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Diet of Pacific cod, Gadus macrocephalus, and predation on the northern pink shrimp, Pandalus borealis, in Pavlof Bay, Alaska.
Abstract
ABSTRACf Analysis of 455 Pacific cod. Gadiu8 macrocepkal1Ul, stomachs collected in 1980 and 1981 from Pavlof Bay, in the western Gulf of Alaska. showed considerable predation on northern pink shimp, Pandalll.s borealis. The most frequently occurring prey items were pink shrimp, P. borealis. 63%; euphausids. 41 %; walleye pollock, Theragra cha!cogl"a1n?na, 27%; and capelin, Mallotus villosus. 26%. Pandalid shrimp and snow (Tanner) crab occurred more frequently with increasing cod size (30-69 cm fork length). Euphausids decreased in frequency ofoccurrence with increasing cod size. Pink shrimp length distributions from cod stomachs and trawl samples were similar. Estimated consumption of pink shrimp by cod in Pavlof Bay ranged from 142 to 857 t over a 112-day period from late May through mid-September 1981. Cod preda tion may be one reason for the failure of the pink shrimp stock to rebuild in Pavlof Bay following closure of the commercial fishery in 1979. Cod predation may also play a role in keeping other reduced pink shrimp stocks in the western Gulf of Alaska from rebuilding to former levels. Pacific cod, Gadus macrocephalus, predation on northern pink shrimp, Pandalus borealis, in Pavlof Bay (Fig. 1) was studied to determine if it is a fac tor in keeping the pink shrimp stock from rebuilding there. National Marine Fisheries Service (NMFS) and Alaska Department of Fish and Game (ADF&G) survey data from the late 1970's indicate that when pink shrimp populations in regions of western Alaska began to decrease, cod abundance started to in crease. Pink shrimp has been reported to be an im portant food item in the diet of Pacific cod in the Gulf of Alaska (Jewett 1978; Hunter 1979). Preda tion of pink shrimp by cod may have substantial in fluence on shrimp stock abundance.
... Pacific cod are just one member of the suite of groundfish species that increased in abundance at this time. However, there has been little documentation of predation on any king crab life stage (Albers and Anderson 1985, Livingston 1989, Yang 1993 2005, Yang et al. 2006, Zheng andKruse 2006). Blau (1986) noted that only 77 of the 12,443 Pacific cod stomachs examined during ADFG pot surveys around Kodiak during 1972-1983 contained king crab. ...
... A corresponding trend of increasing trawl survey catches of cod further suggests that intensified cod predation was likely responsible for the shrimp decline in Kachemak Bay (Fu and Quinn 2000). An examination of Pacific cod stomachs led Albers and Anderson (1985) to conclude that cod predation contributed to the lack of recovery of depressed stock of northern shrimp in Pavlof Bay, Alaska. Similarly, an analysis of North Atlantic stock found Atlantic cod biomass was positively related to ocean temperature and negatively related to northern shrimp biomass (Worm and Myers 2003). ...
... Pacific Cod are large generalist predators that feed on benthic invertebrates (e.g., northern shrimp, Tanner crab, and polychaetes), as well as fish such as Pacific Herring, Pacific Sand Lance, and flatfish (Albers and Anderson 1985, Coad 1995, Yang 2004, Love 2011. In Hecate Strait, invertebrates are more often eaten by juvenile than adult Pacific Cod (Pearsall and Fargo 2007). ...
... There is little movement of Pacific Cod between Strait of Georgia, Hecate Strait, Queen Charlotte Sound, and West Coast Vancouver Island (Westrheim 1982). Pacific Cod in the Bering Sea and Aleutian Islands occur on the shelf in summer for feeding, and move towards the shelf break in the winter for spawning (Albers andAnderson 1985, Shimada andKimura 1994). ...
Conservation priorities (CPs) have been identified as part of systematic conservation planning processes, including Marine Protected Area (MPA) network design, to focus analyses on the most important features (species, habitats, and areas) within a planning area. In this paper, we develop and apply a framework to identify species- and area-based ecological CPs to inform the development of the MPA network in the Northern Shelf Bioregion (NSB) of British Columbia. We focus exclusively on Goal 1 of the Canada – BC Marine Protected Network Strategy (2014): “to protect and maintain marine biodiversity, ecological representation and special natural features”. Species-based CPs were identified based on the characteristics of individual species or higher-level taxa, selecting those that are ecologically important, vulnerable, or of conservation concern. Area-based CPs include areas, spatial features, or habitats that directly support the network objectives under Goal 1. Criteria for identifying ecological CPs were developed based on global best practices and were nested under the network objectives associated with Goal 1, then applied to areas and a candidate list of species found in the NSB. Criteria were applied and evaluated using information from the literature then vetted and augmented by expert opinion. Species that were identified as of conservation concern and those that received high scores for either vulnerability or ecological significance were recommended as ecological CPs. The list of 195 species to be considered as ecological CPs for the NSB includes 65 bony fishes and elasmobranchs, 23 marine mammals (including four Orca ecotypes), one sea turtle, 46 invertebrates, five plants and algae, and 55 marine birds. A total of 17 area-based ecological CPs were recommended, including areas and habitats including areas of climate resilience, degraded areas, representative habitats, and features associated with Ecologically and Biologically Significant Areas (EBSAs; e.g., areas of high productivity or diversity). Several types of spatial features were recommended, including Important Areas, to represent species-based CPs in site selection analyses for the MPA network. Ecological CPs identified from this framework will inform subsequent MPA planning steps, including the development of design strategies and design scenarios.
... The decline of the northern shrimp population in Kachemak Bay may have been part of the serial depletion experienced by many other crustacean populations in Alaskan waters in the early-1980s that included red king crab on the continental shelf around Kodiak Island (Orensanz et al., 1998). Northern shrimp is a major prey of Pacific cod (Gadus macrocephalus, Albers and Anderson, 1985). The continued high level of cod and other groundfish populations since the early-1980s has been implicated in the failure of the the northern shrimp population (Bechtol, 1997) to recover. ...
... The northern shrimp population in Kachemak Bay, Alaska, was simulated with a spawner-recruit relationship, growth, gear selectivity and the weightat-length relationship with parameters estimated for this population by Fu et al. (1999 ; Table 1). Each simulation started with an unexploited population at equilibrium that is harvested for 23 years, equivalent to the period from 1978, when there was a climate regime shift (Albers and Anderson, 1985), to the present (2000). The fishery was "closed" when the estimated SSB dropped below a biomass-based management threshold (BBMT, defined below). ...
Harvest strategies for the northern shrimp (Pandalus borealis) population in Kachemak Bay, Alaska, were analyzed using a length-based population model under various levels of instantaneous fishing mortality (F) and a biomass-based management threshold (BBMT). With constant instantaneous natural mortality (M) ≤0.4 or constant recruitment (R), threshold management, i.e. closing the fishery at population levels below BBMT, is unnecessary when the fishery is managed with an optimal fishing mortality rate (Fopt). However, for a population with a Beverton-Holt recruitment relationship, threshold management is essential to reduce the risk of population extinction. The robustness of establishing guideline levels for F to misspecification of M and R was examined with values of M and R set higher than, lower than, or equal to their perceived true levels. Assessment surveys were assumed to occur once every 1 to 3 years. Underestimation of M results in Fopt values associated with higher cumulative yield and higher risk of falling below population-at-risk threshold taken to be 20% of virgin spawning stock biomass. More frequent surveys help to reduce this risk. On the other hand, misspecification of R has very little effect on forecasting population abundance if the population is sampled annually. Less frequent sampling induces higher risk if R is specified too high, but it has little effect if R is specified too low. In conclusion, frequent sampling and good understanding of M are essential for sound management of fisheries such as those for northern shrimp in Kachemak Bay.
... Smaller walleye pollock and Pacific cod had higher TL values in winter relative to other seasons, but for larger fish seasonal differences were less apparent. The seasonal variations we observed in the trophic positions of walleye pollock and Pacific cod corresponded well with the few seasonal diet studies on gadids in the GOA ( Albers and Anderson 1985;Adams et al. 2007Adams et al. , 2009). In the northern GOA, walleye pollock consumed primarily euphausiids in May and August 2003, while in November their diet shifted to one that was more dominated by decapods, mostly pandalid shrimp ( Adams et al. 2007Adams et al. , 2009. ...
... Likewise, all ages of walleye pollock in the GOA were found to be primarily zooplanktivorous during the summer growing season (Yang and Nelson 2000). In Pavlof Bay, Kodiak Island, Pacific cod consumed primarily pandalid shrimp, followed by euphausiids and crabs, during May 1981; however, in September 1981, fish (walleye pollock, capelin, and other species) dominated the diet and pandalid shrimp were of lesser importance (Albers and Anderson 1985). Both adult walleye pollock ( Adams et al. 2007;Sigler and Csepp 2007) and Pacific cod (Shimada and Kimura 1994) migrate offshore to deeper water during the fall and winter, which gives them access to benthic prey types in higher trophic positions. ...
