Forage Fish Abundance Research Articles

The influence of forage fish abundance on the aggregation of Gulf of Maine Atlantic cod (Gadus morhua) and their catchability in the fishery

Shifts in the distribution and aggregation patterns of exploited fish populations can affect the behavior and success of fishermen and can complicate the interpretation of fisheries-dependent data. Starting in 2006, coinciding with an increase in sand lance (Ammodytes spp.) abundance, Gulf of Maine Atlantic cod (Gadus morhua) concentrated on Stellwagen Bank, a small (405 km2) underwater plateau located in the southwestern portion of the larger (52 461 km2) stock area. The cod fishery in turn concentrated on Stellwagen Bank. Specifically, the proportion of Gulf of Maine cod landings caught in a single 10-minute square area (260 km2) encompassing the tip of Stellwagen Bank increased from 12% in 2005 to 45% in 2010. An increase in landings per unit effort in the fishery coincided with the concentration of the fleet on Stellwagen Bank. Overall, both fisheries-independent and fisheries-dependent data indicate that an increase in sand lance abundance resulted in cod aggregating in a small and predictable area where they were easily caught by the fishery. More broadly, this work illustrates how changes in the distribution patterns of fish and fisherman can decouple trends in abundance and fisheries catch per unit effort.

Diet of a piscivorous seabird reveals spatiotemporal variation in abundance of forage fishes in the Monterey Bay region

Brandt's Cormorant (Phalacrocorax penicillatus) diet was investigated using regurgitated pellets (n=285) collected on 19 sampling days at three locations during the 2006–07 and 2007–08 nonbreeding seasons in the Monterey Bay region. The efficacy of using nested sieves and the all-structure technique to facilitate prey detection in the pellets was evaluated, but this method did not increase prey enumeration and greatly decreased efficiency. Although 29 prey species were consumed, northern anchovy (Engraulis mordax) dominated and speckled sanddab (Citharichthys stigmaeus) also was important in the diet. Few rockfishes (Sebastes spp.) and market squid (Doryteuthis opalescens) were consumed compared with great prevalence in previous studies during the 1970s. El Niño and La Niña during the study provided a unique opportunity to examine predator response to variation in prey availability. Patterns of prey number and diversity were not consistent among locations. Greatest number and diversity of prey occurred at locations within Monterey Bay during La Niña, results not evident at the outer coast location. Short-term specialization occurred but mean prey diversity indicated a generalist feeding mode. This study demonstrated the importance of periodic sampling at multiple locations within a region to detect spatiotemporal variability in the diet of opportunistic generalists.

Congruent energy density trends of fish and birds reflect ecosystem change

Lake Huron, the third largest freshwater lake in the world, has become increasingly oligotrophic since the early 1990s and is also currently experiencing substantial changes in species abundances and diversity. We used long‐term biomonitoring data to calculate whole‐body energy densities for Lake Huron rainbow smelt (Osmerus mordax), lake trout (Salvelinus namaycush), and also for herring gull (Larus argentatus) eggs collected from 1989–2011. Significant temporal declines in energy densities were observed for all three species, and significant declines were found for lake trout size‐at‐age and herring gull egg sizes. For lake trout and herring gulls, these declines occurred during a period of reduced abundance of pelagic forage fish and increased inclusion of terrestrial food in diets of herring gulls. Declining energy density in rainbow smelt occurred concomitant with declining phytoplankton and zooplankton resources, the principal energy source for this species. Reduced production capacity in lower trophic levels appears to be affecting upper trophic levels of the Lake Huron food web, emphasizing the cascading effects of ecosystem change.

The diet of Common GuillemotUria aalgechicks provides evidence of changing prey communities in the North Sea

