Food habits of Steller sea lions (Eumetopias jubatus) off Oregon and northern California, 1986–2007

We described the diet of the eastern stock of Steller sea lions (Eumetopias jubatus) from 1416 scat samples collected from five sites in Oregon and northern California from 1986 through 2007. A total of 47 prey types from 30 families were identified. The most common prey was Pacific hake (Merluccius productus), followed by salmonids (Oncorhynchus spp.), skates (Rajidae), Pacific lamprey (Lampetra tridentata), herrings (Clupeidae), rockfish (Sebastes spp.), and northern anchovy (Engraulis mordax). Steller sea lion diet composition varied seasonally, annually, and spatially. Hake and salmonids were the most commonly identified prey in scats collected during the summer (breeding season), whereas hake and skate were most common in the nonbreeding season. Continued research on Steller sea lion diet and foraging behavior in the southern extent of their range is necessary to address issues such as climate change, interaction with competing California sea lions, and predation impacts on valuable or sensitive fish stocks.

Ichthyoplankton community structure and comparative trophodynamics in an estuarine transition zone

Surveys were conducted to evaluate and compare assemblage structure and trophodynamics of ichthyoplankton, and their variability, in an estuarine transition zone. Environmental gradients in the saltfront region of the Patuxent River subestuary, Chesapeake Bay, were hypothesized to define spatiotemporal distributions and assemblages of ichthyoplankton. Larval fishes, zooplankton, and hydrographic data were collected during spring through early summer 2000 and 2001. Larvae of 28 fish species were collected and species richness was similar each year. Total larval abundance was highest in the oligohaline region down-estuary of the salt front in 2000, but highest at the salt front in 2001. Larvae of anadromous fishes were most abundant at or up-estuary of the salt front in both years. Two ichthyoplankton assemblages were distinguished: 1) riverine—characterized predominantly by anadromous species (Moronidae and Alosinae); and 2) estuarine—characterized predominantly by naked goby (Gobiosoma bosc) (Gobiidae). Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and concentrations of larval prey, specifically the calanoid copepod Eurytemora affinis and the cladoceran Bosmina longirostris, were important indicators of larval fish abundance. In the tidal freshwater region up-estuary of the salt front, there was substantial diet overlap between congeneric striped bass (Morone saxatilis) and white perch (M. americana) larvae, and also larvae of alewife (Alosa pseudoharengus) (overlap= 0.71–0.93). Larval abundance, taxonomic diversity, and dietary overlap were highest within and up-estuary of the salt front, which serves to both structure the ichthyoplankton community and control trophic relationships in the estuarine transition zone.

Ontogenetic and temporal variability in the fat content and fatty acid composition of Atlantic herring (Clupea harengus) from the Bay of Fundy, Canada

Atlantic herring (Clupea harengus) is an ecologically and economically valuable species in many food webs, yet surprisingly little is known about the variation in the nutritional quality of these fish. Atlantic herring collected from 2005 through 2008 from the Bay of Fundy, Canada, were examined for variability in their nutritional quality by using total lipid content (n=889) and fatty acid composition (n=551) as proxies for nutritional value. A significant positive relationship was found between fish length and total lipid content. Atlantic herring also had significantly different fatty acid signatures by age. Fish from 2005 had significantly lower total lipid content than fish from 2006 through 2008, and all years had significantly different fatty acid signatures. Summer fish were significantly fatter than winter fish and had significantly different fatty acid signatures. For all comparisons (ontogenetic, annual, and seasonal) percent concentrations of omega-3, -6, and long-chain monounsaturated fatty acids were the most important for distinguishing between the fatty acid signatures of fish. This study underscores the importance of quantifying variation in prey quality synoptically with prey quantity in food webs over ontogenetic and temporal scales when evaluating the effect of prey nutritional quality on predators and on modeling trophic dynamics.