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... Cod along the coastal shelf of the lower Alaska Peninsula that are smaller than 60 cm prey mostly on invertebrates such as Tanner crabs, polychaetes and crangonid shrimp, while fish species such as walleye pollock were important parts of diets only of cod larger than 60 cm (Yang, 2004). Following the 1976/77 regime shift, however, pandalid shrimp and capelin were the main food species of Pacific cod in Pavlof Bay on the Alaska Peninsula (Albers and Anderson, 1985). Cod isotope ratios should therefore reflect upper trophic levels in an epi-benthic ecosystem. ...
... Despite changing climate and prey availability, it may be that the basic food web structure supporting cod did not change. For example, cod were documented to have switched some prey items following the 1976/77 regime shift (Yang 2004; Albers and Anderson, 1985), but not their foraging location. If the prey items before and after the regime shift held similar trophic positions, the δ 15 N and δ 13 C of cod may not change. ...
Changes in food web dynamics and ocean productivity over the past 4500 years are investigated using stable isotope analysis of nitrogen and carbon in collagen from animal bones preserved in coastal archeological middens on Sanak Island, along the eastern edge of the Aleutian archipelgo. Samples included Steller sea lions, Harbor seals, Northern fur seals, sea otters, Pacific cod and sockeye salmon. Sea otters had the highest δ13C (−11.9 ± 0.7‰) and lowest δ15N values (14.5 ± 1.4‰), Northern fur seals had the lowest δ13C values (−13.6 ± 1.4‰), and Steller sea lions had the highest δ15N values (18.4 ± 1.4‰) of the marine mammals. Cod isotope values were consistent with those of demersal organisms from near shore habitats (−12.5 ± 0.9‰ δ13C, 16.1 ± 1.4‰ δ15N), while salmon values were consistent with those of organisms existing in an open ocean habitat and at a lower trophic level (−15.2 ± 1.4‰ δ13C, 11.5 ± 1.7‰ δ15N). When comparing six different prehistoric time periods, two time periods had significantly different δ 13C for salmon. Otters had significantly different δ15N values in two out of the six prehistoric time periods but no differences in δ13C. The mean δ13C, corrected for the oceanic Suess Effect, of modern specimens of all species (except Northern fur seals) were significantly lower than prehistoric animals. Several hypotheses are explored to explain these differences including a reduction in productivity during the twentieth century in this region of the Gulf of Alaska. If true, this suggests that North Pacific climate regimes experienced during the twentieth century may not be good analogs of North Pacific marine ecosystems during the late Holocene.
... The Pacific cod, Gadus macrocephalus TILESIUS, is widely distributed in the Pacific Ocean, extending from Korea, through the Sea of Japan, Okhotsk and Bering Seas, to California (BAKKALA et al., 1984). The food habit of the Pacific cod has been studied in various areas; the Bering Sea (MITO, 1974;BAKKALA, 1984;LIVINGSTON et al., 1986;WAKABAYASHI, 1986), Gulf of Alaska (JEWETT, 1978;ALBERS and ANDERSON, 1985) and the Okhotsk Sea (TOKRANOV and VINNIKOV, 1991). These studies have pointed out its diverse diet composition and significant impact as a predator on the organisms of commercial importance (e.g. ...
... On the other hand, snow crab Chionoecetes bairdi was reported as the most important food item for the Pacific cod around Kodiak Island (JEWETT, 1978) and in Bristol Bay (BAKKALA, 1984). ALBERS and ANDERSON (1985) found that pink shrimp, Pandalus borealis was the most frequently occurring prey item for the Pacific cod in the Gulf of Alaska. These decapods were known as the abundant organisms in each study area. ...
We collected a total of 336 specimens of Pacific cod, Gadus macrocephalus during April, May and June 1989-1992 off the eastern coast of Hokkaido. Examination of their stomach contents revealed that fishes (mainly walleye pollock, Theragra chalcogramma) and decapod crustaceans (mainly crangonid shrimps) were major diet. The cod showed an obvious body size related dietary shift; the importance of shrimps (Neocrangon communis and Argis lar) and myctophid fishes for 5300 mm individuals switched abruptly to walleye pollock and other fishes (e.g. Sardinops melanostictus, Laemonema longipes, stichaeid and cottid fishes) and octopus, Paroctopus spp. for larger individuals. The cod showed an obvious feeding periodicity with a peak of feeding during 0600-1200 h. The comparison of prey size and prey type (benthos and nekton) for different size classes of predators indicated that the cod diet is determined by predator-prey size relationship.
... g . p a n d a l i d s h r i m p s , A l b e r s a n d Anderson, 1985;king crab, Otto, 1989 andKruse, 1993). These declines have been attributed to a combination of direct effects of ocean warming coupled with increased predation (Albers and Anderson, 1985;Piatt and Anderson, 1996). ...
... p a n d a l i d s h r i m p s , A l b e r s a n d Anderson, 1985;king crab, Otto, 1989 andKruse, 1993). These declines have been attributed to a combination of direct effects of ocean warming coupled with increased predation (Albers and Anderson, 1985;Piatt and Anderson, 1996). ...
Large population declines (>50%) since the early-1970s of some eastern Bering Sea and Aleutian Island apex predator populations (Steller sea lions, murres, and kittiwakes) suggest that major changes have occurred in the structure of the Bering Sea ecosystem. One cause of the decline in mammalian and avian predator populations may be a decrease in availability or abundance of preferred prey (e.g. capelin, juvenile walleye pollock). However, adult groundfish biomass has generally been at high levels, and periods of high adult groundfish biomass coincide with periods of decline of sea lion and seabird populations. Adult groundfish may, therefore, be out-competing other predators for their common prey (i.e. small schooling fish). Three factors may have led to increases in adult groundfish biomass in the southeastern Bering Sea, changes in environmental conditions, present commercial fishing practices, and predator release resulting from overharvesting of marine mammals and some fishes during 1955-75. If the decline in whale and fur seal populations during 1955-75 contributed to the current high biomass of groundfish, then marine mammals once (but no longer) exerted a structuring effect on the Bering Sea eco- system. The current high abundance of piscivorous adult groundfish in the eastern Bering Sea may, therefore, impede the recovery of marine mammal and bird populations to his- torical levels.
... Marmot Bay has a history of trawl surveys dating back to 1972; these have shown that cod and pollock coexist in all parts of the bay (Jackson 2005, Spa - linger 2010). Both fish were found to consume a large variety of prey items, which is consistent with food habit studies in other parts of their range (Bailey & Dunn 1979, Albers & Anderson 1985, Kooka et al. 1998, Yamamura et al. 2002, Yang 2004, Napazakov 2008). A third of the prey items were shared by both species. ...
... While individual pollock tended to specialize on a single prey item, individual cod typically fed on a variety of prey items. The present study confirms the findings of other studies that Tanner crab is a main prey item of cod during all seasons (Jewett 1978, Albers & Anderson 1985, Yang 2004, Yang et al. 2006, Poltev & Stominok 2008). At the same time, Tanner crab as a benthic species is virtually absent from pollock diets (Bailey & Dunn 1979, Clausen 1983, Dwyer et al. 1987, Yamamura et al. 2002, Yang 2004, Yang et al. 2006, Adams et al. 2007), although the gape size of pollock does not necessarily preclude them as a prey item. ...
Seasonal variations in the diets of Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma were examined from fish collected during 5 sampling periods from August 1998 to June 1999 in the Kodiak Island area in the Gulf of Alaska. Both species were shown to be generalist predators, eating a wide variety of fish and invertebrates. Pollock, which are limited to pelagic prey, can be considered more specialized than cod. Cod consumed 78 prey items, and pollock consumed 45 prey items, with 28 items shared by both species. Individual pollock, however, typically concentrated on a single prey item, while individual cod stomachs contained a wider variety of prey. The principal prey of Pacific cod was Tanner crab Chionoecetes bairdi, comprising >28% of the cod diet by weight. The most common prey item for walleye pollock was the euphausiid Thysanoessa. Over the 5 sampling periods, the prey evenness and niche width occupied by the 2 species were similar, but seasonal differences were evident.
... Bivalves and gastropods are important prey species for walrus (Sheffield and Grebmeier, 2009); bivalves are also central in the diet of seabirds like eider ducks (Merkel et al., 2006). Northern shrimp (Pandalus borealis) is an important part of the diet of a number of fish species (Parsons, 2005), such as Atlantic cod (Gadus morhua; Hvingel and Kingsley, 2006;Holt et al., 2020), Pacific cod (Albers and Anderson, 1985), redfish (Sebastes spp.), skates (Rajidae spp.) (Parsons, 2005 and references therein), and Greenland halibut (Reinhardtius hippoglossoides; Chumakov and Podrazhanskaya, 1986). ...