Local differences in feeding conditions have been suggested as a cause of regional variation in seabird demography but multi‐colony comparisons of diet are rare. InUKwaters the main fish eaten by seabirds during the breeding season belong to three families: Ammodytidae, Clupeidae and Gadidae. Climate change and fishing are affecting these fish stocks and so probably impact on predators such as seabirds. We used standardized observations of prey brought in for chicks to make the first integrated assessment of the diet of Common GuillemotUria aalgechicks at aUKscale. Chick diet varied markedly among the 23 colonies sampled between 2006 and 2011. Sandeels (Ammodytidae), probably Lesser SandeelsAmmodytes marinus, were the commonest prey. Their contribution to the diet varied both latitudinally and among marine regions, with the proportion significantly higher for a given latitude on the west coast compared to the east. The non‐sandeel component of the diet showed latitudinal changes, with small clupeids, probably SpratsSprattus sprattus, predominant at southern colonies whereas juvenile gadids were the main alternative to sandeels in the north. Comparison of our Guillemot chick diet with data collected 15–30 years earlier suggests that the proportion of sandeels in the diet has decreased at colonies bordering the North Sea. No significant change was apparent in Atlantic colonies but historical data were limited. The early years of our study coincided with a population explosion of Snake PipefishEntelurus aequoreusin the Northeast Atlantic and North Sea. Pipefish were recorded in Guillemot chick diet at several northern and northwestern colonies in 2006 and 2007 but have been absent since 2009. Spatial and temporal variation in chick diet accorded broadly with patterns expected as a result of rising sea temperatures and impacts of fishing. Guillemot chick diet could potentially be a useful indicator of changes in the distribution and abundance of forage fish.

Irruptive prey dynamics following the groundfish collapse in the Northwest Atlantic: an illusion?

Abstract Frank, K. T., Leggett, W. C., Petrie, B., Fisher, J. A. D., Shackell, N. L., and Taggart, C. T. 2013. Pelagic fish outbreak in the Northwest Atlantic - reality or illusion? – ICES Journal of Marine Science, 70: . The collapse of Northwest Atlantic groundfish in the early 1990s yielded a “natural experiment” within which to explore responses of ecosystems to a major perturbation. The “Pelagic Outburst” hypothesis was developed to explain an up to 900% increase in the abundance of small-bodied forage fishes and macroinvertebrates following this collapse and a subsequent trophic cascade extending across four trophic levels. Recently, this theory has been challenged and an alternative “Suprabenthic Habitat Occupation” (SHO) hypothesis has been advanced; it proposes the prey outburst associated with the forage fish component was an illusion created by changes in the vertical distribution of small pelagic fishes after the cod collapse in favour of a more bottom-oriented distribution that increased their vulnerability to bottom trawls. We evaluated the SHO hypothesis as it applied to the relationship between changes in the biomass of cod and the vertical distribution of herring and sand lance, the major small pelagic species of the Scotian Shelf ecosystem off eastern Nova Scotia. Contrary to predictions of the SHO hypothesis our initial conclusion that a pelagic outburst occurred in that ecosystem was confirmed and we found no evidence of a predator effect on vertical distributions of these species. We also explored the acoustic survey design and execution that generated the data that form the cornerstone of the SHO hypothesis, and the coherence between the behaviour depicted in these data and catch rates in the surface-oriented purse-seine fishery for herring operating at the time of these surveys. In combination, the results of our re-analysis of the population dynamics and behaviour of herring on the eastern Scotian Shelf, lead us to conclude that the SHO hypothesis, at least as it relates to the post-cod collapse dynamics of the affected Northwest Atlantic ecosystems, is not supported.

Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus

Population trends of African penguins Spheniscus demersus in the Western Cape, South Africa, and their breeding success have been linked to the abundance of their main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. During the late 1990s and early 2000s, both fish species increased markedly in abundance, but after 2004, sardine biomass decreased to below average levels. In addition, adults of both stocks were principally located to the east of Cape Agulhas from 2001 to 2009 and were thus distant from seabird colonies on South Africa's West Coast. The number of African penguin pairs counted at Robben Island from 2001 to 2009 and the fledging period of chicks from successful nests increased and decreased in apparent response to the biomass of sardine prior to each breeding season, possibly linked through adult condition at the onset of breeding. Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony. In addi- tion, chick-fledging rates were depressed in 2-chick broods during years when anchovy con- tributed <75% by mass to the diet of breeding birds. Previously reported relationships between the overall abundance of forage fish in South Africa and penguin breeding success were not sup- ported. Taken together, these results highlight the combined importance of ensuring adequate local food availability for seabirds during the reproductive cycle and safeguarding regional prey abundance during the non-breeding season.

