Brenda L. Norcross

Depth and substrate as determinants of distribution of juvenile flathead sole (Hippoglossoides elassodon) and rock sole (Pleuronectes bilineatus), in Kachemak Bay, Alaska

Abstract Three transects in Kachemak Bay, Alaska, were sampled in September 1994, May and August 1995, and February, May, and August 1996. Juvenile flathead sole, Hippoglossoides elassodon, and rock sole, Pleuronectes bilineatus, were the most abundant flatfishes, comprising 65–85% of all flatfishes captured at any period. Collections of fish and sediments were made at regular depth contour intervals of 10 m. Habitat distribution was described by depth at 10 m increments and sediment percent weights of gravel, sand, and mud. Year-round habitat of flathead sole age-0 was primarily from 40 to 60 m, and age-1 habitat was primarily from 40 to 80 m. Summer habitat of rock sole age-0 and -1 was from 10 to 30 m, and in winter they moved offshore to depths of up to 150 m. Both age classes of flathead sole were most abundant on mixed mud sediments, while age-1 were also in high abundance on muddy sand sediments. Rock sole age-0 and-1 were most abundant on sand, though age-1 were also found on a variety of sediments both finer and coarser grained than sand. Flathead sole and rock sole had distinctive depth and sediment habitats. When habitat overlap occurred between the species, it was most often due to rock sole moving offshore in the winter. Abundances were not significantly different among seasons for age-1 flatfishes.

Sediment preference in juvenile pacific flatfishes

Abstract Behavioural preference tests were used to determine if sediment selection played a role in habitat choice. Four species of juvenile pleuronectids were given a choice of eight sediments in a carousel and final choices were recorded after 20 h. Juvenile flatfishes demonstrated strong selection for sediments less than 500 μm. Juvenile starry flounder (Platichthys stellatus) selected larger particles with increasing fish size. Starry flounder under 25 mm in length chose mud, 50–80 mm fish chose mud and mixed mud sediments and larger juveniles (>150 mm) confined themselves to find sand. Juvenile halibut (Hippoglossus stenolepis) at 50–80 mm preferred a combination of mud and fine sand and were spatially segregated. Yellowfin sole (Pleuronectes asper) at 50–80 mm showed a slight preference for mud and mixed mud sediments over sand, a selection that became stronger in larger (>150 mm) fish. Juvenile rock sole (Pleuronectes bilineatus) at 50–80 mm preferred substrata of sand and mixed sand nearly 90% of the time. All species seldom selected sediments which were too coarse to allow the flatfishes to bury themselves, such as granular or pebble substrata. The results of these laboratory studies can be used to predict the distribution of juvenile flatfishes in a nursery area.

Nursery area characteristics of Pleuronectids in coastal Alaska, USA

Juveniles of four species of pleuronectid flatfishes were abundant in bays and nearshore areas around Kodiak Island, Alaska during August 1991. Flatfish nursery areas located in deep water bays such as those surrounding Kodiak Island have not been previously reported. Age-0 rock sole (Pleuronectes bilineatus), flathead sole (Hippoglossoides elassodon), Pacific halibut (Hippoglossus stenolepis) and age-1 yellowfin sole (Pleuronectes asper) were collected close to one another and at first appeared to share nursery areas. Closer examination of associated within-bay distribution, depth, substrate, temperature and salinity data revealed characteristics which limited nursery area overlap. The major concentrations of juveniles of these species could usually be segregated by one or more of the physical parameters investigated. Based on the physical characteristics found to be most important in determining distribution of juveniles for each species, we hypothesize the following relationships. Age-0 rock sole are found predominantly in water depths less than 50 m, on sand or mixed sand substrate outside of or within bays. Age-0 flathead sole are found predominantly in water depths greater than 40 m, on mud or mixed mud substrate throughout bays. Age-0 Pacific halibut are found predominantly in water depths less than 40 m, on mixed sand substrate near or outside mouths of bays. Age-1 yellowfin sole are found predominantly in water depths less than 40 m, on mixed substrates at upper reaches of bays. These hypotheses will be field tested, after which the relationships may be considered for application to broader geographic areas.

