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Green D.B.,Nelson Mandela Metropolitan University | Coetzee J.C.,Fisheries Branch | Rishworth G.M.,Nelson Mandela Metropolitan University | Pistorius P.A.,Nelson Mandela Metropolitan University
Marine Ecology Progress Series

Seabirds forage in a dynamic environment of heterogeneously distributed prey resources. Many seabird species use oceanographic features that promote prey aggregation, as a means of locating prey patches. The combination of tracking data, remote-sensing data and estimates of prey availability is useful in determining how seabirds locate prey. GPS tracks of foraging Cape gannets Morus capensis were collected across 3 breeding seasons and tested for interannual changes in home range size and foraging effort, and compared against the availability of their predominant prey (sardine Sardinops sagax and anchovy Engraulis encrasicolus) as determined from acoustic surveys. Biophysical features associated with foraging were compared to a random point dataset using a binomial general linear mixed model, while foraging distributions of Cape gannets were compared against the placement of marine protected areas (MPAs). The total home range of foraging Cape gannets, breeding at Bird Island, South Africa, propagated westwards over the 3 breeding seasons, which coincided with a concurrent westward contraction in the distribution of sardine and anchovy. Foraging effort showed an apparent increase in response to low prey densities and occurred mostly outside MPAs. Although gannets seemed to forage in relatively cold waters, biophysical features were generally unreliable predictors of gannet foraging distribution. The relationship between home range and prey distribution, coupled with recent declines in local prey availability, demonstrates the ability of gannets to track the distribution of their prey resources. However, the ephemeral and dynamic nature of these prey resources places a major constraint on conservation-based spatial planning involving Cape gannets. © Inter-Research 2015. Source

Johnston T.A.,Ontario Ministry of Natural Resources | Lysack W.,Fisheries Branch | Leggett W.C.,Queens University
Journal of Great Lakes Research

Walleye (Sander vitreus) and sauger (Sander canadensis) are the two most economically valuable and sought-after species in the Lake Winnipeg fishery, the second largest freshwater commercial fishery in Canada. We compared recent temporal trends (1979-2003) in population and life history characteristics of these species across the three main management zones of the lake (north basin, channel region, and south basin). Walleye abundance (gill net catch-per-unit-effort) increased relative to sauger abundance, particularly in the north and south basins, and the ages and sizes of the sampled fish exhibited greater spatial and temporal variabilities in sauger than in walleye. Walleye of the south basin and channel region exhibit a bimodal growth pattern, previously unreported for walleye populations. Growth rates of both walleye and sauger increased, and ages and sizes of maturity generally decreased from 1979 to 2003. However, walleye showed much greater flexibility in these traits, both spatially and temporally, than sauger. Sauger utilize a reproductive strategy of younger age and smaller size at maturity and higher fecundity with smaller, more lipid-rich eggs relative to walleye. Recent environmental and/or harvesting conditions on the lake appear to favour walleye over sauger, and differences in their life histories could make the sauger population more vulnerable to the impacts of commercial harvest than the walleye population. © 2010. Source

Lentz D.C.,Fisheries Branch | Cliford M.A.,Fisheries Branch and
California Fish and Game

The management of trout fishing, trout fisheries, and the culture and distribution of hatchery-reared trout have been important features of inland fishery management programs for over 140 years. California's fishery managers have striven to respond to the perceived needs and preferences of the state's inland anglers and to include the values of the larger society. Over the decades those needs and values have changed and resulted in changes in the direction of trout management. In this paper we look at a series of events over the past 25 years and examine how those events are influencing the direction of California trout management programs. © 2014, Dept. of Fish and Game. All rights reserved. Source

Acierto K.R.,Water Branch | Israel J.,Bureau of Reclamation | Ferreira J.,Fisheries Branch | Roberts J.,Northern Region
California Fish and Game

In this study, a proposed notching of the Fremont Weir was analyzed compared to existing conditions using empirical data to estimate the proportion of juvenile Sacramento River winter-run and Central Valley spring-run Chinook salmon (Oncorhynchus tshawytscha) entrained onto the Yolo Bypass. Using historic flow and rotary screw trap data from water years 1997-2011, we found that entrainment of listed juvenile salmon onto the Yolo Bypass was higher on average across all water year types under evaluated notch conditions than occurred under existing conditions. We found that notching the weir resulted in increased listed juvenile salmon entrainment onto the Yolo Bypass in the months of November through March, but not in April. Our results indicate that lowering the required river stage for Sacramento River flows to enter the Yolo Bypass by notching the Fremont Weir is likely to increase entrainment of listed juvenile salmon onto the bypass for the majority of the listed juvenile salmon emigration seasons. © 2014, Dept. of Fish and Game. All rights reserved. Source

Kreiner A.,National Marine Information and Research Center | Yemane D.,Fisheries Branch | Stenevik E.K.,Norwegian Institute of Marine Research | Moroff N.E.,National Marine Information and Research Center
Fisheries Oceanography

Most reports on the distribution of spawning areas of sardine (Sardinops sagax) in the northern Benguela originate from the 1970s and 1980s. The northern Benguela system was in a high upwelling regime during those decades. Since the early 1990s upwelling favourable winds have decreased and a trend of increasing sea surface temperature (SST) has been observed. Changes in the structure of sardine stock in the northern Benguela have been observed and it has been suggested that a reduced biomass and changes in stock structure has led to decreased spawning in the favourable southern locations, thus preventing a recovery of the sardine stock. The present paper on the contrary shows that there has been a shift in spawning location from the less favourable northern areas in the early 1980s to spawning areas further south in the 2000s. Thus, the failure of the northern Benguela sardine stock to recover since its collapse in the late 1960s cannot be explained by spawning in less favourable areas. The shift in preferred spawning location to more southern areas since the 1980s was to be expected with a general warming of the northern Benguela system. Alternative explanations for the failure of the sardine stock to recover such as a reduction in average length as well as length at 50% maturity, leading to a reduction in reproductive output, increased predation pressure, and increased low oxygen waters are proposed. © 2011 Blackwell Publishing Ltd. Source

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