feeding, habitat requirements, and social behavior.
Between larval and adult stages, some species move large
distances between the ocean and rivers. In some cases,
these movements are associated with spawning, but
long-distance migrations of subadult year classes are also
widely recognized. For other species, individuals complete life cycles within tens of meters of where they originated. Nevertheless, these individuals must also move to
feed, find mates, seek shelter, and avoid adverse environmental conditions. In estuaries, nekton assemblages
include species which complete their life cycles within
the system and many other species which move between
the rivers, estuary, and ocean at various stages of their
development. Within tidal systems, most nekton regularly
move between flooded intertidal and adjacent subtidal
areas and along salinity, thermal, and other environmental
gradients (Kneib, 1997).
Quantifying behavior and understanding ecology
Some aspects of nekton behavior including the determination of swimming speeds, feeding, spawning, and
responses to environmental gradients have been revealed
in studies of captive animals in tanks. In some cases, artifacts caused by captivity, containers, and a lack of a full
spectrum of environmental factors are largely overcome,
and observed behavior likely mimics that in nature. Direct
observations of behavior in natural waterways are
preferred, but field-based research on the movement of
nekton in estuaries is hampered by typically turbid conditions which limit direct observations and the use of video
cameras. Most of what we know about the behavior of
nekton in estuaries is inferred from the analysis of
collections made with nets and other devices which only
capture snapshots of some of what is present at
a particular place and time. Quantifying nekton with nets
and traps is a challenge. Differences in swimming capacities among fishes render no single collection gear totally
effective for all taxa and life stages that may be present
(Rozas and Minello, 1997). Avoidance, escape, and retention are uneven and difficult to measure in towed as well
as passive collection gear. Understanding the behavior of
nekton taxa which have an affinity for structure, an ability
to bury themselves, or a patchy distribution due to schooling is necessary for interpreting the results of studies with
towed and passive collection gear.
Mark-recapture studies using traditional tags have been
useful in determining the net movement of individuals
between two points, and time at large can provide information on age and growth. Movements can be tracked using
networks of detectors for passive integrated transponder
(RFID PIT) tags. Battery-powered acoustic (radio) and
satellite-linked tags allow tracking of movements of large
individuals, often over large distances (McKenzie et al.,
2012). Sonar has been used for decades to mark the locations and estimate abundance, biomass, and relative sizes
of fishes in the water column. More recently, dualfrequency sonar instruments that can generate almost
video-quality image streams of both fishes and macroinvertebrates in situ have provided the best records of nekton
movements and other behaviors (Rakowitz et al., 2012).
The instruments can operate in the most turbid conditions
during day and night, and adjustments to the instruments
can be made based on real-time viewing of the output on
site. Simple viewing of the recordings provides information
comparable to direct observations (e.g., by a diver if the
water is clear) on distributions and interactions of animals
within the viewing field, but post-collection analysis with
advanced software can provide much more information
on length frequency distributions, biomass, school shape,
swimming speeds, turning frequency, and other metrics that
cannot be quantified by other means. This technology continues to advance and provide insights into the behavior of
nekton. Multibeam sonar has already revealed actions and
patterns that dismiss some assumptions about the activities
of estuarine nekton based on decades of data from net
collections.
Summary
Observing, quantifying, and interpreting nekton behavior
remain difficult but are important for informing policy
for the protection and management of nekton and their
habitats. Knowledge about the responses of fishes and
motile macroinvertebrates to environmental cues is fundamental to understanding distributions, migrations, trophic
structure, reproduction, larval transport, and strategies for
habitat restoration, conservation, and fishery harvests.
Advancing technology in the areas of imaging and acoustics will likely advance the quantity and quality of information on the behavioral ecology of nekton.
Bibliography
Gibson, R. N., 1999. Movement and homing in intertidal fishes. In
Horn, M. H., Martin, K. L. M., and Chotkowski, M. A. (eds.),
Intertidal Fishes: Life in Two Worlds. San Diego: Academic
Press.
Kneib, R. T., 1997. The role of tidal marshes in the ecology of estuarine nekton. In Ansell, A. D., Gibson, R. N., and Barnes,
M. (eds.), Oceanography and Marine Biology: An Annual
Review. London: UCL Press, pp. 163–220.
Kotrschal, K., 1999. Sensory systems. In Horn, M. H., Martin,
K. L. M., and Chotkowski, M. A. (eds.), Intertidal Fishes: Life
in Two Worlds. San Diego: Academic Press.
McKenzie, C. T., Parsons, B., Seitz, C., Kopf, R. K., Mesa, M., and
Phelps, Q. (eds.), 2012. Advances in Fish Tagging and Marking
Technology. Bethesda: American Fisheries Society.
Rakowitz, G., Tuser, M., Riha, M., Juza, T., Balk, H., and Kubecka,
J., 2012. Use of high-frequency imaging sonar (DIDSON) to
observe fish behavior towards a surface trawl. Fisheries
Research, 123, 37–48.
Rozas, L. P., and Minello, T. J., 1997. Estimating densities of small
fishes and decapod crustaceans in shallow estuarine habitats:
a review of sampling design with focus on gear selection.
Estuaries, 20, 199–213.
