Fisheries Branch

Cape Town, South Africa

Fisheries Branch

Cape Town, South Africa
Time filter
Source Type

Marean C.W.,Institute of Human Origins | Marean C.W.,Nelson Mandela Metropolitan University | Anderson R.J.,Fisheries Branch | Anderson R.J.,University of Cape Town | And 11 more authors.
Evolutionary Anthropology | Year: 2015

Paleoanthropologists (scientists studying human origins) universally recognize the evolutionary significance of ancient climates and environments for understanding human origins. Even those scientists working in recent phases of human evolution, when modern humans evolved, agree that hunter-gatherer adaptations are tied to the way that climate and environment shape the food and technological resource base. The result is a long tradition of paleoanthropologists engaging with climate and environmental scientists in an effort to understand if and how hominin bio-behavioral evolution responded to climate and environmental change. Despite this unusual consonance, the anticipated rewards of this synergy are unrealized and, in our opinion, will not reach potential until there are some fundamental changes in the way the research model is constructed. Discovering the relation between climate and environmental change to human origins must be grounded in a theoretical framework and a causal understanding of the connection between climate, environment, resource patterning, behavior, and morphology, then move beyond the strict correlative research that continues to dominate the field. © 2015 Wiley Periodicals, Inc.

Bodine K.A.,Texas Parks and Wildlife Department | Shoup D.E.,Oklahoma State University | Olive J.,Arkansas Game and Fish Commission | Krogman R.,Fisheries Branch | Stubbs T.J.,Fisheries and Parks
Fisheries | Year: 2013

We review the peer-reviewed literature regarding sampling of the three most commonly managed ictalurids: Channel Catfish, Blue Catfish, and Flathead Catfish. For each species, we summarize what is known about data quality (accuracy and precision) and sampling efficiency of the most commonly used gears for surveying these species. We identify research needs and provide information to guide gear selection based on different sampling objectives. To rank gear-specific sampling efficiency (catch/h and catch/person-h), we report median catch rates and the interpolated 25th and 75th percentiles of published means. We also describe the accuracy of relative abundance and size-related metrics for each gear. For Channel Catfish, tandem baited hoop nets provide the most efficient (11-24 fish/net/tandem set, 20-60 fish/person-h) and accurate samples. Low-frequency electrofishing provides the most efficient samples of Blue Catfish (23-373 fish/h, 2.1-11.3 fish/person-h) and Flathead Catfish (19-62 fish/h, 2.1-2.5 fish/person-h) and the most accurate samples of Blue Catfish. No accuracy studies exist for Flathead Catfish. Other gears examined for each species may also be useful for some sampling objectives; however, most are inefficient or lack accuracy. © 2013 Copyright Taylor and Francis Group, LLC.

Johnston T.A.,Ontario Ministry of Natural Resources | Lysack W.,Fisheries Branch | Leggett W.C.,Queen's University
Journal of Great Lakes Research | Year: 2012

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.

Atkinson L.J.,University of Cape Town | Leslie R.W.,Fisheries Branch | Field J.G.,University of Cape Town | Jarre A.,University of Cape Town
African Journal of Marine Science | Year: 2011

Research survey data collected over 24 years (1986-2009) were used to explore long-term changes in demersal fish assemblages on the west coast of South Africa. Differences in spatial (latitude and depth) and temporal (seasonal and annual) factors were examined using multivariate analyses. Fish assemblages are clearly influenced by depth, with a distinct change in the region of the shelf break between 300 m and 400 m. There are also geographic differences in fish assemblage from north to south. Multivariate analyses show two clear temporal changes in assemblages, first in the early 1990s and second in the mid-2000s, although the latter change may be confounded by a concurrent change in survey trawl gear. The abundance of three fast-growing, early-maturing species increased over the study period whereas that of two slow-growing, long-lived species decreased, supporting the hypothesis of an increase in fast-growing, early-maturing species and a decline in slow-growing, long-lived species in fished systems. Shifts in demersal fish assemblages coincide temporally with spatial shifts observed in West Coast rock lobster Jasus lalandii and with regime shifts in the pelagic ecosystem. The changes in demersal fish assemblages detected are probably a reflection of long-term indirect effects of fishing in combination with environmental changes. Copyright © NISC (Pty) Ltd.