The symposium, Shellfish—Resources and Invaders of the North, took place 5–7 November 2019 in Tromsø, Norway. Approximately 110 participants presented and discussed 60 talks and 25 posters. Of these, ten articles are published in this symposium issue. The goal of this symposium was to discuss the role of shellfish, both as harvestable resources and as important ecosystem players in northern hemisphere cold marine environments. To provide perspective for the symposium, the development of four major crustacean fisheries (northern shrimp, snow crab, Homarus, Norway lobster) are reviewed. Our review showed that landings of all these fisheries are still in a state of flux due to inherent population dynamics, fishing, and climate change. The talks and posters covered a broad range of state-of-the-art bioecological knowledge and present challenges in the assessment and management of the most ecologically and/or commercially important cold-water shellfish species belonging to the phyla Arthropoda, Mollusca, and Echinodermata. Various alternative harvesting and management techniques were presented along with perspectives for shellfish aquaculture. Methods and models for stock assessment were thoroughly covered as well as the ecological role of shellfish, their population dynamics, new insights into their biology and genetics, and their changing distribution and significance as invasive species.
... For Pacific Cod, this finding is similar to previous observations and might support the hypothesis of Ware and McFarlane (1986) claiming that this species does not have an important influence on Herring natural mortality off the WCVI and that the impact of this predator may have been previously overestimated. This hypothesis is also consistent with several analyses of stomach content data suggesting that Pacific Herring does not dominate the diet of Pacific Cod in the Gulf of Alaska (Jewett, 1978;Albers and Anderson, 1985;Yang and Livingston, 1986;Brodeur and Livingston, 1988;Urban, 2012), although other studies present contrasting results (Westrheim and Harling, 1983;Tinus, 2012). Analyses of stomach contents data in the Gulf of Alaska suggest that Pacific Herring does not dominate the diets of Arrowtooth Flounder, Sablefish or Pacific Halibut (Best and St-Pierre, 1986;Brodeur and Livingston, 1988;Knoth and Foy, 2008), which could explain the lack of negative spatio-temporal covariation of those predators with Pacific Herring. ...
Determining how fish respond to variation in biotic and abiotic conditions is a crucial prerequisite to forecasting changes in productivity and spatial distribution of fish stocks and designing sustainable marine resource management strategies. In the present study, we investigated the physical and biological drivers of the spatio-temporal dynamics of Pacific Herring (Clupea pallasi), which is a marine forage fish species important for commercial fisheries and First Nations in the northeastern Pacific. We fit multivariate spatio-temporal models to fisheries-independent trawl- and acoustics-based data collected off the West Coast of Vancouver Island (WCVI), Canada, during summers over the period 2006–2014. We evaluated the effects of the main ocean environmental drivers of WCVI lower trophic level productivity, including sea surface temperature (SST), chlorophyll a, fluorescence, salinity, oxygen, transmissivity and zooplankton density on variation in Pacific Herring biomass. Models were also used to measure spatio-temporal covariation with other pelagic, semi-pelagic, and bottom-associated fish species occurring off the WCVI to address potential competitive and predation interactions. Through application of these spatio-temporal models we found: (i) Pacific Herring biomass off the WCVI increased during 2006–2014; the highest Pacific Herring biomass was repeatedly found on the continental shelf (depths < 185 m) while low densities were usually observed along the shelf break (depths > 185 m), where Euphausiids, Pacific Hake, Sablefish and Arrowtooth Flounder were more abundant, which could reflect predation avoidance behaviour; (ii), the local biomass of Pacific Herring was related quadratically to the average SST in May; (iii) a positive covariation in spatio-temporal densities between Pacific Herring and its common zooplankton prey, supporting a potential bottom-up control hypothesis; (iv) a negative covariation in spatio-temporal densities between Pacific Herring and both Pacific Hake and Pacific Sardine, which could reflect predation and competitive interactions, respectively; and (v) a positive covariation in spatio-temporal densities between Pacific Herring and several groundfish species (i.e., Arrowtooth Flounder, Sablefish, Pacific Halibut, Pacific Cod), which highlights the need for an accurate assessment of the relative contribution of those species to the total summer predation pressure experienced by Pacific Herring off the WCVI. The findings of this study contribute to a better understanding of the WCVI marine ecosystem.
... In the case of near extinction such as P. goniurus, recovery may take a considerable amount of time. The present high biomass of fish in the GOA probably precludes rapid rebuilding of shrimp stocks (Albers and Anderson, 1985). Pandalid shrimp appear to be more useful as indicators of a cold to warm regime change, so it is unlikely that shrimp population changes will reflect any cooling trend for some time. ...
Pandalid shrimp are important components of the cold-regime boreal marine ecosystem in the Gulf of Alaska. Declines in abundance of several pandalid species occurred quickly after 1977 when an abrupt climate change caused water column warming. Shrimp trawl surveys conducted from 1953 to 1999 were used to describe how species composition changed relative to environmental parameters. Proportions of shrimp in survey catches were found to be negatively correlated (r = -0.72) with the water column temperature anomaly. Pandalid shrimp species which occupied inshore and typically shallower water declined to near extinction, while offshore and deep-water shrimp species maintained low population levels. Possible mechanisms responsible for this decline and their replacement by other species are discussed. Climate change as manifested by changes in water column temperature has an immediate effect on lower trophic levels of boreal marine ecosystems and rapid pandalid shrimp population changes are one of the first indicators that a community regime shift is underway.
... Adult Pacific cod Gadus macrocephalus Tilesius 1810 are not only an abundant and commercially valuable groundfish in the eastern Bering Sea and Gulf of Alaska (A'mar et al ., 2012;Thompson & Lauth, 2012), but are also important ecologically because of their predation effect on benthic species such as crab (e.g. Chionoecetes bairdi , Chionoecetes opilio and Paralithodes camtschaticus) and vertically mobile species such as walleye pollock Theragra chalcogramma (Pallus 1814), pandalid shrimp and various forage fish species (Albers & Anderson, 1985;Livingston, 1989;Livingston & Jurado-Molina, 2000;Aydin & Mueter, 2007;Urban, 2012). Despite their commercial importance and their large predatory effect on other commercially *Author to whom correspondence should be addressed. ...
The diel vertical migration (DVM) of Pacific cod Gadus macrocephalus was examined using depth and temperature data from 250 recaptured archival tags deployed on G. macrocephalus in the eastern Bering Sea and in the Gulf of Alaska near Kodiak Island. DVM of two types, deeper during daytime (type I) and deeper during night-time (type II), occurred frequently (15-40% of all days) in G. macrocephalus released at all sites. Most individuals displayed both diel types, with each type of behaviour lasting up to 58 contiguous days, and day and night depth differences averaging c. 8 m. Despite high among-individual variability, the occurrence of DVM varied significantly with the release site, season (i.e. day-of-year) and bottom depth, with the trend in seasonal occurrence nearly opposite for type I compared to type II DVM. No significance could be attributed to G. macrocephalus fork length, sex or ambient (tag) temperature. Trends in the magnitude of G. macrocephalus depth change were observed, with increased movement often occurring during night-time, dawn and dusk, and at release sites where the bathymetry was more complex. Both type I and type II DVMs were attributed to foraging on prey species that also undergo DVM, and increased vertical movements of G. macrocephalus during crepuscular and night-time periods were attributed to more active foraging during dim-light conditions when G. macrocephalus can potentially exploit a sensory advantage over some of their prey.
... The prey and predators of Pacific cod have been described or reviewed by Albers and Anderson (1985), Livingston (1989Livingston ( , 1991, Lang et al. (2003), Westrheim (1996), andYang (2004). The composition of Pacific cod prey varies to some extent by time and area. ...
... The diet of Pacific cod in western Bering Sea coastal areas has been described to consist primarily of walleye pollock, Pacific sand lance (Ammodytes hexapterus), other fish, and crab (Tokranov and Vinnikov 1991). In the Gulf of Alaska, the diet of Pacific cod consisted of walleye pollock, capelin, other fish, and shrimp (Albers andAnderson 1985, Yang 1993). In the eastern Bering Sea, walleye pollock, other fish, and crab were the primary prey of Pacific cod (Livingston 1991b, Livingston et al 1993. ...
... In the 2004 assessment (Thompson et al. 2004), for example, the correlations between age 1 recruits spawned since 1977 and monthly values of the Pacific Decadal Oscillation (Mantua et al. 1997) were computed and found to be very weak. The prey and predators of Pacific cod have been described or reviewed by Albers and Anderson (1985), Livingston (1989 Livingston ( , 1991), Lang et al. (2003), Westrheim (1996, and Yang (2004). The composition of Pacific cod prey varies to some extent by time and area. ...
... These observations agree with the estimated recruitment peaks for 1984 and 1985, given a 1-year lag from recruitment to the population at age 1 to being largely available to the fishing gear at age 2. Furthermore, despite the 2-year rebound in recruitment, the P. borealis population was not able to rebuild, which could be explained well by the high consumption by predators. Albers and Anderson (1985) also concluded, after studying the diet of Pacific cod in Pavlof Bay, Alaska, that the high consumption of shrimp by cod may have prevented the shrimp population in that area from rebuilding. ...
