Age, Growth, and Mortality

Transcription

1 , Growth, and Mortality and growth used to determine maturity age-related growth rates survival/mortality rates, longevity population age structure Three basic approaches to aging 1. fish held in "confinement" or marked and released at known age and then recaptured primarily validation of aging process 2. Length frequency Assessment through modes in length-frequency distribution Typically most valuable for one or two years Does not work well in locations that do not have well-defined growth seasons or with species that are protracted spawners Spawning biology Frequency age 1 age 2 age 3 age 4 Length

2 3. Anatomical approach most common based on calcified structure structures used depends upon species and latitude all invasive except for scales scale => otolith spine => fin rays => vertebrae => cleithra => opercula => jawbone => many fishes many fishes Catfish, common carp Suckers, sturgeon goosefishes, skates (marine) pikes yellow perch, smallmouth bass paddlefish Annulus is actually the result of closely spaced circuli -2 WHC, collected in fall (just finishing third growing season - Scales may have well-defined annuli in northern U.S. because of defined seasons (at least first several years of life) - Scales from fish living at more equatorial latitudes often lack annuli because of extended growing season - False annuli can be formed when other stressors become involved, such as spawning, drought, etc.

3 Collection of scales Often with knife From particular areas on the fish Take several because regenerated scales will be missing some annuli Scale preparation Scale can be read; if older and opaque, an impression is made by pressing between plastic or acetate slides -2 WHC, collected in fall (just finishing third growing season WHC; collected in July; 5, not 4 (otolith) Regenerated Scale

4 Otoliths lapillus, sagittus, and astericus - "ear bones" sagittal otolith commonly used for aging Otolith removal Cutthroat trout inner ear Otolith videotape Texas Parks and Wildlife Largemouth bass and channel catfish Used whole or sectioned (saw) -6 WHC, spring -4 WHB, spring Opercula (singular: operculum) NOP cleithrum (cleithra plural) -4 YEP, spring -4 SMB, spring 6, spring

5 BBH spine (age 6, spring sample) Flathead catfish spine removal videotape Pectoral fin ray section - lake sturgeon (age 2) Lake sturgeon: fin ray removal - DVD Voyageurs National Park Errors in aging missing the first annulus, esp. on older individuals (many structures) crowding of annuli on older individuals (esp. scales) overestimation of age due to false annuli (esp. scales) fast spring and fall growth --> checks loss of last annuli due to resorption (calcium) or erosion (scales) Back-calculation of length at age If bony structure (e.g., scale) and fish body grow at same rate, then we can easily back-calculate how long that fish was at each annulus Works better for some structures than others (relationship between scale growth and fish body growth is often quite linear; not true for otoliths)

6 First, need to make measurements the same on all fish in sample Simple theory behind back-calculation B A 1 Time of capture (2 mm) This simple example assumes: Fish body length In reality: Fish don t hatch at mm Fish don t immediately begin growing scales as soon as they hatch Fish scale radius Fish total length (mm) White bass, Lake Poinsett, SD Y-int = 47 mm r = Scale radius (mm) Useful for among-water comparisons Examples: Black crappie growth in South Dakota waters Comparison with other sampling parameters We ll deal with this advanced subject in WL 412

7 Mean total length (mm) Brant Statewide Red Plum BLC, SD Length at 3 (mm) Length at 3 (mm) Macroinvertebrates 22 r =.86 2 P = Zooplankton r = -.87 P= Relative Importance Yellow perch 6 SD lakes Lott et al. (1996) structure of fish in entire sample that belong to each age group Key is to have a relatively unbiased sample of the entire size structure for that population (e.g., otoliths rather than scales) group N = 77 Erratic recruitment: white bass, Lake Poinsett, SD Pretty darn stable recruitment! Walleye, Lake Sakakawea, ND Hypothetical largemouth bass population sample showing truncated age structure, perhaps because of excessive angler harvest once bass exceed the minimum length limit of 38 cm?

8 Mortality rates Often measured for annual periods Total annual mortality = natural mortality and angler mortality (exploitation) in a 1- year period Survival = - total annual mortality Walleyes, L. Sakakawea, ND Total annual mortality = 28% % total annual mortality 7% total annual survival Long-lived fish Northern latitudes To Sex or Not To Sex: That is the Question A Case Study of Southern Lake Michigan Yellow Perch % total annual mortality 3% total annual survival Short-lived fish Southern latitudes High exploitation Paul Allen, Thomas Lauer, Thomas McComish, Aquatic Biology and Fisheries Center Ball State University Sample Locations 3 Length Frequency Caught Length group (mm)

9 Length at age (mm) Yellow Perch Growth All Females All Males You are a senior biologist, working for Indiana DNR, and YOU must make the decisions. You must weigh biological value and economics costs when you make your decision. The Question: Do you need to sex the yellow perch that you collect in your annual sample? Remember, there is an economic cost associated with this; it will take more time to process each fish by cutting them open to identify testes and ovaries. Each team: Tell me whether you will or will not sex the fish, and defend that choice (i.e., tell me why).