Lasko G.R.,Ecosystem Restoration Program | Titus R.G.,Fisheries Branch | Ferreira J.R.,Fisheries Branch | Coleman R.M.,California State University, Sacramento
California Fish and Game | Year: 2014

Salmon typically home to their natal streams when returning to spawn in fresh water. Straying, however, is a natural behavior for a small fraction of individuals in a population, and may have an adaptive advantage under some circumstances. In the winter of 2006-2007, tens of thousands of late-fall run Chinook salmon (Oncorhynchus tshawytscha) reared in the Coleman National Fish Hatchery (CNFH) were released at several downstream locations as part of a Sacramento-San Joaquin River Delta survival study. In the winter of 2008-2009, biologists observed a pulse of late-season spawners in the American River, which turned out to be stray late-fall run Chinook salmon from the CNFH, spawning where the American River fall-run Chinook salmon were completing their spawning. Late-fall run Chinook salmon have not been known to spawn in the American River and understanding the reason for this unusual behavior was the basis for this project. We used coded-wire tag inland return data to test the hypothesis that salmon released close to the mouth of the American River are more likely to stray into the river during their return spawning migration than are fish released farther from the river's mouth. Results indicated that straying increased relative to proximity of release location to the mouth of the American River and with respect to downstream releases in general. No salmon released in the vicinity of the CNFH were recovered in the lower American River. This study indicates that release location should be carefully evaluated if future downstream releases are conducted by Sacramento River watershed hatcheries. © 2014, Dept. of Fish and Game. All rights reserved.

Lentz D.C.,Fisheries Branch | Cliford M.A.,Fisheries Branch and
California Fish and Game | Year: 2014

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.

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 | Year: 2015

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.

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 | Year: 2011

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.

Acierto K.R.,Water Branch | Israel J.,Bureau of Reclamation | Ferreira J.,Fisheries Branch | Roberts J.,Northern Region
California Fish and Game | Year: 2014

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.

Green D.B.,Nelson Mandela Metropolitan University | Klages N.T.W.,Two Palms | Crawford R.J.M.,Oceans and Coasts | Coetzee J.C.,Fisheries Branch | And 3 more authors.
ICES Journal of Marine Science | Year: 2015

Seabirds are upper trophic level predators, and are often highly sensitive to changes in the availability of their prey. Altered prey assemblages resulting from fluctuations in oceanographic conditions may be mirrored by shifts in seabird diet. Long-term studies of dietary change in seabirds therefore provide valuable insight into the nature of environmental shifts within the systems in which they forage. In recent decades, the Agulhas region in South Africa has undergone significant oceanographic change related to warming and intensification of the Agulhas current. Concurrent with this change, the population ofCape gannets Morus capensis at Bird Island, Algoa Bay, has grownrapidly, probably as a result of an increased availability of its dominant prey items, sardine Sardinops sagax and anchovy Engraulis encrasicolus.Using one of the longest andmost complete time-series available on diet of a seabird (spanning 34 years), we tested for changes in composition and the abundance of dominant prey species of this population. These observed changeswere also comparedwith acoustic survey estimates of their biomass, and annual catch data. Since 1979, the prey composition has remained similar, but the dietary contribution of sardine and anchovy, which fluctuated inversely to each other, increased over the study period. These shifts seemto be reflective of fluctuations in the stock size of sardine and anchovy. Conversely, a third species, saury Scomberesox saurus, dominant in the non-breedingdiet of the 1980s, decreased significantly in dietary abundance over the following two decades. It is likely that dietary shifts of Cape gannets at Bird Island were related to climate-mediated oceanographic change. The implications of such changes are discussed. © International Council for the Exploration of the Sea 2014. All rights reserved.

Loading Fisheries Branch collaborators
Loading Fisheries Branch collaborators