Because stock-assessment models have become more complex, the question of estimability of population parameters is important. We conducted simulation-estimation experiments with a length-based model of the pink shrimp (Pandalus borealis Krøyer) population in Kachemak Bay, Alaska, to compare the robustness of various modeling approaches to specifications of natural mortality (M), catchability (q), a survey gear selectivity parameter (L50), and data imprecision. Our goal was to determine the estimability of various parameters, particularly M, q, and L50. Simulation results suggest that interannual variations in M and L50 could be estimated, if the underlying values have a trend over time. However, parameter q should be fixed at a chosen value, even when it varies over time. Estimated M for the Kachemak Bay P. borealis population increased in the 1980s, perhaps owing to increased predation mortality by groundfish.
... The abundance of cod has been shown to have an impact on shrimp abundance (Stefánsson et al. 1998), and close linkages between populations of Atlantic cod and northern shrimp have been described for various parts of the North Atlantic (Berenboim et al. 2000; Worm and Myers 2003). Northern shrimp is one of the main preys for cod (Albers and Anderson, 1985; Jónsdóttir et al. 2012; Pálsson and Björnsson 2011). The importance of shrimp as prey for cod decreases with increasing cod length (Berenboim et al. 2000; Jónsdóttir et al. 2012). ...
Despite an increase in northern shrimp (Pandalus borealis) female biomass in the past years, the recruitment of the offshore population north and northeast of Iceland has remained very low. In this study the influence of abiotic and biotic factors were studied in relation to shrimp recruitment. Two factors, cod (Gadus morhua) abundance and summer sea surface temperature, were found to have a negative effect on offshore shrimp recruitment, explaining 71% of the observed variation. Both cod abundance and temperature on the offshore shrimp grounds have increased in the past years, while recruitment has decreased and been at historically low levels since 2005. No significant relationship was found between recruitment and spawning biomass, indicating that recruitment variability is mainly driven by other factors. Cod abundance and summer sea surface temperature are likely to affect different life stages of shrimp, as sea surface temperature influences shrimp during its planktonic phase while cod abundance influences the demersal stage.
... Evacuation rate data are often lacking for sablefish and other species that are difficult to maintain in the laboratory (Sullivan and Smith 1982;Rindorf 2004). As a result, evacuation rates from similar predators feeding on different prey may be substituted from literature values (e.g., Livingston 1983;Albers and Anderson 1985;Cartwright et al. 1998); additionally, these predators may come from different environments. Temperature is thought to be the most critical factor regulating evacuation rates (Persson 1986;Bromley 1994;Jobling 1994;Héroux and Magnan 1996) and also affects estimates of predation impact. ...
At-sea observations of age-1+ sablefish (Anoplopoma fimbria) predation on juvenile salmon (Oncorhynchus spp.) were combined with laboratory studies to determine gastric evacuation rates and used to estimate summer predation impact in the northern region of Southeast Alaska. In June and July 1999, up to 63% of sablefish examined from trawl catches in strait habitat had each consumed one to four juvenile pink (O. gorbuscha), chum (O. keta), or sockeye (O. nerka) salmon. In two laboratory experiments, field-captured sablefish were acclimated without food in compartmentalized flow through tanks with conditions manipulated to reflect the photoperiod and temperature regimes of summer. These predators were offered one whole, pre-weighed juvenile chum salmon, consumption events were observed, and then predators were sacrificed at predetermined time intervals. Prey biomass remaining in the stomach of each predator was weighed, and an exponential model of the decline in percent biomass over time yielded instantaneous evacuation rates of r = 0.049 at 12°C and r = 0.027 at 7°C, respectively. From field data combined with model-derived estimates of meal frequency, we estimated that 0.8-6.0 million juvenile salmon were consumed by age-1+ sablefish in the 500 km2 area of Icy Strait in a 33-day period. Moreover, a 10-year time series of catches indicated that 1999 was a year of unusually high abundance for age-1+ sablefish and relatively low juvenile salmon abundance. We speculate that sablefish predation in 1999 could have impacted abundance of out-migrating juveniles and contributed to low harvests of returning adult pink salmon in 2000 and adult chum salmon in 2002. Our results suggest that sablefish predation on juvenile salmon can occur during episodic, strong year classes of sablefish and may affect adult salmon returns.
... The Pacific cod Gadus macrocephalus is widely distributed in the coastal area of the north Pacific Ocean, from Far Eastern Asia through the Bering Sea to North America, 16 and plays an important role as a consumer in temperate and subarctic marine ecosystems. 17,18 Around the coastal waters of Japan, this species deposits eggs on sandy bottoms at depth of 20-100 m. 19 Larvae begin feeding approximately one week after hatching, 20 and metamorphose to juveniles at 25 mm total length (TL). 21 They live a pelagic life for three or four months before settling down on the bottom at depths of 30-50 m. 22 Although the biology of the Pacific cod has been well studied, few studies on otolith microstructure and somatic growth in the early life stages have been conducted. ...
Microstructures of sagittae and lapilli were examined in relation to somatic growth for reared larvae and juveniles of Pacific cod. The Laird–Gompertz model was fitted to the daily age and somatic growth relationship. Growth increments were deposited on a daily basis in both kinds of otoliths, with a check formed at hatching. Two subsequent checks and an accessory primordia (AP) occurred in the sagittae. The lapillus was adequate for increment width measurement through the early life stages. Sagittal and frontal plane of sagitta was adequate for measurement in the pre-AP and post-AP formation stages, respectively. The shift of desirable plane was caused by changes in otolith and increment shapes with AP formation. Back-calculated total lengths using the biological intercept method did not significantly differ with certain body lengths (P > 0.05), suggesting validity of back-calculation in this species. Using the back-calculated total length, morphological and ecologic changes that seemed to affect checks and AP formations are discussed.
... Fish and invertebrate populations in the northern GOA ecosystem have undergone substantial changes. In the mid-1970s, crab and shrimp stocks declined while salmon and ground fish increased (Albers and Anderson, 1985;Blau, 1986;Francis and Hare, 1994;Hollowed et al., 1994;Thompson and Zenger, 1994;Anderson and Piatt, 1999). These changes coincided with decadal-scale North Pacific adjustments in the atmosphere and ocean (Trenberth and Hurrell, 1994;Mantua et al., 1997). ...
Conductivity–temperature–depth (CTD), acoustic and net samples were taken through a series of passes in the eastern and central Aleutian Island archipelago to document regional differences in the physical and biological conditions. The water column in central passes had elevated salinity and depressed temperatures, indicating upwelling of deep water through the passes. The zooplankton community included the oceanic genera Neocalanus and Eucalanus, and the euphausiid Euphausia pacifica, all oceanic taxa. Eastern passes had significantly lower salinity and elevated temperature relative to the central passes, suggesting a more neritic environment. Calanus marshallae, Pseudocalanus, Acartia and Thysanoessa inermis, common neritic species, were observed in the eastern passes. Canonical correlation indicated that up to 50% of the observed variance in mean zooplankton abundance in the passes could be explained by salinity and temperature. Elevated sound scattering was observed in fronts and eddies in the passes, particularly at the northern ends of the passes, in association with elevated zooplankton abundance and biomass. The central passes were characterized as an oceanic environment, influenced primarily by Alaskan Stream water with its associated interzonal copepod species, while the eastern passes were influenced by the Alaska Coastal Current, which contains a mixture of oceanic and neritic zooplankton species.
... There is substantial variability on both interannual and longer time scales in harvest and recruitment success to major GOA fisheries including shrimp (Pandulus spp.) (e.g. Albers and Anderson, 1985), king crab (Paralithodes spp.) (Blau, 1986), walleye pollock (Theragra chalcogramma) (Hollowed et al., 1994), Pacific cod (Gadus macrocephalus) (Thompson and Zenger, 1994) and salmon (Oncorhynchus spp.) (e.g. Mantua et al., 1997), which appears to be related to North Pacific basin-scale climate changes (Francis and Hare, 1994;Trenberth and Hurrell, 1994;Anderson and Piatt, 1999). ...
Interannual variability in abundance of the dominant euphausiids Thysanoessa inermis, Thysanoessa spinifera and Euphausia pacifica was studied in the northern Gulf of Alaska during the production season from 1998 to 2003. T. inermis abundance increased significantly over the shelf from 1998 to 2002, the abundance of T. spinifera (which also inhabits the shelf) did not change, while the abundance of E. pacifica (usually common on the outer shelf) declined in 2001. Based on the incidence of spermatophores on the females, reproduction of T. inermis occurred during April in all years, and was extended through May in 2000–2002. The major spawning of T. spinifera and E. pacifica occurred from April through July, and from late May through August, respectively. The spawning of T. inermis and T. spinifera appeared to be closely related to the spring diatom bloom on the inner shelf, while the spawning of E. pacifica occurred later in season, when the temperature of the mixed layer increased. A strong increase in abundance of T. inermis, associated with the extended colder phase in the North Pacific, indicates that progressive cooling in 1999–2002 may have resulted in greater reproductive success of the early spawning T. inermis on the inner shelf.