Inter‐annual changes in prey fields trigger different foraging tactics in a large marine predator

We report on inter‐annual comparisons of the foraging behavior of Global Positioning System–equipped chick‐rearing northern gannets (Morus bassanus) in the western Atlantic during years with contrasting oceanographic and prey conditions. We hypothesized that the predators would modify their foraging tactics when small fishes (capelin [Mallotus villosus]) and large pelagic fishes (mackerel, saury) varied in inter‐annual abundances. We predicted differences in (1) diving behavior, (2) spatial, and (3) temporal patterning of foraging behavior. Predictions 1 and 2 were supported, prediction 3 rejected. Dives were significantly deeper (4.3 ± 0.4 vs. 2.7 ± 0.3 m) and longer (10.1 ± 1.0 vs. 5.0 ± 0.2 s), and more U‐shaped dives (dives where birds stayed at more or less one depth) were performed (52% ± 7% vs. 7% ± 2%) in the year with higher abundance of forage fishes. Flight patterns exhibited remarkable spatial and geographic differences: gannets flew significantly (17%) more and foraging ranges were about twice as long when they pursued large pelagic fishes (mean = 122 ± 81 km vs. 62 ± 12 km). The 95% kernel feeding range was 34 times larger when large pelagic fishes were available. Yet foraging trip durations were not different between years. Inter‐annual variation in foraging tactics by the same species at the same colony in successive years was strongly related to prey availability, showing that spatial foraging parameters can be determined largely by ocean and prey conditions.

Multiscale influence of climate on estuarine populations of forage fish: the role of coastal upwelling, freshwater flow and temperature

ABSTRACT: We examined how local- and regional-scale environmental drivers affect patterns ofabundance and recruitment in 2 abundant and ecologically significant forage fishes (Pacific herring Clupea pallasi and surf smelt Hypomesus pretiosus) in the Skagit River estuary (Puget Sound, Wash-ington, USA). We identified associations between survey catch rates and environmental conditions at2 scales: within-season distributional shifts in response to local environmental conditions, and inter-annual patterns of relative year class strength related to both local- and regional-scale drivers. Usingmonthly data that spanned a 9 yr period, we found that a small proportion (<2%) of the total deviancein catch rates for both species was related to within-estuary variation in surface water temperatureand salinity but that a larger fraction (7 and 12% for Pacific herring and surf smelt, respectively) wasexplained by interannual variation in recruitment strength. Annual abundance indices for both spe-cies were uncorrelated with cumulative river discharge and regional sea surface temperature butpositively correlated with an index of cumulative coastal upwelling, suggesting a linkage betweenregional-scale environmental conditions and age-0 recruitment. Moreover, our annual age-0 Pacificherring time series was positively correlated with a similar time series from the Strait of Georgia(~100 km north), further suggesting that age-0 recruitment in these populations is synchronized byregional upwelling as opposed to estuary-specific environmental forcing related to river flows. Thepresent study isolates a potential key process governing age-0 forage fish abundance in this systemand highlights the importance of simultaneously evaluating patterns of variability across multiplespatiotemporal scales in order to identify the primary pathways through which climate may impactestuarine populations.KEY WORDS: Puget Sound · Pacific herring · Surf smelt · Deviance partitioning · Upwelling ·Fish recruitment

Effects of stocked trout on native fish communities in boreal foothills lakes

Nasmith LE, Tonn WM, Paszkowski CA, Scrimgeour GJ. Effects of stocked trout on native fish communities in boreal foothills lakes. Ecology of Freshwater Fish 2010: 19: 279–289. © 2010 John Wiley &amp; Sons A/SAbstract – Ecological effects of stocking nonnative trout into lakes are receiving increased attention, especially in alpine environments. We assessed effects of stocked trout on native forage fishes in the boreal foothills of Alberta (Canada) by comparing fish density, population size structure and spatial and temporal activities in stocked and unstocked lakes over 3 years (2005–2007). The numerically dominant dace (primarily Phoxinus spp.) were larger in stocked lakes, consistent with size‐limited predation. Dace were also more crepuscular and concentrated on the lake‐bottom in stocked lakes, compared to more daytime activity in the water column in unstocked lakes. There were, however, no demonstrable effects of trout on the abundance of forage fish. The lack of major population‐level impacts of stocked trout suggests that current stocking practices, characteristics of boreal foothill lakes (e.g. thermal structure, abundant invertebrates, dense macrophytes) and/or behavioural adjustments of forage fish contribute to healthy native fish populations in our stocked lakes.