Feeding ecology of Atlantic bluefin tuna (Thunnus thynnus) in North Carolina: diet, daily ration, and consumption of Atlantic menhaden (Brevoortia tyrannus)

Diet, gastric evacuation rates, daily ration, and population-level prey demand of bluefin tuna (Thunnus thynnus) were estimated in the continental shelf waters off North Carolina. Bluefin tuna stomachs were collected from commercial fishermen during the late fall and winter months of 2003–04, 2004–05, and 2005–06. Diel patterns in mean gut fullness values were used to estimate gastric evacuation rates. Daily ration determined from mean gut fullness values and gastric evacuation rates was used, along with bluefin tuna population size and residency times, to estimate population-level consumption by bluefin tuna on Atlantic menhaden (Brevoortia tyrannus). Bluefin tuna diet (n= 448) was dominated by Atlantic menhaden; other teleosts, portunid crabs, and squid were of mostly minor importance. The time required to empty the stomach after peak gut fullness was estimated to be ~20 hours. Daily ration estimates were approximately 2% of body weight per day. At current western Atlantic population levels, bluefin tuna predation on Atlantic menhaden is minimal compared to predation by other known predators and the numbers taken in commercial harvest. Bluefin tuna appear to occupy coastal waters in North Carolina during winter to prey upon Atlantic menhaden. Thus, changes in the Atlantic menhaden stock status or distribution would alter the winter foraging locations of bluefin

Dietary variations in three co-occurring rockfish species off the Pacific Northwest during anomalous oceanographic events in 1998 and 1999

Stomach samples from three rockfish species, yellowtail (Sebastes f lavidus), widow (S. entomelas), and canary (S. pinniger) rockfish, seasonally collected off the Pacific Northwest in 1998 and 1999, provided quantitative information on the food habits of these species during and after the 1997–98 El Niño event. Although euphausiids were the most common major prey of all three predators, gelatinous zooplankton and fishes were the most commonly consumed prey items during some seasonal quarters. The influence of the El Niño event was evident in the diets. Anomalous prey items, including the southern euphausiid species Nyctiphanes simplex and juveniles of Pacific whiting (Merluccius productus) frequently appeared in the diets in the spring and summer of 1998. The results of stomach contents analyses, based on 905 stomach samples from 49 trawl hauls during seven commercial fishing trips and from 56 stations during research surveys, were consistent with the timing of occurrence and the magnitude of change in biomass of some zooplankton species reported from zooplankton studies in the northern California Current during the 1997–98 El Niño. Our findings indicate that the observed variations of prey groups in some rockfish diets may be a function of prey variability related to climate and environment changes.

Abundance, condition, and diet of juvenile Pacific ocean perch (Sebastes alutus) in the Aleutian Islands

T he relative value of pelagic habitat for three size classes of juvenile Pacific ocean perch (Sebastes alutus) was investigated by comparing their abundance and condition in two areas of the Aleutian Islands. Diet, zooplankton biomass, and water column temperatures were examined as potential factors affecting observed differences. Juvenile Pacific ocean perch abundance and condition, and zooplankton biomass varied significantly between areas, whereas juvenile Pacific ocean perch diet varied only by size class. Observed differences in fish condition may have been due to the quantity or quality of pelagic prey items consumed. For the delineation of essential demersal fish habitat, important ecological features of the pelagic habitat must therefore be considered.

Development and growth of hatchery-reared larval Florida pompano (Trachinotus carolinus)

Although the Florida pompano (Trachinotus carolinus) is a prime candidate for aquaculture, the problematic production of juveniles remains a major impediment to commercial culture of this species. In order to improve the understanding of larval development and to refine hatchery production techniques, this study was conducted to characterize development and growth of Florida pompano from hatching through metamorphosis by using digital photography and image analysis. Newly hatched larvae were transparent and had a large, elongate yolk sac and single oil globule. The lower and upper jaws as well as the digestive tract were not fully developed at hatching. Rotifers were observed in the stomach of larvae at three days after hatching (DAH), and Artemia spp. were observed in the stomach of larvae at 14 DAH. Growth rates calculated from total length measurements were 0.22 ±0.04, 0.23 ±0.12, and 0.35 ±0.09 mm/d for each of the larval rearing trials. The mouth gape of larvae was 0.266 ±0.075 mm at first feeding and increased with a growth rate of 0.13 ± 0.04 mm/d. Predicted values for optimal prey sizes ranged from 80 to 130 μm at 3 DAH, 160 to 267 μm at 5 DAH, and 454 to 757 μm at 10 DAH. Based on the findings of this study, a refined feeding regime was developed to provide stage- and size-specific guidelines for feeding Florida pompano larvae reared under hatchery con

Use of non-natal estuaries by migratory striped bass (Morone saxatilis) in summer

