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Lec 10: Fish

Lec 10: Fish. I. Fish Research and Limnology II. Taxonomy and Systematics III. Species Richness IV. Life History V. Growth VI. Fisheries and Yield VII. Local Fisheries. 1. I. Fish Research and Limnology. A. Traditionally: A species focus & in isolation

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Lec 10: Fish

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  1. Lec 10: Fish I. Fish Research and Limnology II. Taxonomy and Systematics III. Species Richness IV. Life History V. Growth VI. Fisheries and Yield VII. Local Fisheries 1

  2. I. Fish Research and Limnology • A. Traditionally: A species focus & in isolation • 1. Economic importance as fisheries species; population biology rather than ecology • 2. Relatively large, long lived, • 3. Unique sampling approaches • 4. Very different scales (space, time) than other areas of • aquatic science • B. Fish research rooted in Ichthyology • 1. Natural history • 2. Fisheries science; management of fish stocks • 3. Government management • 4. Not often tought with natural sciences • C. More recent research on fish ecology • 1. Community and Ecosystem approaches • 2. Recently, links between basic ecology & management 2

  3. II. Taxonomy and Systematics • A. What is a fish? • 'Any of numerous cold-blooded aquatic vertebrates of • the superclass Pisces, characteristic of having fins, • gills, and a streamlined body…' Amer. Heritage Dictionary • B. Phylogenetic lineage of common modern fishes • Phylum Chordata • Subphylum Vertebrata • Superclass Agnatha (hagfish, lampreys) • Superclass Gnathostamata (jawed) (includes the tetrapods) • Class Chondrichthyes (cartilaginousfishes) • Class Osteichthyes (bony fish) • Subclass Actinopterygii (ray-finned) • Division Teleosti (42 orders) • -Symetrical tail, advanced • ~94% of inland fishes { 3

  4. Fishes are the most numerous of all vertebratesFish Distributions Amphibians 2500 spp 58% are marine Reptiles 6000 41% are FW Birds 8600 1% occupy both Mammals 4500 Fish 25000 4

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  6. III. Species Richness • A. Negative relationship with latitude and altitude • B. Increases with drainage basin area • -Greater habitat diversity • -More potential colonizers • C. Increases with habitat diversity within-lake • D. Recent glaciation => low diversity • -Versus African Rift valley: • e.g. Lake Malawi has 1,000 spp. • E. Invasions • 1. Competition, predation on adults, eggs • 2. Example: Nile Perch in African Rift lakes • Benefits: productive fishery • Costs: Loss of endemic species (cichlids) 6

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  8. Haplochromis in Lake Malawi – Feeding Specialization

  9. IV. Life History A. Reproductive diversity in fishes is enormous 1. Varies by: size at maturity, # eggs, egg size, reproductive season and timing, longevity, # clutches / female (year, life) 2. Although closely related species usually use similar spawning strategies, there is little general evolutionary trend from primitive to advanced groups. (large variation w/in diverse FW groups like cyprinids, percids) B. Hypothesis: Selection for reproductive strategies that minimize the ratios of: 1. energy expended for reproduction 2. fitness of the genes passed to offspring (F1 => F2) 8

  10. IV. Life History • C. Reproductive Effort - energy or time invested in reproduction • 1. Assumed to be greater in females – choosy a. number of eggs (fecundity) b. fecundity scales geometrically with length c. size of eggs (reproductive investment per individual) d. trade-off between number and size of eggs • 2. Male gametes assumed to be relatively inexpensive, • reproductive effort is expended in : • a. courtship b. territoriality c. parental care 9

  11. IV. Life History • D. Frequency of Reproduction over lifetime 1. Semelparous - • a. spawn once in lifetime, putting eggs in one basket • b. catadromous species do this a lot 2. Iteroparous a. spawn more than once over lifetime b. even out variance in reproductive success….. but contribute a lot of energy to reproduction over lifetime c. single, extended spawning season (fractional spawning) d. multiple spawning seasons - long lived fishes E. Spawning Migrations 1. Hydrodynamic, trophic, reproductive needs met in a given environment? 2. May have to migrate if not: (sardines => whales) 3. Diadromy: Catadromous & Anadromous 10

  12. IV. Life History F. Population Biology 1. Life history traits are extremely plastic in fishes 2. Survival of young more important than fecundity 3. Extremely high juvenile mortality (starvation, predation) limits recruitment to the population 4. Recruitment is variable among age-classes & is reflected in Cohort (or year-class) strength; the number of fish of a given age in a population 5. Small changes in larval and juvenile mortality can affect cohort strength 6. Rare to have several strong, consecutive year-classes 11