Association of predators and prey at frontal features in the California Current: competition, facilitation, and co-occurrence

We investigated variations in the small- to meso-scale abundance and distribution of the 6 most abundant seabird species in the northern California Current — black-footed albatross Phoe- bastria nigripes, sooty shearwater Puffinus griseus, pink-footed shearwater Puffinus creatopus, fork- tailed storm-petrel Oceanodroma furcata, common murre Uria aalge, and Cassin's auklet Ptycho- ramphus aleuticus — during the upwelling season of 2000 and 2002. Covariates (21 total), with importance assessed using logistic and generalized linear modeling and an information theoretic approach, included physical features such as sea surface temperature, dynamic height (apparent water-column pressure), and pycnocline depth; biological factors such as chlorophyll maximum; and food-web factors such as the density of 3 size classes of zooplankton, the density of potential piscine competitors, i.e. Pacific salmon Oncorhynchus spp., and abundance of fish prey such as zooplankton, northern anchovy Engraulis mordax, and the juveniles of salmon and demersal fishes. The most important factors explaining seabird occurrence changed from mesoscale physical features during a food-rich year (2002; exhibited over 15 to 30 km) to smaller-scale occurrence of actual prey patches during a food-poor year (2000; <1 km). Spatial overlap in occurrence of murres and shearwaters with adult salmon was interpreted as co-occurrence and, perhaps, competition for prey species; a negative spatial overlap between shearwaters and abundance of forage fish was interpreted as evidence for prey depletion (or predator-induced alteration of availability) by the birds and other co-occurring predators (salmon). Overall, results and other information indicated the value of adding spatially explicit data on predator and prey species abundance and predator-prey behavior to improve food- web modeling.

Effects of Increasing Chinook Salmon Bag Limits on Alewife Abundance: Implications for Lake Michigan Management Goals

AbstractTo predict effects of modifying the daily bag limit (DBL) on management of Chinook salmon Oncorhynchus tshawytscha and alewives Alosa pseudoharengus, we analyzed harvest and effort data collected from both charter and noncharter anglers during 1997–2005 in Michigan waters of Lake Michigan. Overall, the percent of anglers who caught the DBL of three Chinook salmon was low for charter (10.2%) and noncharter (3.3%) angler groups. However, during 1997–2005, the percent of anglers that caught their DBL increased from 3.3% to 26.5% for charter anglers and from 0.5% to 7.8% for noncharter anglers. To predict harvest under a higher DBL, we fit a discrete negative binomial distribution to the observed daily harvest distribution under the current DBL of three fish. We then used the fitted negative binomial to predict the daily harvest distribution under a DBL of five fish. Using this approach, the potential increase in the number of fish harvested with the higher DBL was minimal, but the additional harvest showed an increasing 1997–2005 trend from 315 to 7,301 fish for charter anglers and from 450 to 18,151 fish for noncharter anglers. There was a positive linear relationship between proportion of anglers harvesting the current DBL and harvest rates, which indicates that angler success is a function of Chinook salmon abundance. Using an age‐structured deterministic population model and the production‐conversion efficiency method, we estimated potential reduction in annual lakewide consumption of alewives by Chinook salmon resulting from a higher DBL. The reduction in consumption averaged 313 metric tons and increased from 28 (1997) to 935 metric tons (2005). We conclude that higher DBLs would have a relatively minor impact on lakewide forage fish abundance but would be more consistent with current management objectives.

Timing of breeding and reproductive performance in murres and kittiwakes reflect mismatched seasonal prey dynamics

