Alaska Fisheries Science Center Research Articles

Light-induced changes in the prey consumption and behavior of two juvenile planktivorous fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 181:41-51 (1999) - doi:10.3354/meps181041 Light-induced changes in the prey consumption and behavior of two juvenile planktivorous fish Clifford H. Ryer*, Bori L. Olla Fisheries Behavioral Ecology Group, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Hatfield Marine Science Center, Newport, Oregon 97365, USA *E-mail: cliff.ryer@hmsc.orst.edu ABSTRACT: Walleye pollock and sablefish, as 0+ yr juveniles, are pelagic particulate feeding planktivores. We conducted a series of laboratory experiments to determine how illumination influences prey consumption in these species, utilizing live Artemia sp. as prey. Both juvenile walleye pollock and sablefish were characterized by a sigmoidal relationship between the log of illumination and the number of prey consumed, with greater prey consumption at higher illuminations. The threshold illumination below which fish were no longer able to visually forage was approximately 5 x 10-7 µE s-1 m-2 for walleye pollock and 5 x 10-5 µE s-1 m-2 for sablefish, indicating that walleye pollock are better adapted for visual feeding at depth or at night than are sablefish. This is consistent with what is known about their vertical distributions at this life stage; walleye pollock make daily vertical migrations which keep them at lower illuminations than sablefish, which remain at or near the water surface throughout the diel cycle. Although feeding more effectively in the light, both species were capable of detecting and capturing prey in darkness. KEY WORDS: Visual threshold · Nonvisual feeding behavior · Illumination · Nocturnal Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 181. Publication date: May 18, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Analysis of Fishing Power Correction Factor Estimates from a Trawl Comparison Experiment

Four published analytical techniques were applied to comparative trawl data to obtain fishing power correction (FPC) factors for 12 major commercial species that were caught by two resource assessment trawls used by the National Marine Fisheries Service (Alaska Fisheries Science Center). Fishing power correction techniques included ratios of catch per unit effort (CPUE), randomized block analysis of variance (ANOVA), standard least-squares regression, and a method developed by Kappenman. All four estimators generally gave similar results for species that were clearly caught in higher proportion by one trawl, but they differed in the magnitude of the adjustment. For Pacific cod Gadus macrocephalus and sablefish Anoplopoma fimbria, which were caught at very similar rates during the experiment, FPC estimates close to 1.0 (no difference between trawls) were obtained from each technique, but they differed regarding which trawl was most efficient. The Kappenman estimator gave FPC estimates of 1.0 for six species. Whenever this estimator did recognize a fishing power difference, it was always in the same direction given by the other techniques. However, the magnitude of the FPC estimate obtained from the Kappenman method was usually less than or equal to those obtained from the other methods. In addition, the Kappenman method does not require a comparative trawling experiment, as do the other methods, which are extremely costly to management agencies in terms of days at sea. Also discussed are sample size requirements and the use of 95% confidence intervals as criteria to decide if a FPC should be applied.

Foraging modes of chinstrap penguins:contrasts between day and night

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 165:161-172 (1998) - doi:10.3354/meps165161 Foraging modes of chinstrap penguins: contrasts between day and night John K. Jansen*, Peter L. Boveng, John L. Bengtson National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, 7600 Sand Point Way N.E., Building 4, Seattle, Washington 98115-0070, USA *E-mail: john.jansen@noaa.gov Penguins rely on vision to travel and hunt at sea. Vision in marine predators, particularly those hunting phototactic prey under a broad range of light intensities, must be better understood to realize how these species respond to changes in their environment. We studied the effects of daily cycles in light intensity on visual predators by examining the duration and timing of chinstrap penguins' Pygoscelis antarctica foraging trips and the size, composition, and timing of their meals. We used radio telemetry and stomach-contents sampling to study adult penguins that were provisioning chicks during the summers of 1993 and 1994 at Seal Island, Antarctica. The penguins rarely initiated or terminated foraging trips at night, but otherwise varied the timing and duration of trips to sea. Cluster analyses using departure and arrival times revealed 5 distinct modes of foraging: 3 were strictly diurnal (early, mid-, and late) and 2 were partly nocturnal (overnight and extended). Durations of diurnal trips (4 to 11 h) were shorter than overnight (13 to 14 h) and extended trips (18 to 22 h). Early and mid-diurnal trips and extended trips were significantly shorter in 1993 than in 1994; late diurnal and overnight trip durations did not differ between years. Diurnal foraging was most common in 1993, whereas overnight foraging predominated in 1994. Shortened diurnal foraging in 1993 appears to have increased the frequency of diurnal foraging by allowing more parent birds to alternate diurnal trips within a single day and by reducing the incidence of birds extending diurnal foraging through the night. That penguins foraged more frequently by day when permitted by shorter trip durations (in 1993) suggests that they opted to forage diurnally whenever possible. Returning diurnal and overnight foragers had greater than 99 and 74% Antarctic krill Euphausia superba by weight in their stomachs, respectively. However, overnight foragers also returned with significant amounts of highly digested remains of pelagic fish, suggesting birds were in offshore waters taking fish during the night. In contrast, only 1 out of 40 diurnal foragers from both years combined had evidence of fish. Thus, the daily light cycle affected both the timing and duration of chinstrap penguin foraging as well as the type of prey consumed during trips to sea. Diel activity patterns · Diet composition · Foraging trip duration · Myctophid fish · Ecological monitoring · Pygoscelis antarctica · Euphausia superba Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 165. Publication date: May 07, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

