Evaluating impacts of forage fish abundance on marine predators

A debate has developed over the ecosystem consequences following the collapse of Atlantic cod throughout the coastal waters of eastern Canada. The explosive increase in pelagic fish abundance in scientific bottom-trawl catches on the eastern Scotian Shelf has been interpreted as being due to either (i) a “pelagic outburst” of forage fish abundance resulting from predator release or conversely (ii) a change in pelagic fish vertical distribution leading to a “suprabenthic habitat occupation” thereby increasing their availability to bottom trawls. These two interpretations have diametrically opposing ecological consequences and suggest different management strategies for these important forage fish species. We argue that an objective evaluation of the available evidence supports the hypothesis that the abundance of forage fish has not increased in response to the demise of cod and other top predators, and the reliance on a single sampling gear with low catchability has biased and will continue to bias the interpretation of demographic trends of pelagic fish populations. We advocate that multiple sampling technologies providing alternative perspectives are needed for the monitoring and management of the various trophic levels if we are to achieve a balanced and objective understanding of marine ecosystems.

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A Cursory Look at the Fishmeal/Oil Industry From an Ecosystem Perspective

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.645023 ◽

2021 ◽

Vol 9 ◽

Author(s):

Lynne Shannon ◽

Lauren Waller

Keyword(s):

South African ◽

Marine Ecosystem ◽

Marine Ecosystems ◽

Forage Fish ◽

Human Consumption ◽

Global Context ◽

Marine Predators ◽

Cultured Fish ◽

Increasing Demand

By supporting the fishmeal industry, are we competing with marine predators? Should we be taking away food from marine predators to subsidize agriculture? If not for human consumption, should forage fish be left in the sea for predators? Are there more sustainable alternatives to fishmeal; can the fishing industry be part of developing these? These are all pressing questions being posed by marine scientists, particularly in the light of the increasing aquaculture industry and associated increasing demand in recent decades for fishmeal and oil to sustain cultured fish. We concisely summarize the global context of marine sourced fishmeal and then use the South African marine ecosystem as a working example. This article draws on research into the trophic role of forage fish in marine ecosystems and ponders whether a reduced demand for fishmeal, given increasing global pressures such as climate change, could benefit marine ecosystems, fisheries on predatory species, and vulnerable marine predators.

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Forage fish abundance is a predictor of timing of breeding and hatching brood size in a coastal seabird

Marine Ecology Progress Series ◽

10.3354/meps11100 ◽

2015 ◽

Vol 519 ◽

pp. 209-220 ◽

Cited By ~ 6

Author(s):

SH Lorentsen ◽

T Anker-Nilssen ◽

KE Erikstad ◽

N Røv

Keyword(s):

Brood Size ◽

Fish Abundance ◽

Forage Fish ◽

Timing Of Breeding

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Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques ◽

10.47886/9781934874141.ch24 ◽

2010 ◽

Keyword(s):

Brown Trout ◽

Brook Trout ◽

Fish Assemblages ◽

Smallmouth Bass ◽

Fish Abundance ◽

Forage Fish ◽

Data Sets ◽

Biotic Factors ◽

Habitat Factors ◽

Habitat Variables

Abstract.—In regional survey studies of habitat and fish assemblages, potentially important biological interactions can be masked by strong gradients in habitat variables and associated collinearities among biological variables. We used structural equation modeling to compare the causal influences of local habitat and biotic factors on fish density in rivers and to determine the extent to which the set of sites chosen for analysis influenced their apparent importance. When all sites in our Michigan data set were used, spatial patterns in brook trout Salvelinus fontinalis biomass were 28 times more sensitive to habitat variables than brown trout Salmo trutta biomass. However, when the sample was restricted to trout streams, then brook trout biomass patterns were twice as sensitive to brown trout biomass as habitat variables. In a similar analysis for smallmouth bass Micropterus dolomieu, habitat factors had the strongest effects on fish densities when the analysis was based on all samples available. However, when the sample was limited to steams in which smallmouth bass actually occurred, direct effects of forage fish abundance and indirect effects of habitat via forage fish abundance were more prominent. In both the trout and smallmouth bass analyses, regional data sets (which included sites where the species of interest was absent) overemphasized the importance of habitat factors on fish abundance, but restricting the sample to sites having the species of interest elevated the importance of biotic factors. In reality, both habitat and biotic factors are important to these species, but the variance structure of the sample being analyzed had an overriding influence on the statistical importance of one versus the other. These findings help to resolve apparently conflicting results of previous studies assessing the relative influence of habitat and biotic factors on population abundance.

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The jellyfish buffet: jellyfish enhance seabird foraging opportunities by concentrating prey

Biology Letters ◽

10.1098/rsbl.2015.0358 ◽

2015 ◽

Vol 11 (8) ◽

pp. 20150358 ◽

Cited By ~ 17

Author(s):

Nobuhiko N. Sato ◽

Nobuo Kokubun ◽

Takashi Yamamoto ◽

Yutaka Watanuki ◽

Alexander S. Kitaysky ◽

...