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 393:247-258 (2009) - DOI: https://doi.org/10.3354/meps08136 Timing of breeding and reproductive performance in murres and kittiwakes reflect mismatched seasonal prey dynamics Michael T. Shultz1,2,4,*, John F. Piatt1, Ann M. A. Harding1, Arthur B. Kettle3, Thomas I. Van Pelt1 1Alaska Science Center, U.S. Geological Survey, 1011 E. Tudor Road, Anchorage, Alaska 99503, USA 2University of Alaska Fairbanks, Department of Biology and Wildlife, 211 Irving 1, Fairbanks, Alaska 99725, USA 3Alaska Maritime National Wildlife Refuge, U.S. Fish and Wildlife Service, 95 Sterling Hwy, Homer, Alaska 99603, USA 4Present address: Iowa State University, Department of Ecology, Evolution, and Organismal Biology, 253 Bessey Hall, Ames, Iowa 50010, USA *Email: mshultz@iastate.edu ABSTRACT: Seabirds are thought to time breeding to match the seasonal peak of food availability with peak chick energetic demands, but warming ocean temperatures have altered the timing of spring events, creating the potential for mismatches. The resilience of seabird populations to climate change depends on their ability to anticipate changes in the timing and magnitude of peak food availability and ‘fine-tune’ efforts to match (‘Anticipation Hypothesis’). The degree that inter-annual variation in seabird timing of breeding and reproductive performance represents anticipated food availability versus energetic constraints (‘Constraint Hypothesis’) is poorly understood. We examined the relative merits of the Constraint and Anticipation Hypotheses by testing 2 predictions of the Constraint Hypothesis: (1) seabird timing of breeding is related to food availability prior to egg laying rather than the date of peak food availability, (2) initial reproductive output (e.g. laying success, clutch size) is related to pre-lay food availability rather than anticipated chick-rearing food availability. We analyzed breeding biology data of common murres Uria aalge and black-legged kittiwakes Rissa tridactyla and 2 proxies of the seasonal dynamics of their food availability (near-shore forage fish abundance and sea-surface temperature) at 2 colonies in Lower Cook Inlet, Alaska, USA, from 1996 to 1999. Our results support the Constraint Hypothesis: (1) for both species, egg laying was later in years with warmer sea-surface temperature and lower food availability prior to egg laying, but was not related to the date of peak food availability, (2) pre-egg laying food availability explained variation in kittiwake laying success and clutch size. Murre reproductive success was best explained by food availability during chick rearing. KEY WORDS: Phenology · Climate change · Food availability · Forage fish · Rissa tridactyla · Uria aalge Full text in pdf format PreviousNextCite this article as: Shultz MT, Piatt JF, Harding AMA, Kettle AB, Van Pelt TI (2009) Timing of breeding and reproductive performance in murres and kittiwakes reflect mismatched seasonal prey dynamics. Mar Ecol Prog Ser 393:247-258. https://doi.org/10.3354/meps08136 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 393. Online publication date: October 30, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

The ability of gadoids to take advantage of a short‐term high availability of forage fish: the example of spawning aggregations in Barents Sea capelin

During 11 March to 4 April 2002, the distribution of Barents Sea capelin Mallotus villosus along the coast of Finnmark, northern Norway, was covered four times by combining acoustic survey with trawling, synoptically and simultaneously sampling capelin and its main fish predators; cod Gadus morhua, haddock Melanogrammus aeglefinus and saithe Pollachius virens. The surveys demonstrated how these gadoid predators were able to exploit such a short‐term abundance of forage fish. The predator aggregation as well as the stomach fullness and proportion of capelin in their diet followed the capelin spawning migration, increasing in areas and periods with increasing capelin abundance. Capelin clearly constituted most of the biomass in stomachs of cod (97%), haddock (87%) and saithe (96%). The stomach fullness was highest in cod and lowest in haddock, although in areas with low capelin abundance, saithe had more capelin in their stomachs. The total length (LT) of capelin in predator stomachs increased with predator LT, but the proportion of capelin in the diet was not influenced by predator LT. The capelin in predator stomachs was significantly smaller than capelin in the trawl hauls, also when compared within the same sex, indicating feeding selectivity towards weaker individuals. Female capelin, being significantly smaller than the males, predominated in the diet of haddock, whereas in cod and saithe the sex ratio was more equal. Male capelin predominated in the predator diet during the pre‐spawning period, whereas the females predominated as the spawning commenced. During the overall study period, most of the female capelin in predator stomachs was in a pre‐spawning or a spawning stage, whereas the majority of the males appeared to be spent. Regardless of sex, the percentage of spent, relative to pre‐spawning or spawning capelin in the diet of the predators, followed the capelin spawning dynamics, increasing with time as the spawning progressed.

Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system

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 329:253-265 (2007) - doi:10.3354/meps329253 Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system J. A. Thayer1,2,*, W. J. Sydeman2 1Marine Ecology Division, PRBO Conservation Science, 4990 Shoreline Highway, Stinson Beach, California 94970, USA 2Wildlife, Fish and Conservation Biology, University of California, One Shields Ave., Davis, California 95616, USA *Email: jthayer@prbo.org ABSTRACT: Ocean climate affects the life history and demography of top marine predators through changes in local prey availability. In the California Current System, abundance and distribution of mid trophic-level forage fish may be affected by seasonal and interannual variability in upwelling. We tested the hypothesis that upwelling influences forage fish availability and response of a seabird, but that the effects differ spatially within a region. We examined the availability of multiple forage species and the reproductive ecology of rhinoceros auklets Cerorhinca monocerata relative to ocean climate over 11 yr (1993 to 2003) for 2 colonies off central California: one near the shelf break and another at the coastline. The upwelling index that we used increased through time, while sea surface temperature (SST) generally decreased. Abundance indices of juvenile rockfish Sebastes spp. fluctuated, while northern anchovy Engraulis mordax decreased. Diet of the auklet reflected availability of prey in the environment. Auklet reproduction was affected by both marine climate and prey availability. Seabird breeding as well as harvest of anchovy, rockfish and Pacific saury Cololabis saira were linked to offspring growth, but growth was not necessarily related to offspring survival. Offspring survival was inversely correlated with SST and positively correlated with mass of prey rather than diet composition. Auklet reproduction was more variable offshore than inshore, possibly reflecting variation in the upwelling cells affecting prey availability within the foraging range of birds from each colony. KEY WORDS: Rhinoceros auklet · Northern anchovy · Juvenile rockfish · Pacific saury · Sea surface temperature · Upwelling · Offspring survival · Growth · Timing of breeding · Prey switching Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 329. Online publication date: January 11, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Site-specific effects on productivity of an upper trophic-level marine predator: Bottom-up, top-down, and mismatch effects on reproduction in a colonial seabird

We investigated the relative roles of bottom-up and top-down factors in limiting productivity of an upper trophic level marine predator. Our primary working hypothesis was that the reproductive success of black-legged kittiwakes ( Rissa tridactyla) a piscivorous, colonial-nesting seabird, was most limited by the abundance, distribution, and species composition of surface-schooling forage fishes. A secondary working hypothesis was that reproductive loss to kittiwake nest predators was greatest during years of reduced prey availability. We report on a broad-scale, integrated study of kittiwakes and their prey in Prince William Sound, Alaska. Our study spanned five breeding seasons (1995–1999) and focused on three colonies that differed in size (ranging from ca. 220 to ca. 7000 breeding pairs) and proximity to each other (50–135 km apart). Kittiwakes in PWS encountered a variety of aquatic habitats, creating a complex foraging environment for breeding birds. We measured kittiwake reproductive success and foraging activities, while simultaneously measuring the abundance of surface schooling forage fishes throughout the foraging range of breeding kittiwakes. The abundance of primary prey species for kittiwakes (Pacific herring Clupea pallasi, Pacific sand lance Ammodytes hexapterus, and capelin Mallotus villosus) varied both annually and regionally, with no one region consistently having the greatest abundance of prey. Likewise, kittiwake reproductive success varied considerably among colonies and years. We found that bottom-up, top-down, timing mismatch, and colony-specific effects were all important to kittiwake productivity. Although bottom-up effects appeared to be strongest, they were not evident in some cases until other effects, such as geographic location (proximity of colony to prey concentrations) and top-down predation, were considered. Important bottom-up effects on kittiwake reproductive success were not only total prey abundance and distribution, but also species, age composition, and chronology of prey occurrence (match/mismatch of timing with critical brood-rearing periods); these effects varied by colony. Top-down effects of predation on kittiwake nest contents (independent of prey abundance) confounded seabird-forage fish relationships. Ultimately, when confounding factors were minimized, non-linear asymptotic relationships were identified between kittiwakes and their prey, with an asymptotic threshold of fish school surface area density of ca. 5 m 2/km 2, beyond which top-down, physiological, or phylogenetic constraints likely restrict further reproductive output. The integrated approach of our investigations provided a more thorough understanding of the mechanisms underlying predator–prey relationships in the complex marine environment. However, such mechanistic theories can only be tested and refined through long-term research and monitoring of much greater duration than the 5-year study reported herein.