Non-avoidance of hydrocarbon laden sediments by juvenile flatfishes

Behavioural tests were used to determine whether juvenile flatfishes were capable of detecting and avoiding sediment containing various concentrations of petroleum hydrocarbons. Three species of juvenile Alaskan flatfishes: rock sole (Pleuronectes bilineatus), yellowfin sole (P. asper), and Pacific halibut (Hippoglossus stenolepis) were tested in laboratory chambers containing contaminated mud or sand offered in combination with clean mud, sand or granule. The flatfishes were able to detect and avoid heavily oiled (2%) sediment, but they did not avoid lower concentrations of oiled sediment (0.05%). Oiled sediment was favoured over unoiled sediment if the unoiled sediment was of the grain size not preferred by that species. Oiled sand or mud was always preferred unoiled granule. The observed lack of avoidance at concentrations likely to occur in the environment may lead to long-term exposure to contaminated sediment following a spill. Recruitment of juveniles may be affected if the exposure to oil is long enough to affect growth and survival.

Electron microprobe analysis of juvenile walleye pollock, Theragra chalcogramma, otoliths from Alaska: a pilot stock separation study

SynopsisThe incorporation of dissolved oceanic constituents in the otoliths of fish has potential as a chemical tracer for reconstructing the early life history of marine fish. Wavelength dispersive spectrometers on an electron microprobe were used to measure Na, Mg, P, S, Cl, K, Ca, and Sr concentrations on the outer margins of 57 juvenile walleye pollock, Theragra chalcogramma, otoliths from five locations in the Gulf of Alaska and Bering Sea. Discriminant analyses that used various combinations of Na, P, K, Sr, and fish standard length and/or age showed that 60–80% of the samples could be assigned to the correct capture locality. While the concentrations of some of the measured elements correlated with standard length or age of the fish, there are measurable differences among localities when concentrations are length or age corrected, mainly due to differences in Na and K concentrations. Elemental composition of otoliths potentially could be used to assign fish from a mixed stock fishery to original stocks, information that is greatly needed for the effective management of fish stocks.

Spatial and Temporal Variability in Juvenile Pacific Herring, Clupea pallasi, Growth in Prince William Sound, Alaska

We examined the spatial and temporal variability of juvenile Pacific herring, Clupea pallasi, growth within Prince William Sound, Alaska. Pacific herring, ranging from post-larval to mature fish, were collected from four spatially segregated bays between October 1995 and March 1998. Linear growth equations from each bay were similar. However, growth rates and wet weight-at-length, reflecting condition, of juvenile Pacific herring cohorts varied seasonally and annually. The short term spatial variability in juvenile Pacific herring growth suggested that each bay was a unique nursery area. The physical and biological conditions within each bay appeared to dictate Pacific herring growth rate.

Variability in the summer diets of juvenile polar cod (Boreogadus saida) in the northeastern Chukchi and western Beaufort Seas

Polar cod (Boreogadus saida) is an important link between top predators and lower trophic levels in high-latitude marine ecosystems. Previous findings describe differences in its diet throughout the western Arctic; however, the causes of this variation are not well known. This study examined the diets of juvenile polar cod collected via demersal trawling methods over three summers in the northeastern Chukchi Sea (2010–2012) and one summer in the western Beaufort Sea (2011) to determine the amount of variability explained by biological, spatial, and interannual factors. Prey were identified, measured for length, and aggregated by percent mean weight into taxonomically coarse prey categories for analysis. Within seas, variation in juvenile polar cod diet composition was significantly related to body size, latitude, longitude, depth, and interannual (Chukchi Sea only) factors. Canonical correspondence analysis indicated body size was the most important factor contributing to the total variance in juvenile polar cod diet in the Chukchi and Beaufort Seas. Body size-based diet differences between the Chukchi and Beaufort Seas were evaluated using non-metric multidimensional scaling. This method revealed that similar-sized polar cod consumed similar-sized prey in both seas, but their diets were more benthically influenced in the Chukchi Sea and more pelagically influenced in the Beaufort Sea. Juvenile polar cod diet compositions vary by body size and region of inhabitance throughout their distribution. Here, we show that body size was the primary factor explaining variation in the summer diet of juvenile polar cod within the Chukchi and Beaufort Seas.