... However, predation by cod on demersal stages of shrimp has been well documented, not only off Labrador (Bowering et al., MS 1983) and eastern Newfoundland (Lilly, 1991) but also in waters off West Greenland (Sidorenko, 1962) and Iceland (Magnússon and Pálsson, 1989) and in the Barents Sea (Mehl, 1989). Similarly, predation by Pacific cod (Gadus macrocephalus) on shrimp has been documented in the Gulf of Alaska (Albers and Anderson, 1985). ...
Biological changes in the ecosystem of the Northeast Newfoundland Shelf during the late-1980s and 1990s included a collapse in the biomass of cod (Gadus morhua), a substantial increase in the biomass of northern shrimp (Pandalus borealis), and an expansion in the area fished for shrimp. The timing and magnitude of changes in cod biomass and the quantity of shrimp consumed by cod were explored to determine if they were consistent with the hypothesis that the increase in shrimp biomass was a consequence of a reduction in predation pressure from cod. Results are equivocal because the timing of both the increase in the shrimp stock and the decline in the cod stock remain unclear and there is considerable uncertainty in the estimates of consumption of shrimp by cod. Nevertheless, it appears that an initial increase in shrimp biomass must have occurred during the early to mid-1980s and was not related to changes in the cod, whereas a larger increase in shrimp biomass in the 1990s was related at least in part to the collapse of the cod.
... In addition, fisheries populations in the GOA ecosystem have undergone substantial changes. In the mid-1970s, the crab and shrimp populations declined while salmon and ground fish populations increased (Albers and Anderson, 1985;Blau, 1986;Francis and Hare, 1994;Hollowed et al., 1994;Thompson and Zenger, 1994;Anderson and Piatt, 1999). These changes coincided with decadal-scale North Pacific adjustments in the atmosphere and ocean (Trenberth and Hurrell, 1994;Mantua et al., 1997). ...
Zooplankton abundance from March through October on the northern Gulf of Alaska shelf in 1998, 1999 and 2000 was dominated by calanoid copepods; the biomass was dominated by calanoids and cnidarians. Although we sampled during the 1997–1998 El Niño, marked interannual differences in the major copepod taxa were not observed. Zooplankton abundance and species composition were influenced primarily by mean water-column salinity, secondarily by the mean temperature above the thermocline. An annual biomass peak, averaging about 0.5 g wet weight m−3, occurred in May and consisted primarily of the oceanic copepod species Neocalanus cristatus, Neocalanus plumchrus and Neocalanus flemingeri. A second biomass peak, 0.5 g wet weight m−3, was observed in August and consisted mainly of the cnidarian Aequorea spp. Copepod production, estimated from daily growth rates using temperature–body size regressions, peaked in May at about 35 mg C m−2 day−1. Initial calculations suggest an annual copepod production on the order of 6 g C m−2 year−1, probably less than 10% of the annual primary production. The apparent resilience of the zooplankton assemblage on the northern Gulf of Alaska shelf to the 1997–1998 ENSO may have been because of its large geographic separation from the faunal boundary between zooplankton communities in the California Current and North Pacific subarctic gyre.
... This is despite the fact that shrimps are the dominant prey of many predatory fishes in temperate coastal waters (e.g. Albers and Anderson 1985;Garrison and Link 2000) and an important link between primary producers and higher trophic levels (Edgar and Shaw 1995a). ...
Human disturbances, such as overfishing, may disrupt predator-prey interactions and modify food webs. Underwater surveys were carried out at six shallow-water reef barrens in temperate waters of northern-central Chile from October to December 2010 to describe the effects of predation, habitat complexity (low, medium and high) and refuge availability on the abundance and population structure of the rock shrimp Rhynchocinetes typus (Rhynchocinetidae), an important mesoconsumer on subtidal hard substrata. Three sites were within managed (restricted access) areas for fishermen, and three were unmanaged (open-access). Field observations and tethering experiments were conducted to examine the relationship between fish and shrimp abundances, and the relative predation rates on shrimps. Direct effects of predation on R. typus body-size distribution were examined from shrimps collected in the field and fish stomachs. The presence and the abundance of R. typus increased with habitat reef complexity and refuge availability. Shrimp abundance was negatively related to fish abundance in managed areas, but not in open-access areas, where shrimp densities were the highest. Also, predation rates and body-size distribution of shrimps were unrelated, although fish consumed more large shrimps than should be expected from their distribution in the field. R. typus occurred most often in shelters with wide openings, offering limited protection against predators, but providing potential aggregation sites for shrimps. Overall, direct effects of predation on shrimp densities and population structure were weak, but indirect effects on shrimp distribution within reefs appear to have been mediated through behavioural responses. Our study highlights the need to assess both numerical and behavioural responses of prey to determine the effects of predator loss on mesoconsumer populations.
... Предполагается, что хищни 一 чество трески служит одной из причин, препятствующих восстановлению промыслового запаса розовой креветки (доминирующего вида в составе пищи -63 %) в зал. Павлова на Аляске (Albers, Anderson, 1985). ...
... Small decapod crustaceans often dominate marine benthic communities (e.g., Austin et al. 1980;Stella et al. 2010), where they are prey for many fishes (Angel and Ojeda 2001;Medina et al. 2004;Kulbicki et al. 2005) and predators of small sessile organisms (Dumont et al. 2009), thereby playing an important role within marine food webs (Howard 1984;Worm and Myers 2003;Dumont et al. 2011). Depletion of predators due to overfishing can release predation risks on mesoconsumers such as shrimps (Albers and Anderson 1985;Worm and Myers 2003) and thereby affect lower trophic levels (Schmitz et al. 1997;Dorn et al. 2006). On the other hand, destruction of coral reefs may increase predation risks on mesoconsumers which use complex coral habitats as refuge. ...
Nonlethal effects of predators on prey behaviour are still poorly understood, although they may have cascading effects through food webs. Underwater observations and experiments were conducted on a shallow fringing coral reef in Malaysia to examine whether predation risks affect diel activity, habitat use, and survival of the rhynchocinetid shrimp Cinetorhynchus hendersoni. The study site was within a protected area where predatory fish were abundant. Visual surveys and tethering experiments were conducted in April-May 2010 to compare the abundance of shrimps and predatory fishes and the relative predation intensity on shrimps during day and night. Shrimps were not seen during the day but came out of refuges at night, when the risk of being eaten was reduced. Shrimp preferences for substrata of different complexities and types were examined at night when they could be seen on the reef; complex substrata were preferred, while simple substrata were avoided. Shrimps were abundant on high-complexity columnar-foliate Porites rus, but tended to make little use of branching Acropora spp. Subsequent tethering experiments, conducted during daytime in June 2013, compared the relative mortality of shrimps on simple (sand-rubble, massive Porites spp.) and complex (P. rus, branching Acropora spp.) substrata under different predation risk scenarios (i.e., different tether lengths and exposure durations). The mortality of shrimps with short tethers (high risk) was high on all substrata while, under low and intermediate predation risks (long tethers), shrimp mortality was reduced on complex corals relative to that on sand-rubble or massive Porites spp. Overall, mortality was lowest on P. rus. Our study indicates that predation risks constrain shrimp activity and habitat choice, forcing them to hide deep inside complex substrata during the day. Such behavioural responses to predation risks and their consequences for the trophic role of invertebrate mesoconsumers warrant further investigation, especially in areas where predatory fishes have been overexploited.
... We believe that warming water column temperatures may allow cod to remain in our study areas throughout the winter instead of migrating offshore when temperatures are cooler (Ketchen 1961). This increased contact with the forage base probably contributed further to the observed decline of shrimps and osmerids that continued well after the end of most inshore shrimp trawl fisheries in the late 1970s (Albers and Anderson 1985). ...
Indices of abundance for capelin in the Newfoundland area collected since the early 1980s include biomass estimates from offshore acoustic surveys, school surface area near spawning beaches from aerial surveys, and catch rates from the inshore commercial fishery. During the 1990s, the offshore acoustic estimates declined dramatically but the inshore in-dices remained stable. This divergence was coincident with below nor-mal water temperatures and changes in capelin biology. The biological changes included large-scale changes in distribution and later spawning, both of which have been linked to the colder water temperatures, and smaller fish size. The dichotomy in the trends of abundance indices has never been fully reconciled. However, based on data from several sources, it appears that the acoustic surveys were underestimating the true population abundance of capelin offshore. It seems likely that the severe environmental conditions during the early 1990s were the major cause of the changes in biology and behavior of capelin, and these changes had their greatest impact on the acoustic estimates.