Increased energy expenditure by a seabird in response to higher food abundance

Variability in forage fish abundance strongly affects seabird behavior and reproductive success, although details of this relationship are unclear. During 1997 and 1998, we measured (1) daily energy expenditure (DEE) of 80 parent black-legged kittiwakes Rissa tridactyla at 2 colonies in Prince William Sound, Alaska (North Icy Bay and Shoup Bay), (2) abundance of surface-schooling forage fishes within the foraging range of each colony, and (3) diet composition, energy delivery rates to nestlings, and reproductive success of kittiwakes at these same colonies. Female DEE was highest at North Icy Bay in 1998, while male DEE did not differ by colony year. Abundances of Pacific herring Clupea pallasi and sand lance Ammodytes hexapterus were highest near North Icy Bay in 1998 and nearly equal in density, although Age 1+ herring comprised the majority of the diet there. Energy delivery rates to nestlings, nestling growth rates, and productivity were also highest at North Icy Bay in 1998. We suggest that female kittiwakes responded to the increased abundance of Age 1+ herring near North Icy Bay in 1998 by increasing their DEE, which in turn positively affected reproductive success. Given that adult kittiwakes have been shown to suffer decreased survival as a response to increased energy expenditure during brood rearing, the positive correlation we observed between increased abundance of a high quality food source, parental effort, and productivity is consistent with maximizing lifetime reproductive success. The lack of a response in male DEE suggests that brood-rearing roles in kittiwakes differ between genders.

Sampling and Statistical Considerations for Hydroacoustic Surveys Used in Estimating Abundance of Forage Fishes in Reservoirs

AbstractAn understanding of the spatial distribution of forage fish resources is required to make informed fishery management decisions. We used mobile hydroacoustics to assess the distribution and abundance of forage fish in Badin Lake, a reservoir in central North Carolina. By sampling a series of cross‐channel and longitudinal transects and analyzing the data using geostatistics, we characterized both large‐ and small‐scale spatial patterns in forage fish density. Forage fish were observed in higher densities in upstream regions of the reservoir and were seen only in surface waters during July 2000 owing to the existence of a strong thermo–oxycline and in two layers (surface and near bottom) during mixed conditions in December 2001. We observed differences in the scale of patchiness (200–700 m) in forage fish distribution depending on the region of the reservoir where sampling took place, and we infer that these patterns are governed by prevailing limnological conditions. Modeling the spatial variation in the acoustic data using geostatistics resulted in similar average densities (July 2000: 0.56 ± 0.28 (mean ± SD) fish/m2; December 2001: 0.57 ± 0.49 fish/m2) and improvements in the precision of abundance estimates based on approximated variance (July 2000: 7.05 × 106 ± 8.30 × 105 fish; December 2001: 7.07 × 106 ± 2.10 × 106 fish) when compared with arithmetic averaging and extrapolation (July 2000: 0.60 ± 0.61 fish/m2, 7.5 × 106 ± 4.61 × 106 fish; December 2001: 0.60 ± 0.69 fish/m2, 8.00 × 106 ± 6.34 × 106 fish). We found that sampling along longitudinal transects is a more efficient way to characterize the spatial patterns of forage fish distribution and to estimate systemwide abundance and biomass than using data collected with both a longitudinal and cross‐channel sampling design in this system.

Spatial Patterns in Assemblage Structures of Pelagic Forage Fish and Zooplankton in Western Lake Superior

We assessed abundance, size, and species composition of forage fish and zooplankton communities of western Lake Superior during August 1996 and July 1997. Data were analyzed for three ecoregions (Duluth-Superior, Apostle Islands, and the open lake) differing in bathymetry and limnological and biological patterns. Zooplankton abundance was three times higher in the Duluth-Superior and Apostle Islands regions than in the open lake due to the large numbers of rotifers. Copepods were far more abundant than Cladocera in all ecoregions. Mean zooplankton size was larger in the open lake due to dominance by large calanoid copepods although size of individual taxa was similar among ecoregions. Forage fish abundance and biomass was highest in the Apostle Islands region and lowest in the open lake ecoregion. Lake herring ( Coregonus artedi), rainbow smelt ( Osmerus mordax) and deepwater ciscoes ( Coregonus spp.) comprised over 90% of the abundance and biomass of fishes caught in midwater trawls and recorded with hydroacoustics. Growth and condition of fish was good, suggesting they were not resource limited. Fish and zooplankton assemblages differed among the three ecoregions of western Lake Superior, due to a combination of physical and limnological factors related to bathymetry and landscape position.

