Download 1 PHYSICAL-BIOLOGICAL COUPLING AND THE CHALLENGE OF

PHYSICAL-BIOLOGICAL COUPLING AND THE CHALLENGE OF UNDERSTANDING
RECRUITMENT IN LARGE LAKES
Co-developers: Ralph E.H. Smith and Stuart A. Ludsin
EXECUTIVE SUMMARY
Research of fish populations in marine systems has demonstrated that early life (e.g., egg, larval)
growth and survival can be vital for determining the strength of year-class additions of juvenile or early
adult animals to the fishable population (i.e., recruitment) for many species. Physical processes (e.g.,
upwelling, gyres, wind-driven circulation) often drive within- and between-year recruitment variation
through both direct and indirect mechanisms in these systems. While many of the same or similar
physical processes exist in large freshwater ecosystems such as the Laurentian Great Lakes, research on
physical control of early life stage success in freshwater fishes in general, and specifically in Great Lakes
fishes, has been comparatively scant. A growing body of research, however, has identified several Great
Lakes species that support valuable fisheries (e.g., walleye Sander vitreus, yellow perch Perca flavescens,
lake whitefish Coregonus clupeaformis), the recruitment of which appears to be controlled by physical
processes operating during early life stages. This Great Lakes Fishery Commission (GLFC) theme area
seeks to provide a foundation for supporting future research aimed at understanding the role that
physical processes play in driving recruitment variation in Great Lakes fishes.
With marine experience as a guide, future research focused on the coupling of physical processes
and fish recruitment in large lakes will be most fruitful if it takes an integrated approach. Driven by
meteorology/climate, bathymetry, or habitat alteration, such processes can act independently,
interactively, or synergistically with biological processes (e.g., competition, predation) and with chemical
conditions (e.g., hypoxia, eutrophication) to influence early life growth, survival, transport, and ultimately
recruitment. Marine research has shown that physical-environmental control of recruitment (the ultimate
product of survival across all early life stages) is common, but can vary spatiotemporally, depending on
other biological attributes of the system. Multi-scale modeling and empirical investigations that consider
interdependencies across life-history stages (e.g., from egg to larval to juvenile or adult recruit) are
therefore to be encouraged. A need also exists for research aimed at applying novel technological systems
for observing and forecasting the physical environment and lower food web and early life-stage
components, to better support empirical or modeling-based understanding of recruitment. More
mechanistic work also is needed to identify species and stocks of Great Lakes fishes, the recruitment of
which is likely to be influenced by physical processes both now and under conditions of continued
anthropogenic variation (e.g., climate change).
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RESEARCH GAPS AND OPPORTUNITES
The characterization of linkages between physical processes and fish recruitment is demanding of
resources and requires a range of expertise in physical limnology, modeling, and the biological aspects of
fisheries ecology. At the same time, the complex biological interactions emphasized in Neuman et al.
(1996) are still expected to operate in large lakes (and marine systems) and cannot be ignored, if we are to
make progress in attaining a predictive understanding of the role of physical processes in the recruitment
process. Hence, if fishery management agencies expect to make headway in their ability to understand
and forecast recruitment variation, comprehensive, multidisciplinary investigations must be conducted
and the results of these investigations integrated. Below, we outline a range of questions to help advance
our understanding of the importance of biophysical coupling to fish recruitment in the Great Lakes, and
afterwards identify several major gaps in information that deserve research.
1. What are the physical processes (e.g., upwelling, ice cover) and features (e.g., currents, gyres, plumes)
that show significant predictability on time scales of a year or less and are exploited by fish ELS?
Does evidence exist to indicate that fish have adapted their life-history to such features in the
Great Lakes?
2. To what extent does variability in these physical processes and features on annual or shorter time scales
affect ELS and recruitment? What are the dominant scales of effect, and can such effects be
generalized to explain similarities and differences among populations and lakes?
3. What is the extent to which ELS can accommodate variability in physical processes (e.g., through
migration, altered development rates, or other responses)? How does such accommodation alter
biological interactions at the population and community level?