... Accepted Article fish families including skates (Rajidae), other flatfishes (Pleuronectidae), or rockfishes (Sebastidae; Jewett, 1978;Albers & Anderson, 1985;Yang, 1993;Adams et al., 2007;Marsh et al., 2012;Urban, 2012;Bizzarro et al., 2017). ...
The contents of 1056 stomachs were included in a trophic‐guild analysis to document separation amongst 16 groundfish species inhabiting Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords in Prince William Sound, Alaska and to determine the relative contribution of C. pallasii and G. chalcogrammus to that separation. A total of five multi‐species feeding guilds and one outlier species were determined through multivariate analyses. Major gradients of trophic separation spanned from invertebrates (mostly shrimps, crabs and unidentified decapods) to fishes (mostly unidentified fishes, C. pallasii and G. chalcogrammus) a pattern that was influenced by intra and interspecific differences in predator lengths. While C. pallasii and G. chalcogrammus were important to the overall guild structure, within‐guild similarities were consistently highest due to unidentified fishes. In general, larger predators consumed the largest C. pallasii and G. chalcogrammus, with the smaller‐on‐average predators consuming smaller C. pallasii and fewer or smaller G. chalcogrammus. Regardless of guild inclusion, groundfishes primarily consumed pre‐recruit C. pallasii and G. chalcogrammus (i.e., younger than age 3 years fishes), which has the potential to negatively influence recruitment of these forage fishes to the adult, spawning population.
... Adult Pacific cod live near the bottom over soft sediments. They feed on Pacific sand lance, Pacific herring, walleye pollock, sculpins, flatfishes, and invertebrates, such as euphausiids, crabs, and shrimp (Albers and Anderson 1985;Jewett 1978;Blackburn 1986;and Westrheim and Harling 1983). Following sinter spawning, they migrate to feed in deeper, cooler waters. ...
... Pacific cod (Gadus macrocephalus) is a late specialist on walleye pollock (Table C.1 in Supplementary materials), but in the Gulf of Alaska it first feeds on shrimp and later on tanner crab before finally feeding on pollock (Urban, 2012). Increased predation by Pacific cod in conjunction with a climate regime shift was suggested as a potential cause of the collapse of fisheries for both pink shrimp and tanner crab (Albers and Anderson, 1985). The current fisheries for Pacific cod selectively target individuals at or above its diet shift toward pollock (Barbeaux et al., 2016), resulting in reductions in its consumption of pollock, but little impact on its consumption of early diet items such as shrimp and crab. ...
In some marine ecosystems, overharvesting marine predators has triggered major changes in trophic structure and ecosystem function. However, harvest levels that are deemed sustainable for one species may still lead to unexpected impacts elsewhere in the ecosystem. For example, by imposing an additional source of mortality, even sustainable harvesting can lead to a reduction in the number of large individuals within a population, and this truncation in size structure is typically more severe when the largest, most valuable size classes are targeted. Often small and large individuals within a species differ in important ways, including in what they consume, so a loss in predator-prey interactions could occur even without changes in overall predator biomass. Here we explore whether a truncation in predator size structure alone can reduce or functionally eliminate linkages between predator and prey. For this outcome to occur, a predator's diet must change as it grows in size. We examined evidence for changes in diets with size among predators in three large marine ecosystems, and used a size-structured population dynamics model to evaluate the extent to which otherwise sustainable fishing results in disproportionate reductions in predation. Modelling suggests that diet shifts occurring late in life history (diet mid-point >45% of the maximum size) led to losses in predation that were more severe than would have been expected from losses in predator biomass. Further, the form of the fishery selectivity was less important than the degree of reduction in biomass within each size class relative to the timing of diet shifts. Empirical diet information demonstrates that piscivores vary widely in their onset to piscivory, and this may buffer the potential impacts of truncation in size structure. However, over half of the piscivores had diet shifts toward specific fish taxa at sizes at or above that which would lead to disproportionate reductions in prey consumption. Information about when and how diets change with predator size could identify ecosystems where harvest may lead to unexpected losses in predator-prey interactions.
... Pandalid shrimps, tanner crabs, amphipods, and groundfishes are important prey to many other marine organisms in PWS. For example, Pacific cod, Gadus microcephalus, preys on pandalid shrimps, amphipods, euphausiids, Tanner crabs, walleye pollock, and polychaetes (Albers and Anderson 1985;Yang et al. 2006). Some marine mammals and seabirds also feed on some of the same prey taxa as these skates. ...
Determining trophic relationships within and among species can provide insight into the structure and function of an ecosystem, and can inform the development of multi-species monitoring and management plans. The goal of this study was to address the need for dietary and trophic information of two common and abundant skates in Prince William Sound (PWS), the Bering skate, Bathyraja interrupta, and longnose skate, Raja rhina. Based on identification and analysis of stomach content data, both species were found to be generalist predators with diets dominated by crustaceans and supplemented with teleosts. The primary source of dietary variability for each species was total length, with spatial variables (i.e., latitude, longitude, and depth) also explaining a large portion of total dietary variability in the Bering skate. However, only a small proportion of the total intraspecific dietary variation was accounted for among the analyzed variables, suggesting substantial individual-based differences in the feeding habits of each species. Trophic level estimates indicated that the Bering skate and longnose skates <100 cm total length (TL) were secondary consumers, whereas longnose skates ≥100 cm TL were more piscivorous, tertiary consumers. Significant interspecific dietary differences were also evident, suggesting trophic separation, likely as a function of skate size. Given their abundance and generalistic feeding behavior, PWS skates can provide a means of monitoring demersal community health; information about their foraging ecology will be valuable in gaining a better understanding of trophodynamics within the PWS food web.
This review paper synthesizes published research and unpublished data on the abundance and distribution patterns, ecology and population dynamics of walleye pollock (Theragra chalcogramma) during their first year of life (age-0) in the Gulf of Alaska. Distribution patterns have been described using mainly trawl catches, but recently, acoustic methodology has been employed, especially in examining vertical distributions. Although age-0 pollock are found throughout the Gulf, the highest catches occurred west of Kodiak Island. Pollock are pelagic for at least their first 6 months of life but show an ontogenetic increase in depth distribution superimposed on a pronounced diel vertical migration at a larger size. Daily growth rates are variable depending on year, season and area, and growth generally ceases during the winter. The diet of age-0 pollock shifts from mainly copepods in early juveniles to euphausiids by fall, with epibenthic organisms becoming important during the winter months. Feeding occurs mainly at night in surface waters. Age-0 pollock are most frequently associated with gelatinous zooplankton (medusae) and older pollock. Many predators on age-0 pollock have been identified; the most important are arrowtooth flounder (Atheresthes stomias), adult pollock, puffins (Fratercula spp.), murres (Una spp.), harbor seals (Phoca vitulina richardsi) and Steller sea lions (Eumetopiasjubatus). Modelling provides some insight into the population dynamics of these juveniles and environmental conditions which interannually affect their survival. These results are discussed relative to the importance of age-0 pollock in the recruitment of this species and to their role in the pelagic ecosystem.
The Sanak Biocomplexity Project is a transdisciplinary research effort focused on a small island archipelago 50 km south of the Alaska Peninsula in the western Gulf of Alaska. This team of archaeologists, terrestrial ecologists, social anthropologists, intertidal ecologists, geologists, oceanographers, paleoecolo- gists, and modelers is seeking to understanding the role of the ancient, historic, and modern Aleut in the structure and functioning of local and regional ecosys- tems. Using techniques ranging from systematic surveys to stable isotope chem- istry, long-term shifts in social dynamics and ecosystem structure are present in the context of changing climatic regimes and human impacts. This paper presents a summary of a range of our preliminary findings.
In the Gulf of Alaska, adult Pacific cod exhibited an annual cycle of condition, gonad index and liver index in which maximum values occurred in ripe fish in March and minima in July. About 30–31 % of prespawning stored energy was expended during the spawning effort. The energy associated with spawning derived from liver (24% and 18%), somatic tissue (22% and 33%) and gonad (53% and 48%) for females and males, respectively. Liver index and gonad index at the time of sampling were directly related in females, but in males gonad index was best related to liver index 1–3 months earlier.The Pacific cod is very similar to the Atlantic cod in terms of energy cycling, maximum gonad sizes, energy expended during spawning and gonadal contribution to energy expenditure. However, in Pacific cod, somatic tissue contributes markedly to energy expended during reproduction. The Pacific cod cod differs from the walleye pollock with respect to gonad index (13% and 20%ν. 20% and 8% for females and males, respectively), spawning weight loss (25%ν. 38%), liver energy loss during spawning (71%ν. 55%) and energy cost of spawning.