For most migratory fish, little is known about the location and size of foraging areas or how long individuals remain in foraging areas, even though these attributes may affect their growth, survival, and impact on local prey. We tested whether striped bass (Morone saxatilis Walbaum), found in Massachusetts in summer, were migratory, how long they stayed in non-natal estuaries, whether observed spatial patterns differed from random model predictions, whether fish returned to the same area across multiple years, and whether fishing effort could explain recapture patterns. Anchor tags were attached to striped bass that were caught and released in Massachusetts in 1999 and 2000, and recaptured between 1999 and 2007. In fall, tagged striped bass were caught south of where they were released in summer, confirming that fish were coastal migrants. In the first summer, 77% and 100% of the recaptured fish in the Great Marsh and along the Massachusetts coast, respectively, were caught in the same place where they were released. About two thirds of all fish recaptured near where they were released were caught 2–7 years after tagging. Our study shows that smaller (400–500 mm total length) striped bass migrate hundreds of kilometers along the Atlantic Ocean coast, cease their mobile lifestyle in summer when they use a relatively localized area for foraging (<20 km2), and return to these same foraging areas in subsequent ye

Assessment of habitat quality for juvenile California halibut (Paralichthys californicus) in a seasonally arid estuary

We evaluated habitat quality for juvenile California halibut (Paralichthys californicus) in a Pacific Coast estuary lacking in strong salinity gradients by examining density, recent otolith growth rates, and gut fullness levels of wild-caught and caged juveniles for one year. Juveniles <200 mm standard length were caught consistently in the inner, central, and outer sections of the estuary. The density of juveniles was two times higher in the inner estuary during most of the year, consistent with active habitat selection by part of the population. A generalized linear model indicated temperature, sampling time, and the interaction between salinity and temperature were significantly related to density. However, the model explained only 21% of the variance. Gut fullness levels of wild-caught juveniles were highest during the summer, but recent otolith growth rates were not related to temperature. The proportion of individuals feeding successfully indicated that seasonal differences in food availability are more important than spatial variation in prey abundance in driving feeding success. Feeding success of caged fishes was limited, precluding the use of growth rates as indicators of local habitat quality. However, marginal increment widths were reliable indicators of somatic growth at low growth rates over two-week periods. The relatively high growth rates and abundance of small wild-caught juveniles found throughout the estuary indicates that the entire estuary system has the potential for serving as nursery habitat.

Food habits of Atlantic white-sided dolphins (Lagenorhynchus acutus) off the coast of New England

Although the Atlantic white-sided dolphin (Lagenorhynchus acutus) is one of the most common dolphins off New England, little has been documented about its diet in the western North Atlantic Ocean. Current federal protection of marine mammals limits the supply of animals for investigation to those incidentally caught in the nets of commercial fishermen with observers aboard. Stomachs of 62 L. acutus were examined; of these 62 individuals, 28 of them were caught by net and 34 were animals stranded on Cape Cod. Most of the net-caught L. acutus were from the deeper waters of the Gulf of Maine. A single stomach was from the continental slope south of Georges Bank. At least twenty-six fish species and three cephalopod species were eaten. The predominant prey were silver hake (Merluccius bilinearis), spoonarm octopus (Bathypolypus bairdii), and haddock (Melanogrammus aeglefinus). The stomach from a net-caught L. acutus on the continental slope contained 7750 otoliths of the Madeira lanternfish (Ceratoscopelus maderensis). Sand lances (Ammodytes spp.) were the most abundant (541 otoliths) species in the stomachs of stranded L. acutus. Seasonal variation in diet was indicated; pelagic Atlantic herring (Clupea harengus) was the most important prey in summer, but was rare in winter. The average length of fish prey was approximately 200 mm, and the average mantle length of cephalopod prey was approximately 50 mm.

Recalculated diet and daily ration of the shortfin mako (Isurus oxyrinchus), with a focus on quantifying predation on bluefish (Pomatomus saltatrix) in the northwest Atlantic Ocean

The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance and availability are reflected in these two biological variables. During the summers of 2001 and 2002, stomach content data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared to index calculations from historical diet data collected from 1972 through 1983. Bluefish (Pomatomus saltatrix) were the predominant prey in the 1972–83 and 2001–02 diets, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001– 02 diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic demands. The daily energetic requirement was broken down by using a calculated energy content for the current diet of 4909 KJ/kg. Based on the proportional energy of bluefish in the diet by weight, an average shortfin mako consumes roughly 500 kg of bluefish per year off the northeast coast of the United States. The results are discussed in relation to the potential effect of intense shortfin mako predation on bluefish abundance in the region.