  13. Fishes >20k spp Herps 8.5k spp Mammals 5k spp Birds 8.5k spp 12

  14. V. Growth • A. Size of fish (state, world records) • <1 cm ‘Stout Infantfish’ • 18m whale shark (eats plankton) • B. Why grow? • 1. Predation risk: Prob(predation) vs. size (-linear) • 2. Fecudity: eggs/female vs. size (exponential) • -small increase in size => large increase in fecundity • 3. Natural mortality: Prob(death by nat. causes) vs. size (-linear) • -less susceptible to lack of food in winter • -small animals are more likely to die by starvation • 4. Social rank • -access to and defense of mates and nest sites 13

  15. News Update Scientists find 'smallest fish' By Roland Pease BBC science correspondent Researchers have found the smallest known fish on record in the peat swamps of the Indonesian island of Sumatra. Individuals of the Paedocypris genus can be just 7.9mm long at maturity, scientists write in a journal published by the UK's Royal Society. But they warn long-term prospects for the fish are poor, because of rapid destruction of Indonesian peat swamps. The fish have to survive in extreme habitats - pools of acid water in a tropical forest swamp. Food is scarce but the Paedocypris - smaller than other fish by a few tenths of a millimetre - can sustain their small bodies grazing on plankton near the bottom of the water. Human threat To keep their size down, the fish have abandoned many of the attributes of adulthood - a characteristic hinted at in their name. Their brain, for example, lacks bony protection and the females have room to carry just a few eggs. The males have a little clasp underneath that might help them fertilize eggs individually. Being so small, the fish can live through even extreme drought, by seeking refuge in the last puddles of the swamp; but they are now threatened by humans. Widespread forest destruction, drainage of the peat swamps for palm oil plantations and persistent fires are destroying their habitat. Science may have discovered Paedocypris just in time - but many of their miniature relatives may already have been wiped out. Story from BBC NEWS:http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4645708.stm

  16. V. Growth • C. Growth and ration • 1. Ration most important determinate of growth • 2. Three critical levels in a ration-growth curve • a. Maintenance • b. Maximum • c. Optimum • -highest GGE • 3. Change in diet critical for growth (Trophic Ontogeny) • -Potential strong effects on zooplankton 14

  17. V. Growth • D. Determinate vs. Indeterminate Growth • 1. Indeterminate growth in many fishes Why? • Think about the forces affecting vertebrate morphology and anatomy in general • 2. Birds & mammals vs. fish • a. Determinate: • -grow rapidly to a relatively uniform, unchanging adult size • b. Indeterminate (mostfishes) • -age, size, maturity not fixed • -mature at relatively small, but variable size, • then keep growing (or grow larger and die) 15

  18. V. Growth F. Why is determining fish growth rate so difficult? 1. Can you rely on size or maturity? 2. Habitat effect (food, temperature) 3. Sampling biases and artifacts 4. Growth of individuals or the population? G. Growth in length 1. Easiest measure besides counting 2. Dependent on vertebral length, related to hard structures used for aging H. Growth in mass 1. Wet weight 2. Relate to length (produce a useful W=aLb eqn.) 3. Condition factor (ratio of weight:length) 16

  19. V. Growth • I. Determining the age of fish • 1. General • -Need 'markers' of time • -Seasonal growth rates in temperate lats. • -Seasonal deposition of bone, scales • -Hard structures reflect growth rates as annuli (influence of reprod?) • 2. Structures • a. Scales • i. non lethal • ii. circuli: like tree rings • iii. problems: false annuli, regenerated scales, • older fish, difficult to observe • iv. cross-validation • b. Bones (Otolith, Operculum) • i. lethal except for fin rays • ii. annuli clearer than circuli • iii. no regeneration, good for older individuals 17

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  21. V. Growth 3. Size-Frequency changes -Discrete cohorts 19

  22. VI. Fisheries and yield • A. Production:Biomass • 1. Production (Biomass / area / time) • 2. Will be higher for small-bodied populations • 3. Will be higher for small fish within populations 20

  23. VI. Fisheries and yield • B. Management • 1. Management of Maximum Sustainable Yield (MSY) Assume population model - gives peak yield at intermediate levels of fishing effort. Stock2 = Stock1 + (A + G) - (M + C) A = weight of new recruits G = Weight due to growth M = natural mortality C = catch At Equilibrium: S1 = S2 => M + C = A + G Works in theory; problems with application K N dN/dt K/2 K N Fishing Effort 21

  24. VI. Fisheries and yield • B. Management • 2. Fishery catch; CPUE • 3. Relationship of lake trophic state and fish production 22

  25. VI. Fisheries and yield B. Management 4. Eutrophication: -Reduced trophic efficiency -Shift to fewer piscivorous fish 5. Morpho-Edaphic Index (MEI) -Fishery production or yield = TDS / mean depth 23

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