4. How important are direct effects of physical processes (e.g., temperature variations outside optimal
range, mortality due to storm events) versus indirect effects mediated through biological
interactions (e.g., match-mismatch between first feeding larvae and zooplankton) to regulating
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recruitment, and what are the responses of population and community structure to these direct and
indirect effects?
5. Do recurring (in space or time) physical features (e.g., gyres, longshore currents, presence of rivers,
river inflows) exert a significant structuring effect on Great Lakes fish communities, including
population (not species) richness and stock differentiation?
RESEARCH NEEDS AND OPPORTUNITIES
• Assess the life-history characteristics of Great Lakes fishes to test for evidence of adaptation to
exploit/tolerate physical processes, and identify fish stocks likely to be more heavily influenced by
physical effects during ELS:
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How general is the susceptibility to different kinds of physical influence among species?
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Which stocks should be vulnerable (predict) and are they (test)?
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For which Great Lakes fishes will a generalized population model based on marine
literature suffice and for which species will specific models be required?
o
How do lakes and their basins vary in the mechanisms and relative importance of ELS
susceptibility to physical processes?
• Determine the relationships among physical and physically driven features in the Great Lakes, community
structure and processes, population structure, and the recruitment of fishes:
o
What is the extent and scale of variability in mesoscale features such as warming rates,
circulation patterns, and other physical features of relevance, and how do these features
affect recruitment success?
o
How are such features related to environmental properties (e.g., turbidity, inorganic
nutrients), lower food web structure and productivity, and overall community structure?
o
Do Great Lakes analogs to marine phenomena such as hydrodynamically-defined larval
retention zones and areas of enhanced prey availability exist?
o
In what ways have fish life-histories adapted to exploit such features?
• Identify the role of behavior in movement patterns of fishes relative to physically-driven patterns in the
environment:
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At what size/life stage do individuals have the ability to move at will (i.e., “behave”), and
how do climate- or biologically-driven delays in development influence movement and
survival during ELS?
o
How plastic is fish behavior during ELS within and among species, and what effect does
this plasticity have on future growth, survival, and recruitment?
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How do ELS use currents to move and find suitable habitats for feeding and survival?
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How do ELS respond to variable patchiness of resources caused by physical processes
(e.g., zooplankton patches associated with Langmuir cells or tributary plumes)?
• Determine the role of physical processes in explaining population richness (sensu Sinclair 1988) and
spawning stock structure within a species:
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Do relationships exist between numbers of local spawning stocks and the numbers or
diversity of hydrodynamic, oceanographic, and tributary features in a system?
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What is the strength and consistency of association between spawning stocks and such
features?
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How does diversity at the stock (subpopulation) level contribute to the ability of
populations to compensate for variability in physical processes?
• Apply (and possibly test) novel technologies to better understand the role of physical processes in fish
recruitment:
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Observing systems with sensors that measure physical (e.g., temperature, dissolved
oxygen, currents) and biological (e.g., zooplankton, predators, competitors) habitat
availability.
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Satellite and acoustic sensors or other tagging methods to document movement patterns
of fish in relation to large-scale physical features
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Data systems and models that can allow prediction of key physical and biological
properties of the environment beyond what can be immediately observed
• Assess the implications of climate change and variation on recruitment of fishes with particular attention
to interactions at different scales of space and time and among populations and stocks.
o
Characterize the expected alteration of predictable physical processes (e.g., enhanced
runoff/river flows in spring, lower water levels in summer, changed thermal stratification
patterns, altered circulation and upwelling, diminished ice cover) on ELS and fish
recruitment
o
Determine the potential for altered phasing between fish and their resources/predators
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•
Characterize the interactive effects of invasive species, harvest, land-use/alteration, and climate-driven
physical processes.
o
In what ways do non-native species increase the susceptibility of native fish species to
physically-driven disruption of habitat quality and biological interactions (e.g. synergistic
impacts of increased spring storms and round goby predation on smallmouth bass eggs?)
o
How do land-use changes alter physical processes and population responses (e.g.,
implications of altered river hydrography and inputs on the location and timing of
optimal ELS habitat)?
o
How might harvest and/or stocking dampen or reinforce effects of mesoscale physical
forcing on reproduction and recruitment of fish?
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