Download Lecture 3: Reproduction

Fish Conservation and
Management
CONS 486
Life history: Reproduction
Ross Chapter 3
Reproduction topics
• Reproduction
– Fecundity
– Life history strategies
• Reproductive Schedules
– Semelparity vs iteroparity
Major theme: Linking science to
conservation & management
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Physiology
Behaviour
Population ecology
Ecosystem ecology
Habitat data
(limnology,
oceanography)
• Life history
• Protecting
populations &
habitats
• Restoring
populations &
habitats
Basic science
Applied
science
Conservation
Management
• Fisheries
exploitation data
• Applied life history
data
• Human
dimensions: socioeconomic data
• Harvest regulations
• Managing fisheries
& habitats
Introduction
• Ingested energy left over after paying off metabolic
costs is placed into growth and reproduction
• Reproductive and growth traits vary among species,
populations, and individuals
– Differences often due to selective pressures &
environmental conditions and habitats
• Differences best understood by considering how
these traits might be adaptive
Fecundity
• Fecundity: the number of eggs per female
• Offspring production: related to number of, and the
fecundity of, females
– Males are pretty useless: fecundity not related to
number of males or amount of sperm produced
Fecundity: Among species variation!
• Among species: highly fecund females have small
eggs and small offspring, and vice versa
– Atlantic cod: 200 000 to 12M eggs; 1.6mm dia.
– Atlantic wolffish: 40 000 eggs; 6mm dia.
– Spiny dogfish shark: 15 eggs, 45mm dia.
• For every rule there are exceptions…
– Smallmouth bass: 2000 to 20 000; 1.5mm dia
• Same diameter as cod, why so few eggs?
Fecundity: Within species variation!
• Within species: fecundity is related to body size
– Larger females have higher fecundity
• Pacific bluefin tuna: fecundity increases with length
(Collette et al. 2013 IUCN)
– ~1.2mm dia.
– ~ 5M eggs at 190 cm FL
– ~25M eggs at 240 cm FL
– Max recorded is 300 cm FL and 450 kg; 15 yr!
Fecundity: Life history strategies
• Life history: traits and schedules that affect an organism’s
life table (i.e., growth, reproduction, survival)
– Geared towards maximizing fitness
• Fecundity is also dependent on level of parental care!
• Least care (broadcast spawning, e.g. tuna): highest
fecundity
• Intermediate care (nest defense, e.g., bass)
• Most care (brooding e.g. sharks): lowest fecundity
Broadcast spawning: pelagic areas
Two-spot red snapper
Discoverwildlife.com
Broadcast spawning: littoral areas
Northern pike
Shelter spawning (hide eggs in habitat)
Rhodeus aka bitterling
Nesting: nest construction, cover
Sockeye salmon
Nesting: bubble nests
Betta species
Parental care: nest guarding
Smallmouth bass
Cichlids utilize several strategies!
Mouth brooding fish
Jawfish
BIG Mouth brooding fish!
Arrowna species
Brooding: live bearing fish
Spiny dogfish
Increasing level of parental care:
Broadcast<scatter<shelter<nesting<guarding<brooding
-Generally increasing level of care related to decreasing
number and size of eggs
Fecundity: Different strokes
• Some species commit minimal energy to an
individual egg and no parental care
– But produce many eggs
• Some species commit considerable energy to each
egg and defend the young rigorously
– But produce few eggs
• WHY doesn’t parental care exist in highly fecund
species?
Fecundity: Why divergent strategies?
• Few, large offspring and parental care may be due
to extreme, consistent and PREDICTABLE predation
risk
– E.g., spawning in littoral areas of lake (bass)
Smallmouth bass defending nest
Bluegill “nest predators”!
Smallmouth bass defending nest
Fecundity: Why divergent strategies?
• Many, small offspring and no parental protection may be
due to UNPREDICTABLE abiotic environments
– I.e., parental care may be pointless if spawning on
exposed gravel shoals away from littoral
– E.g., lake trout or walleye
Broadcast spawning Lake trout
Reproductive schedules
• Two types of schedules:
– Semelparity: spawn once and die
– Iteroparity: repeat spawners
– Types vary among species and even populations
• WHY have these two strategies evolved?
– There are advantages to both!
Reproductive schedules
• Iteroparous: conserve energy by spreading
out reproductive effort over time
– Or do not spawn if conditions unfavourable
Rainbow trout
Reproductive schedules
• Semelparous: put all possible energy into
reproduction
– Risky, but don’t need to hold back to facilitate the
survival of the spawner
Sockeye salmon
Reproductive schedules: American shad
• American shad are members of the herring family
– Anadromous: migrate from SW to FW to spawn
– Native from Florida to NFLD
– Introduced to the Pacific - from Alaska to California
American shad
USGS.gov
Reproductive schedules: American shad
• American shad are semelparous and iteroparous
along native range
• Both strategies work: nearly equivalent lifetime
reproductive output!
Paul Bentzen lab, Dalhousie
Reproductive schedules: American shad
• Shad pops mix in the ocean and all migrate up river
to spawn when river temps are about 18 °C
• Iteroparity related to egg/juvenile survival
– Iteroparity in the north: variable and unpredicatble
environmental conditions; risky
– Semelparity in the south: rearing conditions constant
and predictable
Paul Bentzen lab, Dalhousie
Life history strategies K-selection
• K-selected strategists aka equilibrium species
– E.g., bass; cichlids
• Strategy for stressful or competitive
environments
• Long-lived
• Variable offspring #s
• Parental care
• Generally iteroparous
Life history strategies: r-selection
• R-selected strategists aka opportunistic
species
• E.g., killifish
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Strategy for disturbed environments
Short generation times
Small body sizes
Many eggs
No parental care
Typically iteroparous, can be semelparous
Periodic strategy (r-K compromise!)
• Periodic strategy aka bet-hedging
– E.g., swordfish; majority of fish species
• Bet-hedging: to protect against the wrong choice
• Strategy to deal with variable juvenile survival vs
stable adult survival
• Long-lived
• Large body sizes
• Many eggs over many years
• No parental care
• Typically iteroparous
• Fecundity:
Key definitions
– number of eggs per female
• Semelparous:
– spawns once in its life cycle (sockeye salmon)
• Iteroparous:
– spawns multiple times in its life cycle (rainbow trout)
• Anadromous:
– migrate from saltwater to freshwater to spawn
• Maturity:
– the point when fish are able to sexually reproduce
following energy investment into gonads (and secondary
sexual characteristics – salmon)