Fish community change in Lake Superior, 1970–2000

Changes in Lake Superior's fish community are reviewed from 1970 to 2000. Lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) stocks have increased substantially and may be approaching ancestral states. Lake herring (Coregonus artedi) have also recovered, but under sporadic recruitment. Contaminant levels have declined and are in equilibrium with inputs, but toxaphene levels are higher than in all other Great Lakes. Sea lamprey (Petromyzon marinus) control, harvest limits, and stocking fostered recoveries of lake trout and allowed establishment of small nonnative salmonine populations. Natural reproduction supports most salmonine populations, therefore further stocking is not required. Nonnative salmonines will likely remain minor components of the fish community. Forage biomass has shifted from exotic rainbow smelt (Osmerus mordax) to native species, and high predation may prevent their recovery. Introductions of exotics have increased and threaten the recovering fish community. Agencies have little influence on the abundance of forage fish or the major predator, siscowet lake trout, and must now focus on habitat protection and enhancement in nearshore areas and prevent additional species introductions to further restoration. Persistence of Lake Superior's native deepwater species is in contrast to other Great Lakes where restoration will be difficult in the absence of these ecologically important fishes.

Short-term fluctuations in forage fish availability and the effect on prey selection and brood-rearing in the black-legged kittiwake Rissa tridactyla

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 236:273-287 (2002) - doi:10.3354/meps236273 Short-term fluctuations in forage fish availability and the effect on prey selection and brood-rearing in the black-legged kittiwake Rissa tridactyla Robert M. Suryan1,*, David B. Irons1, Max Kaufman1, Jeb Benson1, Patrick G. R. Jodice2, Daniel D. Roby2, Evelyn D. Brown3 1Migratory Bird Management, US Fish and Wildlife Service, 1011 East Tudor Road, Anchorage, Alaska 99503, USA 2Oregon Cooperative Fish and Wildlife Research Unit, Biological Resources Division-United States Geological Survey and Department of Fisheries and Wildlife, 104 Nash Hall, Oregon State University, Corvallis, Oregon 97331-3803, USA 3School of Fisheries and Ocean Sciences, Institute of Marine Science, University of Alaska Fairbanks, PO Box 757220, Fairbanks, Alaska 99775, USA *Present address: Department of Fisheries and Wildlife, 104 Nash Hall, Oregon State University, Corvallis, Oregon 97331-3803, USA. E-mail: rob.suryan@orst.edu ABSTRACT: To better understand how fluctuations in prey abundance may impact seabird reproductive success, we studied short-term changes in prey populations and their effect on prey selection and brood-rearing in the black-legged kittiwake Rissa tridactyla, a predator of near-surface-schooling forage fishes. Our fine-scale approach involved a weekly assessment of forage fish abundance and brood-rearing conditions during 4 consecutive years (1996 to 1999) at the Shoup Bay kittiwake colony in Prince William Sound, Alaska. We conducted forage fish surveys from a fixed-wing aircraft to determine weekly prey abundance throughout the known foraging range of breeding kittiwakes. Our results provide clear evidence that short-term fluctuations in prey availability are responsible for dramatic, within-season changes in the breeding conditions of black-legged kittiwakes. Adult kittiwakes often showed immediate response to changes in the prey base by altering prey selection; however, there were instances when kittiwakes selected prey species disproportionate to their availability (typically selecting for Pacific herring Clupea pallasi and against Pacific sand lance Ammodytes hexapterus). Changes in prey selection often resulted in striking differences in the amount of time required to obtain a load of food. The cascading effects of longer foraging trips was translated into reduced nestling growth and survival. Of the 3 components of energy provisioning to nestlings (meal delivery rate, meal size, and energy density), meal delivery rate had the strongest and most consistent positive effect on nestling growth and survival. Overall, these results demonstrate that complex foraging conditions limit the reproductive success of a central place-foraging species relying on an ephemeral food source. Moreover, we demonstrated that feeding conditions during the first 2 wk of brood-rearing were most critical for survival of the brood. Given the potential for such marked within-season variation in breeding conditions, it is critical that investigators adequately sample throughout the brood-rearing period, or, alternatively, select that portion that is germane to their study. KEY WORDS: Rissa tridactyla · Forage fish abundance · Clupea pallasi · Ammodytes hexapterus · Prey selection · Nestling provisioning rate · Nestling development Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 236. Online publication date: July 03, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.