Description of embryonic development of Atka mackerel (Pleurogrammus monopterygius)

Atka mackerel (Pleurogrammus monopterygius) is hexagrammid fish that inhabits the temperate and subarctic North Pacific Ocean and neighboring seas (Fig. 1). This highly abundant fish is a critically important prey species (Sinclair and Zeppelin, 2002; Zenger, 2004) that supports a directed commercial trawl fishery (Lowe et al., 2006). Atka mackerel is a demersal spawner and males provide parental care to eggs (Zolotov, 1993). During breeding periods, sexually mature males aggregate on the bottom at nesting sites where they establish territories (Lauth et al., in press). Sexually mature females periodically visit male nesting territories from July to October to spawn batches of demersal egg masses (McDermott and Lowe, 1997; McDermott et al., 2007). Individual nests may consist of multiple egg masses deposited by different females, and males defend nesting territories for a protracted period lasting from the time territories are being established until all eggs within the territory are completely hatched (Lauth et al., 2007). Knowledge about the timing of the reproductive cycle and the use of spawning habitat are important for understanding population structure and the dynamics of stock recruitment, which in turn are important factors in the management of Atka mackerel populations.

Abundance, distribution, and habitat of leatherback turtles (Dermochelys coriacea) off California, 1990−2003

Leatherback turtles (Dermochelys coriacea) are regularly seen off the U.S. West Coast, where they forage on jellyfish (Scyphomedusae) during summer and fall. Aerial line-transect surveys were conducted in neritic waters (<92 m depth) off central and northern California during 1990−2003, providing the first foraging population estimates for Pacific leatherback turtles. Males and females of about 1.1 to 2.1 m length were observed. Estimated abundance was linked to the Northern Oscillation Index and ranged from 12 (coefficient of variation [CV] =0.75) in 1995 to 379 (CV= 0.23) in 1990, averaging 178 (CV= 0.15). Greatest densities were found off central California, where oceanographic retention areas or upwelling shadows created favorable habitat for leatherback turtle prey. Results from independent telemetry studies have linked leatherback turtles off the U.S. West Coast to one of the two largest remaining Pacific breeding populations, at Jamursba Medi, Indonesia. Nearshore waters off California thus represent an important foraging region for the critically endangered Pacific leatherback turtle.

Diets of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, 1993−1999

The diet of Steller sea lions (Eumetopias jubatus) was determined from 1494 scats (feces) collected at breeding (rookeries) and nonbreeding (haulout) sites in Southeast Alaska from 1993 to 1999. The most common prey of 61 species identified were walleye pollock (Theragra chalcogramma), Pacific herring (Clupea pallasii), Pacific sand lance (Ammodytes hexapterus), Pacific salmon (Salmonidae), arrowtooth flounder (Atheresthes stomias), rockfish (Sebastes spp.), skates (Rajidae), and cephalopods (squid and octopus). Steller sea lion diets at the three Southeast Alaska rookeries differed significantly from one another. The sea lions consumed the most diverse range of prey categories during summer, and the least diverse during fall. Diet was more diverse in Southeast Alaska during the 1990s than in any other region of Alaska (Gulf of Alaska and Aleutian Islands). Dietary differences between increasing and declining populations of Steller sea lions in Alaska correlate with rates of population change, and add credence to the view that diet may have played a role in the decline of sea lions in the Gulf of Alaska and Aleutian Islands.

Temporal variation in growth of yellowfin tuna (Thunnus albacares) larvae in the Panama Bight, 1990

Tuna larvae (at flexion, postflexion, and transformation stages) were collected by dip net and light traps at night in the northwestern Panama Bight during the season of reduced upwelling (June−September) of 1990, 1991, 1992, and 1997. The larvae were identified as yellowfin tuna (Thunnus albacares) by mtDNA analysis. Ichthyoplankton data from bongo and Tucker trawl tows were used to examine the potential prey abundance in relation to the mean size-at-age and growth rates of the yellowfin tuna larvae and their otoliths. The most rapid growth rates occurred during June 1990 when plankton volumes were at their highest levels. The lowest plankton volumes coincided with the lowest growth rates and mean sizes-at-age during the August−September 1991 period. High densities of larval fish were prevalent in the ichthyoplankton tows during the 1991 period; therefore intra- and interspecific competition for limited food resources may have been the cause of slower growth (density-dependent growth) in yellowfin tuna larvae The highest mean seasurface temperature and the lowest mean wind stress occurred during an El Niño-Southern Oscillation (ENSO) event during the 1997 period. There appeared to be no clear association between these environmental factors and larval growth rates, but the higher temperatures may have caused an increase in the short-term growth of otoliths in relat