Growth of Pacific cod was related to energy consumption (cal g−1 day−1) and was well described by linear equations. Maintenance ration was 11 and 12 cal g−1 day−1 at 4.5 and 6.5° C, respectively. Cod between 200 and 5000 g had similar growth rates when growth was expressed as a function of consumption (cal g−1 day−1). Laboratory consumption of food averaged 0.9 and 1.3% body weight per day at 4.5 and 6.5° C, respectively. At these temperatures growth was 0.34–0.38% body weight day−1.Maximum stomach volumes equated to approximately 4.7% of body weight with shrimp as prey. At this meal size Pacific cod did not feed the next day. A multiple meal evacuation experiment was used to verify the consumption estimates. A return-to-hunger estimate of the meal size evacuated was 1.5% body weight day−1 at 6.5° C, similar to the 1.3% consumption estimate. For Pacific cod fed a single meal of 1% body weight the estimated instantaneous evacuation rate was 0.63 body weight day−1 at 6.5° C. Meal size markedly affected the evacuation rate.Measured consumption and growth rates are similar to those of Atlantic cod, Gadus morhua.
Northern shrimp (Pandalus borealis) is targeted by commercial fisheries but is also an important prey in the marine food web. In this study, stomach content data were used to study predation on shrimp by three gadoid species, cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), in six inshore areas around Iceland. The results showed that shrimp was more important in the diet of cod compared to the other two predators. However, the overall predation pressure was similar for cod and haddock, due to the high abundance of haddock. Therefore, even though shrimp is not the primary source of food for haddock, this species can have a substantial effect on shrimp stocks when haddock abundance is high. In addition, while cod and haddock did not select for any particular size of shrimp, whiting seemed to preferentially target juvenile shrimp. The results suggest that due to the overall effects of these three predators on shrimp stocks, gadoids need to be included in management of shrimp stocks as predation is one of the major drivers in the development of this important prey stock prey stock.
The literature on the biology of 20 described species of the shrimp genus Pandalus, reported from the Pacific and Atlantic Oceans in the northern hemisphere, is reviewed. Taxonomy, external morphology as well as species descriptions, keys to adult stages and systems for classification and species determination of larvae are covered.Present knowledge on geographic distributions, depth distributions and salinity, temperature, and habitat preferences on the continental shelves and slopes is also accounted for and discussed.Various aspects of the life histories of these species are described. A section on reproductive biology includes a discussion of evolutionary maintenance of protandric hermaphroditism, which is the dominant mode of reproduction in the genus, as well as an account of the present knowledge of the mechanism of sex change in these shrimp. Methods used to describe reproductive cycles as well as results are described and exemplified. Temperature effects on the duration of different phases of the reproductive cycles represented in the genus are discussed.Detailed accounts of adult behaviour in connection with mating, oviposition and hatching are presented. A section on Pandalus larvae includes accounts and discussions of behaviour, nutrition, growth and survival. Adult behaviour is treated on both individual and population levels, and reports on schooling, migrations and food and feeding are reviewed and discussed. Predators, diseases and parasites on Pandalus are reviewed and some information given about competitors.Methods for estimating growth and age and results concerning growth and factors affecting growth are described and reviewed.Population dynamics, including population discrimination, abundance and standing stock estimation, parent stock-recruitment relationships and mortality factors, are discussed and illustrated by examples. In conclusion it is noted that, among crustacean fisheries, that for Pandalus is surpassed in economic value only by that for penaeid shrimp, and the potential for aquaculture is assessed.
Measurements of oxygen consumption rates were made for both fed and unfed Pacific cod Gadus macrocephalus Tilesius at a variety of temperatures. Rates of oxygen consumption were found to be similar to those reported previously for Atlantic cod. At 6.5 °C, Vo2 was described by the equation ml O2 · ind−1 · h−1 = 0.158 (wet wt g0.078); r2 = 0.97. Increase in environmental temperature between 3.5 and 7°C resulted in a linear increase in rates of oxygen consumption. Between 7 and 12 °C, rates of oxygen consumption were similar. When fish were fed a single meal, oxygen consumption rates increased during the 1st and 2nd days after feeding, by ≈ 34 and 18%, respectively, over unfed rates. When fed daily, rates of oxygen consumption increased to peaks of 41–48% over unfed rates, depending on the temperature.
Pacific cod (Gadus macrocephalus) are generalist predators in the Gulf of Alaska (GOA), and are an important predator on other commercially important species. Efficient management of this species can benefit by knowing how these fish adapt to changing environmental conditions, with a focus on how growth and condition are affected by changes in temperature and diet. We conducted a feeding study to understand the relationship between growth, ration, and temperature, and how these factors interact to affect energy allocation strategies. Since growth and condition of juveniles can determine recruitment into the population, this study focused on growth and consumption of age 1+Pacific cod held over 4 temperature treatments (4. °C, 8. °C, 12. °C, and 16. °C) and 3 ration levels (unlimited ration, medium ration, and low ration). We also compared cellular nucleic acid (RNA/DNA) ratios, an instantaneous growth index, total-body lipid, and proximate composition between fish. At 4. °C, 8. °C, and 12. °C, fish at medium and low rations had higher growth rates relative to fish at high rations. Higher food consumption appears to negatively affect digestive ability, assimilation efficiency, and nutrient utilization. RNA/DNA was clearly correlated with growth rates at 4. °C and 8. °C, but this relationship did not hold at higher temperatures. A secondary growth study was conducted to test the reliability of the growth/consumption models derived from the main growth study. Temperature influenced energy reserves (lipid) while tissue growth (protein) was influenced by ration level. Average lipid values were higher at 4. °C than at 8. °C or 12. °C, suggesting a predisposition to heightened lipid synthesis at colder temperatures. Longer durations of warmer water temperature in the GOA could consequently affect energy allocation strategies, with dietary changes in the field potentially amplifying this effect in cold and warm years. This energy allocation strategy could be detrimental with warmer temperatures predicted in the GOA.
This chapter discusses the ecological change that occurs over different timescales. Long-term measures of physically important variables are salinity, precipitation, nutrients, stratification, currents, and coastal wind fields are relatively rare. Climate change, whether of natural or anthropogenic origin, brings with it uncertainty and the potential to upset existing economic and social. structures. The barrier to understanding long-term changes in the Gulf of Alaska (GOA) is the complex nonlinear structures that characterize these systems. The space and timescales of physical and biological variables are different from one another and the relation between a physical change and a biological response might be indirect, nonlinear, and involve several other system components. The observations are used in conjunction with models to evaluate model performance and/or to constrain model predictions and hindcasts. Variations have been detected in winds, surface heat fluxes and runoff, water temperature and salinity, mixed-layer depth, nutrient supply, and circulation properties. The temperature of the ocean at a given location is controlled by heat exchange with the atmosphere, mixing with waters of different temperatures, and the advection of heat into or out of a region by ocean currents. The long-term record of salmon abundance comes from two sources - the historical record of the fisheries and geochemical records in sockeye salmon lake sediments. Development of comprehensive life-stage-based models is one step toward understanding the causes of shrimp and crab population changes in the northern Gulf of Alaska.
Stable isotope ratios of carbon and nitrogen were measured in an unex- ploited population of walleye pollock (Theragra chalcogramma) from Prince William Sound, Alaska (PWS) as a metric of feeding niche. Stable isotope data of pollock were compared with each other and with stable isotope data of age-0 herring (Clupea pallasii). There were significant species, location, and time period differences in synoptically sampled age-0 pollock and herring. Age-0 pollock were generally 13 C-enriched relative to herring even as carbon isotope values varied with time. A positive relationship between 13 C content and length of pollock from Zaikof Bay, PWS, was consistent with a pattern of low 13 C being attribut- able to food subsidies, most likely oceanic zooplankton. The carbon isotope difference between age-0 pollock and age-0 herring increased when 13 C decreased. This coincided with a relative increase in age-0 pollock food chain length compared to age-0 herring. This is posited to reflect reduced overlap in food supply and thus com - petition during a period of inferred high food subsidies. Subsidies are further posited to vary according to hypothesized oceanic zooplankton population cycles. A systematic increase in nitrogen isotope values with respect to size suggested an average ontogenetic food chain length increase of about 1.3 trophic levels over a pollock's life span after age-0. Trophic level variability was consistent with facultative planktivory for all adult sized pollock, including those with lengths over 400 mm, above which there was a sharp trophic level increase. The ability for pollock to maintain
This chapter focuses on ecosystem structure. Ecosystem can be viewed as how the sun's energy is captured and passed from plants to animals and then from animals to animals and the strategies that animals have evolved to capture a share of that energy, use it, and flourish in the Gulf of Alaska. Marine animals thrive in the Gulf of Alaska (GOA) for two basic reasons: (1) the ecosystem is productive, and a lot of food is available to animals living there, and (2) a small number of successful species in the Gulf made the most of the available energy by organizing themselves, as revolving body forms, physiology, and behaviors that allow them to successfully withstand the rigors of the subarctic ocean, capture food, grow, and reproduce faster than they themselves are eaten, harvested, or fall victims to contaminants or disease. The chapter explores the changing structure of the ecosystem during a typical year. The survival strategies of the key species of fish, birds, and mammals that tie them to their habitats are also discussed.