Keyword(s):

Water Column ◽

Trophic Level ◽

Foraging Behaviour ◽

Marine Ecosystems ◽

Forage Fish ◽

Ecological Role ◽

Marine Predators ◽

Trophic Pathways ◽

The World ◽

Negative Impacts

High levels of jellyfish biomass have been reported in marine ecosystems around the world, but understanding of their ecological role remains in its infancy. Jellyfish are generally thought to have indirect negative impacts on higher trophic-level predators, through changes in lower trophic pathways. However, high densities of jellyfish in the water column may affect the foraging behaviour of marine predators more directly, and the effects may not always be negative. Here, we present novel observations of a diving seabird, the thick-billed murre, feeding on fish aggregating among the long tentacles of large jellyfish, by using small video loggers attached to the birds. We show that the birds encountered large jellyfish, Chrysaora melanaster , during most of their dives, commonly fed on fish associated with jellyfish, and appeared to specifically target jellyfish with a high number of fish aggregating in their tentacles, suggesting the use of jellyfish may provide significant energetic benefits to foraging murres. We conclude that jellyfish provide feeding opportunities for diving seabirds by concentrating forage fish, and that the impacts of jellyfish on marine ecosystems are more complex than previously anticipated and may be beneficial to seabirds.

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Using Larval Fish Abundance in the St. Clair and Detroit Rivers to Predict Year-Class Strength of Forage Fish in Lakes Huron and Erie

Journal of Great Lakes Research ◽

10.1016/s0380-1330(91)71343-9 ◽

1991 ◽

Vol 17 (1) ◽

pp. 74-84 ◽

Cited By ~ 12

Author(s):

Charles O. Hatcher ◽

Robert T. Nester ◽

Kenneth M. Muth

Keyword(s):

Larval Fish ◽

Fish Abundance ◽

Forage Fish ◽

Class Strength

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Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator

Journal of Applied Ecology ◽

10.1111/1365-2664.13409 ◽

2019 ◽

Vol 56 (7) ◽

pp. 1751-1760 ◽

Cited By ~ 2

Author(s):

Kate J. Campbell ◽

Antje Steinfurth ◽

Les G. Underhill ◽

Janet C. Coetzee ◽

Bruce M. Dyer ◽

...

Keyword(s):

Fish Abundance ◽

Forage Fish ◽

Foraging Effort ◽

Marine Predator

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Population organisation in reef sharks: new variations in coastal habitat use by mobile marine predators

Marine Ecology Progress Series ◽

10.3354/meps11545 ◽

2016 ◽

Vol 544 ◽

pp. 197-211 ◽

Cited By ~ 12

Author(s):

A Chin ◽

MR Heupel ◽

CA Simpfendorfer ◽

AJ Tobin

Keyword(s):

Habitat Use ◽

Coastal Habitat ◽

Marine Predators ◽

Reef Sharks

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Spatiotemporal distribution of foraging in a marine predator: behavioural drivers of hotspot formation

Marine Ecology Progress Series ◽

10.3354/meps13198 ◽

2020 ◽

Vol 635 ◽

pp. 187-202

Author(s):

T Brough ◽

W Rayment ◽

E Slooten ◽

S Dawson

Keyword(s):

Time Of Day ◽

Spatiotemporal Distribution ◽

Temporal Effects ◽

Marine Predator ◽

Marine Predators ◽

Additive Mixed Models ◽

Density Analysis ◽

The Times ◽

Passive Acoustic ◽

Spatial Locations

Many species of marine predators display defined hotspots in their distribution, although the reasons why this happens are not well understood in some species. Understanding whether hotspots are used for certain behaviours provides insights into the importance of these areas for the predators’ ecology and population viability. In this study, we investigated the spatiotemporal distribution of foraging behaviour in Hector’s dolphin Cephalorhynchus hectori, a small, endangered species from New Zealand. Passive acoustic monitoring of foraging ‘buzzes’ was carried out at 4 hotspots and 6 lower-use, ‘reference areas’, chosen randomly based on a previous density analysis of visual sightings. The distribution of buzzes was modelled among spatial locations and on 3 temporal scales (season, time of day, tidal state) with generalised additive mixed models using 82000 h of monitoring data. Foraging rates were significantly influenced by all 3 temporal effects, with substantial variation in the importance and nature of each effect among locations. The complexity of the temporal effects on foraging is likely due to the patchy nature of prey distributions and shows how foraging is highly variable at fine scales. Foraging rates were highest at the hotspots, suggesting that feeding opportunities shape fine-scale distribution in Hector’s dolphin. Foraging can be disrupted by anthropogenic influences. Thus, information from this study can be used to manage threats to this vital behaviour in the locations and at the times where it is most prevalent.

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