Larval Fishes in Relation to Water Masses of the Central North Pacific Transitional Areas, Including the Shelf Break of West-Central Alaska

Larval fishes and corresponding physical data were sampled along two transects from Seward, Alaska to Oahu, Hawaii in February 1991. The first transect was west along the shelf break (SH) off Kodiak Island, 57°38′ to 55°20′ N, between 149 and 156°W. The second transect, North Hawaii (NH), was south along 158°W from 54°40′N, at Shumigan Islands off the Alaskan Peninsula, to 22°00′ N, near the island of Oahu, Hawaii. No other cruise has specifically sampled fish larvae along a similar transect from Alaska to Hawaii in the winter. Myctophidae, Gonostomatidae and Sternoptychidae dominated our catches. A variety of methods have been used to assign faunal provinces and to define distribution of fishes, from descriptive to empirical to statistical to physical. The result is that zoogeographic zones in the North Pacific have been defined in several ways, depending on the taxa and area studied. The multiplicity of nomenclature complicates comparisons, however the difference may be a matter of semantics. We used Rodens (1991) salinity and temperature limits as an objective method for determining water mass boundaries and analyzing faunal provinces. The subtropical domain had the highest diversity, as expected; however, the subarctic front was a close second. Diversity was the lowest in the subarctic domain and the transition zone. The counter-intuitive low values of diversity and evenness in the transition zone are explained by the vertical distributions of fish in these water masses. When temperature divisions are used to calculate diversity, a true “transition zone” appears between 8 and 19°C. The “transition” of taxa apparently occurred north of the physically derived transition zone. This may be a situation unique to the relatively wide transition zone of February 1991. If not, then future analysis should include frontal zones as part of one large transition zone to reflect the broader subarctic-subtropical transition zone. Regardless of the label or the method used to assign faunal provinces, the distribution of larval fishes is regulated by water mass characteristics.

August diet of age-0 Pacific halibut in nearshore waters of Kodiak Island, Alaska

SynopsisThe objective of this study was to describe the diet of age-0 Pacific halibut,Hippoglossus stenolepis, for the inshore waters of Kodiak Island, Alaska during August 1991. Stomach contents were identified from 170 age-0 halibut captured inshore of the eastern and southern coasts of Kodiak Island, and were analyzed in relation to halibut size, location, depth and substrate of capture. One hundred sixty-eight of 170 fish had eaten crustaceans, of which the predominant prey taxa were Mysidacea (34.3%), Cumacea (33.1%), Gammaridea (26.6%) and Caridea (3.9%). In five of six capture locations, mysids and amphipods were predominant prey. In the remaining area, Sitkinak Strait, cumaceans were the primary food source. At depths less than 10 m, mysids were the predominant prey taxa. Gammarid amphipods were of primary importance at depths of 10–30 m. Halibut captured from 30–70 m fed mainly on cumaceans. Cumaceans and gammarid amphipods were consumed by halibut caught on gravel substrate. Fish caught on substrates of sand and mud fed mainly on mysids and amphipods. Cumaceans were also consumed on sandy substrates. Fish ≤ 45 mm fed on cumaceans. An ontogenetically related shift in diet occurred at 46–55 mm TL, at which size the halibuts primary prey began to shift from cumaceans to mysids. Fish of 46–75 mm consumed increasingly greater proportions of mysids, amphipods and shrimps. The diet of age-0 Pacific halibut along the Kodiak coast during August was related to predator size, and location, depth, and substrate type of capture.

Feasibility of Surgically Implanting Acoustic Tags into Pacific Herring

Abstract Internally implanted acoustic tags represent a potentially valuable approach to assessing the seasonal migration and distribution patterns of Pacific herring Clupea palasii. We examined the feasibility of implanting two sizes of dummy acoustic tags (9 mm in diameter × 21 mm long, 1.6 g; and 7 mm in diameter × 18 mm long, 0.7 g) in Pacific herring that had been held in captivity for nearly a year and that ranged from 165 to 215 mm in fork length (FL) and from 41.6 to 142.6 g. Relatively low mortality (4%) and tag shedding (4%), as well as growth similar to that observed in control fish after 135 d, indicate that, with proper handling, Pacific herring are amenable to surgical implantation of acoustic tags.