In marine systems, most seabirds are considered upper trophic level consumers, yet they may be vulnerable to predation by other marine animals. There are varying accounts of large fish eating birds, but little is known about whether predation by demersal fish predators is an important source of mortality for seabirds. Fish processors in Dutch Harbor, Alaska, have observed seabird remains in Pacific Cod Gadus macrocephalus stomachs. We analyzed seabird remains from Pacific Cod caught off Cape Sarichef in Unimak Pass from mid-January through early April 2011. Of 74 different seabird remains examined, five avian genera were identified. These results provide documentation that Pacific Cod consume seabirds; either by predation or scavenging. Overall, the significance of seabird predation by fish is not well known, but may be episodically important.
Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those of the northern Bering Sea. To understand how climate change may alter predator demand for prey resources, we quantified the relationship between temperature and allometric rates of prey consumption for 3 major groundfish predators: walleye pollock Gadus chalco grammus, Pacific cod Gadus macrocephalus, and arrowtooth flounder Atheresthes stomias. We contrasted regional patterns in foraging rates of more than 120000 fish collected annually from 1981 to 2011 from the eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI). From field observations, we estimate that juveniles and adults of each species eat 1.15 to 3.94 and 0.84 to 3.13 times their body weight (BW) yr(-1), respectively (i.e. 0.2 to 1.2% BW d(-1)), with arrowtooth in all 3 regions and adult EBS Pacific cod exhibiting the highest rates. If historical patterns signify future conditions, we estimate that a 2 degrees C projected increase in water temperature would cause 26 and 14% increases in daily rations of adult EBS pollock and Pacific cod, respectively, whereas we predict a 37% decline in the daily rations of EBS arrowtooth. Similarly, we predict that GOA pollock, Pacific cod and arrowtooth rations would increase markedly (70, 34, and 65%, respectively). Although daily ration of AI arrowtooth may increase by 31%, our models predict 41 and 3% declines in AI pollock and Pacific cod rations, respectively. These results portend (sometimes counterintuitively) region-and species-specific shifts in Alaska groundfish predator for aging rates and trophodynamic interactions concomitant with climate change.
Hypotheses concerning the decline of Steller sea lions in the Gulf of Alaska (GOA) were evaluated based on comparison of data to three other ecosystems that had similar environmental and commercial fishery characteristics. We focus on examining the effects of commercial pinniped harvest, commercial fisheries, and environmental changes. Of the four pinniped species included in this study, only the Steller sea lion population has exhibited a sharp decline in population number. Comparative analysis indicated that the Gulf of Alaska pinniped population has not experienced any unique large-scale perturbations compared to the other ecosystems. Commercial pinniped harvest occurred in all four ecosystems. The history of harvest was shortest for GOA Steller sea lions and the numbers taken were lower than in the Barents Sea and Benguela Current ecosystems. Exploitation rates, though only calculated for years when both harvest numbers and total population size were available, also indicated that the Steller sea lions have experienced very little commercial harvest pressure compared to the other pinniped populations in the three other ecosystems. The age group of animals killed was comparable throughout all ecosystems. Large-scale variability in water temperature was common to all four ecosystems. Although the periodicity of the changes varied among ecosystems, they all appeared to be driven by low pressure systems. The variability of the oscillations in water temperature was lowest for the eastern Pacific ocean (i.e., the GOA and California Current ecosystems) and highest in the Benguela Current. Commercial fisheries played a major part in all four ecosystems. The main species in pinniped diets were often the target of commercial fishing activity leading to potential conflicts between the 2 types of predators (i.e., pinnipeds and commercial fisheries). Exploitation rates in the GOA were comparable to or less than rates in the other ecosystems while the rates were highest in the Barents Sea. Statistical analysis showed that GOA pollock exploitation rates were significantly different from the rates of most other species. Healthy pinniped populations were present in all the ecosystems in this study except for the GOA despite the presence of much commercial fishing activity. This suggests the need for more detailed analysis of the possible role of commercial fisheries in the GOA ecosystem and the management actions taken to alleviate its effects.
It is suggested that Pielou's method (1966a) of estimating the diversity of a plant community from a series of randomly placed quadrats, can be applied to measuring dietary diversity of predatory populations. Treating each stomach as a sampling unit, an equivalent of a quadrat, it is possible to calculate for the whole predatory population the trophic diversity and the average of the trophic diversity with its standard error, and obtain a satisfactory representation of the prey species. The method proposed here may serve to produce important descriptive parameters in comparative ecological studies among sympatric species.
Haddock, cod and whiting were fed on a number of food organisms and the rateof elimination of these from the stomachs was investigated by three methods. These were: (a) the “single meal” technique, in which pre-starved fish were given a single meal and then killed and examined after a given interval of time, (b) the “regular feeding” technique. For this method, fish were given constant meals at regular intervals for a period of about 5 days. By then, it was assumed that the stomach content weight would be fluctuating about some equilibrium value, and that this value could be estimated directly by killing the fish at the middle of a feeding interval, (c) for one food species (Ophiopholis), the rate of decline was observed directly by catching haddock that were known to contain recently eaten Ophiopholis and killing them after they had been kept in deck tanks for various periods.
Consistently different results were obtained from the first two methods, the single meal technique giving lower rates of digestion than the regular feeding technique. This may have been due to the effect of starving the fish for several days prior to its receiving the experimental meal in the case of the “single meal” experiments. It was noted also that method (c) was not strictly comparable with either of methods (a) and (b) but was included as it provided the only data available for Ophiopholis.
It was concluded that the history of the fish immediately prior to each experiment was important and should be described in all digestion experiments. The main food species used was saithe (Pollachius virens), but experiments were also conducted using Centronotus, sprats, three-bearded rockling, sandeels, Nephrops, Carcinus, Nereis, Nephthys, shell-less Mytilus and Ophiopholis.
A comparison of rates of elimination of comparable meals by groups of haddock of different sizes showed that the rate of elimination was dependent, amongst other factors, on the size of the fish. The relationship was found to be
R∝L1·4orr∝W0·44
where r is the rate of elimination from the stomach in g/unit time, L is the length of the fish (cm) and W is the weight of the fish (g).
The relationship r ∝ L1·4 has been used to adjust all experimental results to relate to an arbitrary standard fish length of 40 cm, using a correction factor C = (40/L)1·4 = 175 L−1·4.
Investigation of the effect of temperature showed that rate of elimination was relatedto temperature by the equation
R∝100·035T0
where To is the observed temperature.
Various ways of analysing the effect of meal size on the rate of elimination were examined. The most consistent result was obtained by plotting the logarithms of the rates of elimination (g/h) against the logarithms of the mean stomach content weights, which gave a linear relationship with a slope of 0·46 for each of the main food species (saithe, Crangon, Nereis and Nephthys) using either the single or the regular feeding methods and for experiments conducted at both 6°C and 12°C. This result can be summarised by the equation
R=Q′·x0·46(g/h)
where x is the weight of food in the stomach and Q' is a coefficient equivalent to the rate of elimination when the stomach content weight is 1 g. This can be related to a standard fish 40 cm in length at an arbitrary temperature Te, by rewriting in the form
R=100·035(T−0Tc)x0·46Q/C(g/h)
where L is the length of fish in cm and Q is the rate of elimination of 1 g of food from the stomach of a 40 cm fish at an arbitrary temperature (Te). Using this result, a theoretical equation was derived
(M0·54−x0·54)C=0·54Qt100·035(T0=Tc)
where M is the initial size of a meal and x is the weight of the meal after t hours in the stomach.
This equation states that values of M0.54 − x0.54, adjusted for a standard fish length of 40 cm, when plotted against time in the stomach, should fall on a straight line with a slope equal to 0.54 Qt100.035(To − Te). Observation confirmed that this equation could be applied satisfactorily to the experimental results. Estimates of Q for a range of experimental results are also given.
Estimates were also made of the time that elapses, after a meal has been ingested, before it actually begins to decrease in weight. These tended to be longer for crustaceans than for fish and appeared to be temperature dependent. It also appeared probable that these times were longer for large crustaceans than for small ones.
Comparisons were made of the rates of elimination of food in haddock, cod and whiting stomachs. It appeared that under comparable conditions of fish size, meal size, temperature and experimental method, the rates of elimination of food in these three species were effectively the same.
'freska i kambaly dalnevostochnykh morei (Cod and flounders offar-eastern seas)
- P A Moiseey
MOISEEY, P. A. 1953. 'freska i kambaly dalnevostochnykh morei (Cod and flounders offar-eastern seas). [In Russ.] Nauchno-Issled Inst. Rybn. Khoz. Okeanogr. 40:1-287
The future of the fiShing industry of the United States
- Gilbert
Gilbert (editor). The future of the fiShing industry of the United States, p. 52-60. Univ. Wash. Pub!. Fish., New Ser. 4