05* 

August 12.29 0.002** 18.80 < 0.05* 

Within-year Us P-value X2 P-value 

2002 (100-200 m) 118 0.940 0.25 > 0.05 

2003 (100-200 m) 171 0.503 0.12 > 0.05 

2004 (100-200 m; 20-29 cm TL) 227 0.008** 3.11 > 0.05 

2004 (100-200 m; ≥ 40 cm TL) 493 0.477 0.21 > 0.05 

2004 (< 100 m; 20-29 cm TL) 139 < 0.001*** 0.47 > 0.05 

2004 (< 100 m; ≥ 40 cm TL) 561 0.530 0.76 > 0.05 

Ontogenetic Us P-value X2 P-value 

May 2004 (< 100 m) 522 0.525 1.61 > 0.05 

May 2004 (100-200 m) 187 0.096 1.37 > 0.05 

August 2004 (< 100 m) 145 < 0.001*** 0.09 > 0.05 

August 2004 (100-200 m) 419 < 0.001*** 3.69 > 0.05 
24

Figure 1-- Locations of bottom trawl stations (filled triangles) in the nearshore waters of Kodiak 

Island, Alaska. Fixed sampling stations were sampled during May and August 

annually in 2002, 2003, and 2004. 
25

Figure 2-- Interannual variations in diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) (≥ 40 cm) sampled near Kodiak Island, Alaska, during May 

(top) and August (bottom) of 2002, 2003, and 2004. Significant Kruskal-Wallis tests 

are denoted by * P < 0.05 and ** P < 0.01. 

0

20

40

60

80

100

Other prey

Euphausiids**

Shrimp

Other fish

P. sand lance*

W. pollock*

Capelin

n = 10 n = 17 n = 25

May

Diet composition (% Weight) 

0

20

40

60

80

100

2002 2003 2004

Other prey

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock*

Capelin

n = 24 n = 23 n = 44

August

Year
26

n = 10 n = 24 200

0

20

40

60

80

100 Other prey

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock

Capelin

Figure 3-- Within-year variations in the diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) (≥ 40 cm) sampled near Kodiak Island, Alaska, during 2002 

(top) and 2003 (bottom). 

0

20

40

60

80

100

May August

Diet com

p

osition (% Wei

ght)

Other prey

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock

Capelin

2003

Sampling period

n = 17 n = 23 
27

Figure 4-- Within-year variations in the diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) 20-39 cm (top) and ≥ 40 cm (bottom) sampled in depths 

100-200 m near Kodiak Island, AK in 2004. Significant Mann-Whitney U-tests are 

denoted by * P < 0.05, ** P < 0.01, and *** P < 0.001.

0

20

40

60

80

100

Other prey

Euphausiids**

Shrimp

Other fish

P. sand lance

W. pollock

Capelin**

ATF 20-39 cm

n = 21 n = 37

0

20

40

60

80

00

May August

1

Diet composition (% Weight) 

Other prey

Euphausiids***

Shrimp

Other fish

P. sand lance

W. pollock

Capelin*

ATF ≥ 40 cm

n = 25 n = 44

Sampling period 
28

Figure 5-- Within-year variations in the diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) 20-39 cm (top) and ≥ 40cm (bottom) sampled in depths < 100 

m near Kodiak Island, Alaska, in 2004. Significant Mann-Whitney U-tests are 

denoted by * P < 0.05 and *** P < 0.001.

0

20

40

60

80

100

Other prey*

Euphausiids***

Shrimp

Other fish

P. sand lance*

W. pollock

Capelin***

ATF 20-39 cm

n = 28 n = 23

0

20

40

60

80

00

May August

1

Diet composition (% Weight) 

Other prey

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock*

Capelin*

ATF ≥ 40 cm

n = 41 n = 30

Sampling period 
29

Figure 6-- Ontogenetic variations in the diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) sampled during May 2004 near Kodiak Island, Alaska, in 

depths < 100 m (top) and 100-200 m (bottom). Significant Mann-Whitney U-tests are 

denoted by * P < 0.001. 

0

20

40

60

80

100

20 - 39 ≥ 40

Other prey

Euphausiids

Shrimps

Other fish

P. sandlance

W. pollock

Capelin

n = 21 n = 25

100-200 m

0

20

40

60

80

100 Other prey

Euphausiids*

Shrimps

Other fish

P. sandlance*

W. pollock

Capelin

n = 41

< 100 m

n = 28

Diet composition (% Weight) 

ATF size (cm)
30

Figure 7-- Ontogenetic variations in the diet composition (by % weight) of arrowtooth flounder 

(Atheresthes stomias) sampled during August 2004 near Kodiak Island, Alaska, in 

depths < 100 m (top) and 100-200 m (bottom). Significant Mann-Whitney U-tests are 

denoted by * P < 0.05.

0

20

40

60

80

100 Other prey*

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock

Capelin*

< 100 m

n = 23 n = 30

Diet composition (% Weight) 

0

20

40

60

80

100

20 - 39 ≥ 40

Other prey

Euphausiids

Shrimp

Other fish

P. sand lance

W. pollock*

Capelin*

100-200 m

n = 37 n = 44

ATF size (cm)

RECENT TECHNICAL MEMORANDUMS
 


Copies of this and other NOAA Technical Memorandums are available from the 

National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167 

(web site: www.ntis.gov). Paper and microfiche copies vary in price. 

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of Soviet whaling expeditions in the North Pacific, 1955-1978, 34 p. [Translation: Y. V. Ivashchenko] + 

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vessel attitude, 34 p. NTIS No. PB2007-111255. 

170	 	 RODGVELLER, C. J., J. H. MOSS, and A. M. FELDMANN. 2007. The influence of sampling location, 

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168	 	 ANGLISS, R. P., and R. B. OUTLAW. 2007. Alaska marine mammal stock assessments, 2006, 

244 p. NTIS No. PB 2007-106476.