Fish Conservation and Management

Transcription

1 Fish Conservation and Management CONS 486 Life history: Reproduction Ross Chapter 3

2 Reproduction topics Reproduction Fecundity Life history strategies Reproductive Schedules Semelparity vs iteroparity

3 Major theme: Linking science to conservation & management Physiology Behaviour Population ecology Ecosystem ecology Habitat data (limnology, oceanography) Life history Basic science Applied science Fisheries exploitation data Applied life history data Human dimensions: socioeconomic data Protecting populations & habitats Restoring populations & habitats Conservation Management Harvest regulations Managing fisheries & habitats

4 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

5 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

6 Fecundity: Among species variation! Among species: highly fecund females have small eggs and small offspring, and vice versa Atlantic cod: to 12M eggs; 1.6mm dia. Atlantic wolffish: eggs; 6mm dia. Spiny dogfish shark: 15 eggs, 45mm dia. For every rule there are exceptions Smallmouth bass: 2000 to ; 1.5mm dia Same diameter as cod, why so few eggs?

7 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 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!

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9 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

10 Broadcast spawning: pelagic areas Two-spot red snapper Discoverwildlife.com

11 Broadcast spawning: littoral areas Northern pike

12 Shelter spawning (hide eggs in habitat) Rhodeus aka bitterling

13 Nesting: nest construction, cover Sockeye salmon

14 Betta species Nesting: bubble nests

15 Smallmouth bass Parental care: nest guarding

16 Cichlids utilize several strategies!

17 Mouth brooding fish Jawfish

18 BIG Mouth brooding fish! Arrowna species

19 Spiny dogfish Brooding: live bearing fish

20 Increasing level of parental care: Broadcast<scatter<shelter<nesting<guarding<brooding -Generally increasing level of care related to decreasing number and size of eggs

21 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?

22 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!

23 Smallmouth bass defending nest

24 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

25 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!

26 Reproductive schedules Iteroparous: conserve energy by spreading out reproductive effort over time Or do not spawn if conditions unfavourable Rainbow trout

27 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

28 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

29 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

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31 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

32 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

33 Life history strategies: r-selection R-selected strategists aka opportunistic species E.g., killifish Strategy for disturbed environments Short generation times Small body sizes Many eggs No parental care Typically iteroparous, can be semelparous

34 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

35 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)