In situ observations of the association between juvenile fishes and scyphomedusae in the Bering Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 163:11-20 (1998) - doi:10.3354/meps163011 In situ observations of the association between juvenile fishes and scyphomedusae in the Bering Sea Richard D. Brodeur* National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Washington 98115, USA *E-mail: rbrodeur@afsc.noaa.gov In September 1995, dense aggregations of large scyphomedusae (mainly Chrysaoramelanaster) were observed in 27 midwater deployments of a remotely operated vehicle (ROV) near the Pribilof Islands in the Bering Sea. Age-0 walleye pollock Theragrachalcogramma appeared to be frequently associated with these gelatinous zooplankton. During daytime, up to 30 pollock were observed swimming within the tentacles of these medusae, but when approached by the ROV, the pollock generally left the vicinity of the jellyfish. At night, few such associations were observed and juvenile pollock moved closer to the surface, apparently feeding in loose aggregations, while the medusae remained close to the thermocline (35-40 m). Prowfish Zaprorasilenus were also observed near large medusae, but tended to be found closer to the bell rather than within the tentacles. The lack of any gelatinous material in the stomachs of the pollock suggests that juvenile pollock associate to gain shelter from predation or possibly as a thigmotactic response to biotic structure. The implications of this commensal behavior with gelatinous zooplankton are discussed relative to pollock recruitment in the Eastern Bering Sea. Juvenile pollock · Theragrachalcogramma · Scyphomedusae · Commensalism · Underwater video Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 163. Publication date: March 12, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Effect of light on juvenile walleye pollock shoaling and their interaction with predators

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 167:215-226 (1998) - doi:10.3354/meps167215 Effect of light on juvenile walleye pollock shoaling and their interaction with predators Clifford H. Ryer*, Bori L. Olla Fisheries Behavioral Ecology Group, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Hatfield Marine Science Center, Newport, Oregon 97365, USA *E-mail: cliff.ryer@hmsc.orst.edu Research was undertaken to examine the influence of light intensity on the shoaling behavior, activity and anti-predator behavior of juvenile walleye pollock Theragra chalcogramma. Under a 12 h light/12 h dark photoperiod, juveniles displayed a diurnal shoaling and activity pattern, characterized by fish swimming in cohesive groups during the day, with a cessation of shoaling and decreased swimming speeds at night. Prior studies of schooling fishes have demonstrated distinct light thresholds below which schooling abruptly ceases. To see if this threshold effect occurs in a predominantly shoaling species, like juvenile walleye pollock, another experiment was undertaken in which illumination was lowered by orders of magnitude, giving fish 20 min to adapt to each light intensity. Juvenile walleye pollock were not characterized by a distinct light threshold for shoaling; groups gradually dispersed as light levels decreased and gradually recoalesced as light levels increased. At light levels below 2.8 x 10-6 µE s-1 m-2, juvenile walleye pollock were so dispersed as to no longer constitute a shoal. Exposure to simulated predation risk had differing effects upon fish behavior under light and dark conditions. Brief exposure to a model predator in the dark caused fish to swim faster, for 5 or 6 min, than fish which had been similarly startled in the light. Chronic exposure to a living predator produced similar results; fish tended to swim slower when a predator was present in the light, but faster when a predator was present in the dark. In the light, shoaling and/or schooling provide protection against predators. But in the dark, with fish unable to see one another, increased prey activity resulting from predator disturbance may lead to accelerated dispersal of prey shoals. Thus, perceived predation risk may have different effects upon the spatial distribution of juvenile walleye pollock under light and dark conditions. This has implications for survival, as fish which have become widely scattered during the darkness may take longer to reform shoals at dawn, resulting in greater predation risk. Schooling · Spatial distribution · Twilight hypothesis · Predator-prey · Swimming speed · Illumination Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 167. Publication date: June 18, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Walleye pollock recruitment in Shelikof Strait: applied fisheries oceanography

ABSTRACTFisheries‐Oceanography Coordinated Investigations (FOCI) is a National Oceanic and Atmospheric Administration (NOAA) research programme seeking to understand recruitment processes of commercially exploited Alaskan fishes. The FOCI is mainly comprised of scientists at the Pacific Marine Environmental Laboratory and the Alaska Fisheries Science Center who study both the biotic and abiotic environment, including processes within larval patches through integrated field, laboratory, and modelling studies. The initial focus of studies was walleye pollock (Theragra chakogramma) spawning in Shelikof Strait, Gulf of Alaska. The choice of this population for our research was based on development of a large fishery and the substantial variation in recruitment that was observed in the late 1970s and early 1980s. Also, the early life history of this population is quite predictable and restricted both temporally and spatially. Walleye pollock spawn consistently in a small part of Shelikof Strait in early spring from which a large patch of eggs and later larvae is produced. In most years this concentration of larvae drifts to the south‐west through the strait during April and May. Large numbers of larvae are often found in eddies which frequent the area and we have observed improved feeding conditions for larvae, in as opposed to out of eddies. We have found that first‐feeding larvae have higher survival rates during calm periods, rather than in storms, and that in many years recruitment is largely set by the end of the larval period, although in some years age‐0 juvenile mortality is also important. FOCI now generates information that is being used for management of this resource.