Cross-references
Ichthyofauna
Lobster Migration
452
NEKTON BEHAVIORAL ECOLOGY
Between larval and adult stages, some species move large
distances between the ocean and rivers. In some cases,
these movements are associated with spawning, but
long-distance migrations of subadult year classes are also
widely recognized. For other species, individuals complete life cycles within tens of meters of where they originated. Nevertheless, these individuals must also move to
feed, find mates, seek shelter, and avoid adverse environmental conditions. In estuaries, nekton assemblages
include species which complete their life cycles within
the system and many other species which move between
the rivers, estuary, and ocean at various stages of their
development. Within tidal systems, most nekton regularly
move between flooded intertidal and adjacent subtidal
areas and along salinity, thermal, and other environmental
gradients (Kneib, 1997).
Quantifying behavior and understanding ecology
Some aspects of nekton behavior including the determination of swimming speeds, feeding, spawning, and
responses to environmental gradients have been revealed
in studies of captive animals in tanks. In some cases, artifacts caused by captivity, containers, and a lack of a full
spectrum of environmental factors are largely overcome,
and observed behavior likely mimics that in nature. Direct
observations of behavior in natural waterways are
preferred, but field-based research on the movement of
nekton in estuaries is hampered by typically turbid conditions which limit direct observations and the use of video
cameras. Most of what we know about the behavior of
nekton in estuaries is inferred from the analysis of
collections made with nets and other devices which only
capture snapshots of some of what is present at
a particular place and time. Quantifying nekton with nets
and traps is a challenge. Differences in swimming capacities among fishes render no single collection gear totally
effective for all taxa and life stages that may be present
(Rozas and Minello, 1997). Avoidance, escape, and retention are uneven and difficult to measure in towed as well
as passive collection gear. Understanding the behavior of
nekton taxa which have an affinity for structure, an ability
to bury themselves, or a patchy distribution due to schooling is necessary for interpreting the results of studies with
towed and passive collection gear.
Mark-recapture studies using traditional tags have been
useful in determining the net movement of individuals
between two points, and time at large can provide information on age and growth. Movements can be tracked using
networks of detectors for passive integrated transponder
(RFID PIT) tags. Battery-powered acoustic (radio) and
satellite-linked tags allow tracking of movements of large
individuals, often over large distances (McKenzie et al.,
2012). Sonar has been used for decades to mark the locations and estimate abundance, biomass, and relative sizes
of fishes in the water column. More recently, dualfrequency sonar instruments that can generate almost
video-quality image streams of both fishes and macroinvertebrates in situ have provided the best records of nekton
movements and other behaviors (Rakowitz et al., 2012).
The instruments can operate in the most turbid conditions
during day and night, and adjustments to the instruments
can be made based on real-time viewing of the output on
site. Simple viewing of the recordings provides information
comparable to direct observations (e.g., by a diver if the
water is clear) on distributions and interactions of animals
within the viewing field, but post-collection analysis with
advanced software can provide much more information
on length frequency distributions, biomass, school shape,
swimming speeds, turning frequency, and other metrics that
cannot be quantified by other means. This technology continues to advance and provide insights into the behavior of
nekton. Multibeam sonar has already revealed actions and
patterns that dismiss some assumptions about the activities
of estuarine nekton based on decades of data from net
collections.
Summary
Observing, quantifying, and interpreting nekton behavior
remain difficult but are important for informing policy
for the protection and management of nekton and their
habitats. Knowledge about the responses of fishes and
motile macroinvertebrates to environmental cues is fundamental to understanding distributions, migrations, trophic
structure, reproduction, larval transport, and strategies for
habitat restoration, conservation, and fishery harvests.
Advancing technology in the areas of imaging and acoustics will likely advance the quantity and quality of information on the behavioral ecology of nekton.
Bibliography
Gibson, R. N., 1999. Movement and homing in intertidal fishes. In
Horn, M. H., Martin, K. L. M., and Chotkowski, M. A. (eds.),
Intertidal Fishes: Life in Two Worlds. San Diego: Academic
Press.
Kneib, R. T., 1997. The role of tidal marshes in the ecology of estuarine nekton. In Ansell, A. D., Gibson, R. N., and Barnes,
M. (eds.), Oceanography and Marine Biology: An Annual
Review. London: UCL Press, pp. 163–220.
Kotrschal, K., 1999. Sensory systems. In Horn, M. H., Martin,
K. L. M., and Chotkowski, M. A. (eds.), Intertidal Fishes: Life
in Two Worlds. San Diego: Academic Press.
McKenzie, C. T., Parsons, B., Seitz, C., Kopf, R. K., Mesa, M., and
Phelps, Q. (eds.), 2012. Advances in Fish Tagging and Marking
Technology. Bethesda: American Fisheries Society.
Rakowitz, G., Tuser, M., Riha, M., Juza, T., Balk, H., and Kubecka,
J., 2012. Use of high-frequency imaging sonar (DIDSON) to
observe fish behavior towards a surface trawl. Fisheries
Research, 123, 37–48.
Rozas, L. P., and Minello, T. J., 1997. Estimating densities of small
fishes and decapod crustaceans in shallow estuarine habitats:
a review of sampling design with focus on gear selection.
Estuaries, 20, 199–213.
Cross-references
Ichthyofauna
Lobster Migration
452
NEKTON BEHAVIORAL ECOLOGY