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Biology 450: Fish Week
Lecture 11: Ontogenetic shifts and
dispersal
Scott Heppell
Department of Fisheries and Wildlife
Oregon State University
042 Nash Hall 737-1086, [email protected]
Ontogenetic shifts
Fishery
Ontogeny:
Biology
The
entireFall
development
2006
of an organism, from
fertilization through
maturity
The salmon life cycle
http://www.streamnet.org
More than salmon …
More than benthic species…
© Richard Herrmann, Poway, California, http://www.richardherrmann.com
Types of ontogenetic shifts
•
•
•
•
Habitat/location/migration
Reproductive strategy
Diet
Behavior
Ontogenetic shifts: change in lifestyle associated
with growth and development
•
•
•
Growth rates in habitat x slow, so make a
shift to habitat y
Maximize growth, minimize mortality risk: m/g
Major shifts common in species with very
large changes in body size
–
–
–
–
Larvae
Juveniles
–
Increase in depth with body size
Adults
Spawning adults
Why switch habitats?
(Werner and Gilliam 1984)
Growth Rate (mm/day)
Optimal switching point
Habitat B
Habitat A
Body size
Mortality risk/growth rate (m/g)
Want to minimize mortality (m)
AND maximize growth (g)
Habitat A
Habitat B
Body size
Loggerhead sea turtle growth curve
(mark recapture estimates or width of growth
rings on humerus)
Length
Adult
Subadult
Pelagic
Benthic
juvenile
AGE
Migration
Definition: a move from one
place to another
3 Types
• Local and seasonal movements
• Dispersals
• True migrations
Larvae: pelagic
Small
juveniles:
estuaries,
kelp forests
Adults:
deeper
reefs
Larger juveniles:
nearshore reefs
1. Local and Seasonal
Movements
Involves
• short or long distance
• seasonal to semidiurnal time periods
• horizontal or vertical
movements
Migratory records
• Mather (1962) tagged
two bluefin on June 1
and June 10 in waters
off the Bahamas.
• On September 28
and October 6,
respectively, these
two fish were
recovered near
Bergen, Norway.
4000 nm
2. Dispersal
Includes
• Passive or active movement away
from the breeding habitat over a
wide area (e.g., larval transport,
juvenile dispersal)
• Ontogenetic shifts between
habitats
3. ‘True’ Migration
Involves
• Directed movement between widely
separated and well-defined areas, often at
set times during the year (e.g., feeding to
breeding areas)
• Often ignores local conditions
Why migrate?
• Breeding
– Aggregations for
mating/spawning
– Optimal
birthing/nesting areas
Why migrate?
• Breeding
– Aggregations for
mating/spawning
– Optimal
birthing/nesting areas
• Feeding
– Higher latitudes =
more food
– Food patches often
ephemeral
http://earthobservatory.nasa.com
Migration to Spawning Sites &
Passive or Active Larval Migration
• Improve breeding success
• Reduce impact of environmental
fluctuations
• Larval Dispersal
• Cushing’s (1957) match-mismatch
hypothesis
Evolutionary Perspective
Migration involves specialized behaviors that
have arisen through natural selection
How do we think about this?
Trade Offs:
Costs versus Benefits
Benefits
• Increased feeding opportunities
• Avoidance of adverse environmental conditions
• Improved current reproductive success
Costs
• Energetic cost of migration itself
• Increased predation risks
• Energetic & development costs of any specific
migratory adaptation
• Potential reproductive costs due to decreased lifetime
reproductive effort
Fitness
Summation of:
Probability of survival to age x  lx
Multiplied by
Fecundity and breeding success  mx
Migration favored if:
S lxmx migrators > S lxmx residents
Migration - Maturation Decision
• Given that migration is costly and potentially
dangerous, age or size at maturity may be
delayed
• Some species (some rockfish, sturgeon,
others?) appear to go through a “false
maturation” in which females physiologically
prepare for reproduction but resorb their eggs
instead of completing maturation
Migratory Patterns
• Oceanodromous
• Potamodromous
• Diadromous
Diadromy
Gross ‘87
McDowall ‘87
Gross et al. ‘88
Migration pathways of large
pelagics
• Can follow physical features, such as continental
margins or major currents
• However, “corridor” concept probably too simplified
– Individual variability
– Variation in response to ocean conditions
• Behavior depends on species, time of year, sex, other
factors
– Coastal, pelagic
– Direct, stop-and-feed
• Moving oases of food resources require
behavioral plasticity
Movements of Leatherback Sea Turtles in the Atlantic Ocean as Determined
Using Satellite Transmitters
Why might understanding migration
pathways be important from a management
perspective?
Hector Barrios-Garrido
NOAA
Lutcavage et al. ‘99
Legend: 1998, 1999, Early Jettison
March/April
May
June
July
Oceanodromous
(European Sea Bass,
Dicentrarchus labrax)
Overwintering
Spawning
Aggregation spawning
Why aggregate?
•
•
•
•
Access to mates
Multiple fertilizations
Environmental conditions
Reduced offspring mortality
Management
• Ontogenetic shifts in habitat type dictate that habitat
protections be in place for all life stages
• Highly migratory species do not care about EEZ lines international cooperation and research is required
• Bycatch in high seas fisheries presents a management
and monitoring problem – need for integration among
groups
– Impact may be large but diffuse and therefore difficult to measure
Options?
• Fishing and bycatch quotas
• Gear modification
• Closures
– Spatial, temporal
– Requires consideration
of entire life cycle, migration
rates and habitat use
– Requires careful consideration
of redistribution of effort and
markets
Modeling movement for reserve planning
• Understanding of:
–
–
–
–
Movement patterns
Reproductive strategy
Location of impacts
Suite of management options
Types of movement
Habitat A
“leaking” = stochastic
movement
Habitat B
“reserve”
Types of movement
Habitat A
“spill-over” = densitydependent leaking
Habitat B
“reserve”
Types of movement
Habitat A
“seeding” = larval
transport
Habitat B
“reserve”
Types of movement
Habitat A
Habitat B
“reserve”
“ontogenetic shift” =
deterministic
movement between
habitats due to life
stage transition
RESERVE
NON-RESERVE
Offspring production
Survival and growth
Spillover or leaking
Life stage with
increased survival
Newborn
juvenile
Adult
Newborn
juvenile
Adult
RESERVE
NON-RESERVE
Offspring production
Survival and growth
Spillover or leaking
Egg/larvae
juvenile
Ontogenetic shift
Seeding from reserve
Spawning
Adult
Non-spawn
adult
Spawning
adult
RESERVE
NON-RESERVE
Offspring production
Survival and growth
Spillover or leaking
Egg/larvae
juvenile
juvenile
Ontogenetic shift
Adult
RESERVE
NON-RESERVE
Offspring production
Survival and growth
Spillover or leaking
Egg/larvae
Ontogenetic shift
Seeding from reserve
juvenile
Adult
juvenile
Adult
RESERVE
NON-RESERVE
Offspring production
Survival and growth
Spillover or leaking
Ontogenetic shifts
Seeding from reserve
Egg/larvae
juvenile
Adult
Spawning
adult
Egg/larvae
juvenile
Adult
Spawning
adult
Generic model
Conclusions
• Ontogenetic shifts happen as individuals try to
maximize µ/g
• Shifts happen in habitat selection, reproduction, diet,
and behavior
• Incorporating an understanding of these shifts crucial
to effective management and conservation
• Plasticity in ontogeny is important but not always
well understood
– Manage for variance, not just the mean